1. A. Rosenauer. Transmission Electron Microscopy of Semiconductor Nanostructures An Analysis of Composition and Strain State. Springer Tracts in Modern Physics 182 Springer-Verlag Berlin Heidelberg, 2003 ISBN 3-540-00414-9, 2003. [bibtex-key = Rosenauer2003b]



2. M. Schowalter. Segregation in III-V Halbleiterheterostrukturen. Mensch und Buch Verlag, Berlin, 2003. Note: ISBN: 3-89820-559-2. [bibtex-key = Schowalter2003d]



3. A. Rosenauer. TEM-Untersuchung von epitaktischen Grenzflächen in II-VI/II-V Heterostrukturen (Dissertation). Roderer-Verlag, Regensburg, 1996. [bibtex-key = Rosenauer1996b]



4. Christoph Mahr. Charakterisierungen der Struktur und der chemischen Zusammensetzung von nanoporösem Gold mittels Transmissionselektronenmikroskopie (Characterization of structure and chemical composition of nanoporous gold by transmission electron microscopy). PhD thesis, Universität Bremen, Otto-Hahn-Allee 1,28359 Bremen, Germany, October 2018. [bibtex-key = Mahr2018e]



5. Thorsten Mehrtens. Quantitative STEM an indiumhaltigen Gruppe III-V Halbleiternanostrukturen. PhD thesis, Universität Bremen, 2013. [bibtex-key = Mehrtens2013d]



6. Knut Müller. Transmission electron microscopy of InGaNAs nanostructures using ab-initio structure factors for strain-relaxed supercells. PhD thesis, Universität Bremen, May 2011. Abstract:

   This thesis reports on theoretical, methodical and experimental studies concerning scattering and structural properties of In(x)Ga(1−x)N(y)As(1−y) using transmission electron microscopy (TEM). First, theoretical concepts to describe electron scattering at real crystals including the effects of bonding and static atomic displacements (SAD) are considered. The approach of modified atomic scattering amplitudes (MASA), which uses density functional theory (DFT) to model bonding in an atomistic manner, is exploited to calculate compositiondependent MASA for InGaNAs. Valence force field (VFF) calculations are applied to determine SAD caused by atom size effects. Huang scattering caused by SAD is shown to pile up in the vicinity of Bragg peaks, contrary to the smooth background caused by thermal diffuse scattering (TDS). In simulation studies it is demonstrated that Huang scattering leads to significant attenuation of Bragg beam amplitudes, for which additional absorptive form factors can be defined that are added as an imaginary part to atomic scattering amplitudes (ASA). The reliability of VFF strain relaxation is verified by full DFT calculations of residual forces for supercells with 216 atoms. It is found that atomic forces after VFF relaxation do not exceed 10mRy/Bohr, which translates to a maximum error of 2.58 pm for SAD. Furthermore, results for composition-dependent structure factors calculated by full DFT and atomistic models are compared. This confirms that SAD affect structure factor amplitudes and phases drastically and exhibits that the MASA approach in combination with SAD obtained by VFF meets the full DFT results most accurately. Thus it is possible to account for both bonding and SAD in large supercells containing 106 atoms by modelling bonding via MASA and calculating SAD by VFF. Second, structure factors for GaAs and InAs are measured by parallel and convergent beam electron diffraction (PBED and CBED) to verify the MASA approach. The PBED method was implemented in Bloch wave routines embedded in a least-squares refinement that allows for a refinement of structure factors, Debye-Waller factors, specimen thickness and -orientation. The method is based on extraction of integrated Bragg intensities from electron spot diffraction patterns. Errors in PBED are estimated from the application to simulated diffraction patterns with TDS background, and rules for the recognition of reasonable initial refinement conditions are derived. Then, PBED is applied to the measurement of the 200 structure factors of GaAs and InAs. Conversion to X-ray structure factors yields X(GaAs, 200) = −6.366 ± 0.015 and X(InAs, 200) = 53.687 ± 0.110, respectively. By CBED, X(GaAs, 200) = −6.350 ± 0.015 is measured. All results agree with each other and with expectations from the MASA concept inside the error margins, whereas isolated atom ASA must be rejected. Additionally, Debye-Waller factors for GaAs have been refined to B(Ga) = 0.275 ± 0.003 A² and B(As) = 0.242 ± 0.003 A² at 99K using PBED. Third, above theoretical scattering data is used in composition measurements in InGaNAs solar cell and laser structures via TEM lattice fringe imaging. Lattice strain and chemically sensitive 200 fringe contrast are measured from a single image and compared with simulations based on elasticity theory and the Bloch wave approach. First, a two-beam lattice fringe image formed by beams 000 and 200 is used to investigate the effect of bonding and SAD on composition quantification in In(0.08)Ga(0.92)N(0.03)As(0.97). In particular, neglect of bonding results in a relative error of 25\% for the In content, whereas SAD have small impact. Second, a three-beam imaging technique is developed that utilises beams 000, 200 and 220, for which an L-shaped objective aperture was inserted into an FEI Titan 80/300 microscope. By decomposition of the image into 220 and 020 fringe images, artefacts due to nonlinear imaging are circumvented. Imaging conditions that minimise errors induced by inaccurately known specimen thickness are derived. Bloch wave simulations of reference 200 fringe contrast include structure factors adapted for chemical bonding, SAD, and diffuse losses due to SAD and TDS. As a main application, the threebeam method is applied to In(0.28)Ga(0.72)N(0.025)As(0.975) before and after thermal annealing. Dissolution of In-rich islands and N-rich clusters and formation of a homogeneously thick quantum well with nearly constant stoichiometry is found. The increase by a factor of 20 and blue-shift of 60meV of the photoluminescence peak are finally interpreted by means of the TEM results.

   [bibtex-key = Mueller2011e]



7. Lukas Fuchs, Tom Kirstein, Christoph Mahr, Orkun Furat, Valentin Baric, Andreas Rosenauer, Lutz Mädler, and Volker Schmidt. Using convolutional neural networks for stereological characterization of 3D hetero-aggregates based on synthetic STEM data. Machine Learning: Science and Technology, 5(2):025007, April 2024. Abstract:

   The 3D nano/microstructure of materials can significantly influence their macroscopic properties. In order to enable a better understanding of such structure-property relationships, 3D microscopy techniques can be deployed, which are however often expensive in both time and costs. Often 2D imaging techniques are more accessible, yet they have the disadvantage that the 3D nano/microstructure of materials cannot be directly retrieved from such measurements. The motivation of this work is to overcome the issues of characterizing 3D structures from 2D measurements for hetero-aggregate materials. For this purpose, a method is presented that relies on machine learning combined with methods of spatial stochastic modeling for characterizing the 3D nano/microstructure of materials from 2D data. More precisely, a stochastic model is utilized for the generation of synthetic training data. This kind of training data has the advantage that time-consuming experiments for the synthesis of differently structured materials followed by their 3D imaging can be avoided. More precisely, a parametric stochastic 3D model is presented, from which a wide spectrum of virtual hetero-aggregates can be generated. Additionally, the virtual structures are passed to a physics-based simulation tool in order to generate virtual scanning transmission electron microscopy (STEM) images. The preset parameters of the 3D model together with the simulated STEM images serve as a database for the training of convolutional neural networks, which can be used to determine the parameters of the underlying 3D model and, consequently, to predict 3D structures of hetero-aggregates from 2D STEM images. Furthermore, an error analysis is performed with respect to structural descriptors, e.g. the hetero-coordination number. The proposed method is applied to image data of TiO2-WO3 hetero-aggregates, which are highly relevant in photocatalysis processes. However, the proposed method can be transferred to other types of aggregates and to different 2D microscopy techniques. Consequently, the method is relevant for industrial or laboratory setups in which product quality is to be quantified by means of inexpensive 2D image acquisition.

   [bibtex-key = Fuchs_2024]



8. Tim Grieb, Florian F. Krause, Thorsten Mehrtens, Christoph Mahr, Beeke Gerken, Marco Schowalter, Bert Freitag, and Andreas Rosenauer. GaN atomic electric fields from a segmented STEM detector: Experiment and simulation. Journal of Microscopy, n/a(n/a), 2024. Keyword(s): 4D STEM, centre-of-mass, COM, electric fields, GaN, momentum-resolved STEM, segmented STEM detector. Abstract:

   Summary Atomic electric fields in a thin GaN sample are measured with the centre-of-mass approach in 4D-scanning transmission electron microscopy (4D-STEM) using a 12-segmented STEM detector in a Spectra 300 microscope. The electric fields, charge density and potential are compared to simulations and an experimental measurement using a pixelated 4D-STEM detector. The segmented detector benefits from a high recording speed, which enables measurements at low radiation doses. However, there is measurement uncertainty due to the limited number of segments analysed in this study.

   [bibtex-key = https://doi.org/10.1111/jmi.13276]



9. Christoph Mahr, Jakob Stahl, Beeke Gerken, Valentin Baric, Max Frei, Florian F. Krause, Tim Grieb, Marco Schowalter, Thorsten Mehrtens, Einar Kruis, Lutz Mädler, and Andreas Rosenauer. Characterization of mixing in nanoparticle hetero-aggregates by convolutional neural networks. Nano Select, 5(4):2300128, 2024. Keyword(s): convolutional neural networks, double flame spray pyrolysis, hetero-aggregate, nanoparticle mixing, scanning transmission electron microscopy. Abstract:

   Abstract Formation of hetero-contacts between particles of different materials in nanoparticle hetero-aggregates can lead to new functional properties. Improvement of the functional behavior requires a detailed characterization of mixing between the two types of particles, in order to correlate different mixing with the performance of the material. Scanning transmission electron microscopy (STEM) is an option for this task. To obtain statistically relevant results, STEM-images of many hetero-aggregates have to be acquired and evaluated. This can be time-consuming if it is done manually. In the present work, the applicability of convolutional neural networks for the automated analysis of STEM-images acquired from TiO2\${}\_{2}\$–WO3\${}\_{3}\$ nanoparticle hetero-aggregates is investigated. Hetero-aggregates are obtained in a double flame spray pyrolysis (DFSP) setup, in which a variation of setup parameters is expected to affect the mixing of TiO2\${}\_{2}\$ and WO3\${}\_{3}\$. Mixing is investigated by a measurement of cluster sizes (the number of connected particles of the same material within an aggregate) and coordination numbers (the number of particle contacts with particles of the same or the different material). Results show that the distribution of measured values is wide for both quantities, rendering it challenging to correlate mixing with parameters varied in the DFSP setup.

   [bibtex-key = E_Mahr2024]



10. Manuel Alonso-Orts, Rudolfo Hötzel, Tim Grieb, Matthias Auf der Maur, Maximilian Ries, Felix Nippert, Benjamin März, Knut Müller-Caspary, Markus R. Wagner, Andreas Rosenauer, and Martin Eickhoff. Correlative analysis on InGaN/GaN nanowires: structural and optical properties of self-assembled short-period superlattices. Discover Nano, 18(1):27, 2023. Abstract:

    The influence of self-assembled short-period superlattices (SPSLs) on the structural and optical properties of InGaN/GaN nanowires (NWs) grown by PAMBE on Si (111) was investigated by STEM, EDXS, µ-PL analysis and k·p simulations. STEM analysis on single NWs indicates that in most of the studied nanostructures, SPSLs self-assemble during growth. The SPSLs display short-range ordering of In-rich and In-poor InxGa1-xN regions with a period of 2-3 nm that are covered by a GaN shell and that transition to a more homogenous InxGa1-xN core. Polarization- and temperature-resolved PL analysis performed on the same NWs shows that they exhibit a strong parallel polarized red-yellow emission and a predominantly perpendicular polarized blue emission, which are ascribed to different In-rich regions in the nanostructures. The correlation between STEM, µ-PL and k·p simulations provides better understanding of the rich optical emission of complex III-N nanostructures and how they are impacted by structural properties, yielding the significant impact of strain on self-assembly and spectral emission.

    [bibtex-key = AlonsoOrts2023]



11. Beeke Gerken, Christoph Mahr, Jakob Stahl, Tim Grieb, Marco Schowalter, Florian F. Krause, Thorsten Mehrtens, Lutz Mädler, and Andreas Rosenauer. Material Discrimination in Nanoparticle Hetero-Aggregates by Analysis of Scanning Transmission Electron Microscopy Images. Particle & Particle Systems Characterization, 40(9):2300048, 2023. Keyword(s): double flame spray pyrolysis, energy-dispersive X-ray spectroscopy, hetero-aggregates, hetero-contact, nanoparticle mixing, scanning transmission electron microscopy. Abstract:

    Abstract Hetero-contacts are interfaces between different materials at the nanoscale leading to novel functional properties. In hetero-aggregates, primary particles of at least two different materials are mixed at primary particle or cluster level. Double flame spray pyrolysis (DFSP) is a versatile technique for the controlled synthesis of such materials. Characterization of hetero-aggregates by scanning transmission electron microscopy (STEM) requires acquisition and evaluation of many aggregate images in order to derive statistically significant results. Usually, STEM energy dispersive X-ray spectroscopy (EDXS) is used to acquire elemental maps providing the material distribution of the primary particles within hetero-aggregates. However, the acquisition of a single EDXS map takes up to several minutes. For this reason, determination of material types of primary particles from the intensity in high-angle annular dark field STEM images alone is desirable. These images can be acquired within a couple of seconds. In the present work, a method is suggested which allows for achieving this objective. It can be applied to distinguish materials with a significant difference in their atomic number and hence sufficient material contrast in the STEMÂ images.

    [bibtex-key = E_Gerken2023]



12. Florian F. Krause, Marco Schowalter, Beeke Gerken, Dennis Marquardt, Tim Grieb, Thorsten Mehrtens, Christoph Mahr, and Andreas Rosenauer. Dose efficient annular bright field contrast with the ISTEM method: A proof of principle demonstration. Ultramicroscopy, 245:113661, 2023. Keyword(s): ISTEM, ABF STEM, Light atom imaging, Aperture manufacturing, Principle of reciprocity. [bibtex-key = E_Krause2023a]



13. Cristian Messina, Yongkang Gong, Oumaima Abouzaid, Bogdan-Petrin Ratiu, Tim Grieb, Zhao Yan, Andreas Rosenauer, Sang Soon Oh, and Qiang Li. Deformed Honeycomb Lattices of InGaAs Nanowires Grown on Silicon-on-Insulator for Photonic Crystal Surface-Emitting Lasers. Advanced Optical Materials, 11(5):2201809, 2023. Keyword(s): III–V semiconductors, nanowires, photonic crystals, selective area epitaxy, surface-emitting lasers. Abstract:

    Abstract Photonic crystals can be used to achieve high-performance surface-emitting lasers and enable novel photonic topological insulator devices. In this work, a GaAs/InGaAs heterojunction nanowire platform by selective area metalorganic vapor phase epitaxy for such applications is demonstrated. The nanowires are arranged into deformed honeycomb lattices on silicon-on-insulator substrate to exploit the quadrupolar photonic band-edge mode. Core–shell and axial heterostructures are formed with their crystalline properties studied by scanning transmission electron microscopy. Room-temperature, single mode lasing from both stretched and compressed honeycomb lattices within the telecom-O band, with lasing threshold as low as 1.25 µJ cm−2 is demonstrated. The potential of using InGaAs nanowire-based honeycomb lattices for small-divergence surface-emitting lasers and topological edge mode lasers is investigated. Finite-difference time-domain far field simulations suggest a sub-10° beam divergence can be achieved thanks to the out-of-plane diffraction.

    [bibtex-key = Messina2023]



14. Maximilian Ries, Felix Nippert, Benjamin März, Manuel Alonso-Orts, Tim Grieb, Rudolfo Hötzel, Pascal Hille, Pouria Emtenani, Eser Metin Akinoglu, Eugen Speiser, Julian Plaickner, Jörg Schörmann, Matthias Auf der Maur, Knut Müller-Caspary, Andreas Rosenauer, Norbert Esser, Martin Eickhoff, and Markus R. Wagner. Origin of the spectral red-shift and polarization patterns of self-assembled InGaN nanostructures on GaN nanowires. Nanoscale, 15:7077-7085, 2023. Abstract:

    The luminescence of InxGa1−xN nanowires (NWs) is frequently reported with large red-shifts as compared to the theoretical value expected from the average In content. Both compositional fluctuations and radial built-in fields were considered accountable for this effect{,} depending on the size{,} structure{,} composition{,} and surrounding medium of the NWs. In the present work{,} the emission properties of InGaN/GaN NWs grown by plasma-assisted molecular beam epitaxy are investigated in a comprehensive study combining ultraviolet-Raman and photoluminescence spectroscopy (PL) on vertical arrays{,} polarization-dependent PL on bundles of a few NWs{,} scanning transmission electron microscopy{,} energy-dispersive X-ray spectroscopy{,} and calculations of the band profiles. The roles of inhomogeneous In distribution and radial fields in the context of optical emission properties are addressed. The radial built-in fields are found to be modest{,} with a maximum surface band bending below 350 meV. On the other hand{,} variations in the local In content have been observed that give rise to potential fluctuations whose impact on the emission properties is shown to prevail over band-bending effects. Two luminescence bands with large positive and moderate negative polarization ratios of ≈+80% and ≤−60%{,} respectively{,} were observed. The red-shift in the luminescence is associated with In-rich inclusions in the NWs due to thermodynamic decomposition during growth. The negative polarization anisotropy is suggested to result from spontaneously formed superlattices in the In-rich regions of the NWs. The NWs show a preferred orthogonal absorption due to the dielectric boundary conditions and highlight the extreme sensitivity of these structures towards light polarization.

    [bibtex-key = Ries2023]



15. Gunther Wittstock, Marcus Bäumer, Wilke Dononelli, Thorsten Klüner, Lukas Lührs, Christoph Mahr, Lyudmila V. Moskaleva, Mehtap Oezaslan, Thomas Risse, Andreas Rosenauer, Anne Staubitz, Jörg Weissmüller, and Arne Wittstock. Nanoporous Gold: From Structure Evolution to Functional Properties in Catalysis and Electrochemistry. Chemical Reviews, 123(10):6716-6792, 2023. [bibtex-key = E_Wittstock2023]



16. Tim Grieb, Florian F. Krause, Knut Müller-Caspary, Jan-Philipp Ahl, Marco Schowalter, Oliver Oppermann, Joachim Hertkorn, Karl Engl, and Andreas Rosenauer. Angle-dependence of ADF-STEM intensities for chemical analysis of InGaN/GaN. Ultramicroscopy, 238:113535, 2022. Keyword(s): GaN, InGaN, STEM, Quantitative, Angle-dependent scattering. Abstract:

    In this paper we perform angular resolved annular-dark field (ADF) scanning-transmission electron microscopy (STEM) to study the scattered intensity in an InGaN layer buried in GaN as a function of the scattering angle. We achieved angular resolution with a motorized iris aperture in front of the ADF detector. Using this setup, we investigated how the intensities measured in various angular ranges agree with multislice simulations in the frozen-lattice approximation. We observed a strong influence of relaxation induced surface-strain fields on the ADF intensity, measured its angular characteristics and compared the result with simulations. To assess the agreement of the measured intensity with simulations, we evaluated the specimen thickness in GaN and the indium concentration in InGaN for each angular interval by comparing the measured intensities with simulations. The thickness was strongly overestimated for scattering angles below 40mrad and also the evaluated indium concentration varies with the considered angular range. Using simulations, we investigated which angular ranges show a high sensitivity to variations of the thickness and which intervals strongly depend on the indium concentration. By combining two angular intervals, the indium concentration and the specimen thickness were determined simultaneously, which has potential advantages over the usual quantification method. It is shown that inelastic scattering, surface contamination and mistilt can have an influence on the measured intensity, especially at lower scattering angles below 30-50mrad, which might explain the observed difference between the frozen lattice simulation and the experiment.

    [bibtex-key = Grieb2022]



17. Christoph Mahr, Tim Grieb, Florian F. Krause, Marco Schowalter, and Andreas Rosenauer. Towards the interpretation of a shift of the central beam in nano-beam electron diffraction as a change in mean inner potential. Ultramicroscopy, 236:113503, 2022. Keyword(s): Mean inner potential, Nano-beam electron diffraction, Scanning transmission electron microscopy, Interface, Disc detection. Abstract:

    The measurement of electric fields in scanning transmission electron microscopy (STEM) is a highly investigated field of research. The constant improvement of spatial resolution in STEM and the development of new hardware for the fast acquisition of diffraction patterns even paved the way for the measurement of atomic electric fields. Although the basic principle that an electric field leads to a tilt of the focussed electron probe that can be detected as a shift of the diffraction pattern in the back focal plane of the objective lens seems quite simple, many challenges arose in the measurement of fields in a quantitative way. In the present study we investigate whether a shift of the diffraction pattern that occurs at an interface between two materials can be related to the electric field which is caused by the difference of the mean inner potentials of the two materials. To this end, experiments and simulations are compared. It is demonstrated that the difference in mean inner potential has an influence on the observed effect, but a quantitative interpretation is difficult. The influence of image recording effects such as shot noise and the modulation transfer function are investigated as well as further effects such as e.g. sample tilt. In addition, the influence of the observed effect on a strain measurement is shown.

    [bibtex-key = MAHR2022113503]



18. Christoph Mahr, Jorge Adrian Tapia Burgos, Marco Schowalter, Arne Wittstock, and Andreas Rosenauer. Investigation of the dealloying front in partially corroded alloys. Materials Research Letters, 10(12):824-831, 2022. [bibtex-key = E_Mahr2022a]



19. Alex Ricardo Silva Olaya, Franziska Kühling, Christoph Mahr, Birthe Zandersons, Andreas Rosenauer, Jörg Weissmüller, and Gunther Wittstock. Promoting Effect of the Residual Silver on the Electrocatalytic Oxidation of Methanol and Its Intermediates on Nanoporous Gold. ACS Catal., pp 4415--4429, March 2022. [bibtex-key = Olaya2022]



20. Stefan Wild, Christoph Mahr, Andreas Rosenauer, Thomas Risse, Sergey Vasenkov, and Marcus Bäumer. New Perspectives for Evaluating the Mass Transport in Porous Catalysts and Unfolding Macro- and Microkinetics. Catalysis Letters, 2022. [bibtex-key = E_Wild2022]



21. Tim Grieb, Florian F. Krause, Knut Müller-Caspary, Saleh Firoozabadi, Christoph Mahr, Marco Schowalter, Andreas Beyer, Oliver Oppermann, Kerstin Volz, and Andreas Rosenauer. Angle-resolved STEM using an iris aperture: Scattering contributions and sources of error for the quantitative analysis in Si. Ultramicroscopy, 221:113175, 2021. Keyword(s): Angle-resolved STEM, Quantitative STEM, Plasmon excitation, Inelastic scattering, Phonon correlation, Low-angle scattering. [bibtex-key = GRIEB2021113175]



22. Tim Grieb, Florian F. Krause, Knut Müller-Caspary, Robert Ritz, Martin Simson, Jörg Schörmann, Christoph Mahr, Jan Müssener, Marco Schowalter, Heike Soltau, Martin Eickhoff, and Andreas Rosenauer. 4D-STEM at interfaces to GaN: Centre-of-mass approach & NBED-disc detection. Ultramicroscopy, 228:113321, 2021. Keyword(s): Electric fields, 4D STEM, Interfaces, COM, NBED. [bibtex-key = GRIEB2021113321]



23. Daniel Loof, Oliver Thüringer, Marco Schowalter, Christoph Mahr, Anmona Shabnam Pranti, Walter Lang, Andreas Rosenauer, Volkmar Zielasek, Sebastian Kunz, and Marcus Bäumer. Synthesis and Characterization of Ligand-Linked Pt Nanoparticles: Tunable, Three-Dimensional, Porous Networks for Catalytic Hydrogen Sensing. ChemistryOpen, 10(7):697-712, 2021. Keyword(s): Amines derivatives, bifunctional ligands, heterogeneous catalysis, nanoparticles, platinum. [bibtex-key = Loof2021]



24. Christoph Mahr, Alexandra Dworzak, Marco Schowalter, Mehtap Oezaslan, and Andreas Rosenauer. Quantitative 3D Characterization of Nanoporous Gold Nanoparticles by Transmission Electron Microscopy. Microscopy and Microanalysis, 27(4):678–686, 2021. [bibtex-key = Mahr2021]



25. Christoph Mahr, Knut Müller-Caspary, Tim Grieb, Florian F. Krause, Marco Schowalter, and Andreas Rosenauer. Accurate measurement of strain at interfaces in 4D-STEM: A comparison of various methods. Ultramicroscopy, 221:113196, 2021. Keyword(s): Strain measurement, Ptychography, Interface, 4D-STEM, Patterned apertures. [bibtex-key = MAHR2021113196]



26. Dennis Marquardt, Marco Schowalter, Florian F. Krause, Tim Grieb, Christoph Mahr, Thorsten Mehrtens, and Andreas Rosenauer. Accuracy and precision of position determination in ISTEM imaging of BaTiO3. Ultramicroscopy, 227:113325, 2021. Keyword(s): Imaging scanning transmission electron microscopy, TEM, CTEM, STEM, Tunnel junctions, BaTiO, Atom position determination. [bibtex-key = MARQUARDT2021113325]



27. Andreas Beyer, Florian F Krause, Hoel L Robert, Saleh Firoozabadi, Tim Grieb, Pirmin Kükelhan, Damien Heimes, Marco Schowalter, Knut Müller-Caspary, Andreas Rosenauer, and Kerstin Volz. Influence of plasmon excitations on atomic-resolution quantitative 4D scanning transmission electron microscopy. Scientific Reports, 10:1--15, 2020. [bibtex-key = beyer20]



28. Giulio Guzzinati, Wannes Ghielens, Christoph Mahr, Armand Béché, Andreas Rosenauer, Toon Calders, and Jo Verbeeck. Electron Bessel beam diffraction for precise and accurate nanoscale strain mapping. Applied Physics Letters, 114(24):243501, 2019. [bibtex-key = doi:10.1063/1.5096245]



29. Anastasia Lackmann, Christoph Mahr, Andreas Rosenauer, Marcus Bäumer, and Arne Wittstock. Aerobic Methanol Oxidation over Unsupported Nanoporous Gold: The Influence of an Added Base. Catalysts, 9(5), 2019. Abstract:

    We studied the aerobic oxidation of methanol over nanoporous gold catalysts under neutral and alkaline conditions. We find that under neutral conditions the catalyst has an activation period of about 10 h while upon addition of a base the catalyst becomes active right away. After this activation period, however, the activity of the catalyst is in both cases similar. Moreover, the selectivity was not affected by the base. We tested different bases and found the largest effect when adding OH−. The cation, however, does not play a role. We conclude that it is OH−, which is impacting the reaction and propose a mechanism for the suppression of the activation period. While the catalytic cycle, i.e., the reaction of methanol on the catalyst surface seems unaffected, the transient adsorption of OH− onto the surface can facilitate the activation of molecular oxygen by donating electrons to the surface. Due to the intermediate formation of oxidic Ag species, an effective segregation of surface-near Ag can be induced, which increases the abundance of Ag being essential for the activation of oxygen at the surface. In this way, a more efficient pathway for the generation of active oxygen is opened, allowing the reaction to set in faster.

    [bibtex-key = Lackmann2019]



30. Christoph Mahr, Knut Müller-Caspary, Robert Ritz, Martin Simson, Tim Grieb, Marco Schowalter, Florian F. Krause, Anastasia Lackmann, Heike Soltau, Arne Wittstock, and Andreas Rosenauer. Influence of distortions of recorded diffraction patterns on strain analysis by nano-beam electron diffraction. Ultramicroscopy, 196:74 - 82, 2019. Keyword(s): Strain measurement, Electron diffraction, Image distortions, 4D-STEM, Nanoporous gold. Abstract:

    Images acquired in transmission electron microscopes can be distorted for various reasons such as e.g. aberrations of the lenses of the imaging system or inaccuracies of the image recording system. This results in inaccuracies of measures obtained from the distorted images. Here we report on measurement and correction of elliptical distortions of diffraction patterns. The effect of this correction on the measurement of crystal lattice strain is investigated. We show that the effect of the distortions is smaller than the precision of the measurement in cases where the strain is obtained from shifts of diffracted discs with respect to their positions in images acquired in an unstrained reference area of the sample. This can be explained by the fact that diffraction patterns acquired in the strain free reference area of the sample are distorted in the same manner as the diffraction patterns acquired in the strained region of interest. In contrast, for samples without a strain free reference region such as nanoparticles or nanoporous structures, where we evaluate ratios of lattice plane distances along different directions, the distortions are usually not negligible. Furthermore, two techniques for the detection of diffraction disc positions are compared showing that for samples in which the crystal orientation changes over the investigated area it is more precise to detect the positions of many diffraction discs simultaneously instead of detecting each disc position independently.

    [bibtex-key = Mahr2019]



31. Knut Müller-Caspary, Tim Grieb, Jan Müssener, Nicolas Gauquelin, Pascal Hille, Jörg Schörmann, Johan Verbeeck, Sandra Van Aert, Martin Eickhoff, and Andreas Rosenauer. Electrical Polarization in AlN/GaN Nanodisks Measured by Momentum-Resolved 4D Scanning Transmission Electron Microscopy. Phys. Rev. Lett., 122:106102, March 2019. [bibtex-key = MuellerCaspary2019]



32. Junjie Shi, Arne Wittstock, Christoph Mahr, M. Mangir Murshed, Thorsten M. Gesing, Andreas Rosenauer, and Marcus Bäumer. Nanoporous gold functionalized with praseodymia-titania mixed oxides as a stable catalyst for the water-gas shift reaction. Physical Chemistry Chemical Physics, 21(6):3278--3286, 2019. [bibtex-key = Shi2019]



33. Dipanwita Chatterjee, Shwetha Shetty, Knut Müller-Caspary, Tim Grieb, Florian F. Krause, Marco Schowalter, Andreas Rosenauer, and Narayanan Ravishankar. Ultrathin Au-Alloy Nanowires at the Liquid-Liquid Interface. Nano Lett., 18(3):1903--1907, March 2018. [bibtex-key = Chatterjee2018]



34. Michael Gockeln, Suman Pokhrel, Florian Meierhofer, Jens Glenneberg, Marco Schowalter, Andreas Rosenauer, Udo Fritsching, Matthias Busse, Lutz Mädler, and Robert Kun. Fabrication and performance of Li4Ti5O12/C Li-ion battery electrodes using combined double flame spray pyrolysis and pressure-based lamination technique. Journal of Power Sources, 374:97 - 106, 2018. Keyword(s): Double flame spray pyrolysis (DFSP), LiTiO (LTO), Composite material, Lamination, Li-ion battery, Solvent- and binder-free electrode processing. [bibtex-key = GOCKELN201897]



35. Tim Grieb, Florian F. Krause, Marco Schowalter, Dennis Zillmann, Roman Sellin, Knut Müller-Caspary, Christoph Mahr, Thorsten Mehrtens, Dieter Bimberg, and Andreas Rosenauer. Strain analysis from nano-beam electron diffraction: Influence of specimen tilt and beam convergence. Ultramicroscopy, 190:45 - 57, 2018. [bibtex-key = Grieb2018a]



36. Tim Grieb, M. Tewes, Marco Schowalter, Knut Müller-Caspary, Florian F. Krause, Thorsten Mehrtens, and Andreas Rosenauer. Quantitative HAADF STEM of SiGe in presence of amorphous surface layers from FIB preparation. Ultramicroscopy, 184:29-36, 2018. Keyword(s): NBED, Disc detection, Strain, Electric field measurement. [bibtex-key = Grieb2018]



37. Christoph Mahr, Knut Müller-Caspary, Matthias Graf, Anastasia Lackmann, Tim Grieb, Marco Schowalter, Florian F. Krause, Thorsten Mehrtens, Arne Wittstock, Jörg Weissmüller, and Andreas Rosenauer. Measurement of local crystal lattice strain variations in dealloyed nanoporous gold. Materials Research Letters, 6(1):84-92, 2018. [bibtex-key = Mahr2018]



38. Christoph Mahr, Marco Schowalter, Christoph Mitterbauer, Anastasia Lackmann, Lisa Fitzek, Thorsten Mehrtens, Arne Wittstock, and Andreas Rosenauer. Nanoporous gold dealloyed from AuAg and AuCu: Comparison of structure and chemical composition. Materialia, 2:131 - 137, 2018. Keyword(s): Nanoporous gold, Alloy corrosion, Regions rich in residual material, TEM. Abstract:

    Properties of dealloyed nanoporous gold (npAu) in catalysis, sensing or actuation applications depend on its structure and chemical composition. NpAu is obtained by corrosion of alloys of gold and a less noble metal such as silver or copper. Structural parameters can be tuned by variations in the preparation process. Due to the large number of parameters that can be varied a direct comparison of results obtained with various samples is often difficult. In this report we compare structure and chemical composition of npAu dealloyed from AuAg and AuCu alloys keeping the number of different sample preparation parameters at a minimum.

    [bibtex-key = Mahr2018b]



39. S. Schlichting, G. M. O. Hönig, J. Müßener, P. Hille, T. Grieb, S. Westerkamp, J. Teubert, J. Schörmann, M. R. Wagner, A. Rosenauer, M. Eickhoff, A. Hoffmann, and G. Callsen. Suppression of the quantum-confined Stark effect in polar nitride heterostructures. Communications Physics, 1(1):48, 2018. Abstract:

    Recently, we suggested an unconventional approach (the so-called Internal-Field-Guarded-Active-Region Design “IFGARD�) for the elimination of the quantum-confined Stark effect in polar semiconductor heterostructures. The IFGARD-based suppression of the Stark redshift on the order of electronvolt and spatial charge carrier separation is independent of the specific polar semiconductor material or the related growth procedures. In this work, we demonstrate by means of micro-photoluminescence techniques the successful tuning as well as the elimination of the quantum-confined Stark effect in strongly polar [000-1] wurtzite GaN/AlN nanodiscs as evidenced by a reduction of the exciton lifetimes by up to four orders of magnitude. Furthermore, the tapered geometry of the utilized nanowires (which embed the investigated IFGARD nanodiscs) facilitates the experimental differentiation between quantum confinement and Stark emission energy shifts. Due to the IFGARD, both effects become independently adaptable.

    [bibtex-key = Schlichting2018]



40. M. Alania, A. De Backer, I. Lobato, F.F. Krause, D. Van Dyck, A. Rosenauer, and S. Van Aert. How precise can atoms of a nanocluster be located in 3D using a tilt series of scanning transmission electron microscopy images?. Ultramicroscopy, 181:134 - 143, 2017. Keyword(s): Electron tomography, High-resolution electron microscopy, Precision, Resolution, Cramér-Rao lower bound. [bibtex-key = Alania2017]



41. C. Carmesin, M. Schowalter, M. Lorke, D. Mourad, T. Grieb, K. Müller-Caspary, M. Yacob, J. P. Reithmaier, M. Benyoucef, A. Rosenauer, and F. Jahnke. Interplay of morphology, composition, and optical properties of InP-based quantum dots emitting at the $1.55\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ telecom wavelength. Phys. Rev. B, 96:235309, December 2017. [bibtex-key = PhysRevB.96.235309]



42. N. Chery, T.H. Ngo, M.P. Chauvat, B. Damilano, A. Coruville, P. De Mierry, T. Grieb, T. Mehrtens, F.F. Krause, K. Meller-Caspary, M. Schowalter, B. Gil, A. Rosenauer, and P. Ruterana. The microstructure, local indium composition and photoluminescence in green-emitting InGaN/GaN quantum wells. Journal of Microscopy, 2017. [bibtex-key = Chery2017]



43. N. Gauquelin, K.H.W. van den Bos, A. Beche, F.F. Krause, I. Lobato, S. Lazar, A. Rosenauer, S. Van Aert, and J. Verbeeck. Determining oxygen relaxations at an interface: A comparative study between transmission electron microscopy techniques. Ultramicroscopy, 181:178-190, 2017. Note: Cited By 0. [bibtex-key = Gauquelin2017a]



44. Tim Grieb, Florian F. Krause, Christoph Mahr, Dennis Zillmann, Knut Müller-Caspary, Marco Schowalter, and Andreas Rosenauer. Optimization of NBED simulations for disc-detection measurements. Ultramicroscopy, 181:50 - 60, 2017. Keyword(s): NBED, Disc detection, Strain, Electric field measurement. [bibtex-key = Grieb2017]



45. M. Kracht, A. Karg, J. Schörmann, M. Weinhold, D. Zink, F. Michel, M. Rohnke, M. Schowalter, B. Gerken, A. Rosenauer, P. J. Klar, J. Janek, and M. Eickhoff. Tin-Assisted Synthesis of $\ensuremath{\epsilon} ext{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ by Molecular Beam Epitaxy. Phys. Rev. Applied, 8:054002, November 2017. [bibtex-key = PhysRevApplied.8.054002]



46. Florian F. Krause and A. Rosenauer. Reciprocity Relations in Transmission Electron Microscopy: A Rigorous Deviation. Micron, 92:1--5, 2017. Keyword(s): notacc. [bibtex-key = Krause2017]



47. F.F. Krause, A. Rosenauer, J. Barthel, J. Mayer, K. Urban, R.E. Dunin-Borkowski, H.G. Brown, B.D. Forbes, and L.J. Allen. Atomic resolution elemental mapping using energy-filtered imaging scanning transmission electron microscopy with chromatic aberration correction. Ultramicroscopy, 181:173 - 177, 2017. Keyword(s): Atomic resolution imaging, Elemental mapping, Energy-filtered imaging scanning transmission electron microscopy. [bibtex-key = Krause2017d]



48. Florian F. Krause, Andreas Rosenauer, and Dirk Van Dyck. Imaging theory for the ISTEM imaging mode. Ultramicroscopy, 181:107 - 116, 2017. Keyword(s): ISTEM, Imaging STEM, Incoherent imaging, Image formation, Resolution, Scherzer conditions. [bibtex-key = Krause2017c]



49. Anastasia Lackmann, Christoph Mahr, Marco Schowalter, Lisa Fitzek, Jörg Weissmüller, Andreas Rosenauer, and Arne Wittstock. A comparative study of alcohol oxidation over nanoporous gold in gas and liquid phase. Journal of Catalysis, 353:99 - 106, 2017. Keyword(s): Heterogeneous catalysis, Mesoporous materials, Alcohols, Gold. [bibtex-key = Lackmann201799]



50. Christoph Mahr, Paromita Kundu, Anastasia Lackmann, Daniele Zanaga, Karsten Thiel, Marco Schowalter, Martin Schwan, Sara Bals, Arne Wittstock, and Andreas Rosenauer. Quantitative determination of residual silver distribution in nanoporous gold and its influence on structure and catalytic performance. Journal of Catalysis, 352:52 - 58, 2017. Keyword(s): Nanoporous gold, Residual silver, Quantitative EDXS tomography, CO oxidation, Methanol oxidation, Silver cluster. [bibtex-key = Mahr2017]



51. Florian Meierhofer, Haipeng Li, Michael Gockeln, Robert Kun, Tim Grieb, Andreas Rosenauer, Udo Fritsching, Johannes Kiefer, Johannes Birkenstock, Lutz Mädler, and Suman Pokhrel. Screening Precursor-Solvent Combinations for Li$_4$Ti$_5$O$_{12}$ Energy Storage Material Using Flame Spray Pyrolysis. ACS Appl. Mater. Interfaces, 2017. [bibtex-key = Meierhofer2017]



52. Knut Müller-Caspary, Florian F. Krause, Tim Grieb, Stefan Löffler, Marco Schowalter, Armand Béché, Vincent Galioit, Dennis Marquardt, Josef Zweck, Peter Schattschneider, Johan Verbeeck, and Andreas Rosenauer. Measurement of atomic electric fields and charge densities from average momentum transfers using scanning transmission electron microscopy. Ultramicroscopy, 178:62-80, 2017. Keyword(s): TEM. Abstract:

    Abstract This study sheds light on the prerequisites, possibilities, limitations and interpretation of high-resolution differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM). We draw particular attention to the well-established \{DPC\} technique based on segmented annular detectors and its relation to recent developments based on pixelated detectors. These employ the expectation value of the momentum transfer as a reliable measure of the angular deflection of the \{STEM\} beam induced by an electric field in the specimen. The influence of scattering and propagation of electrons within the specimen is initially discussed separately and then treated in terms of a two-state channeling theory. A detailed simulation study of GaN is presented as a function of specimen thickness and bonding. It is found that bonding effects are rather detectable implicitly, e.g., by characteristics of the momentum flux in areas between the atoms than by directly mapping electric fields and charge densities. For strontium titanate, experimental charge densities are compared with simulations and discussed with respect to experimental artifacts such as scan noise. Finally, we consider practical issues such as figures of merit for spatial and momentum resolution, minimum electron dose, and the mapping of larger-scale, built-in electric fields by virtue of data averaged over a crystal unit cell. We find that the latter is possible for crystals with an inversion center. Concerning the optimal detector design, this study indicates that a sampling of 5 mrad per pixel is sufficient in typical applications, corresponding to approximately 10 × 10 available pixels.

    [bibtex-key = Mueller-Caspary2016d]



53. Jan Müssener, Pascal Hille, Tim Grieb, Jörg Schörmann, Jörg Teubert, Eva Monroy, Andreas Rosenauer, and Martin Eickhoff. Bias-controlled optical transitions in GaN/AlN nanowire heterostructures. ACS Nano, 11:8758-8767, 2017. [bibtex-key = Muessener2017]



54. Meng Qi, William A. O’Brien, Chad A. Stephenson, Victor Patel, Ning Cao, Brian J. Thibeault, Marco Schowalter, Andreas Rosenauer, Vladimir Protasenko, Huili (Grace) Xing, and Mark A. Wistey. Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides. Crystals, 7(6), 2017. Abstract:

    Tensile-strained Ge is a possible laser material for Si integrated circuits, but reports of lasers using tensile Ge show high threshold current densities and short lifetimes. To study the origins of these shortcomings, Ge ridge waveguides with tensile strain in three dimensions were fabricated using compressive silicon nitride (SiNx) films with up to 2 GPa stress as stress liners. A Raman peak shift of up to 11 cm−1 was observed, corresponding to 3.6% hydrostatic tensile strain for waveguides with a triangular cross-section. Real time degradation in tensile-strained Ge was observed and studied under transmission electron microscopy (TEM). A network of defects, resembling dark line defects, was observed to form and propagate with a speed and density strongly correlated with the local strain extracted from both modeled and measured strain profiles. This degradation suggests highly tensile-strained Ge lasers are likely to have significantly shorter lifetime than similar GaAs or InGaAs quantum well lasers.

    [bibtex-key = cryst7060157]



55. Ira V. Rozhdestvenskaya, Enrico Mugnaioli, Marco Schowalter, Martin U. Schmidt, Michael Czank, Wulf Depmeier, and Andreas Rosenauer. The structure of denisovite, a fibrous nanocrystalline polytypic disordered `very complex' silicate, studied by a synergistic multi-disciplinary approach employing methods of electron crystallography and X-ray powder diffraction. IUCrJ, 4(3):223--242, May 2017. Keyword(s): denisovite, minerals, fibrous materials, nanocrystalline materials, electron crystallography, electron diffraction tomography, X-ray powder diffraction, modularity, disorder, polytypism, OD approach, complexity, framework-structured solids, inorganic materials, nanostructure, nanoscience. Abstract:

    Denisovite is a rare mineral occurring as aggregates of fibres typically 200{--}500nm diameter. It was confirmed as a new mineral in 1984, but important facts about its chemical formula, lattice parameters, symmetry and structure have remained incompletely known since then. Recently obtained results from studies using microprobe analysis, X-ray powder diffraction (XRPD), electron crystallography, modelling and Rietveld refinement will be reported. The electron crystallography methods include transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-angle annular dark-field imaging (HAADF), high-resolution transmission electron microscopy (HRTEM), precession electron diffraction (PED) and electron diffraction tomography (EDT). A structural model of denisovite was developed from HAADF images and later completed on the basis of quasi-kinematic EDT data by {\it ab initio} structure solution using direct methods and least-squares refinement. The model was confirmed by Rietveld refinement. The lattice parameters are {\it a} = 31.024(1), {\it b} = 19.554(1) and {\it c} = 7.1441(5){\AA}, {$\beta$} = 95.99(3){$^\circ$}, {\it V} = 4310.1(5){\AA}${\sp 3}$ and space group {\it P}12/{\it a}1. The structure consists of three topologically distinct dreier silicate chains, {\it viz}. two xonotlite-like dreier double chains, [Si${\sb 6}$O${\sb 17}$]${\sp 10{$-$}}$, and a tubular loop-branched dreier triple chain, [Si${\sb 12}$O${\sb 30}$]${\sp 12{$-$}}$. The silicate chains occur between three walls of edge-sharing (Ca,Na) octahedra. The chains of silicate tetrahedra and the octahedra walls extend parallel to the {\it z} axis and form a layer parallel to (100). Water molecules and K${\sp +}$ cations are located at the centre of the tubular silicate chain. The latter also occupy positions close to the centres of eight-membered rings in the silicate chains. The silicate chains are geometrically constrained by neighbouring octahedra walls and present an ambiguity with respect to their {\it z} position along these walls, with displacements between neighbouring layers being either {$\Delta$}{\it z} = {\it c}/4 or {$-$}{\it c}/4. Such behaviour is typical for polytypic sequences and leads to disorder along [100]. In fact, the diffraction pattern does not show any sharp reflections with {\it l} odd, but continuous diffuse streaks parallel to {\it a}* instead. Only reflections with {\it l} even are sharp. The diffuse scattering is caused by (100) nano{\-}lamellae separated by stacking faults and twin boundaries. The structure can be described according to the order{--}disorder (OD) theory as a stacking of layers parallel to (100).

    [bibtex-key = Rozhdestvenskaya:fc5016]



56. Wojciech Rudno-Rudziński, Marcin Syperek, Aleksander Maryński, Janusz Andrzejewski, Jan Misiewicz, Sven Bauer, Vitalii I. Sichkovskyi, Johann P. Reithmaier, Marco Schowalter, Beeke Gerken, Andreas Rosenauer, and Grzegorz Sęk. Control of Dynamic Properties of InAs/InAlGaAs/InP Hybrid Quantum Well-Quantum Dot Structures Designed as Active Parts of 1.55 μm Emitting Lasers. physica status solidi (a), pp 1700455--n/a, 2017. Note: 1700455. Keyword(s): emitting lasers, optical spectroscopy, quantum dots, tunnel injection structures. [bibtex-key = PSSA:PSSA201700455]



57. Junjie Shi, Christoph Mahr, M. Mangir Murshed, Thorsten M. Gesing, Andreas Rosenauer, M. Bäumer, and A. Wittstock. Steam reforming of methanol over oxide decorated nanoporous gold catalysts: a combined in situ FTIR and flow reactor study. Phys. Chem. Chem. Phys., 19:8880-8888, 2017. Abstract:

    Methanol as a green and renewable resource can be used to generate hydrogen by reforming{,} i.e.{,} its catalytic oxidation with water. In combination with a fuel cell this hydrogen can be converted into electrical energy{,} a favorable concept{,} in particular for mobile applications. Its realization requires the development of novel types of structured catalysts{,} applicable in small scale reactor designs. Here{,} three different types of such catalysts were investigated for the steam reforming of methanol (SRM). Oxides such as TiO2 and CeO2 and mixtures thereof (Ce1Ti2Ox) were deposited inside a bulk nanoporous gold (npAu) material using wet chemical impregnation procedures. Transmission electron and scanning electron microscopy reveal oxide nanoparticles (1-2 nm in size) abundantly covering the strongly curved surface of the nanoporous gold host (ligaments and pores on the order of 40 nm in size). These catalysts were investigated in a laboratory scaled flow reactor. First conversion of methanol was detected at 200 [degree]C. The measured turn over frequency at 300 [degree]C of the CeOx/npAu catalyst was 0.06 s-1. Parallel investigation by in situ infrared spectroscopy (DRIFTS) reveals that the activation of water and the formation of OHads are the key to the activity/selectivity of the catalysts. While all catalysts generate sufficient OHads to prevent complete dehydrogenation of methanol to CO{,} only the most active catalysts (e.g.{,} CeOx/npAu) show direct reaction with formic acid and its decomposition to CO2 and H2. The combination of flow reactor studies and in operando DRIFTS{,} thus{,} opens the door to further development of this type of catalyst.

    [bibtex-key = Shi2017]



58. Michael Teck, M. Mangir Murshed, Marco Schowalter, Niels Lefeld, Henrike K. Grossmann, Tim Grieb, Thomas Hartmann, Lars Robben, Andreas Rosenauer, Lutz Mädler, and Thorsten M. Gesing. Structural and spectroscopic comparison between polycrystalline, nanocrystalline and quantum dot visible light photo-catalyst Bi$_2$WO$_6$. Journal of Solid State Chemistry, 254:82-89, 2017. [bibtex-key = Teck2017]



59. Johannes Wild, Thomas N. G. Meier, Simon Pöllath, Matthias Kronseder, Andreas Bauer, Alfonso Chacon, Marco Halder, Marco Schowalter, Andreas Rosenauer, Josef Zweck, Jan Müller, Achim Rosch, Christian Pfleiderer, and Christian H. Back. Entropy-limited topological protection of skyrmions. Science Advances, 3(9), 2017. Abstract:

    Magnetic skyrmions are topologically protected whirls that decay through singular magnetic configurations known as Bloch points. We used Lorentz transmission electron microscopy to infer the energetics associated with the topological decay of magnetic skyrmions far from equilibrium in the chiral magnet Fe1-xCoxSi. We observed that the lifetime Ï„ of the skyrmions depends exponentially on temperature, . The prefactor Ï„0 of this Arrhenius law changes by more than 30 orders of magnitude for small changes of the magnetic field, reflecting a substantial reduction of the lifetime of skyrmions by entropic effects and, thus, an extreme case of enthalpy-entropy compensation. Such compensation effects, being well known across many different scientific disciplines, affect topological transitions and, thus, topological protection on an unprecedented level.

    [bibtex-key = Wilde1701704]



60. K. W. H. van den Bos, Florian F. Krause, Armand Beche, Johan Verbeeck, Andreas Rosenauer, and Sandra Van Aert. Locating light and heavy atomic column positions with picometer precision using ISTEM. Ultramicroscopy, 172:75--81, 2017. [bibtex-key = vandenBos2017]



61. T. Aschenbrenner, M. Schowalter, T. Mehrtens, K. Müller-Caspary, M. Fikry, D. Heinz, I. Tischer, M. Madel, K. Thonke, D. Hommel, F. Scholz, and A.ahr Rosenauer. Composition analysis of coaxially grown InGaN multi quantum wells using scanning transmission electron microscopy. Journal of Applied Physics, 119(17), 2016. Abstract:

    GaNnanotubes with coaxial InGaNquantum wells were analyzed by scanning transmission electron microscopy in order to determine their structural properties as well as the indium distribution across the InGaNquantum wells. For the latter, two process steps are necessary. First, a technique to prepare cross-sectional slices out of the nanotubes has been developed. Second, an existing scanning transmission electron microscopy analysis technique has been extended with respect to the special crystallographic orientation of this type of specimen. In particular, the shape of the nanotubes, their defect structure, and the incorporation of indium on different facets were investigated. The quantum wells preferentially grow on m-planes of the dodecagonally shaped nanotubes and on semipolar top facets while no significant indium signal was found on a-planes. An averaged indium concentration of 6% to 7% was found by scanning transmission electron microscopy analysis and could be confirmed by cathodoluminescence measurements.

    [bibtex-key = Aschenbrenner2016]



62. Daniel Carvalho, Knut Müller-Caspary, Marco Schowalter, Tim Grieb, Thorsten Mehrtens, Andreas Rosenauer, Rafael Ben, Teresa Garcìa, Andrés Redondo-Cubero, Katharina Lorenz, Bruno Daudin, and Francisco M. Morales. Direct Measurement of Polarization-Induced Fields in GaN/AlN by Nano-Beam Electron Diffraction. Scientific Reports, 6:28459, June 2016. Keyword(s): DPC, strain, NBD, SANBED, nano-beam electron diffraction, polarization, polarisation, piezoelectric. Abstract:

    The built-in piezoelectric fields in group III-nitrides can act as road blocks on the way to maximizing the efficiency of opto-electronic devices. In order to overcome this limitation, a proper characterization of these fields is necessary. In this work nano-beam electron diffraction in scanning transmission electron microscopy mode has been used to simultaneously measure the strain state and the induced piezoelectric fields in a GaN/AlN multiple quantum well system.

    [bibtex-key = Carvalho2016]



63. Jochen A. H. Dreyer, Suman Pokhrel, Johannes Birkenstock, Miguel G. Hevia, Marco Schowalter, Andreas Rosenauer, Atsushi Urakawa, Wey Yang Teoh, and Lutz Madler. Decrease of the required dopant concentration for [small delta]-Bi2O3 crystal stabilization through thermal quenching during single-step flame spray pyrolysis. CrystEngComm, 18:2046--2056, 2016. Abstract:

    [small delta]-Bi2O3 is one of the best oxygen ion conductors known. However{,} due to its limited thermal stability and complicated synthesis techniques{,} its applications are limited. Here{,} the synthesis of stable nano-sized [small delta]-Bi2O3 using versatile and rapid flame spray pyrolysis (FSP) combined with in situ Ti and/or Mn doping for an enhanced thermal stability is reported for the first time. Exceptionally low Bi replacing cation concentrations (8 at% Ti) were sufficient to obtain phase-pure [small delta]-Bi2O3 which was attributed to the extraordinarily high temperature gradient during FSP. The required cation amount for [small delta]-phase stabilization was even further reduced by introducing mixtures of Mn and Ti (2.5 at% Mn + 2.5 at% Ti). Rietveld analysis revealed that the [small delta]-Bi2O3 structure is best represented by the Fm[3 with combining macron]m space group containing two closely neighbored 8c and 32f Wyckoff positions. Depending on the amount of Mn/Ti cations{,} about 25% of the possible oxygen positions remain vacant{,} suggesting high bulk oxygen mobility. The enhanced oxygen mobility was confirmed by temperature programmed reduction (H2-TPR) with bulk reduction for [small delta]-Bi2O3 in contrast to exclusive surface reduction for [small beta]-Bi2O3.

    [bibtex-key = Dreyer2016]



64. Andrea Kirsch, M. Mangir Murshed, Marco Schowalter, Andreas Rosenauer, and Thorsten M. Gesing. Nanoparticle Precursor into Polycrystalline Bi2Fe4O9: An Evolutionary Investigation of Structural, Morphological, Optical, and Vibrational Properties. The Journal of Physical Chemistry C, 120(33):18831--18840, 2016. Abstract:

    Mullite-type Bi2Fe4O9 was synthesized using a polyol-mediated method. X-ray powder diffraction (XRD) revealed that the as-synthesized sample is nanocrystalline. It transformed into a rhombohedral perovskite-type BiFeO3 followed by a second transformation into mullite-type Bi2Fe4O9 during heating. Each structural feature, from as-synthesized into crystalline phase, was monitored through temperature-dependent XRD in situ. The locally resolved high resolution transmission electron micrographs revealed that the surface of some heated samples is covered by 4–13 nm sized particles which were identified from the lattice fringes as crystalline Bi2Fe4O9. XRD and Raman spectra demonstrate that the nucleation of both BiFeO3 and Bi2Fe4O9 might simultaneously commence; however, their growth and ratios are dependent on temperature. The diffuse UV/vis reflectance spectra showed fundamental absorption edges between 1.80(1) and 2.75(3) eV. A comparative study between the “derivation of absorption spectrum fitting method� (DASF) and the Tauc method suggests Bi2Fe4O9 to be a direct band gap semiconductor.

    [bibtex-key = Kirsch2016]



65. Florian. F. Krause. Stemming Unwanted Interference: Resolution Improvement by Incoherent Imaging with ISTEM. Imaging & Microscopy, 18(2):40--43, 2016. Keyword(s): notpeer. [bibtex-key = Krause2016c]



66. Florian F. Krause, Marco Schowalter, Tim Grieb, Knut Müller-Caspary, Thorsten Mehrtens, and Andreas Rosenauer. Effects of instrument imperfections on quantitative scanning transmission electron microscopy. Ultramicroscopy, 161:146--160, 2016. Keyword(s): TEM. [bibtex-key = Krause2016]



67. Matthias Lohr, Ralph Schregle, Michael Jetter, Clemens Wächter, Knut Müller-Caspary, Thorsten Mehrtens, Andreas Rosenauer, Ines Pietzonka, Martin Strassburg, and Josef Zweck. Quantitative measurements of internal electric fields with differential phase contrast microscopy on InGaN/GaN quantum well structures. physica status solidi (b), 253:140--144, 2016. Keyword(s): DPC, Efficiency droop, EFTEM, electric fields, GaN, HAADF, IMFP, MQW, QCSE, quantification, STEM. Abstract:

    Piezoelectric and spontaneous polarization play an essential role in GaN-based devices. InGaN quantum wells (QWs) in GaN host material, especially grown along the polar c-direction, exhibit strong internal fields in the QW region due to the indium-induced strain. An exact knowledge of the electric fields is essential, since they are one of the factors limiting the performance of green LDs and LEDs. Differential phase contrast in a scanning transmission electron microscope enables direct, local, and quantitative measurements of these electric fields. For a multi-QW sample, it was possible to determine the piezoelectric field in the range of 43-67 MV m−1 with a resolution of 10 MV m−1 (≡ 10 mV nm−1).

    [bibtex-key = Lohr2016]



68. K. Müller-Caspary, O. Oppermann, T. Grieb, F. F. Krause, A. Rosenauer, M. Schowalter, T. Mehrtens, A. Beyer, K. Volz, and P. Potapov. Materials characterisation by angle resolved scanning transmission electron microscopy. Scientific Reports, 6:37146, 2016. [bibtex-key = Mueller-Caspary2016]



69. H. Ryll, M. Simson, R. Hartmann, P. Holl, M. Huth, S. Ihle, Y. Kondo, P. Kotula, A. Liebel, K. Müller-Caspary, A. Rosenauer, R. Sagawa, J. Schmidt, H. Soltau, and L. Strüder. A pnCCD-based, fast direct single electron imaging camera for TEM and STEM. Journal of Instrumentation, 11(04):P04006, 2016. Abstract:

    We report on a new camera that is based on a pnCCD sensor for applications in scanning transmission electron microscopy. Emerging new microscopy techniques demand improved detectors with regards to readout rate, sensitivity and radiation hardness, especially in scanning mode. The pnCCD is a 2D imaging sensor that meets these requirements. Its intrinsic radiation hardness permits direct detection of electrons. The pnCCD is read out at a rate of 1,150 frames per second with an image area of 264 x 264 pixel. In binning or windowing modes, the readout rate is increased almost linearly, for example to 4000 frames per second at 4× binning (264 x 66 pixel). Single electrons with energies from 300 keV down to 5 keV can be distinguished due to the high sensitivity of the detector. Three applications in scanning transmission electron microscopy are highlighted to demonstrate that the pnCCD satisfies experimental requirements, especially fast recording of 2D images. In the first application, 65536 2D diffraction patterns were recorded in 70 s. STEM images corresponding to intensities of various diffraction peaks were reconstructed. For the second application, the microscope was operated in a Lorentz-like mode. Magnetic domains were imaged in an area of 256 x 256 sample points in less than 37 seconds for a total of 65536 images each with 264 x 132 pixels. Due to information provided by the two-dimensional images, not only the amplitude but also the direction of the magnetic field could be determined. In the third application, millisecond images of a semiconductor nanostructure were recorded to determine the lattice strain in the sample. A speed-up in measurement time by a factor of 200 could be achieved compared to a previously used camera system.

    [bibtex-key = Ryll2016]



70. Marc Sauerbrey, Jan Höcker, Meikel Wellbrock, Marco Schowalter, Jon-Olaf Krisponeit, Knut Müller-Caspary, Andreas Rosenauer, Gang Wei, Lucio Colombi Ciacchi, Jens Falta, and Jan Ingo Flege. Ultrasmooth Ru(0001) Films as Templates for Ceria Nanoarchitectures. Crystal Growth & Design, 16(8):4216--4224, 2016. Abstract:

    Single crystalline magnetron sputter-deposited Ru(0001) epitaxial thin films on c-plane sapphire were prepared and used as a template for reactive CeO2 growth. Low-energy electron microscopy and diffraction, as well as transmission electron microscopy and atomic force microscopy, experiments were performed to investigate the crystallinity and morphology of the prepared films. Multiple cycles of Ar+ sputtering and high-temperature annealing produces films of exceptional surface quality. High-temperature reactive ceria growth leads to perfectly aligned triangular single-crystalline CeO2(111) islands of extraordinary morphological and structural homogeneity. At the chosen growth conditions, ceria nucleation takes place only at V-shaped surface defects on the otherwise atomically flat Ru terraces, opening up the possibility to influence the nucleation by introducing artificial surface defects using standard etching techniques. Due to their high crystallinity and extraordinary surface quality, these substrates present a low-cost alternative to Ru single crystals for model studies in heterogeneous catalysis and also allow for the use of destructive investigation techniques and irreversible surface modifications.

    [bibtex-key = Sauerbrey2016]



71. Junjie Shi, Christoph Mahr, M. Mangir Murshed, Volkmar Zielasek, Andreas Rosenauer, Thorsten M. Gesing, Marcus Bäumer, and Arne Wittstock. A versatile sol-gel coating for mixed oxides on nanoporous gold and their application in the water gas shift reaction. Catal. Sci. Technol., 6:5311--5319, 2016. Abstract:

    Based on a sol-gel coating method{,} a series of nanoporous gold (npAu) catalysts functionalized with titania-ceria mixed oxides were prepared. Metal-oxides with different composition were formed inside the mesoporous material (ligaments and pores [similar]45 nm) after thermal treatment at over 200 [degree]C for 2 h. The water-gas shift (WGS) reaction (H2O + CO [rightward arrow] H2 + CO2) was studied in a continuous flow reactor at ambient pressure using these Ce-TiOx/npAu catalytic materials. Formation of CO2 was observed at temperatures between 200 [degree]C and 450 [degree]C. The addition of CeO2 to TiO2 resulted in an strongly increased activity; the sample (with the molar ratio of Ce : Ti = 1 : 2 abbreviated as Ce1Ti2Ox/npAu) shows the highest activity which was nearly twice as high as the activity of all other samples at 300 [degree]C. The loss of activity after 2 catalytic runs was only about 10% at 450 [degree]C for the Ce1Ti2Ox/npAu sample and no coarsening was observed. Raman spectroscopic characterization of the materials indicates a dynamic correlation between the crystallization (oxygen storage) of the metal-oxides under oxidizing and reducing conditions.

    [bibtex-key = Shi2016]



72. P. S. Sokolov, M. Yu. Petrov, T. Mehrtens, K. Müller-Caspary, A. Rosenauer, D. Reuter, and A. D. Wieck. Reconstruction of nuclear quadrupole interaction in (In,Ga)As/GaAs quantum dots observed by transmission electron microscopy. Phys. Rev. B, 93:045301, January 2016. Abstract:

    A microscopic study of the individual annealed (In,Ga)As/GaAs quantum dots is done by means of high-resolution transmission electron microscopy. The Cauchy-Green strain-tensor component distribution and the chemical composition of the (In,Ga)As alloy are extracted from the microscopy images. The image processing allows for the reconstruction of the strain-induced electric-field gradients at the individual atomic columns extracting thereby the magnitude and asymmetry parameter of the nuclear quadrupole interaction. Nuclear magnetic resonance absorption spectra are analyzed for parallel and transverse mutual orientations of the electric-field gradient and a static magnetic field.

    [bibtex-key = Sokolov2016]



73. Anda Sulce, Felix Bulke, Marco Schowalter, Andreas Rosenauer, Ralf Dringen, and Sebastian Kunz. Reactive oxygen species (ROS) formation ability and stability of small copper (Cu) nanoparticles (NPs). RSC Adv., 6:76980--76988, 2016. Abstract:

    A protocol to functionalize small copper nanoparticles (Cu NPs{,} 1-5 nm) with hydrophilic ligands is presented. The method was applied to prepare Cu NPs stabilized by cysteine{,} glutathione{,} proline{,} or OH-. These four types of Cu NPs were tested with respect to their stability and ability to form reactive oxygen species (ROS) in presence of H2O2. The ligands were found to affect both{,} ROS formation and particle stability. However{,} compared to Cu cations{,} the Cu NPs were much less effective in terms of forming ROS in the presence of H2O2. Application of copper ion chelators demonstrated that the formation of ROS in samples containing Cu NPs was mainly caused by Cu cations leached from the particles{,} but not by nanoparticle-specific effects. Our results suggest that a secure application of Cu in the form of NPs is restricted to reductive conditions{,} as under oxidizing conditions Cu NPs will degrade by the leaching of Cu ions.

    [bibtex-key = Sulce2016]



74. Dan Zhou, Knut Müller-Caspary, Wilfried Sigle, Florian F. Krause, Andreas Rosenauer, and van Aken Peter. Sample tilt effects on atom column position determination in ABF-STEM imaging. Ultramicroscopy, 160:110--117, 2016. Keyword(s): Annular bright-field imaging. Abstract:

    The determination of atom positions from atomically resolved transmission electron micrographs is fundamental for the analysis of crystal defects and strain. In recent years annular bright-field (ABF) imaging has become a popular imaging technique owing to its ability to map both light and heavy elements. Contrast formation in \{ABF\} is partially governed by the phase of the electron wave, which renders the technique more sensitive to the tilt of the electron beam with respect to the crystal zone axis than high-angle annular dark-field imaging. Here we show this sensitivity experimentally and use image simulations to quantify this effect. This is essential for error estimation in future quantitative \{ABF\} studies.

    [bibtex-key = Zhou2016]



75. Jochen A.H. Dreyer, Henrike K. Grossmann, Jinfan Chen, Tim Grieb, Bill B. Gong, Patrick H.-L. Sit, Lutz Mädler, and Wey Yang Teoh. Preferential oxidation of carbon monoxide over Pt-FeO$_{x}$/CeO$_{2}$ synthesized by two-nozzle flame spray pyrolysis. Journal of Catalysis, 329:248-261, 2015. [bibtex-key = Dreyer2015]



76. H.K. Grossmann, T. Grieb, F. Meierhofer, M.J. Hodapp, D. Noriler, A. Gröhn, H.F. Meier, U. Fritsching, K. Wegner, and L. Mädler. Nanoscale mixing during double-flame spray synthesis of heterostructured nanoparticles. J. Nanopart. Res., 17:174, 2015. [bibtex-key = Grossmann2015a]



77. Florian F. Krause, Jan-Philipp Ahl, Darius Tytko, Pyuck-Pa Choi, Ricardo Egoavil, Marco Schowalter, Thorsten Mehrtens, Knut Müller-Caspary, Johan Verbeeck, Dierk Raabe, Joachim Hertkorn, Karl Engl, and Andreas Rosenauer. Homogeneity and composition of AlInGaN: A multiprobe nanostructure study. Ultramicroscopy, 156(0):29--36, 2015. Keyword(s): HAADF STEM. Abstract:

    Abstract The electronic properties of quaternary AlInGaN devices significantly depend on the homogeneity of the alloy. The identification of compositional fluctuations or verification of random-alloy distribution is hence of grave importance. Here, a comprehensive multiprobe study of composition and compositional homogeneity is presented, investigating AlInGaN layers with indium concentrations ranging from 0 to 17 at\% and aluminium concentrations between 0 and 39 at\% employing high-angle annular dark field scanning electron microscopy (HAADF STEM), energy dispersive X-ray spectroscopy (EDX) and atom probe tomography (APT). \{EDX\} mappings reveal distributions of local concentrations which are in good agreement with random alloy atomic distributions. This was hence investigated with \{HAADF\} \{STEM\} by comparison with theoretical random alloy expectations using statistical tests. To validate the performance of these tests, \{HAADF\} \{STEM\} image simulations were carried out for the case of a random-alloy distribution of atoms and for the case of In-rich clusters with nanometer dimensions. The investigated samples, which were grown by metal-organic vapor phase epitaxy (MOVPE), were thereby found to be homogeneous on this nanometer scale. Analysis of reconstructions obtained from \{APT\} measurements yielded matching results. Though \{HAADF\} \{STEM\} only allows for the reduction of possible combinations of indium and aluminium concentrations to the proximity of isolines in the two-dimensional composition space. The observed ranges of composition are in good agreement with the \{EDX\} and \{APT\} results within the respective precisions.

    [bibtex-key = Krause2015d]



78. Christoph Mahr, Knut Müller-Caspary, Tim Grieb, Marco Schowalter, Thorsten Mehrtens, Florian. F. Krause, Dennis Zillmann, and Andreas Rosenauer. Theoretical study of precision and accuracy of strain analysis by nano-beam electron diffraction. Ultramicroscopy, 158(0):38--48, 2015. Keyword(s): Strain measurement. Abstract:

    Abstract Measurement of lattice strain is important to characterize semiconductor nanostructures. As strain has large influence on the electronic band structure, methods for the measurement of strain with high precision, accuracy and spatial resolution in a large field of view are mandatory. In this paper we present a theoretical study of precision and accuracy of measurement of strain by convergent nano-beam electron diffraction. It is found that the accuracy of the evaluation suffers from halos in the diffraction pattern caused by a variation of strain within the area covered by the focussed electron beam. This effect, which is expected to be strong at sharp interfaces between materials with different lattice plane distances, will be discussed for convergent-beam electron diffraction patterns using a conventional probe and for patterns formed by a precessing electron beam. Furthermore, we discuss approaches to optimize the accuracy of strain measured at interfaces. The study is based on the evaluation of diffraction patterns simulated for different realistic structures that have been investigated experimentally in former publications. These simulations account for thermal diffuse scattering using the frozen-lattice approach and the modulation-transfer function of the image-recording system. The influence of Poisson noise is also investigated.

    [bibtex-key = Mahr2015]



79. Knut Müller-Caspary. Messung atomarer elektrischer Felder. Physik in unserer Zeit, 46(3):110--111, 2015. Abstract:

    Dank der enormen Weiterentwicklung aberrationskorrigierter Elektronenoptik erreicht die Raster-Transmissionselektronenmikroskopie (STEM) heute eine Aufl{\"o}sung von 50 pm (1 pm = 10-12 m). Damit er{\"o}ffnet sich der Blick in subatomare Details, wie atomare elektrische Felder oder Ladungstransfers bei chemischen Bindungen.

    [bibtex-key = Mueller-Caspary2015d]



80. Knut Müller-Caspary, Andreas Oelsner, and Pavel Potapov. Two-dimensional strain mapping in semiconductors by nano-beam electron diffracion employing a delay-line detector. Applied Physics Letters, 107:072110, 2015. Abstract:

    A delay-line detector is established for electron detection in the field of scanning transmission electron microscopy (STEM) and applied to two-dimensional strain mapping in Si-based field effect transistors. We initially outline the functional principle of position-sensitive delay-line detection, based on highly accurate time measurements for electronic pulses travelling in meandering wires. In particular, the detector is a single-counting device essentially providing an infinite time stream of position-resolved events so that acquisition speed is not hindered by detector read-outs occuring in conventional charge-coupled devices. By scanning the STEM probe over stressor- and gate regions of a field effect transistor on a 100x100 raster, 10,000 diffraction patterns have been acquired within 3-6.5 min, depending on the scan speed. Evaluation of the 004 and 220 reflections yields lateral and vertical strain at a spatial resolution of 1.6nm. Dose-dependent strain precisions of 1.2-1.8x10^{-3} could be achieved for frame times of 40 and 20 ms, respectively. Finally, the detector is characterised as to quantum efficiency and further scopes of application are outlined.

    [bibtex-key = Mueller-Caspary2015a]



81. Suman Pokhrel, Johannes Birkenstock, Arezoo Dianat, Janina Zimmermann, Marco Schowalter, Andreas Rosenauer, Lucio Colombi Ciacchi, and L. Madler. In situ high temperature X-ray diffraction, transmission electron microscopy and theoretical modeling for the formation of WO3 crystallites. CrystEngComm, 17:6985--6998, 2015. Abstract:

    We study the transformation that WO3 nanoparticles produced by Flame Spray Pyrolysis undergo when subjected to heating and cooling cycles by means of accurate in situ XRD and HRTEM investigations supported by atomistic modeling at the level of Density Functional Theory. As-deposited particles{,} initially in the monoclinic phase{,} reversibly transform into the high-temperature orthogonal and tetragonal phases (and vice versa) irrespective of the direction of the temperature gradient. However{,} upon heating the particles experience an irreversible change of morphology as a consequence of evaporation/reprecipitation processes leading to the formation of larger particles{,} some of which are elongated (aspect ratios of up to 3 : 1) along various crystallographic directions of the tetragonal unit cell. On the basis of the results of extensive ab initio thermodynamic calculations of surface energies and first-principles molecular dynamics simulations of the growth process{,} we rationalize these findings in terms of different surface stabilities and reactivities towards gas-phase deposition of molecular WO3 presented by the nanocrystal facets.

    [bibtex-key = Pokhrel2015]



82. U. Rossow, L. Hoffmann, H. Bremers, E.R. Buss, F. Ketzer, T. Langer, A. Hangleiter, T. Mehrtens, M. Schowalter, and A. Rosenauer. Indium incorporation processes investigated by pulsed and continuous growth of ultrathin InGaN quantum wells. Journal of Crystal Growth, 414(0):49--55, 2015. Note: Proceedings of the Seventeenth International Conference on Metalorganic Vapor Phase Epitaxy. Keyword(s): A1. Surface processes. Abstract:

    Abstract We study the incorporation of indium into Al x Ga 1 − x N /GaN quantum well (QW) structures with high indium concentrations above 25\% for \{QW\} thicknesses in the range 2 nm down to half a c-lattice constant under pulsed and continuous growth conditions. We want to clarify which processes limit the incorporation of indium and lead to a degrading layer structure. The data are discussed in the context of the adlayer proposed by theory (Northrup et al., 2000) [1]. The interplay of the adlayer with the incoming flux, the high desorption rate and segregation of indium can consistently explain the various observed phenomena.

    [bibtex-key = Rossow2015]



83. Michael Adam, Marcus Bäumer, Marco Schowalter, Johannes Birkenstock, Michaela Wilhelm, and Georg Grathwohl. Generation of Pt- and Pt/Zn-containing ceramers and their structuring as macro/microporous foams. Chemical Engineering Journal, 247(0):205--215, 2014. Keyword(s): Polysiloxane. [bibtex-key = Adam2014]



84. M. Dries, S. Hettler, B. Gamm, E. Müller, W. Send, K. Müller, A. Rosenauer, and D. Gerthsen. A nanocrystalline Hilbert phase-plate for phase-contrast transmission electron microscopy. Ultramicroscopy, 139(0):29--37, 2014. Keyword(s): Transmission electron microscopy. [bibtex-key = Dries2014]



85. Elias Goldmann, Matthias Paul, Florian F. Krause, Knut Müller, Jan Kettler, Thorsten Mehrtens, Andreas Rosenauer, Michael Jetter, Peter Michler, and Frank Jahnke. Structural and emission properties of InGaAs/GaAs quantum dots emitting at 1.3 micrometers. Applied Physics Letters, 105(15):152102, 2014. [bibtex-key = Goldmann2014]



86. Tim Grieb, Knut Müller, Emmanuel Cadel, Andreas Beyer, Marco Schowalter, Etienne Talbot, Kerstin Volz, and Andreas Rosenauer. Simultaneous Quantification of Indium and Nitrogen Concentration in InGaNAs Using HAADF-STEM. Microscopy and Microanalysis, 20:1740, 9 2014. Abstract:

    ABSTRACT To unambiguously evaluate the indium and nitrogen concentrations in In x Ga1−x N y As1−y , two independent sources of information must be obtained experimentally. Based on high-resolution scanning transmission electron microscopy (STEM) images taken with a high-angle annular dark-field (HAADF) detector the strain state of the InGaNAs quantum well is determined as well as its characteristic HAADF-scattering intensity. The strain state is evaluated by applying elasticity theory and the HAADF intensity is used for a comparison with multislice simulations. The combination of both allows for determination of the chemical composition where the results are in accordance with X-ray diffraction measurements, three-dimensional atom probe tomography, and further transmission electron microscopy analysis. The HAADF-STEM evaluation was used to investigate the influence of As-stabilized annealing on the InGaNAs/GaAs sample. Photoluminescence measurements show an annealing-induced blue shift of the emission wavelength. The chemical analysis precludes an elemental diffusion as origin of the energy shift—instead the results are in agreement with a model based on an annealing-induced redistribution of the atomic next-neighbor configuration.

    [bibtex-key = Grieb2014]



87. H.K. Grossmann, T. Grieb, and S. Schopf, Y.H. Ng, R. Amal, and L. Mädler. Flame made oxide heterojunctions for photocatalytic water splitting. Chem. Ing. Tech., 86:1427, 2014. [bibtex-key = Grossmann2014_proc]



88. Dominik Heinz, Mohamed Fikry, Timo Aschenbrenner, Marco Schowalter, Tobias Meisch, Manfred Madel, Florian Huber, Matthias Hocker, Manuel Frey, Ingo Tischer, Benjamin Neuschl, Thorsten Mehrtens, Knut Müller, Andreas Rosenauer, Detlef Hommel, Klaus Thonke, and Ferdinand Scholz. GaN tubes with coaxial non- and semipolar GaInN quantum wells. Phys. Status Solidi (c), 11:648--651, 2014. Abstract:

    We present the position-controlled growth of GaN nanotubes with coaxial GaInN quantum wells by using ZnO nanowires grown on top of GaN pyramids as templates. High resolution scanning transmission electron microscopy allows us to perform a detailed structural analysis of individual tubes. In particular, we report about structural properties like indium incorporation, thickness, and homogeneity of quantum wells realized on nonpolar m-plane side facets or on semipolar tips. Additionally, high resolution spatially and spectrally resolved cathodoluminescence spectroscopy performed at low temperature enables us to clearly identify the quantum well luminescence contributions for different kinds of facets on a single tube. The luminescence of the quantum wells deposited at variable temperatures shows a clear spectral shift in the cathodoluminescence signal, yielding an activation energy for the indium desorption from the m-plane side facets of about 1.6 eV.

    [bibtex-key = Heinz2014]



89. R. R. Juluri, A. Rath, A. Ghosh, A. Bhukta, R. Sathyavathi, D. Narayana Rao, Knut Müller, Marco Schowalter, Kristian Frank, Tim Grieb, Florian Krause, Andreas Rosenauer, and Parlapalli Vencata Satyam. Coherently Embedded Ag Nanostructures in Si: 3D Imaging and their application to SERS. Scientific Reports, 4:4633, April 2014. Abstract:

    Surface enhanced Raman spectroscopy (SERS) has been established as a powerful tool to detect very low-concentration bio-molecules. One of the challenging problems is to have reliable and robust SERS substrate. Here, we report on a simple method to grow coherently embedded (endotaxial) silver nanostructures in silicon substrates, analyze their three-dimensional shape by scanning transmission electronmicroscopy tomography anddemonstratetheiruseas ahighlyreproducibleandstablesubstratefor SERS measurements. Bi-layers consisting of Ag and GeOx thin films were grown on native oxide covered silicon substrate using a physical vapor deposition method. Followed by annealing at 800C under ambient conditions, this resulted in the formation of endotaxial Ag nanostructures of specific shape depending upon the substrate orientation. These structures are utilized for detection of Crystal Violet molecules of 5 3 10 2 10 M concentrations. These are expected to be one of the highly robust, reusable and novel substrates for single molecule detection.

    [bibtex-key = Juluri2014]



90. H. Kauko, B. O. Fimland, T. Grieb, A. M. Munshi, K. Müller, A. Rosenauer, and A. T. J. van Helvoort. Near-surface depletion of antimony during the growth of GaAsSb and GaAs/GaAsSb nanowires. Journal of Applied Physics, 116(14):144303, 2014. Abstract:

    The near-surface reduction of the Sb mole fraction during the growth of GaAsSb nanowires (NWs) and GaAs NWs with GaAsSb inserts has been studied using quantitative high-angle annular dark field scanning transmission electron microscopy (STEM). A model for diffusion of Sb in the hexagonal NWs was developed and employed in combination with the quantitative STEM analysis. GaAsSb NWs grown by Ga-assisted molecular beam epitaxy (MBE) and GaAs/GaAsSb NWs grown by Ga- and Au-assisted MBE were investigated. At the high temperatures employed in the NW growth, As-Sb exchange at and outward diffusion of Sb towards the surface take place, resulting in reduction of the Sb concentration at and near the surface in the GaAsSb NWs and the GaAsSb inserts. In GaAsSb NWs, an increasing near-surface depletion of Sb was observed towards the bottom of the NW due to longer exposure to the As beam flux. In GaAsSb inserts, an increasing change in the Sb concentration profile was observed with increasing post-insert axial GaAs growth time, resulting from a combined effect of radial GaAs overgrowth and diffusion of Sb. The effect of growth temperature on the diffusion of Sb in the GaAsSb inserts was identified. The consequences of these findings for growth optimization and the optoelectronic properties of GaAsSb are discussed.

    [bibtex-key = Kauko2014a]



91. H. Kauko, T. Grieb, A. M. Munshi, K. Mller, A. Rosenauer, B. O. Fimland, and A. T. J. van Helvoort. The Outward Diffusion of Sb during Nanowire Growth Studied by Quantitative High-Angle Annular Dark Field Scanning Transmission Electron Microscopy. Microscopy and Microanalysis, 20:186--187, 8 2014. [bibtex-key = Kauko2014]



92. L. Mädler, A. Gröhn, T. Grieb, F. Meierhofer, U. Fritsching, K. Wegner, and H.K. Grossmann. Size -and composite-controlled synthesis of multi oxide nanoparticles using double-flame spray pyrolysis. Chem. Ing. Tech., 86:1541, 2014. [bibtex-key = maedler2014_proc]



93. Knut Müller, Florian F. Krause, Armand Béché, Marco Schowalter, Vincent Galioit, Stefan Löffler, Johan Verbeeck, Josef Zweck, Peter Schattschneider, and Andreas Rosenauer. Atomic electric fields revealed by a quantum mechanical approach to electron picodiffraction. Nature Communications, 5:5653:1--8, December 2014. Keyword(s): DPC, STEM, electric field. Abstract:

    By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmission electron microscopy (STEM) is currently crossing the border to probing subatomic details. A major challenge is the measurement of atomic electric fields using differential phase contrast (DPC) microscopy, traditionally exploiting the concept of a field-induced shift of diffraction patterns. Here we present a simplified quantum theoretical interpretation of DPC. This enables us to calculate the momentum transferred to the STEM probe from diffracted intensities recorded on a pixel array instead of conventional segmented bright-field detectors. The methodical development yielding atomic electric field, charge and electron density is performed using simulations for binary GaN as an ideal model system. We then present a detailed experimental study of SrTiO3 yielding atomic electric fields, validated by comprehensive simulations. With this interpretation and upgraded instrumentation, STEM is capable of quantifying atomic electric fields and high-contrast imaging of light atoms.

    [bibtex-key = Mueller2014]



94. A. Rath, J. K. Dash, R. R. Juluri, A. Ghosh, T. Grieb, M. Schowalter, F. F. Krause, K. Müller, A. Rosenauer, and P. V. Satyam. A study of the initial stages of the growth of Au-assisted epitaxial Ge nanowires on a clean Ge(100) surface. CrystEngComm, 16:2486--2490, 2014. Abstract:

    We report on the interfacial phenomena that occur at the initial stages of Ge nanowire growth using gold as the catalyst on Ge(100) substrates under ultra high vacuum (UHV) conditions using molecular beam epitaxy (MBE). Room temperature deposition of a thin Au layer using MBE showed a wetting nature while de-wetting has been observed at 500 [degree]C and higher temperatures. The deposition of a thin layer of Ge at this condition resulted in the formation of Ge nanostructures and Au islands on Ge pedestals{,} corresponding to the initial growth of the Ge nanowires. Ge deposition at 600 [degree]C yielded larger Ge nanowires below the Au/AuGe catalyst interface due to the enhancement of the lateral material transport.

    [bibtex-key = Rath2014]



95. Andreas Rosenauer, Florian F. Krause, Knut Müller, Marco Schowalter, and Thorsten Mehrtens. Conventional Transmission Electron Microscopy Imaging beyond the Diffraction and Information Limits. Phys. Rev. Lett., 113:096101, August 2014. Abstract:

    There are mainly two complementary imaging modes in transmission electron microscopy (TEM): Conventional TEM (CTEM) and scanning TEM (STEM). In the CTEM mode the specimen is illuminated with a plane electron wave, and the direct image formed by the objective lens is recorded in the image plane. STEM is based on scanning the specimen surface with a focused electron beam and collecting scattered electrons with an extended disk or ring-shaped detector. Here we show that combination of CTEM imaging with STEM illumination generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. This new imaging mode improves imaging characteristics, is more robust against chromatic aberration, exhibits direct structural imaging with superior precision, visualizes light elements with excellent contrast, and even allows us to overcome the conventional information limit of a microscope.

    [bibtex-key = Rosenauer2014b]



96. Ahin Roy, Subhajit Kundu, Knut Müller, Andreas Rosenauer, Saransh Singh, Prita Pant, M. P. Gururajan, Praveen Kumar, J. Weissmüller, Abhishek Kumar Singh, and N. Ravishankar. Wrinkling of Atomic Planes in Ultrathin Au Nanowires. Nano Letters, 14(8):4859--4866, 2014. Abstract:

    A detailed understanding of structure and stability of nanowires is critical for applications. Atomic resolution imaging of ultrathin single crystalline Au nanowires using aberration-corrected microscopy reveals an intriguing relaxation whereby the atoms in the close-packed atomic planes normal to the growth direction are displaced in the axial direction leading to wrinkling of the (111) atomic plane normal to the wire axis. First-principles calculations of the structure of such nanowires confirm this wrinkling phenomenon, whereby the close-packed planes relax to form saddle-like surfaces. Molecular dynamics studies of wires with varying diameters and different bounding surfaces point to the key role of surface stress on the relaxation process. Using continuum mechanics arguments, we show that the wrinkling arises due to anisotropy in the surface stresses and in the elastic response, along with the divergence of surface-induced bulk stress near the edges of a faceted structure. The observations provide new understanding on the equilibrium structure of nanoscale systems and could have important implications for applications in sensing and actuation.

    [bibtex-key = Roy2014]



97. J. Schmidt, R. Hartmann, P. Holl, M. Huth, G. Lutz, K. Müller, A. Rosenauer, H. Ryll, S. Send, M. Simson, D. Steigenhöfer, J. Soltau, H. Soltau, and L. Strüder. Extending the dynamic range of fully depleted pnCCDs. Journal of Instrumentation, 9(10):P10008, 2014. Keyword(s): pnCCD, direct electron detection, CCD, fast, ultrafast. Abstract:

    pnCCDs are a special type of charge coupled devices (CCD) which were originally developed for applications in X-ray astronomy. At X-ray Free Electron Lasers (XFEL) pnCCDs are used as imaging X-ray spectrometers due to their outstanding characteristics like high readout speed, high and homogeneous quantum efficiency, low readout noise, radiation hardness and high pixel charge handling capacity. They can be used both as single-photon counting detectors for X-ray spectroscopy and as integrating detectors for X-ray imaging with count rates up to 10 4 photons of 1 keV per pixel and frame. However, extremely high photon intensities can result in pixel saturation and charge spilling into neighboring pixels. Because of this charge blooming effect, spatial information is reduced. Based on our research concerning the internal potential distribution we can enhance the pixel full well capacity even more and improve the quality of the image. This paper describes the influence of the operation voltages and space charge distribution of the pnCCD on the electric potential profile by using 2D numerical device simulations. Experimental results with signal injection from an optical laser confirm the simulation models.

    [bibtex-key = Schmidt2014]



98. Marco Schowalter, Ingo Stoffers, Florian F. Krause, Thorsten Mehrtens, Knut Müller, Malte Fandrich, Timo Aschenbrenner, Detlef Hommel, and Andreas Rosenauer. Influence of Static Atomic Displacements on Composition Quantification of AlGaN/GaN Heterostructures from HAADF-STEM Images. Microscopy and Microanalysis, 20:1463--1470, 10 2014. [bibtex-key = Schowalter2014]



99. Duggi V. Sridhara Rao, Ramachandran Sankarasubramanian, Kuttanellore Muraleedharan, Thorsten Mehrtens, Andreas Rosenauer, and Dipankar Banerjee. Quantitative Strain and Compositional Studies of InGaAs Epilayer in a GaAs-based pHEMT Device Structure by TEM Techniques. Microscopy and Microanalysis, 20:1262--1270, 8 2014. Abstract:

    In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the InxGa1 − xAs channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the InxGa1 − xAs layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the InxGa1 − xAs channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.

    [bibtex-key = SridharaRao2014]



100. Olesea Volciuc, Vladimir Sergentu, Ion Tiginyanu, Marco Schowalter, Veaceslav Ursaki, Andreas Rosenauer, Detlef Hommel, and Jürgen Gutowski. Photonic Crystal Structures Based on GaN Ultrathin Membranes. Journal of Nanoelectronics and Optoelectronics, 9(2):271--275, 2014. Keyword(s): GAN ULTRATHIN MEMBRANES, NANOSTRUCTURE FABRICATION, PHOTONIC CRYSTALS, THEORY AND DESIGN. Abstract:

     We report on maskless fabrication of ultrathin (d ∼ 15 nm) nanoperforated GaN membranes exhibiting a triangular lattice arrangement of holes with a diameter of 150 nm, and show that these membranes represent an intermediate case between two-dimensional (2D) and three-dimensional (3D) photonic crystals (PhC). A calculation of the dispersion law in the approximation of scalar waves is indicative of the occurrence of surface and bulk modes, further, there is a range of frequencies where only surface modes can exist. Advantages of the occurrence of two types of modes in ultrathin nanoperforated GaN membranes from the point of view of their incorporation in photonic and optoelectronic integrated circuits are discussed.

     [bibtex-key = Volciuc2014]



101. Tobias Bollhorst, Tim Grieb, Andreas Rosenauer, Gerald Fuller, Michael Maas, and Kurosch Rezwan. Synthesis route for the self-assembly of submicrometer-sized colloidosomes with tailorable nanopores. Chem. Mater., 25:3464, 2013. [bibtex-key = Bollhorst2013]



102. Malte Fandrich, Thorsten Mehrtens, Timo Aschenbrenner, Thorsten Klein, Martina Gebbe, Stephan Figge, Carsten Kruse, Andreas Rosenauer, and Detlef Hommel. Nitride based heterostructures with Ga- and N-polarity for sensing applications. Journal of Crystal Growth, 370(0):68--73, 2013. Keyword(s): A1. Characterization, A3. Metalorganic vapor phase epitaxy, A3. Molecular beam epitaxy, B1. Nitrides, B3. Sensors. Abstract:

     In this paper, a first comparative study on the sensing behavior of AlGaN/GaN and AlInN/GaN heterostructures is presented, especially with respect to the impact of crystal polarity. Ga-polar samples were grown completely by metal-organic vapor-phase epitaxy (MOVPE), whereas N-polar structures were realized by a combination of molecular-beam epitaxy and MOVPE. The epitaxial structures were characterized by high resolution X-ray diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy, particularly with regard to strain, surface and interface roughness. Sheet carrier density and mobility of the 2-dimensional charge carrier gas were determined by Hall measurements. The heterostructures were applied as open-gate sensors and their sensing behavior was analyzed by exposure to different polar liquids. Generally, the device sensitivity is dominated by the sheet carrier density indicating a direct correlation between localized carriers at the interface and surface. A superior carrier concentration in N-polar samples enhanced their response to polar fluids. Due to a higher sheet carrier density, AlInN-based devices are more sensitive to polar liquids compared to conventional AlGaN/GaN heterostructures.

     [bibtex-key = Fandrich2013]



103. Tim Grieb, Knut Müller, Rafael Fritz, Vincenzo Grillo, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. Quantitative chemical evaluation of dilute GaNAs using ADF STEM: Avoiding surface strain induced artifacts. Ultramicroscopy, 129(0):1--9, 2013. Keyword(s): Quantitative. Abstract:

     The high angle annular dark field intensity (HAADF) in scanning transmission electron microscopy (STEM) can be used for a quantitative evaluation of the chemical composition in dilute GaNAs quantum wells by comparison with simulated intensities. As the scattered intensity is highly sensitive to surface strain fields originating from the quantum wells embedded in GaAs, the \{HAADF\} intensity is difficult to evaluate in a quantitative way as long as strain contrast cannot be distinguished from chemical contrast. We present a method to achieve full 2D \{HAADF\} \{STEM\} compositional mapping of GaNAs/GaAs quantum well systems by making use of information from two different camera lengths.

     [bibtex-key = Grieb2013]



104. L. Hoffmann, H. Bremers, H. Jönen, U. Rossow, M. Schowalter, T. Mehrtens, A Rosenauer, and A. Hangleiter. Atomics scale investigations of ultra-thin GaInN/GaN quantum wells with high indium content. Applied Physics Letters, 102:102110, 2013. Abstract:

     Using scanning transmission electron microscopy (STEM), we have studied ultra-thin (<2 nm) GaInN quantum wells (QWs) on c-plane GaN with high indium content (>25 \%) suitable for blue-green light emitting devices. We are able to analyze the QW on an atomic scale with high resolution STEM and derive the indium content quantitatively. In our analysis, we find that indium is not only incorporated into the QW but also into the barriers under certain growth conditions. We observe indium tails or even plateau-like structures in the barriers, caused by excess indium being supplied during quantum well growth.

     [bibtex-key = Hoffmann2013a]



105. H. Kauko, T. Grieb, R. Bjørge, M. Schowalter, A.M. Munshi, H. Weman, A. Rosenauer, and A.T.J. van Helvoort. Compositional characterization of GaAs/GaAsSb nanowires by quantitative HAADF-STEM. Micron, 44(0):254--260, 2013. Keyword(s): HAADF-STEM. Abstract:

     The Sb concentration in axial GaAs1−xSbx inserts of otherwise pure GaAs nanowires has been investigated with quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The Sb concentration was quantified by comparing the experimental image intensities normalized to the incident beam intensity with intensities simulated with a frozen lattice multislice approach. Including static atomic displacements in the simulations was found to be crucial for correct compositional analysis of GaAs1−xSbx. \{HAADF\} intensities of individual nanowires were analysed both across the nanowires, exploiting their hexagonal cross-sectional shape, and along the evenly thick central part of the nanowires. From the cross-sectional intensity profiles, a decrease in the Sb concentration towards the nanowire outer surfaces was found. The longitudinal intensity profiles revealed a gradual build-up of Sb in the insert. The decrease of the Sb concentration towards the upper interface was either gradual or abrupt, depending on the growth routine chosen. The compositional analysis with quantitative HAADF-STEM was verified by energy dispersive X-ray spectroscopy.

     [bibtex-key = Kauko2013]



106. Florian F. Krause, Knut Müller, Dennis Zillmann, Jacob Jansen, Marco Schowalter, and Andreas Rosenauer. Comparison of intensity and absolute contrast of simulated and experimental high-resolution transmission electron microscopy images for different multislice simulation methods. Ultramicroscopy, 134(0):94--101, 2013. Keyword(s): Stobbs factor. [bibtex-key = Krause2013a]



107. Fabian Meder, Julia Wehling, Artur Fink, Beate Piel, Kaibo Li, Kristian Frank, Andreas Rosenauer, Laura Treccani, Susan Koeppen, Andreas Dotzauer, and Kurosch Rezwan. The role of surface functionalization of colloidal alumina particles on their controlled interactions with viruses. Biomaterials, 34(17):4203--4213, 2013. Keyword(s): Virus-material interaction. Abstract:

     Materials that interact in a controlled manner with viruses attract increasing interest in biotechnology, medicine, and environmental technology. Here, we show that virus-material interactions can be guided by intrinsic material surface chemistries, introduced by tailored surface functionalizations. For this purpose, colloidal alumina particles are surface functionalized with amino, carboxyl, phosphate, chloropropyl, and sulfonate groups in different surface concentrations and characterized in terms of elemental composition, electrokinetic, hydrophobic properties, and morphology. The interaction of the functionalized particles with hepatitis A virus and phages \{MS2\} and PhiX174 is assessed by virus titer reduction after incubation with particles, activity of viruses conjugated to particles, and imaged by electron microscopy. Type and surface density of particle functional groups control the virus titer reduction between 0 and 99.999\% (5 log values). For instance, high sulfonate surface concentrations (4.7 groups/nm2) inhibit attractive virus-material interactions and lead to complete virus recovery. Low sulfonate surface concentrations (1.2 groups/nm2), native alumina, and chloropropyl-functionalized particles induce strong virus-particle adsorption. The virus conformation and capsid amino acid composition further influence the virus-material interaction. Fundamental interrelations between material properties, virus properties, and the complex virus-material interaction are discussed and a versatile pool of surface functionalization strategies controlling virus-material interactions is presented.

     [bibtex-key = Meder2013]



108. Thorsten Mehrtens, Knut Müller, Marco Schowalter, Dongzhi Hu, Daniel M. Schaadt, and Andreas Rosenauer. Measurement of indium concentration profiles and segregation efficiencies from high-angle annular dark field-scanning transmission electron microscopy images. Ultramicroscopy, 131(0):1--9, 2013. Keyword(s): HAADF-STEM. Abstract:

     Abstract We investigated segregation of indium in an InxGa1−xAs/GaAs heterostructure via high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), where contrast strongly depends on the nuclear charges of the scattering atoms (Z-contrast). Indium concentration maps have been deduced from HAADF-STEM images by comparing normalized measured intensities with multislice simulations in the frozen lattice approach. Segregation coefficients were derived following the segregation model of Muraki et al. [1]. This is demonstrated for HAADF-STEM images recorded in [100] and [110] zone-axes. Determined indium concentrations and segregation coefficients are compared with results from composition analysis by lattice fringe analysis (CELFA) measurements and energy-dispersive X-ray analysis (EDX).

     [bibtex-key = Mehrtens2013c]



109. T. Mehrtens, M. Schowalter, D. Tytko, P. Choi, D. Raabe, L. Hoffmann, H. Jönen, U. Rossow, A. Hangleiter, and A. Rosenauer. Measurement of the indium concentration in high indium content InGaN layers by scanning transmission electron microscopy and atom probe tomography. Applied Physics Letters, 102(13):132112, 2013. Keyword(s): gallium compounds, III-V semiconductors, indium compounds, light emitting diodes, quantum well lasers, scanning-transmission electron microscopy, semiconductor quantum wells, wide band gap semiconductors. [bibtex-key = Mehrtens2013a]



110. T Mehrtens, M Schowalter, D Tytko, P Choi, D Raabe, L Hoffmann, H Jönen, U Rossow, A Hangleiter, and A Rosenauer. Measuring composition in InGaN from HAADF-STEM images and studying the temperature dependence of Z-contrast. Journal of Physics: Conference Series, 471(1):012009, 2013. Abstract:

     In this contribution, the indium concentration profile of an In x Ga 1− x N/GaN five-fold multi quantum well structure is measured from high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images. The results are compared with an atom probe tomography study. Indium concentrations in the range of 26 at.\% to 33 at.\% are measured in the centre of the quantum wells. An additional indium layer of 14 at.\% has been found on top of the quantum wells. In the second part, the temperature dependence of measured intensities in GaN is investigated. Here, multislice calculations in the frozen lattice approximation are carried out in dependence of specimen thickness and compared to experimental data. An increase of intensity with specimen temperature is found.

     [bibtex-key = Mehrtens2013b]



111. K Müller, H Ryll, I Ordavo, M Schowalter, J Zweck, H Soltau, S Ihle, L Strüder, K Volz, P Potapov, and A Rosenauer. STEM strain analysis at sub-nanometre scale using millisecond frames from a direct electron read-out CCD camera. Journal of Physics: Conference Series, 471(1):012024, 2013. Abstract:

     We report on strain analysis by nano-beam electron diffraction with a spatial resolution of 0.5nm and a strain precision in the 4-7·10 −4 range. Series of up to 160000 CBED patterns have been acquired in STEM mode with a semi-convergence angle of the incident probe of 2.6mrad, which enhances the spatial resolution by a factor of 5 compared to nearly parallel illumination. Firstly, we summarise 3 different algorithms to detect CBED disc positions accurately: selective edge detection and circle fitting, radial gradient maximisation and cross-correlation with masks. They yield equivalent strain profiles in growth direction for a stack of 5 In x Ga 1−x N y As 1−y /GaAs layers with tensile and compressive strain. Secondly, we use a direct electron read-out pnCCD detector with ultrafast readout hardware and a quantum efficiency close to 1 both to show that the same strain profiles are obtained at 200 times higher readout rates of 1kHz and to enhance strain precision to 3.5·10 −4 by recording the weak 008 disc.

     [bibtex-key = Mueller2013a]



112. U. Rossow, A. Kruse, H. Jönen, L. Hoffmann, F. Ketzer, T. Langer, R. Buss, H. Bremers, A. Hangleiter, T. Mehrtens, M. Schowalter, and A. Rosenauer. Optimizing the growth process of the active zone in GaN based laser structures for the long wavelength region. Journal of Crystal Growth, 370(0):105--108, 2013. Keyword(s): A3. Low press. metalorganic vapor phase epitaxy, A3. Quantum wells, A3. Laser epitaxy, B1. Nitrides, B2. Semiconducting III-V materials. Abstract:

     In x Ga 1 − x N /GaN quantum well (QW) structures grown on c-plane surfaces for long wavelength laser structures have been investigated. We found that temperature ramping in the barriers improves the layer structure in avoiding V-pit formation and improves the homogeneity of indium incorporation. In choosing proper temperature profiles degradation of the QWs can be avoided. We demonstrate optical gain for wavelengths larger than 500 nm using structures with an active zone grown in such way.

     [bibtex-key = Rossow2013]



113. A. Schneider, K. Sebald, A. Dev, K. Frank, A. Rosenauer, and T. Voss. Towards optical hyperdoping of binary oxide semiconductors. Journal of Applied Physics, 113(14):143512, 2013. Keyword(s): antimony, high-frequency effects, high-speed optical techniques, II-VI semiconductors, nanostructured materials, semiconductor doping, surface structure, wide band gap semiconductors. [bibtex-key = Schneider2013]



114. V.C. Srivastava, K.B. Surreddi, S. Scudino, M. Schowalter, V. Uhlenwinkel, A. Schulz, J. Eckert, A. Rosenauer, and H.-W. Zoch. Microstructural characteristics of spray formed and heat treated Al-(Y, La)-Ni-Co system. Journal of Alloys and Compounds, 578:471--480, 2013. Keyword(s): Spray forming. Abstract:

     Abstract Recent studies on the synthesis of bulk Al-RE (Rare Earth)-TM (Transition Metal) based materials, from melt spun ribbons and gas atomized powders, have shown that partially amorphous or nano-crystalline structures lead to a high specific strength. In the present study, therefore, spray atomization and deposition process has been used to produce plates of Al85Y8Ni5Co2 (deposit D1) and Al83Y5La5Ni5Co2 (deposit D2) systems so as to synthesize bulk deposit of nano-crystalline and/or partially amorphous materials in a single step. The rapid solidification and high undercooling of droplets during atomization and the chilling effect on undercooled liquid upon deposition give rise to the above microstructural features. The microstructural features of deposits as well as overspray powders were studied using optical, scanning and transmission electron microscope. The alloys invariably showed a large fraction of nano-crystalline structure and amorphous features, characterized by featureless regions at optical resolution, along with distribution of primary equilibrium phases. The differential scanning calorimetric (DSC) analysis of the deposits showed similar crystallization features as observed during crystallization of fully amorphous melt spun ribbons of respective compositions. The transmission electron microscopy of deposit \{D1\} showed the presence of 50-100 nm size fcc-Al precipitates in an amorphous matrix decorated with 5-20 nm fcc-Al crystallites. The annealing treatment of deposits at different temperatures, determined from the crystallization peak temperatures of the deposits, showed precipitation of nanoscale fcc-Al and intermetallic phases giving rise to a remarkable increase in hardness values. The bulk hardness of the deposits \{D1\} and \{D2\} was 391 and 427 HV, respectively. Whereas, the annealed deposits showed a bulk hardness value of 476 \{HV\} for deposit \{D1\} and 583 \{HV\} for deposit \{D2\} at annealing temperature of 298 and 380 °C, respectively. An attempt has been made to bring out the possible mechanism of microstructural evolution during spray deposition of the above alloy systems, and the effect of microstructural features on the hardness values has been discussed.

     [bibtex-key = Srivastava2013]



115. M Tewes, F F Krause, K Müller, P Potapov, M Schowalter, T Mehrtens, and A Rosenauer. Quantitative Composition Evaluation from HAADF-STEM in GeSi/Si Heterostructures. Journal of Physics: Conference Series, 471(1):012011, 2013. Abstract:

     High-angle annular dark field scanning transmission electron microscopy has been successfully used for composition evaluation in various material systems. In this work, the quantitative applicability of this method to GeSi/Si heterostructures was studied. Reference images were simulated by frozen lattice multislice simulations for different Ge concentrations accounting for static atomic displacements and biaxial strain due to pseudomorphic growth. Specimen thickness and composition are obtained by comparison of simulated and normalised experimental intensities. The measured thickness of a pure Si wedge specimen is compared to thickness determined from Pendell{\"o}sung fringes in dark field micrographs. The deviation is below 10 nm coinciding with the accuracy of prior works. The composition of a GeSi-layer structure was measured in a calibration sample of known concentration and good agreement is found. Two-dimensional concentration maps of a GeSi/Si transistor structure were created. Measured concentrations agree with nominal values. However, strain fields in the Si lead to a variation of the image intensity causing an artificial fluctuation of the measured concentrations of ±4\%.

     [bibtex-key = Tewes2013]



116. S. Van Aert, A. De Backer, G. T. Martinez, B. Goris, S. Bals, G. Van Tendeloo, and A. Rosenauer. Procedure to count atoms with trustworthy single-atom sensitivity. Phys. Rev. B, 87:064107, February 2013. [bibtex-key = VanAert2013]



117. Julia Wehling, Eike Volkmann, Tim Grieb, Andreas Rosenauer, Michael Maas, Laura Treccani, and Kurosch Rezwan. A critical study: Assessment of the effect of silica particles from 15 to 500Â nm on bacterial viability. Environmental Pollution, 176(0):292--299, 2013. Keyword(s): Silica. Abstract:

     The current opinion on the toxicity of nanomaterials converges on a size-dependent phenomenon showing increasing toxicity with decreasing particle sizes. We demonstrate that SiO2 particles have no or only a mild effect on the viability of five bacterial strains, independently from the particle size. A two-hour exposure to 20 mg L−1 of 15, 50 and 500 nm sized SiO2 particles neither alters bacterial adenosine triphosphate (ATP) levels nor reduces the number of colony forming units (CFU). Additionally, we tested the effect of Al2O3-coated LUDOX®-CL (ACS 20) with a primary particle size of 20 nm. In contrast, these particles caused a significant reduction of \{ATP\} levels and CFU. Fluorescence microscopy revealed that \{ACS\} 20 induced a pronounced agglomeration of the bacteria, which led to underestimated counts in regard of CFU. Bactericide effects as indicated by decreased \{ATP\} levels can be explained by bactericide additives that are present in the \{ACS\} 20 suspension.

     [bibtex-key = Wehling2013]



118. Thorsten M. Gesing, Marco Schowalter, Claudia Weidenthaler, M. Mangir Murshed, Gwilherm Nenert, Cecilia B. Mendive, Mariano Curti, Andreas Rosenauer, J.-Christian Buhl, Hartmut Schneider, and Reinhard X. Fischer. Strontium doping in mullite-type bismuth aluminate: a vacancy investigation using neutrons, photons and electrons. J. Mater. Chem., 22:18814--18823, 2012. Abstract:

     We report on strontium doped dibismuth-nonaoxoaluminate(iii) produced at 1023 K. Partial substitution of bismuth by strontium in the structure yields oxygen vacancies for charge balance. Introducing oxygen vacancies rearranged the associated Al2O7 double-tetrahedra forming {"}Al3O10{"} tri-clusters which were identified by multi-quantum 27Al MAS NMR. Both STEM-EDX and XPS showed homogeneous distribution of strontium in the bulk and on the surface{,} respectively. Moreover{,} XPS confirms the valence state of bismuth after doping. The orientations of bismuth 6s2 lone electron pairs were calculated using DFT methods. The amount of strontium in the crystal structure was further confirmed from the decomposition product SrAl12O19 formed during the temperature-dependent X-ray powder diffraction. The structural proof was carried out by refining the structure of (Bi0.94Sr0.06)2Al4O8.94 from powder neutron and X-ray diffraction data. Rietveld refinements clearly showed the under occupation of one oxygen site and the shift of two aluminum atoms from the double-tetrahedra to two tri-cluster sites.

     [bibtex-key = Gesing2012a]



119. Tim Grieb, Knut Müller, Rafael Fritz, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. A method to avoid strain field induced artifacts in 2D chemical mapping of dilute GaNAs by HAADF STEM. Microsc. Microanal., 18(2):1028--1029, 2012. Abstract:

     Scanning transmission electron microscopy (STEM) using a high-angleannular dark field (HAADF) detector can be used to investigate the chemical composition of ternary semiconductors as the scattering intensity highly depends on the specimen's chemical properties. In Ref. [1] a method for the evaluation of the indium concentration in InGaN quantum wells was suggested which is based on a comparison of experimental image intensities with simulations carried out with the frozen lattice approximation. We recently showed [2] that this approximation can also be used to compute the image intensity for GaNAs quantum wells embedded in GaAs. In GaNAs electron scattering is predominated by Huang scattering at static atomic displacements which has the effect that, under the applied imaging conditions, GaNAs quantum wells appear brighter in HAADF STEM images compared to GaAs. Quantitative analysis of the nitrogen concentration of GaNAs layers pseudomorphically grown in a GaAs matrix is also hindered by the surface strain fields that occur in vicinity of the interfaces. These strain fields decrease the image intensity thus leading to dark stripes in the GaAs regions that are running parallel to the interfaces. This effect of strain fields on STEM imaging of interfaces was explained in Ref. [3] for InGaAs and in Ref. [4] for InGaNAs and leads to artifacts in the evaluation of chemical composition. In this contribution we suggest a method combining two STEM images taken under different camera lengths to render full 2d-mapping of the nitrogen concentration possible. The HAADF STEM image in Fig. 1 a) was taken with detection angles between 36 and approximately 218 mrad corresponding to a camera length of 196 mm at our Titan 80/300 TEM. One can clearly see that the intensity close to the quantum well is decreased. As a consequence, the evaluated concentration profile shown in Fig. 2 a) contains two dips on each side of the quantum well where the nitrogen concentration is artificially negative. The concentration in the center of the well is not affected by the strain fields and was checked by high-resolution X-ray diffraction measurements and strain state analysis from the STEM image. We confirm by multislice simulations that GaAs shows less scattering intensity in regions affected by surface strain at high scattering angles, whereas the intensity increases in the low-angle regime. Using an inner detector radius of about 14 mrad, the increase at low angles balances the decrease of the intensities at high angles so that the dips disappear. For this reason the STEM image in Fig. 1 b) was taken with lower detection angles between 14 and approximately 87 mrad (camera length of 478 mm) directly after taking the image in Fig. 1 a). ...

     [bibtex-key = Grieb2012d]



120. Tim Grieb, Knut Müller, Oleg Rubel, Rafael Fritz, Claas Gloistein, Nils Neugebohrn, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. Determination of Nitrogen Concentration in Dilute GaNAs by STEM HAADF Z-Contrast Imaging and improved STEM-HAADF strain state analysis. Ultramicroscopy, 117:15--23, 2012. Abstract:

     The nitrogenconcentration of GaN0.01≤x≤0.05As1−x quantum wells was determined from high resolution scanning transmission electron microscopy (HRSTEM) images taken with a high-angle annular dark field (HAADF) detector. This was done by applying two independent methods: evaluation of the scattering intensity and strainstateanalysis. The HAADF scattering intensity was computed by multislice simulations taking into account the effect of static atomic displacements and thermal diffuse scattering. A comparison of the mean intensity per atom column on the experimental images with these simulations enabled us to generate composition maps with atomic scale resolution. STEM simulations of large supercells proved that local drops of the HAADF intensity observed close to embedded quantum wells are caused by surface strain relaxation. The same STEM images were evaluated by strainstateanalysis. We suggest a real space method which is not affected by fly-back errors in HRSTEM images. The results of both evaluation methods are in accordance with data obtained from X-ray diffraction measurements.

     [bibtex-key = Grieb2012]



121. Katharina I. Gries, Fabian Heinemann, Andreas Rosenauer, and Monika F. In vitro growth of flat aragonite crystals between the layers of the insoluble organic matrix of the abalone Haliotis laevigata. Journal of Crystal Growth, 358(0):75--80, 2012. Keyword(s): A1. Biocrystallization. Abstract:

     Nacre of abalone shells consists of aragonite platelets and organic material, the so-called organic matrix. During the growth process of the shell the aragonite platelets grow into a scaffold formed by the organic matrix. In this work we tried to mimic this growth process by placing a piece of the insoluble organic matrix (which is a part of the organic matrix) of the abalone Haliotis laevigata in a crystallization device which was flowed through by CaCl2 and NaHCO3 solutions. Using this setup amongst others flat aragonite crystals grow on the insoluble organic matrix. When investigating these crystals in a transmission electron microscope it is possible to recognize similarities to the structure of nacre, like the formation of mineral bridges and growth between layers of the insoluble organic matrix. These similarities are presented in this paper.

     [bibtex-key = Gries2012]



122. Dongchao Hou, Apurba Dev, Kristian Frank, Andreas Rosenauer, and Tobias Voss. Oxygen-Controlled Photoconductivity in ZnO Nanowires Functionalized with Colloidal CdSe Quantum Dots. The Journal of Physical Chemistry C, 116(36):19604--19610, 2012. Abstract:

     ZnO nanowire arrays were functionalized with colloidal CdSe quantum dots stabilized by 3-mercaptopropionic acid to form hybrid devices. The photoconductivity of the nanowire/quantum-dot devices was studied under selective photoexcitation of the quantum dots, and it was found that the dynamics strongly depend on the gas environment. Desorption of surface oxygen from both the ZnO nanowires and the CdSe quantum dots, activated by electron tunnelling between the nanowires and the quantum dots, is found to be the dominating process that determines the dynamics of the photoconductivity in the hybrid nanowire/quantum-dot devices.

     [bibtex-key = Hou2012]



123. Thorsten Mehrtens, Stephanie Bley, Parlapalli Venkata Satyam, and Andreas Rosenauer. Optimization of the preparation of GaN-based specimens with low-energy ion milling for (S)TEM. Micron, 43(8):902--909, 2012. Keyword(s): Scanning transmission electron microscopy, Focused ion beam, Argon ion milling, Low-energy ion milling, Stopping and range of ions in matter. Abstract:

     We report on optimization of electron transparent GaN based specimens for transmission electron microscopy (TEM) and scanning TEM (STEM) studies by combining focused ion beam thinning and low-energy (<=500eV) Ar-ion milling. Energy dependent ion milling effects on GaN based structures are investigated and the quality of ion milled samples is compared with that of specimens prepared by wet chemical etching. Defects formed during ion milling lead to amorphization of the specimen. The experimental results are compared with Monte-Carlo simulations using the SRIM (stopping and range of ions in matter) software. Specimen thickness was deduced from high-angle annular dark field STEM images by normalization of measured intensities with respect to the intensity of the scanning electron probe and comparison with multislice simulations in the frozen lattice approach. The results show that the thickness of the amorphous surface layer can be successfully reduced below 1 nm by low energy ion milling, leading to a homogeneous image contrast in TEM and STEM, so that good conditions for quantitative analysis can be achieved. For an ion energy of 400 eV the thickness measurements resulted in an etching rate of about 6-8 nm/min.

     [bibtex-key = Mehrtens2012a]



124. Knut Müller, Andreas Rosenauer, Marco Schowalter, Josef Zweck, Rafael Fritz, and Kerstin Volz. Strain measurement in semiconductor heterostructures by scanning transmission electron microscopy. Microscopy and Microanalysis, 18(05):995--1009, 2012. Abstract:

     This article deals with the measurement of strain in semiconductor heterostructures from convergent beam electron diffraction patterns. In particular, three different algorithms in the field of (circular) pattern recognition are presented that are able to detect diffracted disc positions accurately, from which the strain in growth direction is calculated. Although the three approaches are very different as one is based on edge detection, one on rotational averages, and one on cross correlation with masks, it is found that identical strain profiles result for an In x Ga1−x N y As1−y /GaAs heterostructure consisting of five compressively and tensile strained layers. We achieve a precision of strain measurements of 7-9·10−4 and a spatial resolution of 0.5-0.7 nm over the whole width of the layer stack which was 350 nm. Being already very applicable to strain measurements in contemporary nanostructures, we additionally suggest future hardware and software designs optimized for fast and direct acquisition of strain distributions, motivated by the present studies.

     [bibtex-key = Mueller2012]



125. Knut Müller, Henning Ryll, Ivan Ordavo, Sebastian Ihle, Lothar Strüder, Kerstin Volz, Josef Zweck, Heike Soltau, and Andreas Rosenauer. Scanning transmission electron microscopy strain measurement from millisecond frames of a direct electron charge coupled device. Applied Physics Letters, 101(21):212110, 2012. Keyword(s): CCD image sensors, electron detection, electron probes, nanostructured materials, scanning-transmission electron microscopy, semiconductor materials, strain measurement. Abstract:

     A high-speed direct electron detection system is introduced to the field of transmission electron microscopy and applied to strain measurements in semiconductor nanostructures. In particular, a focused electron probe with a diameter of 0.5 nm was scanned over a fourfold quantum layer stack with alternating compressive and tensile strain and diffracted discs have been recorded on a scintillator-free direct electron detector with a frame time of 1 ms. We show that the applied algorithms can accurately detect Bragg beam positions despite a significant point spread each 300 kV electron causes during detection on the scintillator-free camera. For millisecond exposures, we find that strain can be measured with a precision of 1.3  × 10−3, enabling, e.g., strain mapping in a 100×100 nm2 region with 0.5 nm resolution in 40 s.

     [bibtex-key = Mueller2012c]



126. A. Rath, J. K. Dash, R. R. Juluri, A. Rosenauer, Marcos Schoewalter, and P. V. Satyam. Growth of oriented Au nanostructures: Role of oxide at the interface. Journal of Applied Physics, 111(6):064322, 2012. Keyword(s): annealing, electron energy loss spectra, elemental semiconductors, field emission electron microscopy, gold, metallic thin films, molecular beam epitaxial growth, nanofabrication, nanoparticles, scanning electron microscopy, silicon, silicon compounds, transmission electron microscopy, vacuum deposition. [bibtex-key = Rath2012a]



127. A. Rath, J. K. Dash, R. R. Juluri, M. Schowalter, K. Müller, A. Rosenauer, and P. V. Satyam. Nano scale phase separation in Au-Ge system on ultra clean Si (100) surfaces. Journal of Applied Physics, 111:104319, 2012. Abstract:

     We report on the formation of lobe-lobe (bi-lobed) Au-Ge nanostructures under ultra high vacuum (UHV) conditions (\approx 3 imes 10^{-10} mbar) on clean Si(100) surfaces. For this study, \approx 2.0 nm thick Au samples were grown on the substrate surface by molecular beam epitaxy (MBE). Thermal annealing was carried out inside the UHV chamber at temperature \apprx 500{\deg}C and following this, nearly square shaped Au_{x}Si_{1-x} nano structures of average length \approx 48 nm were formed. A \approx 2 nm Ge film was further deposited on the above surface while the substrate was kept at a temperature of \approx 500{\deg}C. Well ordered Au-Ge nanostructures where Au and Ge residing side by side (lobe-lobe structures) were formed. In our systematic studies, we show that, gold-silicide nanoalloy formation at the substrate (Si) surface is necessary for forming phase separated Au-Ge bilobed nanostructures. Electron microscopy (TEM, STEM-EDS, SEM) studies were carried out to determine the structure of Au - Ge nano systems. Rutherford backscattering Spectrometry measurements show gold inter-diffusion into substrate while it is absent for Ge.

     [bibtex-key = Rath2012]



128. Marco Schowalter, Knut Müller, and Andreas Rosenauer. Scattering amplitudes and static atomic correction factors for the composition-sensitive 002 reflection in sphalerite ternary III--V and II--VI semiconductors. Acta Crystallographica Section A, 68(1):68--76, January 2012. Keyword(s): scattering factors, static atomic displacements, modified atomic scattering amplitudes, correction factor. Abstract:

     Modified atomic scattering amplitudes (MASAs), taking into account the redistribution of charge due to bonds, and the respective correction factors considering the effect of static atomic displacements were computed for the chemically sensitive 002 reflection for ternary III-V and II-VI semiconductors. MASAs were derived from computations within the density functional theory formalism. Binary eight-atom unit cells were strained according to each strain state s (thin, intermediate, thick and fully relaxed electron microscopic specimen) and each concentration (x = 0, ..., 1 in 0.01 steps), where the lattice parameters for composition x in strain state s were calculated using continuum elasticity theory. The concentration dependence was derived by computing MASAs for each of these binary cells. Correction factors for static atomic displacements were computed from relaxed atom positions by generating 50 × 50 × 50 supercells using the lattice parameter of the eight-atom unit cells. Atoms were randomly distributed according to the required composition. Polynomials were fitted to the composition dependence of the MASAs and the correction factors for the different strain states. Fit parameters are given in the paper.

     [bibtex-key = Schowalter2012a]



129. Marco Schowalter, Andreas Rosenauer, and Kerstin Volz. Parameters for temperature dependence of mean-square displacements for B-, Bi- and Tl-containing binary III-V compounds. Acta Crystallographica Section A, 68(3):319--323, 2012. Keyword(s): Debye-Waller factors, mean-square displacements, force constants, phonon density of states, phonon dispersion relations, density functional theory. Abstract:

     Mean-square displacements were computed within the harmonic approximation from ab initio force constants for binary B-, Tl- and Bi-containing III-V compounds in sphalerite crystal structures in the temperature range from 0 to 1000 K in steps of 1 K. An Einstein model with a temperature-dependent characteristic frequency was used to model the temperature dependence of the mean-square displacements. A Gaussian was fitted to the temperature dependence of the characteristic frequency and parameters of the Gaussian are given. Phonon dispersion relations and densities of states derived during the computation of the mean-square displacements are also shown.

     [bibtex-key = Schowalter2012]



130. K. Sebald, M. Seyfried, S. Klembt, S. Bley, A. Rosenauer, D. Hommel, and C. Kruse. Strong coupling in monolithic microcavities with ZnSe quantum wells. Applied Physics Letters, 100(16):161104--161104-4, 2012. Keyword(s): microcavity lasers, quantum well lasers, scanning electron microscopy, transmission electron microscopy, zinc compounds, 4255Px, 4255Sa. Abstract:

     Strong light-matter coupling is demonstrated in monolithic microcavities with only three ZnSe quantum wells embedded. Basis for this observation is the excellent structural quality of the sample as confirmed by scanning transmission electron microscopy measurements. A comparative large energy splitting between the upper and lower polariton (LP) of about 19 meV is observed by reflectivity measurements in real and k-space. Efficient polariton relaxation is shown by photoluminescence measurements at low temperatures in k-space. These beneficial properties of the sample result in a nonlinear increase of the lower polariton population in excitation density dependent measurements before the photonic cavity emission becomes dominant.

     [bibtex-key = Sebald2012]



131. Huanjun Zhang, Amir R. Gheisi, Andreas Sternig, Knut Müller, Marco Schowalter, Andreas Rosenauer, Oliver Diwald, and Lutz Mädler. Bulk and Surface Excitons in Alloyed and Phase-Separated ZnO-MgO Particulate Systems. ACS Applied Materials & Interfaces, 4(5):2490--2497, 2012. Abstract:

     The rational design of composite nanoparticles with desired optical and electronic properties requires the detailed analysis of surface and bulk contributions to the respective overall function. We use flame spray pyrolysis (FSP) to generate nanoparticles of the ternary Zn-Mg-O system the compositions of which range from solid solutions of Zn2+ ions in periclase MgO to phase separated particle mixtures which consist of periclase (cubic) MgO and wurtzite (hexagonal) ZnO phases. The structure and composition of the composite ZnxMg1-xO (0 ≤ x ≤ 0.3) particles are investigated using X-ray diffraction and high-resolution transmission electron microscopy, whereas UV diffuse reflectance and photoluminescence (PL) spectroscopy are used for the investigation of their optical properties. Vacuum annealing has been carried out to track the effects of stepwise elimination of surface adsorbates on the photoexcitation and PL emission properties. We demonstrate that for Zn0.1Mg0.9O particles, the admixed ZnO suppresses the MgO specific surface excitons and produces a PL emission band at 470 nm. Although gaseous oxygen partially reduces the emission intensity of hydroxylated particles, it leads to entire quenching in completely dehydroxylated samples after vacuum annealing at 1173 K. Consequently, surface hydroxyls at the solid-gas interface play a significant role as protecting groups against the PL-quenching effects of O2. The obtained results are relevant for the characterization of ZnO-based devices as well as for other metal oxide materials where the impact of the surface composition on the photoelectronic properties is usually neglected.

     [bibtex-key = Zhang2012]



132. W. Van den Broek, A. Rosenauer, B. Goris, G.T. Martinez, S. Bals, S. Van Aert, and D. Van Dyck. Correction of non-linear thickness effects in HAADF STEM electron tomography. Ultramicroscopy, 116(0):8--12, 2012. Keyword(s): HAADF STEM tomography. Abstract:

     In materials science, high angle annular dark field scanning transmission electron microscopy is often used for tomography at the nanometer scale. In this work, it is shown that a thickness dependent, non-linear damping of the recorded intensities occurs. This results in an underestimated intensity in the interior of reconstructions of homogeneous particles, which is known as the cupping artifact. In this paper, this non-linear effect is demonstrated in experimental images taken under common conditions and is reproduced with a numerical simulation. Furthermore, an analytical derivation shows that these non-linearities can be inverted if the imaging is done quantitatively, thus preventing cupping in the reconstruction.

     [bibtex-key = Broek2012]



133. Balint Aradi, Peter Deak, Huynh Anh Huy, Andreas Rosenauer, and Thomas Frauenheim. Role of Symmetry in the Stability and Electronic Structure of Titanium Dioxide Nanowires. The Journal of Physical Chemistry C, 115(38):18494--18499, 2011. Abstract:

     The stability and electronic structure of bare [001] nanowires of anatase and rutile have been investigated using ab initio density functional calculations. It was found that symmetry plays an important role in both properties below a critical diameter. Up to 2.1 nm in anatase and 3.7 nm in rutile, those {100}-walled anatase and {110}-walled rutile wires are most stable, which retain the nonsymmorphic character of the bulk space group. Our results explain the observed properties of atomic size anatase nanowires. The wires with screw symmetry also show a consistently larger gap in their electronic structures compared to similarly walled wires without it. Additionally, in rutile the indirect or direct character of the band structure is coupled to the presence or absence of the screw axis.

     [bibtex-key = Aradi2011]



134. T. Aschenbrenner, G. Kunert, W. Freund, C. Kruse, S. Figge, M. Schowalter, C. Vogt, J. Kalden, K. Sebald, A. Rosenauer, J. Gutowski, and D. Hommel. Catalyst free self-organized grown high-quality GaN nanorods. physica status solidi (b), 248(8):1787--1799, 2011. Keyword(s): MBE, MOVPE, nanorods, nitrides, TEM, III-V semiconductors. [bibtex-key = Aschenbrenner2011]



135. Heiko Dartsch, Christian Tessarek, Timo Aschenbrenner, Stephan Figge, Carsten Kruse, Marco Schowalter, Andreas Rosenauer, and Detlef Hommel. Electroluminescence from InGaN quantum dots in a fully monolithic GaN/AlInN cavity. Journal of Crystal Growth, 320(1):28--31, 2011. Keyword(s): A1. Electroluminescence. Abstract:

     We present for the first time electroluminescence from InGaN quantum dots inside a monolithic nitride based cavity. The structure consists of a 40-fold bottom GaN/Al0.82In0.18N distributed Bragg reflector (DBR), a single InGaN quantum dot layer inside a 5 λ n-type (bottom) and p-type (top) doped GaN cavity and a 10-fold GaN/Al0.82In0.18N top DBR. Structural properties have been investigated by scanning transmission electron microscopy. Optical reflectivity measurements are in good agreement with calculations which predict a peak reflectivity of 92% and a quality factor of 220. Electroluminescence shows a pronounced emission at the spectral position of the cavity mode near 500 nm.

     [bibtex-key = Dartsch2011a]



136. J. K. Dash, A. Rath, R. R. Juluri, P. Santhana Raman, K. Müller, A. Rosenauer, and P. V. Satyam. DC heating induced shape transformation of Ge structures on ultra clean Si (5 5 12) surfaces. Journal of Physics: Condensed matter, 23:135002, 2011. Abstract:

     We report the growth of Ge nanostructures and microstructures on ultraclean, high vicinal angle silicon surfaces and show that self-assembled growth at optimum thickness of the overlayer leads to interesting shape transformations, namely from nanoparticle to trapezoidal structures, at higher thickness values. Thin films of Ge of varying thickness from 3 to 12 ML were grown under ultrahigh vacuum conditions on a Si(5 5 12) substrate while keeping the substrate at a temperature of 600°C. The substrate heating was achieved by two methods: (i) by heating a filament under the substrate (radiative heating, RH) and (ii) by passing direct current through the samples in three directions (perpendicular, parallel and at 45° to the -110 direction of the substrate). We find irregular, more spherical-like island structures under RH conditions. The shape transformations have been found under DC heating conditions and for Ge deposition more than 8 ML thick. The longer sides of the trapezoid structures are found to be along -110 irrespective of the DC current direction. We also show the absence of such a shape transformation in the case of Ge deposition on Si(111) substrates. Scanning transmission electron microscopy measurements suggested the mixing of Ge and Si. This has been confirmed with a quantitative estimation of the intermixing using Rutherford backscattering spectrometry (RBS) measurements. The role of DC heating in the formation of aligned structures is discussed. Although the RBS simulations show the presence of a possible SiOx layer, under the experimental conditions of the present study, the oxide layer would not play a role in determining the formation of the various structures that were reported here.

     [bibtex-key = Dash2011a]



137. J. K. Dash, A. Rath, R. R. Juluri, P. Santhana Raman, K. Müller, M. Schowalter, R. Imlau, A. Rosenauer, and P. V. Satyam. Shape transformation of SiGe structures on ultra clean Si(5 5 7) and Si(5 5 12) surfaces. Journal of Physics: Conference Series, 326(1):012021, 2011. Abstract:

     We report growth of Ge nano/micro structures on ultra clean, high vicinal silicon surfaces of Si(5 5 7) and Si(5 5 12) under two substrate heating conditions: direct current (DC) and radiative heating (RH). These were grown under ultra high vacuum conditions while keeping the substrate at a temperature of 600°C. The results for 10 monolayer (ML) and 12 ML thick Ge deposited on the above surfaces show spherical island structures for RH conditions while aligned trapezoidal structures were observed under DC conditions of heating. We find that the longer side of trapezoid structures are along <1bar 10> irrespective of DC current direction. In the case of 10 ML Ge deposited on Si (5 5 7), elongated SixGe1−x nanostructures with an average length of ≈300 nm and a length/width ratio of ≈3.3 have been formed along the step edges. Under similar conditions for 10 ML Ge growth on Si(5 5 12), we found aligned SixGe1−x trapezoidal microstructures of length ≈6.25 μm and an aspect ratio of ≈3.0. Scanning transmission electron microscopy (STEM) measurements showed the mixing of Ge and Si at the interface and throughout the over-layer. Detailed electron microscopy studies (scanning electron microscopy (SEM) and STEM) reveal the structural aspects of these microstructures.

     [bibtex-key = Dash2011]



138. J. Falta, Th. Schmidt, S. Gangopadhyay, Chr. Schulz, S. Kuhr, N. Berner, J. I. Flege, A. Pretorius, A. Rosenauer, K. Sebald, H. Lohmeyer, J. Gutowski, S. Figge, T. Yamaguchi, and D. Hommel. Cleaning and growth morphology of GaN and InGaN surfaces. physica status solidi (b), 248(8):1800--1809, 2011. Keyword(s): chemical analysis, scanning tunneling microscopy, quantum dots, X-ray photoemission spectroscopy. Abstract:

     The structure and chemistry of clean GaN surfaces and InGaN thin films and nanostructures grown by metal organic vapour pressure epitaxy (MOVPE) has been studied by means of X-ray photoemission spectroscopy, low-energy electron diffraction as well as scanning tunneling microscopy (STM) and transmission electron microscopy. Thermal annealing strongly improves the cleanliness of samples after dry nitrogen transfer and related exposure to residual oxygen. Nitrogen plasma assisted cleaning is shown to successfully further remove carbon contaminations, while Ga deposition with subsequent desorption to is shown to be superior for an enhanced reduction of surface oxygen. Using STM, the surface morphology has been studied in dependence on major growth parameters at various stages of InGaN MOVPE growth. The formation of nano-islands is reported for different growth conditions. By means of micro-photoluminescence measurements, we find samples to show strong photoluminescence from quantum-dot-like structures, however, the corresponding growth front is found to be rather flat throughout InGaN deposition. This leads to the conclusion that the formation of quantum dots does not proceed in a Stranski-Krastanov-like fashion but most likely during overgrowth.Scanning tunneling micrograph and height profile of 3.9 nm InGaN grown by MOVPE at 700 °C, after growth interruption and 1 min post-growth annealing at the growth temperature. The surface exhibits a two-dimensional islands morphology.

     [bibtex-key = Falta2011]



139. Stephan Figge, Timo Aschenbrenner, Carsten Kruse, Gerd Kunert, Marco Schowalter, Andreas Rosenauer, and Detlef Hommel. A structural investigation of highly ordered catalyst- and mask-free GaN nanorods. Nanotechnology, 22(2):025603, 2011. Abstract:

     GaN nanorods were grown on r -plane sapphire substrates by a two-step approach. Nucleation sites for the nanorods were provided by the formation of AlN islands during nitridation in a metal organic vapor phase system. These islands are a -plane oriented as expected for nitride growth on r -plane sapphire. The nanorods themselves were grown by plasma assisted molecular beam epitaxy. The nanorods show an inclination towards the surface normal of 28.3° and are highly ordered. Studies with high resolution x-ray diffraction polar plots reveal the epitaxial relationship between the substrate and nanorods as a c -direction growth on inclined m -plane facets of the nitridated islands. The determined lattice constants show nanorods which are strain free. The growth direction of the nanorods has been confirmed in a transmission electron microscope by convergent beam electron diffraction patterns to be in the N-polar {[000\bar {1}]} direction.

     [bibtex-key = Figge2011a]



140. M. Florian, F. Jahnke, A. Pretorius, A. Rosenauer, H. Dartsch, C. Kruse, and D. Hommel. Influence of growth imperfections on optical properties of nitride pillar VCSEL microcavities. physica status solidi (b), 248(8):1867--1870, 2011. Keyword(s): lasers, laser diodes, microcavities, optical properties, III-V semiconductors. Abstract:

     For vertical-cavity surface-emitting laser pillar microcavities with three-dimensional optical mode confinement, we theoretically study the influence of growth imperfections on the cavity quality factor. Mode calculations based on a vectorial transfer-matrix approach are used to simulate layer thickness fluctuations as well as a gradual variation of the layer thickness across the micropillar for an AlGaN/GaN material system. Experimental estimates for the layer thickness profile are obtained with transmission electron microscopy Z-contrast images.

     [bibtex-key = Florian2011]



141. Tim Grieb, Knut Müller, Oleg Rubel, Rafael Fritz, Claas Gloistein, Nils Neugebohrn, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. Determination of Nitrogen Concentration in Dilute GaNAs by STEM HAADF Z-Contrast Imaging. Journal of Physics: Conference Series, 326(1):012033, 2011. Abstract:

     We determine the nitrogen concentration of GaNAs quantum wells by evaluation of high resolution scanning transmission electron microscopy (STEM) images using a high-angle annular dark field detector. Although nitrogen has a smaller atomic number than Ga the image intensity increases with the nitrogen content. This is explained by the influence of static atomic displacements by comparison with frozen lattice simulations. The resulting nitrogen concentrations agree with high resolution X-ray diffraction measurements and strain state analysis applied to STEM images.

     [bibtex-key = Grieb2011b]



142. Katharina Gries, Fabian Heinemann, Meike Gummich, Andreas Ziegler, Andreas Rosenauer, and Monika Fritz. Influence of the Insoluble and Soluble Matrix of Abalone Nacre on the Growth of Calcium Carbonate Crystals. Crystal Growth & Design, 11(3):729--734, 2011. Abstract:

     During the growth process of the nacre layer in abalone shells, aragonite platelets are built into a preformed organic matrix. This matrix consists of chitin and different proteins that may affect the morphology and the crystal structure of the developed platelets. The organic matrix can be divided into two fractions: the soluble and the insoluble matrix. The soluble matrix has influence on the precipitation rates of calcium carbonate crystals and also the insoluble matrix affects crystal growth. In this work we investigated the collective influence of soluble and insoluble matrix in a crystallization device which contained the insoluble matrix and was flowed through by CaCl2 and NaHCO3 solutions. The presence of 0.02 μg/mL soluble matrix promoted the growth of flat CaCO3 crystals on the surface layers of the insoluble matrix of Haliotis laevigata. The crystals could be identified as aragonite using electron diffraction in the transmission electron microscope (TEM). Furthermore the addition of 1 μg/mL soluble matrix inhibited largely crystal growth on the surface of the insoluble matrix. Our findings indicate that components of the soluble matrix are required for a controlled nucleation and growth of flat aragonite crystals on the insoluble matrix.

     [bibtex-key = Gries2011]



143. Vincenco Grillo, Knut Müller, Frank Glas, Kerstin Volz, and Andreas Rosenauer. Toward Simultaneous Assessment of In and N in InGaAsN Alloys by Quantitative STEM-ADF Imaging. Microscopy and Microanalysis, 17:1862--1863, 7 2011. Abstract:

     ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7-August 11, 2011.

     [bibtex-key = Grillo2011a]



144. V. Grillo, K. Müller, K. Volz, F. Glas, T. Grieb, and A. Rosenauer. Strain, composition and disorder in ADF imaging of semiconductors. Journal of Physics: Conference Series, 326(1):012006, 2011. Abstract:

     The effect of strain, composition and disorder in ADF images is systematically studied as a function of detection angle in order to understand the main contrast mechanisms. We demonstrate that the complex phenomenology in ADF images can be accounted for by accurate simulations and modelling. The advantage of an accurate modelling on the image interpretation will be demonstrated in the case of dislocations, chemical analysis of InGaP/GaAs and most noticeably the measurement of both In and N content in quaternary InGaAsN.

     [bibtex-key = Grillo2011]



145. Robert Imlau, Knut Müller, Oleg Rubel, Rafael Fritz, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. Investigation of optical and concentration profile changes of InGaNAs/GaAs heterostructures induced by thermal annealing. Journal of Physics: Conference Series, 326(1):012038, 2011. Abstract:

     In this contribution we compare optical and structural properties of In 0.2 Ga 0.8 N 0.024 As 0.976 quantum wells before and after annealing at 550 C and 600 C in an N 2 atmosphere. We measure strain and chemically sensitive contrast to determine local indium and nitrogen concentrations using a TEM 3-beam image formed by the 000, 220 and 200 beams. For quantification of the concentrations Bloch wave simulations are used, which include bonding and static atomic displacements. The samples were grown by metal-organic vapour phase epitaxy, prepared with focused ion beams (FIB), thinned with low energy ion milling and investigated in a Cs-corrected Titan 80/300 microscope using an L-shaped objective aperture. Imaging conditions with the Laue circle centre at (0 4.2 0) are used as they show a weak dependence on the lamella thickness. Absorption measurements show a blueshift of the band gap of 19 +/- 7meV (550 C) and 36 +/- 7 meV (600 C) after annealing. The average nitrogen concentration was found to be 2\% and is unaffected by the annealing temperature. In contrast, the mean indium concentration appears to decrease from 18.5 +/- 2\% before to 15 +/- 1\% after annealing. Together with the blueshift, this observation is discussed in terms of a modification of electron structure factors, caused by preferred coordination of N to In atoms.

     [bibtex-key = Imlau2011b]



146. Carsten Kruse, Wojciech Pacuski, Tomasz Jakubczyk, Jakub Kobak, Jan A Gaj, Kristian Frank, Marco Schowalter, Andreas Rosenauer, Matthias Florian, Frank Jahnke, and Detlef Hommel. Monolithic ZnTe-based pillar microcavities containing CdTe quantum dots. Nanotechnology, 22(28):285204, 2011. Abstract:

     Micropillars of different diameters have been prepared by focused ion beam milling out of a planar ZnTe-based cavity. The monolithic epitaxial structure, deposited on a GaAs substrate, contains CdTe quantum dots embedded in a ZnTe λ-cavity delimited by two distributed Bragg reflectors (DBRs). The high refractive index material of the DBR structure is ZnTe, while for the low index material a short-period triple MgTe/ZnTe/MgSe superlattice is used. The CdTe quantum dots are formed by a novel Zn-induced formation process and are investigated by scanning transmission electron microscopy. Micro-photoluminescence measurements show discrete optical modes for the pillars, in good agreement with calculations based on a vectorial transfer matrix method. The measured quality factor reaches a value of 3100.

     [bibtex-key = Kruse2011]



147. G Kunert, W Freund, T Aschenbrenner, C Kruse, S Figge, M Schowalter, A Rosenauer, J Kalden, K Sebald, J Gutowski, M Feneberg, I Tischer, K Fujan, K Thonke, and D Hommel. Light-emitting diode based on mask-Â and catalyst-free grown N-polar GaN nanorods. Nanotechnology, 22(26):265202, 2011. Abstract:

     We report on the fabrication of a light-emitting diode based on GaN nanorods containing InGaN quantum wells. The unique system consists of tilted N-polar nanorods of high crystalline quality. Photoluminescence, electroluminescence, and spatially resolved cathodoluminescence investigations consistently show quantum well emission around 2.6 eV. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy measurements reveal a truncated shape of the quantum wells with In contents of (15 ± 5)\%.

     [bibtex-key = Kunert2011]



148. Thorsten Mehrtens, Stephanie Bley, Marco Schowalter, Kathrin Sebald, Moritz Seyfried, Jürgen Gutowski, Stephan S A Gerstl, Pyuck-Pa Choi, Dierk Raabe, and Andreas Rosenauer. A (S)TEM and atom probe tomography study of InGaN. Journal of Physics: Conference Series, 326(1):012029, 2011. Abstract:

     In this work we show how the indium concentration in high indium content In x Ga 1−x N quantum wells, as they are commonly used in blue and green light emitting diodes, can be deduced from high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. This method bases on introducing normalized intensities which can be compared with multislice simulations to determine the specimen thickness or the indium concentration. The evaluated concentrations are compared with atom probe tomography measurements. It is also demonstrated how the quality of focused ion beam prepared TEM-lamellas can be improved by an additional etching with low energy ions.

     [bibtex-key = Mehrtens2011]



149. Knut Müller, Marco Schowalter, Andreas Rosenauer, Dongzhi Hu, Daniel M. Schaadt, Michael Hetterich, Philippe Gilet, Oleg Rubel, Rafael Fritz, and Kerstin Volz. Atomic scale annealing effects on InGaNAs studied by TEM three-beam imaging. Physical Review B, 84(4):045316, July 2011. Abstract:

     A transmission electron microscopy (TEM) method for simultaneous measurement of indium and nitrogen content in InGaNAs at atomic scale is introduced, tested, and applied to investigate thermal annealing effects on structural properties. Our technique is based on the extraction of strain and chemical sensitive contrast from a single three-beam TEM lattice fringe image by subsequent decomposition into 220 and 020 two-beam fringe images, being free of nonlinear imaging artifacts. From comparison with simulated strain and 020 fringe amplitude, concentration maps and profiles are derived. For this purpose, the Bloch-wave approach is used with structure factors adapted for chemical bonding, static atomic displacements, as well as diffuse losses due to static and thermal disorder. Application to In0.28Ga0.72N0.025As0.975 before and after annealing at 670 °C yields dissolution of In-rich islands and N-rich clusters and formation of a quantum well with nearly constant thickness and homogeneous elemental distributions, resulting in symmetric profiles along growth direction. To verify that these structural transitions are indeed correlated with typically observed changes of optical properties during thermal annealing, photoluminescence spectra are presented, revealing an increase in intensity by a factor of 20 and a strong blue shift of 60 meV.

     [bibtex-key = Mueller2011c]



150. K. Müller, M. Schowalter, O. Rubel, D. Z. Hu, D. M. Schaadt, M. Hetterich, P. Gilet, R. Fritz, K. Volz, and A. Rosenauer. TEM 3-beam study of annealing effects in InGaNAs using ab-initio structure factors for strain-relaxed supercells. Journal of Physics: Conference Series, 326(1):012026, 2011. Abstract:

     We report on a Transmission Electron Microscopy 3-beam technique based on the interference of 000, 200 and 220. Nonlinear imaging artefacts are eliminated by Fourier filtering, yielding 200 and 220 lattice fringe images, from which chemically sensitive contrast and strain are measured, respectively. In this way, In and N composition can be mapped at atomic scale in quaternary InGaNAs by comparison with simulated reference data. Our Bloch wave simulations are based on structure factors derived from supercells with 10 6 atoms, which have been strain-relaxed by valence force field methods. Additionally, the influence of electron redistributions due to chemical bonding is accounted for by modified atomic scattering amplitudes derived from density functional theory. By comparing local compositions in an annealed In 0.28 Ga 0.72 N 0.025 As 0.975 sample with its as-grown counterpart, we find homogenisation of InGaNAs layer thickness and stoichiometry upon annealing.

     [bibtex-key = Mueller2011]



151. Angelika Pretorius, Thomas Schmidt, Timo Aschenbrenner, Tomohiro Yamaguchi, Christian Kübel, Knut Müller, Heiko Dartsch, Detlef Hommel, Jens Falta, and Andreas Rosenauer. Microstructural and compositional analyses of GaN based nanostructures. Physica Status Solidi, 248:1822--1836, 2011. Abstract:

     Composition and microstructure of GaN-based island structures and distributed Bragg reflectors (DBRs) were investigated with transmission electron microscopy (TEM). We analysed free-standing InGaN islands and islands capped with GaN. Growth of the islands performed by molecular beam epitaxy (MBE) and metal organic vapour phase epitaxy (MOVPE) resulted in different microstructures. The islands grown by MBE were plastically relaxed. Cap layer deposition resulted in a rapid dissolution of the islands already at early stages of cap layer growth. These findings are confirmed by grazing-incidence X-ray diffraction (GIXRD). In contrast, the islands grown by MOVPE relax only elastically. Strain state analysis (SSA) revealed that the indium concentration increases towards the tips of the islands. For an application as quantum dots, the islands must be embedded into DBRs. Structure and composition of AlyGa1-yN/GaN Bragg reflectors on top of an AlGaN buffer layer and InxAl1-xN/GaN Bragg reflectors on top of a GaN buffer layer were investigated. Specifically, structural defects such as threading dislocations (TDs) and inversion domains (IDs) were studied, and we investigated thicknesses, interfaces and interface roughnesses of the layers. As the peak reflectivities of the investigated DBRs do not reach the theoretical predictions, possible reasons are discussed.

     [bibtex-key = Pretorius2011]



152. A Rath, J K Dash, R R Juluri, A Rosenauer, and P V Satyam. Temperature-dependent electron microscopy study of Au thin films on Si (1 0 0) with and without a native oxide layer as barrier at the interface. Journal of Physics D: Applied Physics, 44(11):115301, 2011. Abstract:

     Real-time electron microscopy observation on morphological changes in gold nanostructures deposited on Si (1 0 0) surfaces as a function of annealing temperatures has been reported. Two types of interfaces with silicon substrates were used prior to gold thin film deposition: (i) without native oxide and on ultra-clean reconstructed Si surfaces and (ii) with native oxide covered Si surfaces. For ≈2.0 nm thick Au films deposited on reconstructed Si (1 0 0) surfaces using the molecular beam epitaxy method under ultra-high vacuum conditions, aligned four-fold symmetric nanogold silicide structures formed at relatively lower temperatures (compared with the one with native oxide at the interface). For this system, 82\% of the nanostructures were found to be nanorectangle-like structures with an average length of ≈27 nm and aspect ratio of 1.13 at ≈700 °C. For ≈5.0 nm thick Au films deposited on Si (1 0 0) surface with native oxide at the interface, the formation of a rectangular structure was observed at higher temperatures (≈850 °C). At these high temperatures, desorption of gold silicide followed the symmetry of the substrate. Native oxide at the interface was found to act like a barrier for the inter-diffusion phenomena. Structural characterization was carried out using advanced electron microscopy methods.

     [bibtex-key = Rath2011]



153. Andreas Rosenauer, Thorsten Mehrtens, Knut Müller, Katharina Gries, Marco Schowalter, Stephanie Bley, Parlapalli Venkata Satyam, Adrian Avramescu, Karl Engl, and Stephan Lutgen. 2D-composition mapping in InGaN without electron beam induced clustering of indium by STEM HAADF Z-contrast imaging. Journal of Physics: Conference Series, 326(1):012040, 2011. Abstract:

     Investigation of composition in InGaN quantum wells and quantum dots by TEM is hampered by formation of electron beam induced agglomeration of indium, which occurs if the specimen is exposed to the electron beam for a few minutes. In this contribution we demonstrate that compositional analysis of InGaN nanostructures is possible without this artifact if STEM Z-contrast imaging is applied instead of parallel beam illumination. The suggested method for composition analysis in InGaN is based on a comparison of intensity normalized with respect to the incident electron beam with simulated image intensity. Simulations are performed with the STEMsim program using the frozen lattice multislice approximation for which static atomic displacements were taken into account.

     [bibtex-key = Rosenauer2011e]



154. Andreas Rosenauer, Thorsten Mehrtens, Knut Müller, Katharina Gries, Marco Schowalter, Parlapalli Venkata Satyam, Stephanie Bley, Christian Tessarek, Detlef Hommel, Katrin Sebald, Moritz Seyfried, Jürgen Gutowski, Adrian Avramescu, Karl Engl, and Stephan Lutgen. Composition mapping in InGaN by scanning transmission electron microscopy. Ultramicroscopy, 111:1316--1327, 2011. Keyword(s): Quantitative STEM, Composition determination, Multislice simulation, Frozen lattice simulation. Abstract:

     We suggest a method for chemical mapping that is based on scanning transmission electron microscopy (STEM) imaging with a high-angle annular dark field (HAADF) detector. The analysis method uses a comparison of intensity normalized with respect to the incident electron beam with intensity calculated employing the frozen lattice approximation. This procedure is validated with an In0.07Ga0.93N layer with homogeneous In concentration, where the STEM results were compared with energy filtered imaging, strain state analysis and energy dispersive X-ray analysis. Good agreement was obtained, if the frozen lattice simulations took into account static atomic displacements, caused by the different covalent radii of In and Ga atoms. Using a sample with higher In concentration and series of 32 images taken within 42 min scan time, we did not find any indication for formation of In rich regions due to electron beam irradiation, which is reported in literature to occur for the parallel illumination mode. Image simulation of an In0.15Ga0.85N layer that was elastically relaxed with empirical Stillinger-Weber potentials did not reveal significant impact of lattice plane bending on STEM images as well as on the evaluated In concentration profiles for specimen thicknesses of 5, 15 and 50 nm. Image simulation of an abrupt interface between GaN and In0.15Ga0.85N for specimen thicknesses up to 200 nm showed that artificial blurring of interfaces is significantly smaller than expected from a simple geometrical model that is based on the beam convergence only. As an application of the method, we give evidence for the existence of In rich regions in an InGaN layer which shows signatures of quantum dot emission in microphotoluminescence spectroscopy experiments.

     [bibtex-key = Rosenauer2011a]



155. Th. Schmidt, M. Siebert, J. I. Flege, S. Figge, S. Gangopadhyay, A. Pretorius, T.-L. Lee, J. Zegenhagen, L. Gregoratti, A. Barinov, A. Rosenauer, D. Hommel, and J. Falta. Mg and Si dopant incorporation and segregation in GaN. physica status solidi (b), 248(8):1810--1821, 2011. Keyword(s): defects, dopants, photoelectron microscopy, segregation, X-ray standing waves. Abstract:

     The surface segregation of Mg and Si dopant species and their atomic incorporation sites in GaN films grown by metal-organic vapour phase epitaxy (MOVPE) on sapphire (0001) substrates have been analysed by X-ray photoemission spectro-microscopy and X-ray standing waves (XSW). As revealed by spectro-microscopy, both Mg and Si tend to segregate to the surface. In case of Mg, an enhanced surface dopant concentration is found even after sputter-removal of several tens of nanometres, which confirms a segregation mechanism proposed earlier [S. Figge et al., Appl. Phys. Lett. 81, 4748 (2002)]. Si doping has been found to result in the formation of facetted grooves in the GaN films. The surface silicon concentration at the facets is determined to be about 2.5 times higher as compared to the planar (0001) surface by micro-spectroscopy. XSW results show that with increasing Mg dopant concentration, non-substitutional lattice sites are progressively occupied. The results can quantitatively be explained by Mg atoms incorporated in an anti-bixbyite-like structure and is related to inversion domain boundaries. For Si doping, no evidence is found for the occupation of non-substitutional sites. However, a decrease in crystal quality is observed with increasing Si concentration.X-ray photoemission micrograph of a Si doped GaN film showing a facetted groove at the lower left corner of the image. The local spectra (see inset) reveal Si enrichment at the facets.

     [bibtex-key = Schmidt2011]



156. C. Tessarek, S. Figge, T. Aschenbrenner, S. Bley, A. Rosenauer, M. Seyfried, J. Kalden, K. Sebald, J. Gutowski, and D. Hommel. Strong phase separation of strained InGaN layers due to spinodal and binodal decomposition: Formation of stable quantum dots. Phys. Rev. B, 83:115316, March 2011. Abstract:

     InGaN quantum dots were grown by metal-organic vapor phase epitaxy using a phase-separation process based on spinodal and binodal decomposition. Uncapped structures were grown which show InGaN phases with two different In contents on the surface. The high-In-content phase accumulates to huge islands while the low-In content phase forms flat meander and quantum-dot-like structures on the surface. The dissolution of the high-In-containing phase is very sensitive to the growth temperature of the GaN capping while there is no significant change of the InGaN quantum dot structures. The samples were investigated with transmission and scanning electron microscopy, photoluminescence measurements, and x-ray diffraction. A narrow growth window concerning the InxGa1-xN composition was found in which the formation of quantum dots takes place. This growth window is in good agreement with the InGaN miscibility gap calculated for a strained InGaN layer. A detailed theoretical discussion is presented and the quantum dot and island formation will be explained by a strain-modified spinodal and binodal decomposition model.

     [bibtex-key = Tessarek2011]



157. Jianping Xiao, Agnieszka Kuc, Suman Pokhrel, Marco Schowalter, Satyam Parlapalli, Andreas Rosenauer, Thomas Frauenheim, Lutz Mädler, Lars G. M. Pettersson, and Thomas Heine. Evidence for Fe2+ in Wurtzite Coordination: Iron Doping Stabilizes ZnO Nanoparticles. Small, 7(20):2879--2886, 2011. Keyword(s): density functional theory, doping, iron, nanoparticles, zinc oxide. Abstract:

     First-principles calculations are used to investigate the structural and electronic properties of Fe-doped ZnO nanoparticles. Based on extensive validation studies surveying various density functionals, the hybrid functional PBE0 is employed to calculate the structures, formation energies, and electronic properties of Fe in ZnO with Fe concentrations of 6.25, 12.5, and 18.75 at\%. Substitution of Zn by Fe, zinc vacancies, and interstitial oxygen defects is studied. High-resolution inner-shell electron energy loss spectroscopy measurements and X-ray absorption near-edge structure calculations of Fe and O atoms are performed. The results show that Fe-doped ZnO nanoparticles are structurally and energetically more stable than the isolated FeO (rocksalt) and ZnO (wurtzite) phases. The Fe dopants distribute homogeneously in ZnO nanoparticles and do not significantly alter the host ZnO lattice parameters. Simulations of the absorption spectra demonstrate that Fe2+ dominates in the Fe-doped ZnO nanoparticles reported recently, whereas Fe3+ is present only as a trace.

     [bibtex-key = Xiao2011]



158. T. Aschenbrenner, H. Dartsch, C. Kruse, M. Anastasescu, M. Stoica, M. Gartner, A. Pretorius, A. Rosenauer, Thomas Wagner, and D. Hommel. Optical and structural characterization of AlInN layers for optoelectronic applications. J. Appl. Phys., 108(6):063533, 2010. Keyword(s): aluminium compounds, annealing, distributed Bragg reflectors, extinction coefficients, III-V semiconductors, indium compounds, MOCVD coatings, refractive index, semiconductor epitaxial layers, surface morphology, surface roughness, transmission electron microscopy, vapour phase epitaxial growth, wide band gap semiconductors, X-ray diffraction. [bibtex-key = Aschenbrenner2010a]



159. M Dries, B Gamm, K Schultheiss, A Rosenauer, R Schröder, and D Gerthsen. Object-wave Reconstruction by Carbon-Film-Based Zernike- and Hilbert-Phase Plate Microscopy: A Theoretical Study Not Restricted to Weak Phase Objects. Microscopy and Microanalysis, 16(Supplement S2):552--553, 2010. Abstract:

     ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010 Recent advances in the application of physical phase plates (PP) have opened up novel imaging possibilities in transmission electron microscopy (TEM). However, any image in TEM corresponds to the absolute square of the aberrated object-wave function, which causes a complete loss of phase information. Besides electron holography and through-focal series reconstruction a novel technique was proposed to recover the object-wave function by the use of a PP [1]. This technique, which is not restricted to weak-phase objects and linear image formation, requires three images to be taken at different arbitrary phase shifts induced by a centrosymmetric, matter-free, ideal PP. Nonlinear image contributions are effectively eliminated in the differences of two images obtained at different phase shifts. Taking into account the contrast transfer function, the object-wave function can be derived from analytical expressions. While some electrostatic approaches [2] aim at the realization of an ideal PP, amorphous carbon (a-C) film-based PPs are always affected by the scattering of electrons within the a-C film. This causes a reduction of the amplitude of the electrons coherently scattered in the sample, denoted as damping in the following. Moreover, characteristic image artefacts are produced by noncentrosymmetric approaches such as the Hilbert-PP. Phase-contrast images taken by noncentrosymmetric and/or a-C film-based PPs therefore have to be corrected with respect to undesired effects induced by the PP, before object-wave reconstruction is possible.

     [bibtex-key = Dries2010]



160. B. Gamm, M. Dries, K. Schultheiss, H. Blank, A. Rosenauer, R.R. Schr�er, and D. Gerthsen. Object wave reconstruction by phase-plate transmission electron microscopy. Ultramicroscopy, 110(7):807--814, 2010. Keyword(s): Phase plate. Abstract:

     A method is described for the reconstruction of the amplitude and phase of the object exit wave function by phase-plate transmission electron microscopy. The proposed method can be considered as in-line holography and requires three images, taken with different phase shifts between undiffracted and diffracted electrons induced by a suitable phase-shifting device. The proposed method is applicable for arbitrary object exit wave functions and non-linear image formation. Verification of the method is performed for examples of a simulated crystalline object wave function and a wave function acquired with off-axis holography. The impact of noise on the reconstruction of the wave function is investigated.

     [bibtex-key = Gamm2010]



161. Saji George, Suman Pokhrel, Tian Xia, Benjamin Gilbert, Zhaoxia Ji, Marco Schowalter, Andreas Rosenauer, Robert Damoiseaux, Kenneth A. Bradley, Lutz Mädler, and André E. Nel. Use of a Rapid Cytotoxicity Screening Approach To Engineer a Safer Zinc Oxide Nanoparticle through Iron Doping. ACS Nano, 4(1):15--29, 2010. Note: PMID: 20043640. Abstract:

     The establishment of verifiably safe nanotechnology requires the development of assessment tools to identify hazardous nanomaterial properties that could be modified to improve nanomaterial safety. While there is a lot of debate of what constitutes appropriate safety screening methods, one approach is to use the assessment of cellular injury pathways to collect knowledge about hazardous material properties that could lead to harm to humans and the environment. We demonstrate the use of a multiparameter cytotoxicity assay that evaluates toxic oxidative stress to compare the effects of titanium dioxide (TiO2), cerium oxide (CeO2), and zinc oxide (ZnO) nanoparticles in bronchial epithelial and macrophage cell lines. The nanoparticles were chosen on the basis of their volume of production and likelihood of spread to the environment. Among the materials, dissolution of ZnO nanoparticles and Zn2+ release were capable of ROS generation and activation of an integrated cytotoxic pathway that includes intracellular calcium flux, mitochondrial depolarization, and plasma membrane leakage. These responses were chosen on the basis of the compatibility of the fluorescent dyes that contemporaneously assess their response characteristics by a semiautomated epifluorescence procedure. Purposeful reduction of ZnO cytotoxicity was achieved by iron doping, which changed the material matrix to slow Zn2+ release. In summary, we demonstrate the utility of a rapid throughput, integrated biological oxidative stress response pathway to perform hazard ranking of a small batch of metal oxide nanoparticles, in addition to showing how this assay can be used to improve nanosafety by decreasing ZnO dissolution through Fe doping.

     [bibtex-key = George2010]



162. Thorsten M. Gesing, Marco Schowalter, Claudia Weidenthaler, Andreas Rosenauer, Hartmut Schneider, and Reinhard X. Fischer. Mullite-type (Bi${\sb 1{$-$\it x}}$Sr${\sb {\it x}} ){\sb 2}$Al${\sb 4}$O${\sb 9{$-$\it x}/2}$: HT-XRPD, TEM and XPS investigations. Acta Crystallographica Section A, 66(a1):s182--s183, September 2010. [bibtex-key = Gesing2010]



163. Knut Müller, Marco Schowalter, Andreas Rosenauer, Jacob Jansen, Kenji Tsuda, John Titantah, and Dirk Lamoen. Refinement of chemically sensitive structure factors using parallel and convergent beam electron nanodiffraction. Journal of Physics: Conference Series, 209(1):012025, 2010. Abstract:

     We introduce a new method to measure structure factors from parallel beam electron diffraction (PBED) patterns. Bloch wave refinement routines were developed which can minimise the difference between simulated and experimental Bragg intensities via variation of structure factors, Debye parameters, specimen thickness and -orientation. Due to plane wave illumination, the PBED refinement is highly efficient not only in computational respect, but also concerning the experimental effort since energy filtering is shown to have no significant effect on the refinement results. The PBED method was applied to simulated GaAs diffraction patterns to derive systematic errors and rules for the identification of plausible refinement results. The evaluation of experimental GaAs PBED patterns yields a 200 X-ray structure factor of -6.33±0.14. Additionally, we obtained -6.35±0.13 from two-dimensional convergent beam electron diffraction refinements. Both results confirm density functional theory calculations published by Rosenauer et al. and indicate the inaccuracy of isolated atom scattering data, which is crucial e.g. for the composition evaluation by lattice fringe analysis.

     [bibtex-key = Mueller2010b]



164. Knut Müller, Marco Schowalter, Andreas Rosenauer, Oleg Rubel, and Kerstin Volz. Effect of bonding and static atomic displacements on composition quantification in InGaNAs. Phys. Rev. B, 81(7):075315, February 2010. [bibtex-key = Mueller2010a]



165. Suman Pokhrel, Johannes Birkenstock, Marco Schowalter, Andreas Rosenauer, and Lutz Mädler. Growth of Ultrafine Single Crystalline WO3 Nanoparticles Using Flame Spray Pyrolysis. Crystal Growth & Design, 10(2):632--639, 2010. Abstract:

     Flame spray pyrolysis (FSP) has been employed for the syntheses of single crystalline WO3 nanoparticles using tungsten precursors with tungsten in usual (+6) and unusual (+4 and 0) oxidation states. The WO3 nanoparticles have been characterized by powder X-ray diffraction and the patterns have been refined using the Rietveld and the Le Bail method (space group P21/n, monoclinic system; the averaged lattice parameters of the three WO3: a = 7.3913(4) Å, b = 7.5630(5) Å, c = 7.6615(6) Å, β = 90.78(3)°, Z = 8, V = 423.19 Å3). Because of the very small crystallite sizes, non-Bragg scattering is observed. The crystallite sizes derived from Rietveld or Le Bail analyses were in the range of 6−8 nm, reasonably agreeing with the crystallite sizes (7−10 nm) determined from Brunauer−Emmett−Teller and microscopic analysis where each particle is basically a small single crystal. Well-developed lattice fringes of 3.860−3.994 Å were illustrated by high resolution transmission electron microscopy (HRTEM). Indexing of selected area electron diffraction (SAED) patterns of all WO3 revealed that the crystals are isostructural with the monoclinic phase having pseudocubic lattice parameters. The wide spot HRTEM image additionally examined in reciprocal space by calculating the corresponding power spectrum further proved the single-crystalline nature of the nanoparticles. The development of economic precursors and the systematic studies on the crystallization and assembly behavior of tungsten oxide products presented here now opens the door for the production of ultrafine single crystalline, single phase WO3 nanomaterial.

     [bibtex-key = Pokhrel2010a]



166. Andreas Rosenauer, Katharina Gries, Knut Müller, Marco Schowalter, Angelika Pretorius, Adrian Avramescu, Karl Engl, and Stephan Lutgen. Measurement of composition profiles in III-nitrides by quantitative scanning transmission electron microscopy. Journal of Physics: Conference Series, 209(1):012009, 2010. Abstract:

     In this paper we demonstrate a quantitative method for composition evaluation based on comparison of normalized image intensity with simulations carried out with the frozen lattice approximation. The method is applied to evaluate composition profiles of Al x Ga 1−x N/GaN layers. We measure ratios of image intensities obtained in regions with unknown and with known Al-concentration x , respectively. We show that estimation of specimen thickness combined with evaluation of intensity ratios allows quantitative measurement of composition profiles. Delocalization effects at interfaces due to instrumental resolution and dynamic electron diffraction are simulated. These effects can well be described by convolution with a Lorentzian. Measured intensity profiles can be corrected for delocalization effects using statistical parameter estimation so that deconvolution is avoided.

     [bibtex-key = Rosenauer2010c]



167. A. Schaefer, A. Sandell, L.E. Walle, V. Zielasek, M. Schowalter, A. Rosenauer, and M. Bäumer. Chemistry of thin film formation and stability during praseodymium oxide deposition on Si(111) under oxygen-deficient conditions. Surface Science, 604(15–16):1287--1293, 2010. Keyword(s): Praseodymium oxide. Abstract:

     The growth of thin praseodymium oxide films on silicon (111) using small deposition rates under oxygen-deficient conditions was investigated in the range from submonolayer up to six monolayers coverage by transmission electron microscopy (TEM) and photoemission spectroscopy (PES). A detailed analysis of the silicon 2p and oxygen 1 s core level and valence band spectra reveals chemical reactions between deposited species, substrate, and the growing film. Silicate, silicide and oxide species are coexisting over the entire range of coverages investigated. Cross sectional TEM shows silicide inclusions extending from the surface several nanometers into the substrate and affecting the substrate band bending at the interface. The reactivity of the praseodymia overlayer leads to reactions in the as-deposited film even at room temperature and render it unstable. The article aims at providing a coherent picture of the chemistry proceeding during interface formation and film growth at low rates of deposition (0.06 nm/min). The results will be discussed in comparison to studies using higher rates, emphasizing the possibility of growth rate dependent reactions between substrate and deposited material and, consequently, distinctly different film compositions and structures for different rates of deposition.

     [bibtex-key = Schaefer2010]



168. Patrick Sonström, Johannes Birkenstock, Yulia Borchert, Laura Schilinsky, Peter Behrend, Katharina Gries, Knut Müller, Andreas Rosenauer, and Marcus Bäumer. Nanostructured Praseodymium Oxide: Correlation between phase transitions and catalytic activity. ChemCatChem, 2:694--704, 2010. Abstract:

     Praseodymia gives rise to a rich phase diagram with a large number of phases between the limiting stoichiometries Pr2O3 and PrO2 that differ only slightly in oxygen content (PrnO2n-2). This chemical and crystallographic variability allows the system to release or incorporate lattice oxygen easily at sufficiently high temperatures and thus renders the material interesting as a catalyst for redox reactions according to a Mars-van Krevelen mechanism. Nanostructured praseodymia samples are investigated in this study with respect to their catalytic properties, focusing on methane oxidation and selective NO reduction by CO and CH4. To correlate catalytic activity and crystallographic changes, complementary high-temperature X-ray diffraction measurements have been carried out. The determined temperatures of transitions between different oxide phases agree well with peaks in the temperature-programmed reduction measurements, confirming the direct connection between the availability of lattice oxygen and crystallographic transformations. The catalytic activity for methane oxidation and NO reduction sets in at 450-500°C, at which temperature the starting material—mainly Pr6O11―transforms into the next oxygen-depleted phase Pr7O12. With respect to NO reduction, the results show that it is possible to employ both methane and carbon monoxide as reducing agents in the absence of oxygen, in agreement with a Mars-van Krevelen mechanism. Nevertheless, the use of CO instead of CH4 offers considerable advantages, as no deactivation due to carbon residues takes place in this case. Whereas, in an excess of oxygen, NO reduction is inhibited independently of the reducing agent, it is shown that NO reduction can proceed if the O2 concentration remains below a critical concentration.

     [bibtex-key = Sonstroem2010]



169. V.C. Srivastava, K.B. Surreddi, S. Scudino, M. Schowalter, V. Uhlenwinkel, A. Schulz, J. Eckert, A. Rosenauer, and H.-W. Zoch. Microstructure and mechanical properties of partially amorphous Al85Y8Ni5Co2 plate produced by spray forming. Materials Science and Engineering: A, 527(10–11):2747--2758, 2010. Keyword(s): Spray deposition. Abstract:

     A 12 mm thick Al85Y8Ni5Co2 plate was spray deposited on a 30 mm thick copper substrate pre-heated to 383 K. The deposit microstructure consists of an amorphous phase, 50–150 nm fcc-Al grains, 0.2–0.7 ÃŽÂ¼m Al2Y and Al3Y intermetallic phases and some unidentified phases. The hardness of different microstructural features and the compressive strength of the deposit, after extrusion at 723 K, were evaluated. The small size overspray particles as well as the deposit show a glass transition phenomenon. The total crystallization energy of the deposit is 121 J/g compared to 83.9 J/g for the small sized overspray powder, indicating its high metastability. A compressive strength of 925 MPa and a deformation strain of 9\% were achieved for the deposit after extrusion. The novel microstructural features in the deposit are attributed to the “chilling effectâ€Â� on highly undercooled or partially solidified large-size droplets during deposition onto the pre-heated substrate, and the rapid heat extraction thereof due to a close contact at the deposit/substrate interface.

     [bibtex-key = Srivastava2010]



170. B. Butz, R. Schneider, D. Gerthsen, M Schowalter, and A. Rosenauer. Decomposition of 8.5 mol. Y2O3-doped zirconia and its contribution to the degradation of ionic conductivity. Acta Materialia, 57:5480--5490, 2009. [bibtex-key = Butz2009a]



171. Katharina Gries, Roland Kröger, Christian Kübel, Monika Fritz, and Andreas Rosenauer. Investigations of voids in the aragonite platelets of nacre. Acta Biomaterialia, 5(8):3038--3044, 2009. Keyword(s): Nacre. Abstract:

     We studied the structure of the aragonite platelets of Haliotis laevigata nacre, using conventional transmission electron microscopy, Z-contrast, electron tomography, energy-dispersive X-ray analysis and electron energy-loss spectroscopy. We observed faceted voids several nanometers wide within the aragonite platelets. The electron tomography investigations showed that the voids are distributed more or less randomly in the studied specimen and allowed an estimation of the order of magnitude of the width and the volumetric content of the voids. Further investigations of these voids revealed that they contain an increased amount of carbon, which suggests the existence of organic material within the voids.

     [bibtex-key = Gries2009a]



172. Katharina Gries, Roland Kröger, Christian Kübel, Marco Schowalter, Monika Fritz, and Andreas Rosenauer. Correlation of the orientation of stacked aragonite platelets in nacre and their connection via mineral bridges. Ultramicroscopy, 109(3):230--236, 2009. Keyword(s): Nacre. Abstract:

     In this work, we studied the correlation of the orientation of stacked aragonite platelets of Haliotis laevigata nacre, using selected area diffraction (SAD) in transmission electron microscopy (TEM). From the position of the center of Laue circle (COLC) within the diffraction patterns the tilt angles of the investigated platelets relatively to a reference platelet (oriented in zone axis) are determined. The strong correlation of the platelets supports the existence of mineral bridges, which connect the stacked platelets and enable a transfer of the platelet orientation during growth. Electron tomography and subsequent reconstruction of the obtained data yield information about the shape of the mineral bridges. The crystalline structure of the material within the mineral bridges was investigated by high resolution \{TEM\} (HRTEM).

     [bibtex-key = Gries2009]



173. C Kuebel, K Gries, R Kröger, M Fritz, and A Rosenauer. Microstructure of Aragonite Platelets in Nacre. Microscopy and Microanalysis, 15:900--901, 7 2009. Abstract:

     ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 - July 30, 2009

     [bibtex-key = Kuebel2009]



174. Knut Müller, Marco Schowalter, Jacob Jansen, Kenji Tsuda, John Titantah, Dirk Lamoen, and Andreas Rosenauer. Refinement of the 200 structure factor for GaAs using parallel and convergent beam electron nanodiffraction data. Ultramicroscopy, 109:802--814, 2009. Keyword(s): GaAs, Structure factor refinement, Bonding, Parallel beam electron diffraction, Convergent beam electron diffraction. Abstract:

     We present a new method to measure structure factors from electron spot diffraction patterns recorded under almost parallel illumination in transmission electron microscopes. Bloch wave refinement routines have been developed to refine the crystal thickness, its orientation and structure factors by comparison of experimentally recorded and calculated intensities. Our method requires a modicum of computational effort, making it suitable for contemporary personal computers. Frozen lattice and Bloch wave simulations of GaAs diffraction patterns are used to derive optimised experimental conditions. Systematic errors are estimated from the application of the method to simulated diffraction patterns and rules for the recognition of physically reasonable initial refinement conditions are derived. The method is applied to the measurement of the 200 structure factor for GaAs. We found that the influence of inelastically scattered electrons is negligible. Additionally, we measured the 200 structure factor from zero loss filtered two-dimensional convergent beam electron diffraction patterns. The precision of both methods is found to be comparable and the results agree well with each other. A deviation of more than 20\% from isolated atom scattering data is observed, whereas close agreement is found with structure factors obtained from density functional theory [A. Rosenauer, M. Schowalter, F. Glas, D. Lamoen, Phys. Rev. B 72 (2005), 085326-1], which account for the redistribution of electrons due to chemical bonding via modified atomic scattering amplitudes.

     [bibtex-key = Mueller2009b]



175. Andreas Rosenauer, Katharina Gries, Knut Müller, Angelika Pretorius, Marco Schowalter, Adrian Avramescu, Karl Engl, and Stephan Lutgen. Measurement of specimen thickness and composition in AlGaN/GaN using high-angle annular dark field images. Ultramicroscopy, 109(9):1171--1182, 2009. Keyword(s): Quantitative STEM Z-contrast imaging. Abstract:

     In scanning transmission electron microscopy using a high-angle annular dark field detector, image intensity strongly depends on specimen thickness and composition. In this paper we show that measurement of image intensities relative to the intensity of the incoming electron beam allows direct comparison with simulated image intensities, and thus quantitative measurement of specimen thickness and composition. Simulations were carried out with the frozen lattice and absorptive potential multislice methods. The radial inhomogeneity of the detector was measured and taken into account. Using a focused ion beam (FIB) prepared specimen we first demonstrate that specimen thicknesses obtained in this way are in very good agreement with a direct measurement of the thickness of the lamella by scanning electron microscopy in the FIB. In the second step we apply this method to evaluate the composition of AlxGa1-xN/GaN layers. We measured ratios of image intensities obtained in regions with unknown and with known Al-concentration x, respectively. We show that estimation of the specimen thickness combined with evaluation of intensity ratios allows quantitative measurement of the composition x. In high-resolution images we find that the image intensity is well described by simulation if the simulated image is convoluted with a Gaussian with a half-width at half-maximum of 0.07 nm.

     [bibtex-key = Rosenauer2009a]



176. A. Schaefer, V. Zielasek, Th. Schmidt, A. Sandell, M. Schowalter, O. Seifarth, L. E. Walle, Ch. Schulz, J. Wollschläger, T. Schroeder, A. Rosenauer, J. Falta, and M. Bäumer. Growth of praseodymium oxide on Si(111) under oxygen-deficient conditions. Phys. Rev. B, 80:045414, July 2009. [bibtex-key = Schaefer2009]



177. M. Schowalter, A. Rosenauer, J. T. Titantah, and D. Lamoen. Computation and parametrization of the temperature dependence of Debye-Waller factors for group IV, III-V and II-VI semiconductors. Acta Crystallogr., Sect. A, 65(1):5--17, January 2009. Keyword(s): Debye-Waller factors, semiconductors, force constants, phonon densities of states. Abstract:

     We calculated the temperature dependence of the Debye-Waller factors for a variety of group IV, III-V and II-VI semiconductors from 0.1 to 1000 K. The approach used to fit the temperature dependence is described and resulting fit parameters are tabulated for each material. The Debye-Waller factors are deduced from generalized phonon densities of states which were derived from first principles using the WIEN2k and the ABINIT codes.

     [bibtex-key = Schowalter2009]



178. M. Schowalter, A. Rosenauer, J. T. Titantah, and D. Lamoen. Temperature-dependent Debye-Waller factors for semiconductors with the wurtzite-type structure. Acta Crystallogr., Sect. A, 65(3):227--231, May 2009. Abstract:

     We computed Debye-Waller factors in the temperature range from 0.1 to 1000 K for AlN, GaN, InN, ZnO and CdO with the wurtzite-type structure. The Debye-Waller factors were derived from phonon densities of states obtained from Hellmann-Feynman forces computed within the density-functional-theory formalism. The temperature dependences of the Debye-Waller factors were fitted and fit parameters are given.

     [bibtex-key = Schowalter2009a]



179. V. C. Srivastava, K. B. Surreddi, S. Scudino, M. Schowalter, V. Uhlenwinkel, A. Schulz, A. Rosenauer, H.-W. Zoch, and J. Eckert. Spray forming of Bulk Al85Y8Ni5Co2 with co-existing amorphous, nano- and micro-crystalline Structures. Transactions of the Indian In, 62:331--5, 2009. [bibtex-key = Srivastava2009]



180. J. T. Titantah, D. Amoen, M. Schowalter, and A. Rosenauer. Density-functional theory calculation of the electron energy-loss near-edge structure of Li-Intercalated graphite. Carbon, 47:2501--2510, 2009. [bibtex-key = Titantah2009b]



181. J. T. Titantah, D. Lamoen, M. Schowalter, and A. Rosenauer. Modified atomic scattering amplitudes and size effects on the 002 and 220 electron structure factors of multiple Ga$_{1-x}$In$_x$As/GaAs quantum wells. J. Appl. Phys., 105(8):084310, 2009. Keyword(s): arsenic compounds, density functional theory, gallium arsenide, gallium compounds, III-V semiconductors, indium compounds, lattice constants, Monte Carlo methods, nanostructured materials, semiconductor heterojunctions, semiconductor quantum wells. [bibtex-key = Titantah2009a]



182. Jo Verbeeck, Peter Schattschneider, and Andreas Rosenauer. Image simulation of high resolution energy filtered TEM images. Ultramicroscopy, 109(4):350--360, 2009. Keyword(s): Image simulation. Abstract:

     Inelastic image simulation software is presented, implementing the double channeling approximation which takes into account the combination of multiple elastic and single inelastic scattering in a crystal. The approach is described with a density matrix formalism. Two applications in high resolution energy filtered (EFTEM) transmission electron microscopy (TEM) images are presented: thickness-defocus maps for SrTiO 3 and exit plane intensities for an ( LaAlO 3 ) 3 ( SrTiO 3 ) 3 multilayer system. Both systems show a severe breakdown in direct interpretability which becomes worse for higher acceleration voltages, thicker samples and lower excitation edge energies. Since this effect already occurs in the exit plane intensity, it is a fundamental limit and image simulations in \{EFTEM\} are indispensable just as they are indispensable for elastic high resolution \{TEM\} images.

     [bibtex-key = Verbeeck2009]



183. A. Pretorius, K. Müller, T. Yamaguchi, R. Kröger, D. Hommel, and A. Rosenauer. Concentration Evaluation in Nanometre-Sized InGaN Islands Using Transmission Electron Microscopy, pages 17--20. Springer Netherlands, 2008. [bibtex-key = Pretorius2008b]



184. Bernhard Gehl, Andreas Frömsdorf, Vesna Aleksandrovic, Thomas Schmidt, Angelika Pretorius, Jan-Ingo Flege, Sigrid Bernstorff, Andreas Rosenauer, Jens Falta, Horst Weller, and Marcus Bäumer. Structural and Chemical Effects of Plasma Treatment on Close-Packed Colloidal Nanoparticle Layers. Advanced Functional Materials, 18(16):2398--2410, 2008. Keyword(s): Adsorption, GISAXS, Nanoparticle layers, Plasma, XPS. Abstract:

     The interaction of nitrogen, oxygen, and hydrogen plasmas with spin-coated arrays of colloidal cobalt-platinum particles was investigated with a large variety of microscopic and spectroscopic techniques. It could be demonstrated that the organic ligands of the nanoparticles can be completely removed. Yet, due to the short (∼1.6 nm) interparticle distances within the layers, strong degradation and sintering effects are observed after hydrogen and nitrogen plasma treatments. In the case of oxygen plasma, the shape and size of the individual particles are unaffected and can be preserved, even if a short hydrogen plasma is subsequently applied to reduce the particles back to their metallic state. Nevertheless, the mesoscopic order of the particle arrays is slightly decreased as observed by the breakup of larger ordered areas into smaller domains forming island-trench structures. Probing the surface chemistry of the particles with temperature programmed desorption, a rather complex surface chemistry is found to result from the plasma treatments. The first TPD spectrum after the cleaning process with oxygen and subsequent hydrogen plasmas reveals that the particles are loaded with adsorbed and implanted hydrogen. After removal of this hydrogen, subsequent TPD spectra using CO as a probe molecule, show broad signals between 190 and 360 K pointing to nonmetallic surface properties. While the platinum was found to be completely reduced, XPS measurements reveal a remaining fraction of oxidic cobalt species which are enriched at the surface. Thus, although the structure of the close-packed Co-Pt nanoparticle arrays can be qualitatively preserved during plasma-based ligand removal, the treatment leads to a complex materials system the chemical properties of which are influenced by the particle components, the substrate, and the plasma media.

     [bibtex-key = Gehl2008]



185. Birte Jürgens, Holger Borchert, Kirsten Ahrenstorf, Patrick Sonström, Angelika Pretorius, Marco Schowalter, Katharina Gries, Volkmar Zielasek, Andreas Rosenauer, Horst Weller, and Marcus Bäumer. Colloidally Prepared Nanoparticles for the Synthesis of Structurally Well-Defined and Highly Active Heterogeneous Catalysts. Angewandte Chemie International Edition, 47(46):8946--8949, 2008. Keyword(s): colloids, heterogeneous catalysis, nanoparticles, oxidation, supported catalysts. [bibtex-key = Juergens2008]



186. D. Litvinov, M. Schowalter, A. Rosenauer, B. Daniel, J. Fallert, W. Löffler, H. Kalt, and M. Hetterich. Determination of critical thickness for defect formation of CdSe/ZnSe heterostructures by transmission electron microscopy and photoluminescence spectroscopy. physica status solidi (a), 205(12):2892--2897, 2008. Keyword(s): 68.37.Lp, 68.37.Og, 68.55.ag, 68.65.Fg, 78.55.Et. Abstract:

     We report on the investigation of CdSe/ZnSe heterostructures by transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). CdSe layers with nominal thicknesses tCdSe between 0.5 and 8 monolayers (ML) were embedded in a ZnSe matrix and grown on a GaAs(001) substrate by molecular-beam epitaxy at 280 °C. The Cd-distribution was obtained from high-resolution TEM lattice fringe images using composition evaluation by lattice fringe analysis technique. The measured minimum, average and maximum Cd-concentrations and the overall CdSe contents in the layers increase with the nominal CdSe layer thickness and reach a constant value at tCdSe = 4 ML. The measured CdSe content in the regions with the maximal Cd-concentration continues to increase for tCdSe ≥ 5 ML. The increasing of measured Cd-concentrations/CdSe contents is correlated with a red shift of PL spectra. In the CdSe layers with tCdSe ≥ 5 ML, formation of defects is observed. The increasing density of defects and decreasing intensity of PL spectra with tCdSe suggest that the critical thickness for defect formation during CdSe growth on the ZnSe(001) is between 4 ML and 5 ML. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

     [bibtex-key = Litvinov2008]



187. J. Pizarro, P.L. Galindo, E. Guerrero, A. Yanez, M. P. Guerrero, A. Rosenauer, D. L. Sales, and S.I. Molina. Simulation of high angle annular dark field scanning transmission electron microscopy images of large nanostructures. Applied Physics Letters, 93(15):153107--153107-3, 2008. Keyword(s): indium compounds, nanowires, scanning electron microscopy, semiconductor quantum wires, 6146Km, 6837Hk, 6865La. Abstract:

     High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is a powerful tool to quantify size, shape, position, and composition of nano-objects with the assessment of image simulation. Due to the high computational requirements needed, nowadays it can only be applied to a few unit cells in standard computers. To overpass this limitation, a parallel software (SICSTEM) has been developed. This software can afford HAADF-STEM image simulations of nanostructures composed of several hundred thousand atoms in manageable time. The usefulness of this tool is exemplified by simulating a HAADF-STEM image of an InAs nanowire.

     [bibtex-key = Pizarro2008]



188. Andreas Rosenauer, Marco Schowalter, John T. Titantah, and Dirk Lamoen. An emission-potential multislice approximation to simulate thermal diffuse scattering in high-resolution transmission electron microscopy. Ultramicroscopy, 108(12):1504--1513, 2008. Keyword(s): Thermal diffuse scattering. Abstract:

     Thermal diffuse scattered electrons significantly contribute to high-resolution transmission electron microscopy images. Their intensity adds to the background and is peaked at positions of atomic columns. In this paper we suggest an approximation to simulate intensity of thermal diffuse scattered electrons in plane-wave illumination transmission electron microscopy using an emission-potential multislice algorithm which is computationally less intensive than the frozen lattice approximation or the mutual intensity approach. Intensity patterns are computed for Au and InSb for different crystal orientations. These results are compared with intensities from the frozen lattice approximation based on uncorrelated vibration of atoms as well as with the frozen phonon approximation for Au. The frozen phonon method uses a detailed phonon model based on force constants we computed by a density functional theory approach. The comparison shows that our suggested emission-potential method is in close agreement with both the frozen lattice and the frozen phonon approximations.

     [bibtex-key = Rosenauer2008]



189. J. T. Titantah, D. Lamoen, M. Schowalter, and A. Rosenauer. Size effects and strain state of Ga(1-x)In(x)As/GaAs multiple quantum wells: Monte Carlo study. Phys. Rev. B, 78:165326, October 2008. [bibtex-key = Titantah2008]



190. R. Kroeger, T. Paskova, S. Figge, D. Hommel, and A. Rosenauer. Interfacial structure of a-plane GaN grown on r-plane sapphire. Appl. Phys. Lett., 90:081918, 2007. [bibtex-key = Kroeger2007a]



191. Radian Popescu, Erich Müller, Matthias Wanner, Dagmar Gerthsen, Marco Schowalter, Andreas Rosenauer, Artur Böttcher, Daniel Löffler, and Patrick Weis. Increase of the mean inner Coulomb potential in Au clusters induced by surface tension and its implication for electron scattering. Phys. Rev. B, 76(23):235411, December 2007. Abstract:

     Electron holography in a transmission electron microscope was applied to measure the phase shift Δφ induced by Au clusters as a function of the cluster size. Large Δφ observed for small Au clusters cannot be described by the well-known equation Δφ=CEV0t (CE, interaction constant; V0, mean inner Coulomb potential (MIP) of bulk gold; and t, cluster thickness). The rapid increase of the Au MIP with decreasing cluster size derived from Δφ can be explained by the compressive strain of surface atoms in the cluster.

     [bibtex-key = Popescu2007]



192. Angelika Pretorius, Knut Müller, Roland Kröger, Detlef Hommel, Andreas Rosenauer, and Tomohiro Yamaguchi. Concentration measurement in free-standing InGaN nano-islands with transmission electron microscopy. Microscopy and Microanalysis, 13 (Suppl. 03):312--313, 2007. [bibtex-key = Pretorius2007a]



193. EHM Rossi, A. Rosenauer, and G. Van Tendeloo. Influence of strain, specimen orientation and background estimation on composition evaluation of InAs/GaAs by TEM. Philosophical Magazine, 87(29):4461--4473, 2007. Abstract:

     The influence of strain, specimen orientation and background estimation on the accuracy of CELFA results is investigated using displacement vectors, calculated by finite differences, in the Darwin-Howie-Whelan equations. The calculations allow a simulation of the complex amplitudes of the beams, computation of the image Fourier components and application of the CELFA method to the simulated image Fourier components. The evaluated indium concentration can also be compared with the concentration profile used as input for simulation of the displacements. An equation for the true background has been derived and it is shown that background estimation by a polynomial fitting is the major error in the application of the CELFA method. It is also shown that under proper conditions (thickness <70 nm and an orientation such that the centre of the Laue circle is between [20; 0; 0] and [20; 1.75; 0]), the systematic errors, due the presence of strain effects, are not more than about 100 · (ΔX/Xtrue) ≍ ± 5\%.

     [bibtex-key = Rossi2007]



194. J. T. Titantah, D. Lamoen, M. Schowalter, and A. Rosenauer. Bond length variation in Ga(1-x)In(x)As crystals from the Tersoff potential. J. Appl. Phys., 101(12):123508, 2007. Keyword(s): gallium arsenide, indium compounds, III-V semiconductors, ab initio calculations, bond lengths, crystal binding, elastic constants, melting point, band structure. [bibtex-key = Titantah2007a]



195. J. T. Titantah, D. Lamoen, M. Schowalter, and A. Rosenauer. Temperature effect on the 002 structure factor of ternary Ga(1-x)In(x)As crystals. Phys. Rev. B, 76(7):073303, August 2007. Abstract:

     In this work, we study the effect of relaxation of the atomic positions and lattice parameter of mixed Ga1−xInxAs systems on the 002 electron atomic scattering amplitudes (ASA). The ASAs are shown to vary strongly with lattice parameter but to be indistinguishable for different In concentrations when the lattice parameter is held fixed. The resulting relationship between ASA and lattice parameter is then used in a finite temperature, zero pressure Monte Carlo relaxation of the mixed crystal. The consequence of the use of this atomic scattering amplitude is a reduction of the structure factor, leading to an increase of the In concentration at which the 002 structure factor vanishes. This method directly includes the effect of temperature on the ASA and on the structure factors and therefore does not require an explicit knowledge of the Debye-Waller factor.

     [bibtex-key = Titantah2007]



196. K. Volz, T. Torunski, O. Rubel, W. Stolz, P. Kruse, D. Gerthsen, M. Schowalter, and A. Rosenauer. Annealing effects on the nanoscale indium and nitrogen distribution in Ga(NAs) and (GaIn)(NAs) quantum wells. J. Appl. Phys., 102(8):083504, 2007. Keyword(s): annealing, gallium arsenide, gallium compounds, III-V semiconductors, impurity distribution, indium compounds, photoluminescence, Rutherford backscattering, semiconductor epitaxial layers, semiconductor heterojunctions, semiconductor quantum wells, transmission electron microscopy. Abstract:

     III/V semiconductors containing dilute amounts of nitrogen are metastable and need to be thermally treated after growth to optimize optoelectronic properties. The influence of thermal annealing on the nitrogen depth profile in metal organic vapor phase epitaxygrown Ga(NAs)/GaAs as well as (GaIn)(NAs)/GaAs heterostructures is examined on a nanometer scale by combining several high resolution transmission electron microscopy techniques, also with Rutherford backscattering spectrometry. Annealing conditions, which are optimized for quaternary alloys with respect to photoluminescence intensity, do not result in element redistribution for the In containing material. Contrary to the quaternary material, the result of annealing the ternary Ga(NAs) is a pronounced pileup of the nitrogen profile without any out diffusion of nitrogen. These findings have important influence on device structures, which often contain Ga(NAs) barriers for strain-compensation purposes together with (GaIn)(NAs) active regions. In the light of metastability considerations for the ternary and quaternary alloy, one can conclude that the In contained in the quaternary material stabilizes the material and suppresses phase separation. Consequently (GaIn)(NAs) is more stable than its ternary counterpart Ga(NAs).

     [bibtex-key = Volz2007]



197. P. Kruse, M. Schowalter, D. Lamoen, A. Rosenauer, and D. Gerthsen. Determination of the mean inner potential in III-V semiconductors, Si and Ge by density functional theory and electron holography. Ultramicroscopy, 106(2):105--113, 2006. Keyword(s): Mean inner potential. Abstract:

     The mean inner potentials of various III-V semiconductors, Si and Ge have been calculated by density functional theory methods. For that purpose, the Coulomb potential of slabs consisting of a crystal and vacuum region has been computed and averaged inside the crystal region. The computed values are in agreement with experimental values obtained by electron holography for Si and GaAs. For the other semiconductors, the deviations are smaller than 0.8 V. The results from density functional theory are approximately 10\% smaller than the values derived from atomic scattering factors computed by Hartree Fock calculations.

     [bibtex-key = Kruse2006]



198. R. Kröger, C. Kruse, C. Roder, D. Hommel, and A. Rosenauer. Relaxation in crack-free AlN/GaN superlattices. physica status solidi (b), 243(7):1533--1536, 2006. Keyword(s): 42.79.Fm, 68.37.Lp, 68.55.Ln, 68.65.Cd, 71.72.Ff, 83.85.St. Abstract:

     An AlN/GaN superlattice structure for the use as low index material in distributed Bragg reflectors in the blue-violet spectral region was studied by transmission electron microscopy in cross section and plan view. The superlattice is found to partially relax during growth via the introduction of threading dislocations. Dislocation loops are found to form spontanously at discrete superlattice thicknesses indicating the accumulation of point defects. Such defects might hamper the light transmission in the targeted wavelength range. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

     [bibtex-key = Kroeger2006]



199. D. Litvinov, D. Gerthsen, A. Rosenauer, M. Schowalter, T. Passow, P. Feinäugle, and M. Hetterich. Transmission electron microscopy investigation of segregation and critical floating-layer content of indium for island formation in $In_{x}Ga_{1-{}x}As$. Phys. Rev. B, 74(16):165306, October 2006. Abstract:

     We have investigated InxGa1−xAs layers grown by molecular-beam epitaxy on GaAs(001) by transmission electron microscopy (TEM) and photoluminescence spectroscopy. InGaAs layers with In concentrations of 16, 25, and 28 \% and respective thicknesses of 20, 22, and 23 monolayers were deposited at 535 °C. The parameters were chosen to grow layers slightly above and below the transition between the two- and three-dimensional growth mode. In-concentration profiles were obtained from high-resolution TEM images by composition evaluation by lattice fringe analysis. The measured profiles can be well described applying the segregation model of Muraki et al. [Appl. Phys. Lett. 61, 557 (1992)]. Calculated photoluminescence peak positions on the basis of the measured concentration profiles are in good agreement with the experimental ones. Evaluating experimental In-concentration profiles it is found that the transition from the two-dimensional to the three-dimensional growth mode occurs if the indium content in the In floating layer exceeds 1.1±0.2 monolayers. The measured exponential decrease of the In concentration within the cap layer on top of the islands reveals that the In floating layer is not consumed during island formation. In addition, In0.25Ga0.75As quantum wells were grown at different temperatures between 500 °C and 550 °C. The evaluation of concentration profiles shows that the segregation efficiency increases from R=0.65 to R=0.83. The strong increase of R with the growth temperature is explained by the large growth rate of 1.5 ML∕s. Comparison with the temperature dependence of published segregation efficiencies obtained at lower growth rates reveals increasing temperature dependence and decreasing segregation efficiency with increasing growth rate.

     [bibtex-key = Litvinov2006]



200. A. Rosenauer, D. Gerthsen, and V. Potin. Strain state analysis of InGaN/GaN - sources of error and optimized imaging conditions. Phys. Status Solidi A, 203(1):176--184, January 2006. Keyword(s): InGaN/GaN, In, Ga, N, optimised imaging conditions, optimized imaging conditions, aberrations, strain, strain state. Abstract:

     Transmission electron microscopy investigation of the chemical composition of In_{x}Ga_{1-x}N/GaN layers by strain state analysis can lead to substantial artefacts. We evaluated simulated images in dependence of specimen thickness, specimen orientation and objective lens defocus. We observed that the measurement is in agreement with the true strain profile for certain conditions only. An analysis of error sources revealed that artefacts are mainly caused by a combination of delocalization and the composition dependence of the phases of the beams contributing to the image formation. The delocalization effect is minimized for interference of the undiffracted beam with one of the 000±2 beams. The least chemical shift of the phases is obtained using the 000+2 beam and a strong excitation of 000+4. Images simulated for these conditions taking into account lattice plane bending and strain using finite-element calculations revealed a good agreement of evaluated and true strain profiles.

     [bibtex-key = Rosenauer2006b]



201. M. Schowalter, A. Rosenauer, and D. Gerthsen. Influence of surface segregation on the optical properties of semiconductor quantum wells. Applied Physics Letters, 88(11):111906--111906-3, 2006. Keyword(s): III-V semiconductors, gallium arsenide, indium compounds, photoluminescence, semiconductor quantum wells, surface segregation, 6835Dv, 7855Cr, 7867De. Abstract:

     We studied the influence of surface segregation on optical properties of semiconductor quantum wells. This effect leads to significant deviations of composition profiles from expected rectangular profiles. The model of Muraki is used to simulate composition profiles of InGaAs/GaAs quantum wells for different segregation efficiencies from which we derive potentials for electrons and holes. To compute eigenenergies the Schr{\"o}dinger equation is numerically solved. The transition energies are calculated from the energy differences of electrons and holes as a function of segregation efficiency. We find that the optical properties are influenced for segregation efficiencies larger than 0.7.

     [bibtex-key = Schowalter2006c]



202. M. Schowalter, A. Rosenauer, D. Lamoen, P. Kruse, and D. Gerthsen. Ab initio computation of the mean inner Coulomb potential of wurtzite-type semiconductors and gold. Applied Physics Letters, 88(23):232108--232108-3, 2006. Keyword(s): APW calculations, II-VI semiconductors, III-V semiconductors, ab initio calculations, aluminium compounds, cadmium compounds, density functional theory, electric potential, gallium compounds, gold, indium compounds, monolayers, wide band gap semiconductors, zinc compounds, 7361Ey, 7361Ga. Abstract:

     We report on the computation of mean inner Coulomb potentials of technologically important wurtzite-type semiconductors AlN, GaN, InN, ZnO, and CdO and of gold within the density functional theory formalism. We used a slab geometry with (11-20) and (110) surfaces, respectively. Structures consisting of several monolayers of material and an adjacent vacuum region were generated and the Coulomb potential was computed using the full potential linearized augmented plane wave method. The mean inner Coulomb potential was obtained by computing the difference of the potentials averaged inside the innermost monolayer of the slab and within the center plane of the vacuum region.

     [bibtex-key = Schowalter2006b]



203. Meng-Ku Chen, Yung-Chen Cheng, Jiun-Yang Chen, Cheng-Ming Wu, C.C. Yang, Kung-Jen Ma, Jer-Ren Yang, and Andreas Rosenauer. Effects of silicon doping on the nanostructures of InGaN/GaN quantum wells. Journal of Crystal Growth, 279(1-2):55--64, 2005. Keyword(s): A1. Segregation. Abstract:

     We compare the results of strain state analysis (SSA) and photoluminescence (PL) of six InGaN/GaN quantum well samples with un-doped, well-doped, and barrier-doped structures. Based on the \{SSA\} images, a strain relaxation model is proposed for describing the nanostructure differences between the three sets of sample of different doping conditions. In the barrier-doped samples, the hetero-structure-induced strains are fully relaxed such that spinodal decomposition is effectively induced. Therefore, strongly clustering nanostructures are observed. In the well-doped samples, strains are partially relaxed and the spinodal decomposition process can be slightly induced. Hence, weaker composition fluctuations are observed. Then, in the un-doped samples, the un-relaxed strains result in higher miscibility between InN and GaN, leading to the relatively more uniform composition distributions. Between the low- and high-indium samples, higher indium content leads to a stronger clustering behavior. The strain relaxations in the well-doped and barrier-doped samples result in their unclear S-shaped behaviors of \{PL\} spectral peaks. The enhanced carrier localization and reduced quantum-confined Stark effect in the barrier-doped samples are responsible for their significant increases of radiative efficiency.

     [bibtex-key = Chen2005]



204. Yung-Chen Cheng, Cheng-Ming Wu, C. C. Yang, Gang Alan Li, Andreas Rosenauer, Kung-Jen Ma, Shih-Chen Shi, and L. C. Chen. Effects of interfacial layers in InGaN/GaN quantum-well structures on their optical and nanostructural properties. Journal of Applied Physics, 98(1):014317, 2005. Keyword(s): indium compounds, gallium compounds, III-V semiconductors, wide band gap semiconductors, semiconductor quantum wells, nanostructured materials, photoluminescence, electroluminescence, Stark effect. [bibtex-key = Cheng2005]



205. T. Li, E. Hahn, D. Gerthsen, A. Rosenauer, A. Strittmatter, L. Reissmann, and D. Bimberg. Indium redistribution in an InGaN quantum well induced by electron-beam irradiation in a transmission electron microscope. Applied Physics Letters, 86(24):241911, 2005. Keyword(s): indium compounds, gallium compounds, III-V semiconductors, wide band gap semiconductors, semiconductor quantum wells, electron beam effects, transmission electron microscopy, internal stresses. [bibtex-key = Li2005]



206. E. Müller, P. Kruse, D. Gerthsen, M. Schowalter, A. Rosenauer, D. Lamoen, R. Kling, and A. Waag. Measurement of the mean inner potential of ZnO nanorods by transmission electron holography. Applied Physics Letters, 86(15):154108--154108-3, 2005. Keyword(s): II-VI semiconductors, electron holography, nanoparticles, transmission electron microscopy, wide band gap semiconductors, zinc compounds, 4240Lx, 6146+w, 6837Lp. Abstract:

     The mean inner potential of ZnO was measured by means of electron holography in a transmission electron microscope. Accurate measurements of the mean inner potential by transmission electron holography are often hampered by imprecise knowledge of the sample thickness. To overcome this problem, ZnO nanorods with a well-defined geometry and diameter were used in our study. Holograms were taken under kinematical diffraction conditions using high-resolution transmission electron microscopy images for magnification calibration. The phase shift of the transmitted beam of the image wave with respect to the reference wave traveling through the vacuum yields the mean inner potential which was determined to be (15.9±1.5) V for ZnO.

     [bibtex-key = Mueller2005]



207. E. Piscopiello, A. Rosenauer, A. Passaseo, E. H. Montoya Rossi, and G. Van Tendeloo. Segregation in In(x)Ga(1-x)As/GaAs Stranski-Krastanow layers grown by metal-organic chemical vapour deposition. Philosophical Magazine, 85(32):3857--3870, 2005. Abstract:

     Using quantitative high-resolution transmission electron microscopy we studied the chemical morphology of wetting layers in In x Ga1− x As/GaAs quantum dot structures which were optimized for applications to optical devices operating around 1.3 µm. The samples are grown by low-pressure metal-organic chemical vapour deposition on GaAs substrates. The In concentration profiles of the wetting layers are evaluated with the composition evaluation by lattice fringe analysis method. The profiles reveal a clear signature of segregation. A fit of the profiles with the Muraki et al. model for segregation reveals a segregation efficiency R = 0.65 ± 0.05 at the growth temperature of 550°C, which is significantly lower than segregation efficiencies observed in samples grown by molecular beam epitaxy at similar temperatures.

     [bibtex-key = Piscopiello2005]



208. A. Rosenauer, M. Schowalter, F. Glas, and D. Lamoen. First-principles calculations of 002 structure factors for electron scattering in strained In(x)Ga(1-x)As. Phys. Rev. B, 72:085326, August 2005. Keyword(s): structure factor, strain, InGaAs, In, Ga, As, first-principles calculation, electron scattering. Abstract:

     This work provides values of electron scattering 002 structure factors for InxGa1−xAs as a function of the In concentration x=0 to 1. These results allow accurate compositional analysis of pseudomorphically grown In_xGa_{1−x}As/GaAs layers by transmission electron microscopy methods relying on the chemical sensitivity of the (002) beam. The calculations go beyond the limits of the isolated atom approximation, because they take into account charge redistribution effects between atomic sites in the crystal, strain, and static atomic displacements.The computations were performed by the full potential linearized augmented plane-wave method using a generalized gradient approximation for the exchange and correlation part of the potential. The calculations of strained InxGa1−xAs correspond to the strain state in specimens with large, small, and intermediate thickness in the electron beam direction. Additionally, the effect of static atomic displacements is taken into account. All results are listed in a parameterized form. The calculated 002 structure factor vanishes at an In concentration of 16.4\%. This value is in a good agreement with previously reported experimental measurements. Hence, our results are a significant improvement with respect to the isolated atom approximation which is conventionally applied in transmission electron microscopy simulations, and which predicts a value of 22.5\%.

     [bibtex-key = Rosenauer2005]



209. E. Roventa, G. Alexe, R. Kröger, D. Hommel, and A. Rosenauer. Structural investigations of spatial correlation of CdSe/ZnSe quantum dot stacks grown by molecular beam epitaxy. Journal of Crystal Growth, 278(1-4):316--319, 2005. Note: 13th International Conference on Molecular Beam Epitaxy. Keyword(s): A3. Migration enhanced epitaxy. Abstract:

     Spatial correlation of five-fold stacks of CdSe quantum dots inserted in ZnSSe spacers have been investigated using transmission electron microscopy and grazing incidence X-ray diffraction. Lateral and vertical ordering has been found depending on the spacer layer thickness. This can be interpreted as self-organized ordering process induced by lattice mismatch strain. Also, anisotropy of two-fold symmetry has been observed.

     [bibtex-key = Roventa2005]



210. Th. Schmidt, E. Roventa, T. Clausen, J. I. Flege, G. Alexe, S. Bernstorff, C. Kübel, A. Rosenauer, D. Hommel, and J. Falta. Ordering mechanism of stacked CdSeZnS(x)Se(1-x) quantum dots: A combined reciprocal-space and real-space approach. Phys. Rev. B, 72:195334, November 2005. [bibtex-key = Schmidt2005]



211. M. Schowalter, J. T. Titantah, D. Lamoen, and P. Kruse. Ab initio computation of the mean inner Coulomb potential of amorphous carbon structures. Applied Physics Letters, 86(11):112102--112102-3, 2005. Keyword(s): APW calculations, Monte Carlo methods, ab initio calculations, carbon, electron holography, noncrystalline structure, slabs, surface potential, 6143Bn, 6143Er, 6835Bs. Abstract:

     The mean inner Coulomb potential (MIP) of amorphous carbon structures was computed for slabs with mass densities between �=2.0 g/cm3 and �=3.5 g/cm3 by the full potential linearized augmented plane-wave (FLAPW) method. The amorphous carbon structures consisting of 64 carbon atoms were generated by a classical metropolis Monte Carlo procedure using the Tersoff potential for carbon. The MIP shows a linear dependence on the mass density. Values of the MIP of the amorphous carbon structures are compared with experimental values and with computed values for the MIP of graphite and diamond.

     [bibtex-key = Schowalter2005]



212. V.A. Volodin, M.D. Efremov, R.S. Matvienko, V.V. Preobrazhenskii, B.R. Semyagin, N.N. Ledentsov, I.R. Soshnikov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Dichroism in transmission of light by an array of self-assembled GaAs quantum wires on a nanofaceted A(311) surface. Physics of the Solid State, 47(2):366--369, 2005. [bibtex-key = Volodin2005]



213. Yung-Chen Cheng, En-Chiang Lin, Cheng-Ming Wu, C.C. Yang, Jer-Ren Yang, Andreas Rosenauer, Kung-Jen Ma, Shih-Chen Shi, L.C. Chen, Chang-Chi Pan, and Jen-Inn Chyi. Nanostructures and carrier localization behaviors of green-luminescence InGaN/GaN quantum-well structures of various silicon-doping conditions. Applied Physics Letters, 84(14):2506--2508, 2004. Keyword(s): III-V semiconductors, gallium compounds, indium compounds, photoluminescence, quantum confined Stark effect, semiconductor doping, semiconductor quantum wells, silicon, wide band gap semiconductors, 6172Vv, 6865Fg, 7855Cr, 7867De. Abstract:

     The results of photoluminescence (PL), detection-energy-dependent photoluminescence excitation (DEDPLE), excitation-energy-dependent photoluminescence (EEDPL), and strain state analysis (SSA) of three InGaN/GaN quantum-well (QW) samples with silicon doping in the well, barrier and an undoped structure are compared. The SSA images show strongly clustering nanostructures in the barrier-doped sample and relatively weaker composition fluctuations in the undoped and well-doped samples. Differences in silicon doping between the samples give rise to the differences in DEDPLE and EEDPL spectra, as a result of the differences in carrier localization. In addition, the PL results provide us clues for speculating that the S-shaped PL peak position behavior is dominated by the quantum-confined Stark effect in an undoped InGaN/GaN QW structure. © 2004 American Institute of Physics.

     [bibtex-key = Cheng2004a]



214. Yung-Chen Cheng, Cheng-Ming Wu, Meng-Kuo Chen, C. C. Yang, Zhe-Chuan Feng, Gang Alan Li, Jer-Ren Yang, Andreas Rosenauer, and Kung-Je Ma. Improvements of InGaN/GaN quantum-well interfaces and radiative efficiency with InN interfacial layers. Applied Physics Letters, 84(26):5422--5424, 2004. Keyword(s): indium compounds, gallium compounds, III-V semiconductors, wide band gap semiconductors, semiconductor quantum wells, photoluminescence, electroluminescence, monolayers. [bibtex-key = Cheng2004]



215. D. Litvinov, D. Gerthsen, A. Rosenauer, M. Hetterich, A. Grau, Ph. Gilet, and L. Grenouillet. Determination of the nitrogen distribution in InGaNAs/GaAs quantum wells by transmission electron microscopy. Appl. Phys. Lett., 85:3743--3745, 2004. Abstract:

     We report on measurements of the nitrogen-concentration profile in an InGaNAs heterostructure by high-resolution transmission electron microscopy. Two samples grown by gas-source molecular-beam epitaxy on GaAs(001) substrates were investigated which contain InGaAs and InGaNAs wells with the same thickness and In concentration. The indium concentration was determined by high-resolution x-ray diffractometry. Indium-concentration profiles were obtained with the composition evaluation by lattice fringe analysis (CELFA) technique from the sample with the InGaAs wells exploiting the chemical sensitivity of the diffracted (002) beam. Nitrogen-concentration profiles were measured in the InGaNAs wells by comparison of the CELFA results observed in the samples with and without nitrogen.

     [bibtex-key = Litvinov2004a]



216. R. Otto, H. Kirmse, I. Häusler, W. Neumann, A. Rosenauer, D. Bimberg, and L. Muller-Kirsch. Determination of composition and strain field of a III/V quaternary quantum dot system. Applied Physics Letters, 85(21):4908--4910, 2004. Keyword(s): III-V semiconductors, gallium arsenide, indium compounds, internal stresses, nucleation, semiconductor quantum dots, transmission electron microscopy, 6835Gy, 6837Lp, 6865Hb. Abstract:

     A system composed of a double layer of stacked quantum dots (QDs) of (In,Ga)As and Ga(Sb,As) was investigated by quantitative high-resolution transmission electron microscopy. The layers were grown by metalorganic chemical vapor deposition on a GaAs substrate. The strain field of the lower quantum dots determines the nucleation in the subsequent layer. Investigating this effect, the strain field as well as the composition could be measured at high resolution. Local changes of lattice distances could be quantified with a precision of 0.003 nm. The error in determining the local composition inside the InxGa1-xAs resp., GaSbyAs1-y QDs amounts to ΔxIn=0.02 and ΔySb=0.03.

     [bibtex-key = Otto2004]



217. M. Schowalter, D. Lamoen, A. Rosenauer, P. Kruse, and D. Gerthsen. First-principles calculations of the mean inner Coulomb potential for sphalerite type II-VI semiconductors. Appl. Phys. Lett., 85(21):4938--4940, November 2004. Keyword(s): mip, sphalerite, semiconductor, mean inner Coulomb potential. Abstract:

     The mean inner Coulomb potential (MIP) of ZnS, CdS, ZnSe, CdSe, ZnTe, and CdTe has been calculated for a (110) slab geometry by the full potential linearized augmented plane-wave (FLAPW) method using both the local density approximation (LDA) and a generalized gradient approximation (GGA) for the exchange and correlation part of the potential. Typical differences between values calculated within the LDA and the GGA are smaller than typical experimental error bars in literature. We use experimental and self-consistently calculated lattice parameters for the calculation of the MIP. Values calculated for ZnS are compared with experimental values.

     [bibtex-key = Schowalter2004a]



218. D. Gerthsen, E. Hahn, B. Neubauer, V. Potin, A. Rosenauer, and M. Schowalter. Indium distribution in epitaxially grown InGaN layers analyzed by transmission electron microscopy. physica status solidi (c), 0(6):1668--1683, 2003. Keyword(s): 64.75 +g, 68.37.Lp, 68.55.Nq, 81.05 Ea, 81.15Gh, 81.15.Hi. Abstract:

     An overview is given about microstructure and composition analyses of InGaN quantum wells embedded in Ga(Al)N barriers to study the mechanisms which determine the In distribution in epitaxially grown InGaN layers. The applied technique is transmission electron microscopy (TEM). The main prerequisite for this work was the development of a technique based on high-resolution lattice fringe images that allows quantitative chemical analyses of InGaN on an atomic scale. A large variety of samples was investigated that were produced by molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE). The effect of the deposition temperature, growth rate, strain and high-temperature annealing treatments on the average In concentration and In distribution was studied to assess the influence of phase separation, In surface segregation and In desorption. Composition fluctuations in InGaN are always observed on two different lateral scales independent of the growth technique and particular set of growth parameters but the strength of the composition fluctuations can be influenced by the details of the growth. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

     [bibtex-key = Gerthsen2003a]



219. P. Kruse, A. Rosenauer, and D. Gerthsen. Determination of the mean inner potential in III-V semiconductors by electron holography. Ultramicroscopy, 96(1):11--16, 2003. Keyword(s): III-V semiconductors. Abstract:

     The mean inner potential of GaAs(14.18V), InAs(14.50V), GaP(14.35V) and InP(14.50V) has been measured by transmission electron holography using the phase shift of the (000)-beam of the first hologram sideband. To provide a defined specimen geometry we used 90° wedges obtained by the cleavage technique. The exact excitation condition as well as the acceleration voltage of the electrons were determined from convergent beam electron diffraction images. The magnification is extracted from two-beam lattice fringe images and dynamical effects are taken into account by Bloch-wave calculations.

     [bibtex-key = Kruse2003]



220. D. Litvinov, A. Rosenauer, and D. Gerthsen. Transformation of Shockley into Frank stacking faults in a ZnS 0.04 Se 0.96 /GaAs (001) heterostructure. Philosophical Magazine Letters, 83(9):575--581, 2003. Abstract:

     We report the transformation of Shockley partial dislocations (PDs) into Frank PDs in lattice-matched ZnS 0.04 Se 0.96 /GaAs(001) as investigated by transmission electron microscopy. The ZnS 0.04 Se 0.96 layers, with a nominal thickness of 70 nm, were grown on GaAs(001) by metal-organic chemical vapour deposition at 350°C. We mainly find stacking-fault pairs on the (111) and planes that are bound by Shockley PDs with Burgers vector . Different reactions are observed between PDs taking place in situ in the electron microscope, leading to the transformation of Shockley PDs into Frank PDs with and stacking faults on the or planes.

     [bibtex-key = Litvinov2003a]



221. M. Schowalter, A. Rosenauer, D. Gerthsen, M. Grau, and M.-C. Amann. Quantitative measurement of the influence of growth interruptions on the Sb distribution of GaSb/GaAs quantum wells by transmission electron microscopy. Appl. Phys. Lett., 83(15):3123--3125, October 2003. Keyword(s): growth, GaSb, Ga, Sb, GaAs, Ga, As, quantum wells, quantum well,. Abstract:

     We investigated the influence of growth interruptions on the morphology of molecular-beam epitaxy grown GaSb/GaAs multiquantum-well structures by transmission electron microscopy (TEM). Profiles of the chemical composition of the GaSb layers were deduced from high-resolution TEM images with the lattice fringe analysis method. We found clear indications of segregation of Sb in GaAs-on-GaSb for a sample grown with growth interruption before and after the growth of the quantum wells. Its efficiency R=0.7860 was derived by fitting the measured composition profiles with the model of Muraki. Determination of the total amounts of deposited GaSb yields a higher amount of GaSb in a sample grown without interruption.

     [bibtex-key = Schowalter2003a]



222. Elisabeth Kurtz, B. Dal Don, M. Schmidt, H. Kalt, C. Klingshirn, D. Litvinov, A. Rosenauer, and D. Gerthsen. Self-Organized Semiconductor Quantum Islands in A Semiconducting Matrix. In Baldassare Bartolo, editor, Spectroscopy of Systems with Spatially Confined Structures, volume 90 of NATO Science Series, pages 633--651. Springer Netherlands, 2002. [bibtex-key = Kurtz2002]



223. E. Hahn, A. Rosenauer, D. Gerthsen, J. Off, V. Perez-Solorzano, M. Jetter, and F. Scholz. In-Redistribution in a GaInN Quantum Well upon Thermal Annealing. physica status solidi (b), 234(3):738--741, 2002. Keyword(s): 64.75.+g, 66.30.Xj, 68.37.Lp, 78.55.Cr, 81.05.Ea. Abstract:

     A GaInN quantum-well structure with an average In-concentration of 16 per cent, grown by metal organic chemical vapor deposition (MOCVD) on a SiC substrate, was studied by transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL) before and after an one-hour annealing treatment at 980 °C. Due to the heat treatment, the formation of In-rich clusters with extensions between 10 nm and 100 nm and In-concentrations above 80 per cent was observed. Nevertheless, the PL exhibits a blue shift in the PL-peak energy of about 90 meV compared to the as-grown sample and do not show a significant influence of the In-rich clusters on the emission wavelength.

     [bibtex-key = Hahn2002a]



224. D. Litvinov, A. Rosenauer, D. Gerthsen, P. Kratzert, M. Rabe, and F. Henneberger. Influence of the growth procedure on the Cd distribution in CdSe/ZnSe heterostructures: Stranski--Krastanov versus two-dimensional islands. Applied Physics Letters, 81(4):640--642, 2002. Keyword(s): cadmium compounds, zinc compounds, II-VI semiconductors, semiconductor heterojunctions, molecular beam epitaxial growth, semiconductor growth, island structure, interface structure, atomic force microscopy, transmission electron microscopy, chemical interdiffusion. [bibtex-key = Litvinov2002c]



225. D. Litvinov, A. Rosenauer, D. Gerthsen, N. N. Ledentsov, D. Bimberg, G. A. Ljubas, V. V. Bolotov, V. A. Volodin, M. D. Efremov, V. V. Preobrazhenskii, B. R. Semyagin, and I. P. Soshnikov. Ordered arrays of vertically correlated GaAs and AlAs quantum wires grown on a GaAs(311)A surface. Applied Physics Letters, 81(6):1080--1082, 2002. Keyword(s): gallium arsenide, aluminium compounds, III-V semiconductors, semiconductor quantum wires, semiconductor epitaxial layers, semiconductor superlattices, transmission electron microscopy, self-assembly, photoluminescence. [bibtex-key = Litvinov2002b]



226. D. Litvinov, A. Rosenauer, D. Gerthsen, and H. Preis. Electron microscopy investigation of the defect configuration in CdSe/ZnSe quantum dot structures. Philosophical Magazine A, 82(7):1361--1380, 2002. Abstract:

     Abstract In this study we report the dependence of the defect configuration observed in CdSe/ZnSe quantum dot structures on the ZnSe cap layer thickness by transmission electron microscopy (TEM) and reflection high-energy electron diffraction (RHEED). The samples were grown by molecular-beam epitaxy at 350°C. The nominal thickness of the CdSe layers was approximately 3 monolayers and the cap layer thickness was varied in the range from 3 to 60 nm. In all samples, RHEED showed a transition from the two-dimensional (2D) to the three-dimensional (3D) growth mode during the CdSe deposition. By TEM we found pairs of stacking faults (SFs) lying on one of the two pairs of lattice planes given by {(111)-(1 11)} and {(111)-(111)}. The SFs are bound by Shockley partial dislocations. Both of the SFs forming one pair originate from the same stair-rod dislocation with Burgers vector b = ⅙{110} lying at the CdSe-ZnSe interface inside a Cd-rich region (island). Measuring the atomic displacements in the vicinity of the SFs, we obtained that all SFs have an intrinsic nature. At the line of contact of two SFs that belong to different pairs, we observed stair-rod dislocations with b = ⅓{100} which are inclined to the interface. The length of all dislocation lines and the sizes of the SFs increase with increasing ZnSe cap layer thickness. We find that the 2D-3D transition observed by RHEED is most probably caused by defect formation, which is discussed with respect to the relaxation of strain in the CdSe layer.

     [bibtex-key = Litvinov2002]



227. T. Passow, K. Leonardi, H. Heinke, D. Hommel, D. Litvinov, A. Rosenauer, D. Gerthsen, J. Seufert, G. Bacher, and A. Forchel. Quantum dot formation by segregation enhanced CdSe reorganization. Journal of Applied Physics, 92(11):6546--6552, 2002. Keyword(s): II-VI semiconductors, X-ray diffraction, cadmium compounds, molecular beam epitaxial growth, photoluminescence, semiconductor growth, semiconductor quantum dots, semiconductor quantum wells, surface segregation, transmission electron microscopy, zinc compounds, 6835Dv, 6865Fg, 6865Hb, 7855Et, 7866Hf, 8105Dz, 8115Hi. Abstract:

     The influence of the growth conditions during capping of CdSe/ZnSe quantum structures grown on GaAs(001) by molecular-beam epitaxy (MBE) were systematically investigated by high-resolution x-ray diffraction, transmission electron microscopy, and temperature dependent, partly time-resolved photoluminescence spectroscopy. The results clearly indicate formation of quantum wells with potential fluctuations if conventional MBE is used for capping the CdSe by ZnSe. In contrast, quantum dot formation occurs using migration enhanced epitaxy for this growth step. In the latter case, quantum dots can be obtained without formation of stacking faults. © 2002 American Institute of Physics.

     [bibtex-key = Passow2002]



228. V. Potin, A. Rosenauer, D. Gerthsen, B. Kuhn, and F. Scholz. Comparison of the Morphology and In Distribution of Capped and Uncapped InGaN Layers by Transmission Electron Microscopy. physica status solidi (b), 234(3):947--951, 2002. Keyword(s): 68.37.Lp, 68.55.Nq, 68.65.Fg, 81.05.Ea. Abstract:

     We have compared and analysed the morphology of capped and uncapped thin InGaN layers by transmission electron microscopy. The samples were grown under the same conditions by metal-organic chemical vapour deposition. The capped layer appears to be homogenous in thickness whereas the uncapped one is characterized by the presence of large islands. Moreover, the In distribution was determined in both samples by quantitative high-resolution transmission electron microscopy. The average indium concentration was found to be comparable. Fluctuations of the In concentration on a large scale occur in both cases whereas fluctuations on a scale of a few nanometers are more pronounced in the capped layer.

     [bibtex-key = Potin2002]



229. D. Gerthsen, B. Neubauer, A. Rosenauer, T. Stephan, H. Kalt, O. Schon, and M. Heuken. InGaN composition and growth rate during the early stages of metalorganic chemical vapor deposition. Applied Physics Letters, 79(16):2552--2554, 2001. Keyword(s): III-V semiconductors, MOCVD, gallium compounds, indium compounds, lattice constants, photoluminescence, red shift, semiconductor growth, semiconductor quantum wells, spectral line intensity, transmission electron microscopy, wide band gap semiconductors, 6865Fg, 7855Cr, 7867De, 8107St, 8115Gh. Abstract:

     Transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were applied to study the metalorganic chemical vapor deposition of InGaN and the correlation between the structural properties and luminescence of GaN/InxGa1-xN-quantum well structures. A series of samples was grown varying only the growth duration for the InGaN under otherwise unaltered growth conditions. Composition analyses were carried out by measuring local lattice parameters from TEM images, which are directly related to the local In concentration. A rising average In concentration from 6.5 per cent to 15.4 per cent and a decreasing growth rate are observed with increasing growth duration. All samples show an inhomogeneous In distribution containing In-rich agglomerates with a size of only a few nanometers and less pronounced composition fluctuations on a scale of some 10 nm. The redshift of the PL peak energy with increasing quantum well thickness indicates that the luminescence is predominantly determined by the piezoelectric field. © 2001 American Institute of Physics.

     [bibtex-key = Gerthsen2001a]



230. S. Kret, P. Ruterana, A. Rosenauer, and D. Gerthsen. Extracting Quantitative Information from High Resolution Electron Microscopy. physica status solidi (b), 227(1):247--295, 2001. Keyword(s): 68.35.Dv, 68.37.Lp, 68.55.Nq, 68.65.-k, S7.12, S7.14, S8.13. Abstract:

     Despite the development of high-resolution electron microscopy (HREM) that allows imaging of most materials, the extraction of quantitative information at atomic scale still requires considerable additional efforts. This review presents the recent developments on techniques that can be used to determine the local strain, chemical composition or atomic structure retrieval in HREM. The source of noise in images and effective methods for improving the signal-to-noise ratio in direct or Fourier space are discussed. The artefacts of filtering are commented. In all the methods, the sample thickness has to be determined. A detailed analysis of the thin foil relaxation effect on the measured distortion fields is presented as well as the possibilities of using finite element calculations for its modelling. The local composition measurement based on the chemically sensitive reflections; pattern recognition and the measurement of lattice parameters are described. Examples from semiconductor heterostructures are discussed. The current state of the strategies used for the retrieval of the atomic configuration of defects from HRTEM images is briefly presented. The limits of detection and the accuracy of the methods are summarised; and it is pointed out that electron holography, focal series reconstruction and the coming Cs corrected microscopes will help to obtain this information with better accuracy.

     [bibtex-key = Kret2001]



231. E. Kurtz, M. Schmidt, M. Baldauf, S. Wachter, M. Grün, H. Kalt, C. Klingshirn, D. Litvinov, A. Rosenauer, and D. Gerthsen. Suppression of lateral fluctuations in CdSe-based quantum wells. Applied Physics Letters, 79(8):1118--1120, 2001. Keyword(s): cadmium compounds, II-VI semiconductors, semiconductor quantum wells, fluctuations, photoluminescence, semiconductor growth, spectral line breadth, molecular beam epitaxial growth. Abstract:

     We report a reduction of inhomogeneous broadening in CdSe-related quantum wells in ZnSe by employing a growth technique that uses a CdS-compound source instead of the standard Cd elemental source for molecular-beam epitaxy. Assisted by the low sticking coefficient of sulfur and possibly an exchange reaction between S and Se, only a small S contamination is observed. A comparison with standard layers reveals an increase in quality and homogeneity by a strong reduction of the photoluminescence (PL) linewidth. Samples obtained by our method show extremely little lateral confinement as indicated by a lack of sharp single dot emission lines in micro PL and the absence of the extensive redshift observed in temperature dependent PL of fluctuating well potentials.

     [bibtex-key = Kurtz2001a]



232. N. Ledentsov, D. Litvinov, A. Rosenauer, D. Gerthsen, I. Soshnikov, V. Shchukin, V. Ustinov, A. Egorov, A. Zukov, V. Volodin, M. Efremov, V. Preobrazhenskii, B. Semyagin, D. Bimberg, and Zh. Alferov. Interface structure and growth mode of quantum wire and quantum dot GaAs-AlAs structures on corrugated (311)A surfaces. Journal of Electronic Materials, 30:463--470, 2001. Keyword(s): Chemie und Materialwissenschaften. Abstract:

     GaAs-AlAs corrugated superlattices (CSL) are formed on spontaneously nanofaceted (311)A surfaces. Using high-resolution transmission electron microscopy (HRTEM) along the $$[\bar 233]$$ zone axis with an appropriate image evaluation technique to enhance the contract between GaAs and AlAs we found two distinct lateral periodicities along the $$[0\bar 11]$$ directions for two different CSL layer thickness regimes. For multilayer deposition with GaAs layer thickness exceeding 1 nm the lateral periodicity of 3.2 nm is clearly revealed. The contrast originates from the thickness modulation of both AlAs and GaAs layers with a period of 3.2 nm in the $$[0\bar 11]$$ direction. The corrugation height is about 1 nm and it is symmetric for both upper and lower GaAs-AlAs interfaces. Thicker sections of the thickness-modulated AlAs and GaAs layers of the CSL are shifted by a half period with respect to each other. In the regime when the GaAs deposited average thickness is below 1 nm, which is necessary for complete coverage of the AlAs surface, a lateral periodicity of ≈1.5–2 nm is additionally revealed. We attribute this effect to the formation of local GaAs clusters dispersed on a corrugated (311)A AlAs surface resulting in a local phase reversal of the AlAs surface in their vicinity upon subsequent overgrowth. This reversal can be explained by the same effect as the phase shift of the surface corrugation upon heteroepitaxy on (311)A. In our model AlAs does not wet the GaAs cluster surface, unless different more energetically favorable scenario is possible. This causes accumulation of AlAs in the vicinity of the GaAs cluster and, as a result, the local phase reversal of the AlAs surface. The AlAs corrugated surface domains with different phases coexist on the surface resulting in an additional periodicity revealed in the HREM contrast modulation. Additionally HRTEM studies indicate that the AlAs-GaAs interface inclination angles in both regimes are 40° and 140° with respect to the flat (311) surface in an argreement with the {331} facet geometry model proposed by R. Nötzel, N.N. Ledentsov, L. Däweritz, M. Hohenstein, and K. Ploog.

     [bibtex-key = Ledentsov2001]



233. D. Litvinov, A. Rosenauer, D. Gerthsen, H. Preis, K. Fuchs, and S. Bauer. Growth and vertical correlation of CdSe/ZnSe quantum dots. Journal of Applied Physics, 89(7):3695--3699, 2001. Keyword(s): II-VI semiconductors, cadmium compounds, island structure, molecular beam epitaxial growth, reflection high energy electron diffraction, semiconductor epitaxial layers, semiconductor growth, semiconductor quantum dots, transmission electron microscopy, zinc compounds, 6865Hb, 8105Dz, 8107Ta, 8115Hi. Abstract:

     The growth and vertical organization of CdSe quantum dots in three-layer stacks consisting of CdSe with a nominal thickness of 2.5 monolayers (ML) and ZnSe spacers with thicknesses between 10 and 20 ML was investigated by reflection high energy electron diffraction during the growth and different transmission electron microscopy techniques. The samples were grown by molecular beam epitaxy at 400 °C. It was found that up to 10 ML spacer thickness all three CdSe layers and ZnSe spacers form one broad (Cd, Zn)Se alloy layer with a small Cd concentration containing Cd-rich islands with a size of ∼15 nm. For spacers with a larger thickness (12-20 ML) three separated ternary (Cd, Zn)Se layers are observed which contain Cd-rich inclusions (small islands) with a size of less than 10 nm. A preferential vertical correlation of the small islands occurs for the 12 ML spacer thickness. With increasing spacer thickness, the number of the correlated small islands is reduced displaying a tendency to uncorrelated growth. © 2001 American Institute of Physics.

     [bibtex-key = Litvinov2001]



234. A. Rosenauer, D. Gerthsen, D. Van Dyck, M. Arzberger, G. Böhm, and G. Abstreiter. Quantification of segregation and mass transport in In(x)Ga(1-x)As/GaAs$ Stranski-Krastanow layers}. Phys. Rev. B, 64(24):245334, December 2001. Abstract:

     We report on transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy measurement of mass transport and segregation in InAs Stranski-Krastanow layers grown on GaAs(001) by molecular beam epitaxy at growth temperatures of 480 and 530 °C. Plan-view TEM reveals regularly shaped islands with a density of 7.8×1010 cm-2 (480 °C) and 1.5×1010 cm-2 (530 °C), respectively. Uncapped islands were investigated by strain state analysis of electron wave functions reconstructed from high-resolution TEM images. In-concentration profiles of the islands were obtained by the measurement of lattice-parameter profiles of the islands and the application of finite-element calculations. We find that the islands contain Ga-atoms with a percentage of 50\% (480 °C) and 67\% (530 °C). The capped InAs-layers were investigated with PL and TEM. In agreement with TEM, PL indicates a smaller and deeper potential well of the islands grown at 480 °C. Concentration profiles of the wetting layers were measured with TEM using the composition evaluation of lattice fringe images method, clearly revealing segregation profiles. The obtained segregation efficiency of In-atoms is 0.77±0.02 (480 °C) and 0.82±0.02 (530 °C). As an explanation for the strong mass transport of Ga from the substrate to the islands we show that the segregation of In atoms during the growth of the binary InAs can lead to the generation of vacancies in the metal sublattice. The vacancies are filled by Ga-atoms migrating along the surface or by a diffusion of the vacancies from the wetting layer and the islands into the GaAs buffer, leading to a unidirectional diffusion of Ga atoms from the buffer into the Stranski-Krastanow layer.

     [bibtex-key = Rosenauer2001c]



235. A Rosenauer, D Van Dyck, M Arzberger, and G Abstreiter. Compositional analysis based on electron holography and a chemically sensitive reflection. Ultramicroscopy, 88(1):51--61, 2001. Keyword(s): Compositional analysis. Abstract:

     A method for compositional analysis of low-dimensional heterostructures is presented. The suggested procedure is based on electron holography and the exploitation of the chemically sensitive (0 0 2) reflection. We apply an off-axis imaging condition with the (0 0 2) beam strongly excited and centered on the optic axis. The first side band of the hologram is centered using an “emptyâ€� reference hologram obtained for a hole of the specimen. From the centered side band we use the phase of the central (0 0 0) and the amplitude of the (0 0 2) reflections to evaluate the local composition and the local specimen thickness in an iterative and self-consistent way. Delocalization effects that lead to a shift of the spatial information of (0 0 0) and (0 0 2) reflections are taken into account. The application of the procedure is demonstrated with an AlAs/GaAs(0 0 1) superlattice with a period of 5 nm. The concentration profiles obtained are discussed in relation to segregation. The measured segregation efficiency is R=0.51±0.02.

     [bibtex-key = Rosenauer2001d]



236. M. Schowalter, A. Rosenauer, D. Gerthsen, M. Arzberger, M. Bichler, and G. Abstreiter. Investigation of In segregation in InAs/AlAs quantum-well structures. Appl. Phys. Lett., 79(26):4426--4428, December 2001. Keyword(s): segregation, InAs, In, As, InAs/AlAs, AlAs, Al, As, quantum-well. Abstract:

     In this letter, we report the investigation of In segregation in InAs/AlAs heterostructures. InAs layers with different thicknesses were grown by molecular beam epitaxy on GaAs ~001! substrates. The layers were investigated by transmission electron microscopy. Profiles of the chemical composition of the InAs layers in the @001# direction were deduced from high-resolution lattice fringe images using the composition evaluation by lattice fringe analysis method. The segregation efficiency was derived by fitting the measured In concentration profiles with the segregation model of Muraki et al. [K. Muraki et al., Appl. Phys. Lett. 61, 557 (1992)]. We obtain efficiency of R=0.7760 for the segregation of In in AlAs/InAs at a temperature of 530 °C.

     [bibtex-key = Schowalter2001]



237. I.L. Krestnikov, A.V. Sakharov, W.V. Lundin, Yu.G. Musikhin, A.P. Kartashova, A.S. Usikov, A.F. Tsatsul’nikov, N.N. Ledentsov, Zh.I. Alferov, I.P. Soshnikov, E. Hahn, B. Neubauer, A. Rosenauer, D. Litvinov, D. Gerthsen, A.C. Plaut, A.A. Hoffmann, and D. Bimberg. Lasing in the vertical direction in InGaN/GaN/AlGaN structures with InGaN quantum dots. Semiconductors, 34(4):481--487, 2000. [bibtex-key = Krestnikov2000]



238. D. Litvinov, A. Rosenauer, D. Gerthsen, and N. N. Ledentsov. Character of the Cd distribution in ultrathin CdSe layers in a ZnSe matrix. Phys. Rev. B, 61:16819--16826, June 2000. [bibtex-key = Litvinov2000]



239. N. Peranio, A. Rosenauer, D. Gerthsen, S. V. Sorokin, I. V. Sedova, and S. V. Ivanov. Structural and chemical analysis of CdSe/ZnSe nanostructures by transmission electron microscopy. Phys. Rev. B, 61:16015--16024, June 2000. [bibtex-key = Peranio2000]



240. A. Rosenauer, W. Oberst, D. Litvinov, D. Gerthsen, A. Förster, and R. Schmidt. Structural and chemical investigation of $In_{0.6}Ga_{0.4}As$ Stranski-Krastanow layers buried in GaAs by transmission electron microscopy. Phys. Rev. B, 61(12):8276--8288, March 2000. Abstract:

     We report a detailed structural and chemical study of buried and free-standing In_0.6Ga_0.4As Stranski-Krastanow islands. The layers were grown by molecular-beam epitaxy on GaAs(001) substrates. We investigated two different types of samples with nominal In_0.6Ga_0.4As layer thicknesses of 1.5 and 2 nm. The growth was interrupted for 0, 60, or 180 s prior to the deposition of the 10-nm-thick GaAs cap layer. The chemical and structural analyses of the In_0.6Ga_0.4As layers were carried out with high-resolution transmission electron microscopy. The chemical morphology of the buried layers was evaluated with the composition evaluation by lattice-fringe analysis (CELFA) method. The free-standing islands were investigated by strain state analysis combined with finite element calculations. The density and size distribution of the islands was obtained by conventional plan-view transmission electron microscopy. We found two types of islands: Coherent islands with a lateral size of approximately 13 nm and large islands (40-100 nm) showing plastical strain relaxation. The density of the defect-free small islands decreases with increasing duration of the growth interruption whereas the density and size of the large islands increases. A detailed study of the wetting layer with the CELFA method revealed about a 4-nm-thick In_xGa_{1-x}As layer. The total amount of In contained in the wetting layer decreases with increasing duration of the growth interruption. Composition profiles in growth direction were measured. Their shape is explained by mainly three effects: Segregation of In, incorporation of migrating In into the growing cap layer, and strain-driven migration of In and Ga. An inhomogeneous In concentration increasing from bottom to top is observed in free-standing islands.

     [bibtex-key = Rosenauer2000a]



241. D. Schikora, S. Schwedhelm, D. J. As, K. Lischka, D. Litvinov, A. Rosenauer, D. Gerthsen, M. Strassburg, A. Hoffmann, and D. Bimberg. Investigations on the Stranski--Krastanow growth of CdSe quantum dots. Applied Physics Letters, 76(4):418--420, 2000. Keyword(s): semiconductor quantum dots, molecular beam epitaxial growth, self-assembly, island structure, stacking faults, cadmium compounds, II-VI semiconductors, reflection high energy electron diffraction, photoluminescence, monolayers. [bibtex-key = Schikora2000a]



242. I.P. Soshnikov, V.V. Lundin, A.S. Usikov, I.P. Kalmykova, N.N. Ledentsov, A. Rosenauer, B. Neubauer, and D. Gerthsen. Specifics of MOCVD formation of In(x)Ga(1−x)N inclusions in a GaN matrix. Semiconductors, 34(6):621--625, 2000. [bibtex-key = Soshnikov2000]



243. M. Strassburg, Th. Deniozou, A. Hoffmann, R. Heitz, U. W. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, D. Gerthsen, S. Schwedhelm, K. Lischka, and D. Schikora. Coexistence of planar and three-dimensional quantum dots in CdSe/ZnSe structures. Applied Physics Letters, 76(6):685--687, 2000. Keyword(s): cadmium compounds, zinc compounds, II-VI semiconductors, semiconductor quantum dots, semiconductor heterojunctions, island structure, transmission electron microscopy, monolayers, photoluminescence. [bibtex-key = Strassburg2000b]



244. A F Tsatsul'nikov, I L Krestnikov, W V Lundin, A V Sakharov, A P Kartashova, A S Usikov, Zh I Alferov, N N Ledentsov, A Strittmatter, A Hoffmann, D Bimberg, I P Soshnikov, D Litvinov, A Rosenauer, D Gerthsen, and A Plaut. Formation of GaAsN nanoinsertions in a GaN matrix by metal-organic chemical vapour deposition. Semiconductor Science and Technology, 15(7):766, 2000. Abstract:

     Coherent ultrathin GaAsN insertions are formed in a GaN matrix by predeposition of an ultrathin GaAs layer on a GaN surface, followed by annealing in an NH 3 atmosphere and overgrowth with GaN. During the overgrowth, most of the As atoms are substituted by N, with a dense array of coherent GaAsN nanodomains with lateral sizes of about 3-4 nm formed in the GaN matrix. We report a green luminescence due to GaAsN insertions, surviving at high observation temperatures and excitation densities.

     [bibtex-key = Tsatsulnikov2000]



245. A. Rosenauer and D. Gerthsen. Atomic Scale Strain and Composition Evaluation from High-Resolution Transmission Electron Microscopy Images. In Peter W. Hawkes, editor, , volume 107 of Advances in Imaging and Electron Physics, pages 121--230. Elsevier, 1999. Abstract:

     Publisher Summary This chapter describes the program package digital analysis of lattice images (DALI), which was developed to quantify high-resolution transmission electron microscopy (HRTEM) image information. These programs are applied to semiconductor heteroepitaxial layers where the strain state and the composition on an atomic scale are of particular interest. The basis of one possible approach to solve the task of determination of strain and composition on an atomic scale is measurement of local lattice parameters—that is, measurement of the distance between adjacent atomic columns. This simply requires the detection of the intensity maxima positions in a high-resolution image that can be considered a fingerprint of the local lattice parameter. It is not necessary to know the actual position of the atomic columns with respect to the intensity maxima position if the transmission electron microscope (TEM) specimen thickness does not change significantly and composition-insensitive imaging conditions are chosen to avoid chemical shifts of the contrast pattern. Local composition can be extracted directly if the relationship between composition and lattice parameter is known.

     [bibtex-key = Rosenauer1999b]



246. R. Engelhardt, U.W. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, and D. Gerthsen. Room-temperature lasing of strain-compensated CdSe/ZnSSe quantum island laser structures. Journal of Applied Physics, 86(10):5578--5583, 1999. Keyword(s): II-VI semiconductors, MOCVD coatings, cadmium compounds, excitons, plastic deformation, quantum well lasers, zinc compounds, 4255Px, 4260By, 7135-y, 8530Vw. Abstract:

     Efficient resonant excitonic waveguiding is achieved in laser structures, grown by metallorganic chemical vapor deposition, with stacked CdSe quantum islands which were separated by ternary ZnSSe barriers. Plastic relaxation within the stack is shown to be suppressed by adjusting the sulfur content in the barriers to compensate the strain. Excitonic lasing with low threshold intensities is demonstrated well above room temperature with Ith77 K=0.8 kW/cm2 and Ith300 K=55 kW/cm2. © 1999 American Institute of Physics.

     [bibtex-key = Engelhardt1999]



247. I. L. Krestnikov, M. Strassburg, M. Caesar, A. Hoffmann, U. W. Pohl, D. Bimberg, N. N. Ledentsov, P. S. Kop'ev, Zh. I. Alferov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Control of the electronic properties of CdSe submonolayer superlattices via vertical correlation of quantum dots. Phys. Rev. B, 60:8695--8703, September 1999. [bibtex-key = Krestnikov1999a]



248. D. Luerssen, R. Bleher, H. Richter, Th. Schimmel, H. Kalt, A. Rosenauer, D. Litvinov, A. Kamilli, D. Gerthsen, K. Ohkawa, B. Jobst, and D. Hommel. Radiative recombination centers induced by stacking-fault pairs in ZnSe/ZnMgSSe quantum-well structures. Applied Physics Letters, 75(25):3944--3946, 1999. Keyword(s): zinc compounds, magnesium compounds, II-VI semiconductors, wide band gap semiconductors, semiconductor quantum wells, stacking faults, defect states, interface states, interface structure, photoluminescence, atomic force microscopy, transmission electron microscopy, excitons. [bibtex-key = Luerssen1999]



249. A. Rosenauer and D. Gerthsen. Composition evaluation by the lattice fringe analysis method using defocus series. Ultramicroscopy, 76(1):49--60, 1999. [bibtex-key = Rosenauer1999c]



250. E Schomburg, S Brandl, K.F Renk, N.N Ledentsov, V.M Ustinov, A.E Zhukov, A.R Kovsh, A.Yu Egorov, R.N Kyutt, B.V Volovik, P.S Kop'ev, Zh.I Alferov, A Rosenauer, D Litvinov, D Gerthsen, D.G Pavel'ev, and Y.I Koschurinov. Miniband transport in a semiconductor superlattice with submonolayer barriers. Physics Letters A, 262(4-5):396--401, 1999. Keyword(s): 85.30.Vw. Abstract:

     We report on the observation of miniband transport in a GaAs/AlAs superlattice with submonolayer AlAs barriers. An X-ray analysis indicated the superlattice periodicity, and a composition analysis by a high-resolution transmission electron microscopy study revealed that the barriers contained Al rich islands (antidots). From the current-voltage characteristic we derived a miniband width (105 meV), which was significantly wider than for multilayer-thick barrier superlattices; photoluminescence spectra were consistent with miniband formation.

     [bibtex-key = Schomburg1999]



251. M. Strassburg, R. Heitz, V. Türck, S. Rodt, U.W. Pohl, A. Hoffmann, D. Bimberg, I.L. Krestnikov, V.A. Shchukin, N.N. Ledentsov, Zh.I. Alferov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Three-dimensionally confined excitons and biexcitons in submonolayer-CdSe/ZnSe superlattices. Journal of Electronic Materials, 28(5):506--514, 1999. Keyword(s): CdSe/(Zn, Mg)(S, Se), excitonic localization, gain, resonant waveguiding. [bibtex-key = Strassburg1999a]



252. A.F. Tsatsul’Nikov, B.V. Volovik, N.N. Ledentsov, M.V. Maximov, A.Yu Egorov, A.R. Kovsh, V.M. Ustinov, A.E. Zhukov, P.S. Kop’Ev, Zh.I. Alferov, I.A. Kozin, M.V. Belousov, I.P. Soshnikov, P. Werner, D. Litvinov, U. Fischer, A. Rosenauer, and D. Gerthsen. Lasing in structures with InAs quantum dots in an (Al, Ga)As matrix grown by submonolayer deposition. Journal of Electronic Materials, 28(5):537--541, 1999. Keyword(s): Lasing, quantum dots, submonolayer, vertical correlation. [bibtex-key = Tsatsul’Nikov1999]



253. T. Walter, A. Rosenauer, R. Wittmann, D. Gerthsen, F. Fischer, T. Gerhard, A. Waag, G. Landwehr, P. Schunk, and T. Schimmel. Structural properties of BeTe/ZnSe superlattices. Phys. Rev. B, 59:8114--8122, March 1999. [bibtex-key = Walter1999]



254. Stephan Kaiser, Herbert Preis, Wolfgang Gebhardt, Oliver Ambacher, Helmut Angerer, Martin Stutzmann, Andreas Rosenauer, and Dagmar Gerthsen. Quantitative Transmission Electron Microscopy Investigation of the Relaxation by Misfit Dislocations Confined at the Interface of GaN/Al$_{ extbf{2}}$O$_{ extbf{3}}$(0001). Japanese Journal of Applied Physics, 37(Part 1, No. 1):84--89, 1998. [bibtex-key = Kaiser1998]



255. B. Neubauer, A. Rosenauer, D. Gerthsen, O. Ambacher, and M. Stutzmann. Analysis of composition fluctuations on an atomic scale in Al(0.25)Ga(0.75)N by high-resolution transmission electron microscopy. Applied Physics Letters, 73(7):930--932, 1998. Keyword(s): aluminium compounds, gallium compounds, wide band gap semiconductors, III-V semiconductors, stoichiometry, fluctuations, transmission electron microscopy, lattice constants, semiconductor heterojunctions, interface structure, semiconductor epitaxial layers. [bibtex-key = Neubauer1998]



256. A. Rosenauer, U. Fischer, D. Gerthsen, and A. Förster. Composition evaluation by lattice fringe analysis. Ultramicroscopy, 72:121--133, 1998. Abstract:

     In this paper we present a compositional analysis, by high-resolution transmission electron microscopy of a 2 nm In$_x$Ga$_{1−x}$As layer (nominal In-content 60\%) which was deposited on GaAs (0 0 1) and capped with 10 nm GaAs. A three-beam condition close to the (1 0 0) zone axis is used. The lattice fringe images result from the interference of the (0 0 0), (0 0 4) and (0 0 2) beams with the latter centered on the optical axis. Due to the chemical sensitivity of the (0 0 2) beam, the obtained contrast patterns strongly depend on the In-content x averaged along the electron beam direction. We suggest a simple analysis procedure that uses the ratio A002/A004 of the (0 0 2) and (0 0 4) reflections of local image cell diffractograms, respectively, which is a bijective function of x. Furthermore, we show that the suggested method does not require the exact knowledge of the objective lens defocus and the sample thickness in the electron beam direction. In order to check the reliability of the gained results, a finite-element calculation of the strain state is performed which is based on the evaluated In-concentration profile. The results of the finite-element calculation are compared with an evaluation of the image using atomic scale strain measurements. The investigations of the In$_x$Ga$_{1−x}$As layer showed that the GaAs overgrowth caused a structural modification of the initial island structure which is transformed into an In$_x$Ga$_{1−x}$As layer with a rather homogeneous thickness and an In-content that varies locally. Reasons for the morphological transition are discussed.

     [bibtex-key = Rosenauer1998a]



257. M. Strassburg, V. Kutzer, U. W. Pohl, A. Hoffmann, I. Broser, N. N. Ledentsov, D. Bimberg, A. Rosenauer, U. Fischer, D. Gerthsen, I. L. Krestnikov, M. V. Maximov, P. S. Kop'ev, and Zh.I. Alferov. Gain studies of (Cd, Zn)Se quantum islands in a ZnSe matrix. Applied Physics Letters, 72(8):942--944, 1998. Keyword(s): cadmium compounds, zinc compounds, II-VI semiconductors, semiconductor quantum dots, island structure, monolayers, refractive index, transmission electron microscopy, biexcitons, excitons, phonon spectra, quantum well lasers, stimulated emission. [bibtex-key = Strassburg1998]



258. M. Hetterich, M. Grün, W. Petri, C. Märkle, C. Klingshirn, A. Wurl, U. Fischer, A. Rosenauer, and D. Gerthsen. Elastic and plastic strain relaxation in ultrathin CdS/ZnS quantum-well structures grown by molecular-beam epitaxy. Phys. Rev. B, 56:12369--12374, November 1997. [bibtex-key = Hetterich1997]



259. Marcus J. Kastner, Gabriella Leo, Doris Brunhuber, Andreas Rosenauer, Herbert Preis, Berthold Hahn, Markus Deufel, and Wolfgang Gebhardt. Investigations on strain relaxation of ZnS(x)Se(1−x) layers grown by metalorganic vapor phase epitaxy. Journal of Crystal Growth, 172(1-2):64--74, 1997. Abstract:

     We investigated the strain relaxation process of ternary ZnSxSe1−x layers using high-resolution X-ray diffractometry (XRD), Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). The samples were grown by low pressure \{MOVPE\} on (001) GaAs substrates. \{XRD\} analysis shows that after exceeding a critical layer thickness strain relaxation occurs first in the [1-10] direction and the layer unit cell is monoclinically distorted. A detailed structural characterization and strain measurements for various compositions and layer thicknesses were carried out. \{TEM\} and \{RBS\} channeling measurements reveal an anisotropic distribution of defects not confined at the interface. Their contribution to the observed strain relaxation will be discussed. It is demonstrated that the introduction of a thin ZnSe layer between substrate and ZnSxSe1−x epilayer will drastically slow down the relaxation process and hamper the formation of stacking faults at the heterointerface.

     [bibtex-key = Kastner1997]



260. A. Rosenauer, U. Fischer, D. Gerthsen, and A. Forster. Composition evaluation of In(x)Ga(1-x)As Stranski-Krastanow-island structures by strain state analysis. Applied Physics Letters, 71(26):3868--3870, 1997. Keyword(s): indium compounds, gallium arsenide, III-V semiconductors, island structure, transmission electron microscopy, lattice constants, molecular beam epitaxial growth, semiconductor epitaxial layers, finite element analysis, segregation, semiconductor growth. [bibtex-key = Rosenauer1997b]



261. A. Rosenauer, T. Remmele, D. Gerthsen, K. Tillmann, and A. Förster. Atomic scale strain measurements by the digital analysis of transmission electron microscopic lattice images. Optik (Stuttgart), 105(3):99--107, 1997. Note: Eng. Keyword(s): Experimental study, TEM, Electron microscopy, High-resolution methods, Measuring methods, Stress analysis, Layer thickness, Crystals, Semiconductor materials. [bibtex-key = Rosenauer1997]



262. U. Woggon, W. Langbein, J. M. Hvam, A. Rosenauer, T. Remmele, and D. Gerthsen. Electron microscopic and optical investigations of the indium distribution in GaAs capped In(x)Ga(1-x)As islands. Applied Physics Letters, 71(3):377--379, 1997. Keyword(s): indium compounds, gallium arsenide, III-V semiconductors, semiconductor quantum dots, buried layers, transmission electron microscopy, photoluminescence, molecular beam epitaxial growth, semiconductor growth, semiconductor epitaxial layers. [bibtex-key = Woggon1997]



263. Marcus J. Kastner, Berthold Hahn, Claus Auchter, Markus Deufel, Andreas Rosenauer, and Wolfgang Gebhardt. Structural characterization and MOVPE growth of ZnCdSe and ZnSSe layers, quantum wells and superlattices. Journal of Crystal Growth, 159(1-4):134--137, 1996. Note: Proceedings of the seventh international conference on II-VI compouds and devices. Abstract:

     A brief report will be given on the structural investigation and the growth of single layers, quantum wells (SQWs) and superlattices (SLs) of ZnCdSe and ZnSSe on GaAs(001) by MOVPE. Crystalline quality, stoichiometry, strain and other structural parameters were determined by high-resolution X-ray diffraction (HRXRD). Lattice relaxation of ZnSSe was investigated and the influence of a ZnSe buffer will be discussed. Dislocation structures have been investigated by transmission electron microscopy (TEM). The dynamical scattering theory was utilized to obtain best fits to measured X-ray rocking curves. Reciprocal space maps were recorded to analyze the unit cell distortion and to obtain information about the degree of relaxation.

     [bibtex-key = Kastner1996]



264. A. Rosenauer, S. Kaiser, T. Reisinger, J. Zweck, W. Gebhardt, and D. Gerthsen. Digital analysis of high resolution transmission electron microscopy lattice images. Optik, 102:63--69, 1996. Abstract:

     The method DALI (digital analysis of HRTEM lattice images) is introduced. Applications of DALI have been shown in previous papers. In this paper, we give a more detailed treatment of the procedure. DALI allows the calculation of local and averaged displacements and lattice distances directly from HRTEM lattice images. It contains a noise reduction procedure, a procedure for lattice site detection with an error estimation and evaluation procedures for displacements and lattice distances. As an example, DALI is applied to the investigation of a Cd/sub x/Zn/sub 1-x/Se/ZnSe quantum well structure

     [bibtex-key = Rosenauer1996a]



265. A. Rosenauer, T. Reisinger, F. Franzen, G. Schutz, B. Hahn, K. Wolf, J. Zweck, and W. Gebhardt. Transmission electron microscopy and reflected high-energy electron-diffraction investigation of plastic relaxation in doped and undoped ZnSe/GaAs(001). Journal of Applied Physics, 79(8):4124--4131, 1996. Keyword(s): DISLOCATIONS, DOPED MATERIALS, EPITAXIAL LAYERS, MOLECULAR BEAM EPITAXY, PLASTICITY, RHEED, STRESS RELAXATION, TEM, VPE, ZINC SELENIDES. [bibtex-key = Rosenauer1996]



266. K. Tillmann, A. Thust, M. Lentzen, P. Swiatek, A. Förster, K. Urban, W. Laufs, D. Gerthsen, T. Remmele, and A. Rosenauer. Determination of segregation, elastic strain and thin-foil relaxation in In(x)Ga(1-x)As islands on GaAs(001) by high resolution transmission electron microscopy. Philosophical Magazine Letters, 74(5):309--315, 1996. Abstract:

     Lattice-parameter mismatch-induced strains in three-dimensional coherent InxGa1-xAs islands grown on GaAs(001) substrates have been determined experimentally on an atomic scale by a digital analysis of images obtained by high-resolution transmission electron microscopy. The strain distributions in the islands were simulated by finite-element calculations. The simulated strain distributions are found to be in good agreement with measured data, taking into account the thin-foil relaxation of electron-transparent specimens in addition to the well known elastic strain relief. Clear evidence is given for an indium segregation causing a misfit gradient between the interface and the islands' surface.

     [bibtex-key = Tillmann1996]



267. W.S. Kuhn, A. Lusson, B. Qu'Hen, C. Grattepain, H. Dumont, O. Gorochov, S. Bauer, K. Wolf, M. Wörz, T. Reisinger, A. Rosenauer, H.P. Wagner, H. Stanzl, and W. Gebhardt. The metal organic vapour phase epitaxy of ZnTe: III. Correlation of growth and layer properties. Progress in Crystal Growth and Characterization of Materials, 31(1-2):119--177, 1995. Abstract:

     The crystalline structure, surface morphology, optical properties and purity of ZnTe layers grown by \{MOVPE\} were investigated. Various substrates, different combinations of metalorganics and various growth conditions were studied. The results of three different \{MOVPE\} growth systems and reactor cells are compared. A variety of methods were used to study the structure and morphology (e.g. TEM, HRTEM, X-ray diffraction, Nomarski microscopy, photo reflection, Raman scattering). The preparation of the GaAs and ZnTe surfaces is well advanced but problematic for GaSb. For heterostructures like ZnTe on GaAs (001) with about 7\% mismatch, the crystalline structure is mainly dominated by interfacial misfit dislocations and threading dislocations penetrating about 300 nm into the ZnTe layer. With better matched substrates (GaSb or ZnTe) or different orientations (GaAs (111)), the threading dislocations can nearly be eliminated. The comparison of growth studies with MOVPE, \{MBE\} and \{ALE\} reveals that the initial growth of ZnTe on GaAs (001) is mainly determined by the misfit and its relaxation. The first ≈4 monolayers are characterized by a pseudomorphous, 2D growth mode. The following surface roughening is caused by a relaxation through a 3D growth mode with islands. Once the relaxation is completed, the surface smoothens and recovers the 2D growth mode. The initial growth stages, representing the Stranski-Krastanov mechanism, are dependent on the surface termination of the substrate and on the growth method and parameters. The surface morphology of thicker ZnTe layers (>0.1 μm on GaAs (001)) grown by \{MOVPE\} is solely determined by the conditions at the growing interface (adsorption and decomposition of the precursors, desorption of undesired species, quantities of released Zn and Te, surface stoichiometry). These interface conditions are dependent on the precursor combination, the kinetic or mass transport limitation and the reactor hydrodynamics. The studies of the layer properties were sometimes bothered by a thin native oxide with the structure ZnTe/Te/ZnO. Purity and optical quality were tested by low temperature PL. The strain induced by the cooling of the ZnTe/GaAs structures grown at 300-400°C renders the identification of the radiative transitions difficult. However, many transitions and radiative centers are now identified. Under many growth conditions, the (A0Asl, X1) transition which is due to As from substrate autodoping, dominates the spectra. Hence, stoichiometry and inhomogeneity of the GaAs substrates are reflected in the spectra. But also precursor combination, partial pressures and growth temperatures have a significant influence on the \{PL\} spectra. The substrate type (GaAs, GaSb, ZnTe) is reflected in the spectra by transitions due to outdiffusion and by the Y-lines which are related to the misfit dislocations. Transitions induced by layer contaminations like Cu, Li, O and N were found. With the alkyl combination DEZn/DIPTe, reproducible growth of samples is possible showing \{PL\} spectra dominated by free excitons. The frequently appearing \{I1c\} and I'1c transitions might be due to a \{VZn\} vacancy or a vacancy donor complex. Complex relations to the growth stoichiometry were found. \{SIMS\} measurements helped to further identify the layer impurities. The layer purity is affected by extrinsic impurities due to substrate outdiffusion (As, Ga), contaminations from growth system (O, Cu) and precursors (Li). Impurities like H and C (and N) which are intrinsic to the \{MOVPE\} process, depend on the dissociation kinetics of the precursors which are themselves dependent on the growth parameters (e.g. temperature, carrier gas). The origins of the extrinsic impurities are identified as far as possible.

     [bibtex-key = Kuhn1995]



268. S. Lankes, B. Hahn, C. Meier, F. Hierl, M. Kastner, A. Rosenauer, and W. Gebhardt. Photoreflectance measurements on ZnSe/ZnS0.25Se0.75SQW. physica status solidi (a), 152(1):123--131, 1995. Abstract:

     A series of ZnSe/ZnS0.25Se0.75 single quantum wells (SQW) of various well thicknesses are grown on (001) GaAs with low pressure metalorganic vapour phase epitaxy (MOVPE). Photoreflectance measurements (PR) show pronounced structures which are assigned to excitonic transitions between quantum well states. The structural properties of the samples are determined with high resolution X-ray diffraction and transmission electron microscopy. The model of Mathieu et al. is used to calculate excitonic states in a QW and a fitting procedure is developed which allows an estimate of the band offset. The structure exhibits a type II alignment which is also supported by photoluminescence (PL) measurements and which is mainly the result of a strain induced shift of the ZnS0.25Se0.75 conduction band.

     [bibtex-key = Lankes1995]



269. A. Rosenauer, T. Reisinger, E. Steinkirchner, J. Zweck, and W. Gebhardt. High resolution transmission electron microscopy determination of Cd diffusion in CdSeZnSe single quantum well structures. Journal of Crystal Growth, 152(1-2):42--50, 1995. Abstract:

     The diffusion coefficient D(T) of Cd in CdSeZnSe single quantum well (SQW) structures grown pseudomorphically on GaAs(001) is determined by high resolution transmission electron microscopy of annealed \{SQWs\} and subsequent digital analysis of lattice images. \{SQWs\} of 2 monolayer (ML) thickness were grown by molecular beam epitaxy. During growth the CdSe quantum wells (QWs) broaden to about 7 \{ML\} CdZnSe as measured by reflection high energy electron diffraction (RHEED). We find for the diffusion coefficient of Cd in ZnSe at temperatures between 340 and 400° C D(T) = 1.9 × 10−4 [cm2/s] · exp(− 1.8 [eV]/kT).

     [bibtex-key = Rosenauer1995a]



270. K Wolf, S Jilka, A Rosenauer, G Schutz, H Stanzl, T Reisinger, and W Gebhardt. High-resolution X-ray diffraction investigations of epitaxially grown ZnSe/GaAs layers. Journal of Physics D: Applied Physics, 28(4A):A120, 1995. Abstract:

     Single-crystalline ZnSe layers were grown by metal-organic vapour phase and molecular beam epitaxy on (001) oriented GaAs substrates. The lattice mismatch between layer and substrate at growth temperature causes a strain in the layer material, which is relaxed by the nucleation of misfit dislocations. The relaxation process starts at the critical thickness, which depends on the growth conditions. The crystalline quality and the residual strain of the epilayers were investigated with a high-resolution X-ray diffractometer. Additionally, the intensity distribution of the scattered X-rays in the directions perpendicular and parallel to the reciprocal lattice vector (004) was observed by a two-reflection analyser crystal. For the system ZnSe/GaAs, this intensity distribution depends on the degree of strain relaxation, which is dependent on the layer thickness. The results are compared with transmission electron microscopy results.

     [bibtex-key = Wolf1995]



271. M. Grün, M. Hetterich, C. Klingshirn, A. Rosenauer, J. Zweck, and W. Gebhardt. Strain relief and growth modes in wurtzite type epitaxial layers of CdSe and CdS and in CdSe/CdS superlattices. Journal of Crystal Growth, 138(1-4):150--154, 1994. Abstract:

     The relaxation of the mismatch-induced strain in (0001) wurtzite type epilayers of CdSe and CdS and of related superlattices on GaAs(111) is discussed. For CdSe/GaAs(111), high-resolution electron microscopy shows that the misfit dislocations are 60° dislocations, the glide of which is limited to the plane parallel to the interface. The epilayers are therefore free of in-grown threading arms. The thickness of that region in the layer, which is significantly strained, is found to be larger in case of a two-dimensional growth mode than in case of a three-dimensional one.

     [bibtex-key = Gruen1994]



272. A. Naumov, H. Stanzl, K. Wolf, A. Rosenauer, S. Lankes, and W. Gebhardt. Exciton recombination in ZnSexTe1−x/ZnTe {QWs} and ZnSexTe1−x epilayers grown by metalorganic vapour phase epitaxy. Journal of Crystal Growth, 138(1-4):595--600, 1994. Abstract:

     We present the optical characterization of \{MOVPE\} grown ZnSexTe1−x epilayers with 0<x<0.35 and ZnSexTe1−x single quantum wells (SQWS) with Lz=2.0−8.5 nm. The structures were investigated using photoreflectance and photoluminescence spectroscopy. Transmission electron microscope analysis was used to determine quantum well thickness. The studied ZnSe0.3Te0.7 \{SWQs\} show a bright emission band with a halfwidth ≈ 10 meV in the spectral region of 100−250 meV below the band gap of the corresponding mixed crystal. We suggest a type \{II\} bands alignment in ZnSexTe1−x/ZnTe single quantum wells.

     [bibtex-key = Naumov1994]



273. S. Bauer, A. Rosenauer, P. Link, W. Kuhn, J. Zweck, and W. Gebhardt. Misfit dislocations in epitaxial ZnTe/GaAs (001) studied by {HRTEM}. Ultramicroscopy, 51(1-4):221--227, 1993. Abstract:

     Single-crystalline ZnTe epilayers were grown by atmospheric-pressure metal organic vapor phase epitaxy (MOVPE) and hot wall epitaxy (HWE) on (001) GaAs. The misfit of lattice constants is -7.5% at the growth temperature of 350°C. Conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) have been used to investigate the misfit dislocations in the ZnTe/GaAs (001) system. The types and distribution of the observed dislocations are independent of growth techniques used. The most common line defects at the ZnTe/GaAs interface are 60° and Lomer dislocations with Burgers vectors of 12a〈110〉. Their respective abundance ratio is 2:1. Less than 3% of the 60° dislocations dissociate into partial dislocations limiting a stacking fault. The distances between parallel {111} planes terminating at the interface have been determined from an analysis of about 1 μm of the projected ZnTe/GaAs interface. The distribution fits by a Gaussian with an average distance of 57 Å. This allows an estimate of the residual biaxial strain at the interface which is found to be compressive with a magnitude less than 0.6%. The distances of the observed dislocation cores form a histogram. Its special shape shows four maxima at about 0, 5, 9 and 12×12as〈110〉. They can be explained by a model for the correlated nucleation of misfit dislocations in highly mismatched heterostructures like ZnTe/GaAs.

     [bibtex-key = Bauer1993]



274. M. Grun, C. Klingshirn, A. Rosenauer, J. Zweck, and W. Gebhardt. Spatial confinement of misfit dislocations at the interface of CdSe/GaAs(111). Applied Physics Letters, 63(21):2947--2948, 1993. Keyword(s): 6172Ff, 6855Ln, 6865+g, BURGERS VECTOR, CADMIUM SELENIDES, ELECTRON MICROSCOPY, EPITAXIAL LAYERS, GALLIUM ARSENIDES, HETEROSTRUCTURES, INTERFACE STRUCTURE, MISFIT DISLOCATIONS. Abstract:

     High�resolution electron microscopy of wurtzite type CdSe epilayers grown on (111) GaAs revealed that interfacial misfit dislocations are perfect 60° dislocations with Burgers vectors parallel to the interface. Glide is therefore limited to the (0001) interface plane and the extension of dislocations into the epilayer is suppressed. Single�beam bright field imaging shows that the 7 per cent mismatched epilayer is free of a dislocation network in its volume.

     [bibtex-key = Grun1993]



275. Tim Grieb, Christoph Mahr, Florian F. Krause, Knut Müller-Caspary, Marco Schowalter, Martin Eickhoff, and Andreas Rosenauer. Measuring electric fields with 4D-STEM: Demonstration of pitfalls by the example of GaN and SiGe. In European Microscopy Congress (EMC) 2024, Kopenhagen (Dänemark), [poster], 2024. Keyword(s): Konferenz. [bibtex-key = E_Grieb2024a]



276. Christoph Mahr, Florian F. Krause, Jakob Stahl, Beeke Gerken, Marco Schowalter, Tim Grieb, Lutz Mädler, and Andreas Rosenauer. Characterization of structure and mixing in nanoparticle hetero-aggregates using convolutional neural networks: 3D-reconstruction versus 2D-projection. In European Microscopy Congress (EMC) 2024, Kopenhagen (Dänemark), [talk], 2024. Keyword(s): Konferenz. [bibtex-key = E_Krause2024]



277. Marco Schowalter, Alexander Karg, Christoph Mahr, Martin Eickhoff, and Andreas Rosenauer. Computation of concentration dependent properties of $\varepsilon$/$\kappa$-(InGa)$_2$O$_3$ and its application to the measurement of strain in heterostructures. In International Workshop on Gallium Oxide and Related Materials (IWGO), Berlin [poster], 2024. Keyword(s): Konferenz. [bibtex-key = E_Schowalter2024]



278. Tim Grieb, Florian F. Krause, Thorsten Mehrtens, Christoph Mahr, Marco Schowalter, and Andreas Rosenauer. GaN atomic electric fields from STEM: Panther vs. EMPAD. In Microscopy Conference (MC) 2023, Darmstadt, [Poster IM6.P002], 2023. [bibtex-key = E_Grieb2023]



279. Florian F. Krause, Tim Grieb, Christoph Mahr, Marco Schowalter, Thorsten Mehrtens, Rudolpho Hötzel, Stephan Figge, Martin Eickhoff, and Andreas Rosenauer. Electrical Fields in AlN/GaN-Nanowires Measured with Aberration-Corrected 4D-STEM. In Microscopy Conference (MC) 2023, Darmstadt, [Vortrag IM6.003], 2023. [bibtex-key = E_Krause2023]



280. Florian F. Krause, Christoph Mahr, Marco Schowalter, and Andreas Rosenauer. An adaptive scanning scheme for dose efficient acquisition of EDX-maps. In International Microscopy Congress (IMC20) 2023, Busan (Südkorea), [poster AS-08.P.0625], 2023. [bibtex-key = E_Krause2023b]



281. Christoph Mahr, Beeke Gerken, Jakob Stahl, Valentin Baric, Lutz Mädler, and Andreas Rosenauer. Investigation of 2D and 3D mixing properties in nanoparticle hetero-aggregates using convolutional neural networks. In International Microscopy Congress (IMC20) 2023, Busan (Südkorea), [talk SS-05.1.0445], 2023. Keyword(s): Konferenz. [bibtex-key = E_Mahr2023a]



282. Christoph Mahr, Tim Grieb, Florian F. Krause, Marco Schowalter, and Andreas Rosenauer. Can a difference in mean inner potential be measured from a shift of the central disc in nano-beam electron diffraction?. In Microscopy Conference (MC) 2023, Darmstadt, [Poster IM6.P001], 2023. [bibtex-key = E_Mahr2023]



283. Marco Schowalter, Patrick Vogt, Justin Bich, Alexander Karg, Christoph Mahr, Tim Grieb, Florian F. Krause, Martin Eickhoff, and Andreas Rosenauer. Composition and strain of pseudomorphic $\alpha$-(AlGa)$_2$O$_3$ on sapphire (0001) substrates. In Microscopy Conference (MC) 2023, Darmstadt, [Poster MS3.P001], 2023. [bibtex-key = E_Schowalter2023]



284. Jakob Stahl, Tobias Tabeling, Christoph Mahr, Suman Pokhrel, Andreas Rosenauer, Udo Fritsching, and Lutz Mädler. Quantification of the Mixing Process of Two Nanoparticle Producing Flames for the Design of Hetero-Contacts. In PARTEC, International Congress on Particle Technology 2023, Nürnberg, [Vortrag], 2023. [bibtex-key = E_Stahl2023]



285. Tim Grieb, Thorsten Mehrtens, Florian F. Krause, Christoph Mahr, Marco Schowalter, Dennis Marquardt, and Andreas Rosenauer. Composition Analysis of III/V Semiconductors by Quantitative Scanning Transmission Electron Microscopy. In DGKK/DEMBE 2022, Bremen, [talk], 2022. Keyword(s): Konferenz. [bibtex-key = E_Grieb2022]



286. Mehtap Oezaslan, Alexandra Dworzak, Christoph Mahr, Paul Paciok, Andreas Rosenauer, and Marc Heggen. Effect of the Potentiostatic and Potentiodynamic Dealloying on the Structure and Chemical Distribution of Ag Atoms in Au-Enriched Nanoparticles. In The Electrochemical Society Meeting (ECS) 2022, Atlanta (USA), [Vortrag C04.795], 2022. [bibtex-key = Oezaslan2022]



287. M. Eickhoff A. Karg, M. Kracht, M. Schowalter, B. Gerken, D. Zink, M. Weinhold, M. Rohnke, J. Schörmann, J. Janek, A. Rosenauer, P. Klar. Tin assisted MBE-growth of e-Ga2O3. In Proceedings of the 26th annual meeting of the german crystallographic society (DGK) in Essen, 2018. [bibtex-key = Karg2018]



288. Florian F. Krause, Christoph Mahr, Marco Schowalter, Beeke Gerken, Thorsten Mehrtens, Andreas Rosenauer, Dirk van Dyck, Hamish G. Brown, Benjamin D. Forbes, Leslie J. Allen, Juri and Barthel, Joachim Meyer, Knut Urban, and Rafal Dunin-Borkowski. ISTEM: strongly incoherent imaging for ultra-high resolution TEM (Vortrag). In 19th International Microscopy Congress (IMC) 2018, Sydney (Australien) [Vortrag IT9.2.357], 2018. [bibtex-key = Krause2018a]



289. Florian F. Krause, Marco Schowalter, Tim Grieb, Christoph Mahr, and Andreas Rosenauer. tibaDESC: precise measurement of diffraction pattern distortions for quantitative STEM (Poster). In 19th International Microscopy Congress (IMC) 2018, Sydney (Australien) [Poster IT9.316], 2018. [bibtex-key = Krause2018]



290. Christoph Mahr, Paromita Kundu, Anastasia Lackmann, Daniele Zanaga, Marco Schowalter, Martin Schwan, Sara Bals, Arne Wittstock, and Andreas Rosenauer. Residual silver in dealloyed nanoporous gold: quantitative spatial distribution and influence on structure and catalytic performance (Kurzvortrag, Poster). In 19th International Microscopy Congress (IMC) 2018, Sydney (Australien) [Kurzvortrag PS4.862], 2018. [bibtex-key = Mahr2018d]



291. Christoph Mahr, Knut Müller-Caspary, Martin Simson, Robert Ritz, Matthias Graf, Anastasia Lackmann, Tim Grieb, Marco Schowalter, Florian F Krause, Thorsten Mehrtens, Arne Wittstock, Heike Soltau, Jörg Weissmüller, and Andreas Rosenauer. Measurement of local crystal lattice strain variations in dealloyed nanoporous gold (Vortrag). In 19th International Microscopy Congress (IMC) 2018, Sydney (Australien) [Vortrag PS1.3.173], 2018. [bibtex-key = Mahr2018c]



292. N. Chery, N. T. Huong, M.P. Chauvat, B. Damilano, B. Gil, T. Grieb, M. Schowalter, A. Rosenauer, X. Portier, and P. Ruterana. Local structure and composition versus the optical properties of InGaN/GaN QWs for emission in and past the green gap. In MSM XX 2017, Oxford (GB), 2017. [bibtex-key = Chery2017_conf]



293. N. Gauquelin, K.H.W. van den Bos, A. Beche, F.F. Krause, I. Lobato, S. Lazar, A. Rosenauer, S. Van Aert, and J. Verbeeck. Determining oxygen relaxations at an interface: A comparative study between transmission electron microscopy techniques. In Microscopy Conference 2017 (MC 2017), Lausanne (CH), 2017. [bibtex-key = Gauquelin2017]



294. A. Karg, M. Kracht, M. Schowalter, B. Gerken, J. Bläsing, M. Rohnke, J. Schörmann, J. Janek, A. Rosenauer, and M. Eickhoff. MBE-growth and structural properites of e-Ga2O3. In Proceedings of the International Workshop on Gallium Oxide and related materials (IWGO 2017) in Parma, 2017. [bibtex-key = karg2017]



295. Florian F. Krause, Marco Schowalter, Tim Grieb, Knut Müller-Caspary, Thorsten Mehrtens, and Andreas Rosenauer. Effects of instrument imperfections on high resolution quantitative scanning transmission electron microscopy (Poster). In 4th Conference on Frontiers of Aberration Corrected Electron Microscopy (PICO 2017), Vaalsbroek (NL), 2017. [bibtex-key = Krause2017b]



296. Florian F Krause, Marco Schowalter, Marcus Müller, Jan-Philipp Ahl, Tilman Schimpke, Sebastian Metzner, Joachim Hertkorn, Frank Bertram, Thorsten Mehrtens, Peter Veit, Karl Engl, Martin Strassburg, Jürgen Christen, and Andreas Rosenauer. Structural and copositional multiprobe investigations of AlInGaN semiconductor structures and core-shell nanorod LEDs (Invited Talk). In Society of Photo-Optical Instrumentation Engineers Photonics West 2017 (SPIE Photonics West 2017) , San Francisco (USA), 2017. [bibtex-key = Krause2017a]



297. Paromita Kundu, Daniele Zanaga, Christoph Mahr, Anastasia Lackmann, Marco Schowalter, Martin Schwan, Andreas Rosenauer, Arne Wittstock, and Sara Bals. 3D Microstructural and Quantitative Compositional Analysis of Residual Ag in Nanoporous Au catalyst by STEM-EDS Tomography. In Microscience Microscopy Congress 2017 (MMC 2017), Manchester (UK), [Talk], 2017. [bibtex-key = Kundu2017]



298. Christoph Mahr, Paromita Kundu, Anastasia Lackmann, Daniele Zanaga, Marco Schowalter, Martin Schwan, Sara Bals, Arne Wittstock, and Andreas Rosenauer. Residual Silver in Dealloyed Nanoporous Gold: Quantitative Spatial Distribution and Influence on Structure and Catalytic Performance. In Microscopy Conference 2017 (MC 2017), Lausanne (CH), [Talk], 2017. [bibtex-key = Mahr2017a]



299. M. Müller, S. Metzner, T. Hempel, P. Veit, F. Bertram, F F Krause, T Mehrtens, K. Müller-Caspary, A Rosenauer, T. Schimpke, A. Avramescu, M. Strassburg, and J. Christen. Accessing optical and compositional properties of InGaN/GaN core-shell nanorods at the nanometer scale (Talk). In 9th International Conference on Materials for Advanced Technologies (ICMAT 2017) , Singapur (Singapur), 2017. [bibtex-key = Mueller2017]



300. M. Müller, S. Metzner, T. Hempel, P. Veit, F. Bertram, F F Krause, T Mehrtens, K. Müller-Caspary, A Rosenauer, T. Schimpke, A. Avramescu, M. Strassburg, and J. Christen. Nano-scale correlation of the optical, structural, and compositional properties of InGaN/GaN core-shell nanorod LEDs (Talk). In 5th International Conference on Light-Emitting Devices and Their Industrial Applications (LEDIDA 2017) , Yokohama (J), 2017. [bibtex-key = Mueller2017a]



301. Knut Müller-Caspary, Martial Duchamp, Florian F. Krause, Armand Beche, Marco Schowalter, Florian Winkler, Stefan Löffler, Heike Soltau, Josef Zweck, Peter Schattschneider, Johan Verbeeck, Sandra Van Aert, Rafal Dunin-Borkowski, and Andreas Rosenauer. Mapping atomic electric fields and charge densities by four-dimensional STEM (Invited Talk). In 24th Congress & General Assembly of the International Union of Crystallography (IUCR 2017), Hyderabat (Indien), 2017. [bibtex-key = Mueller-Caspary2017]



302. Knut Müller-Caspary, Martial Duchamp, Florian F. Krause, Armand Beche, Florian Winkler, Stefan Löffler, Heike Soltau, Josef Zweck, Johan Verbeeck, Sandra Van Aert, Rafal Dunin-Borkowski, and Andreas Rosenauer. Mapping atomic electric fields and charge densities by momentum-resolved STEM (Invited Talk). In Microscopy Conference 2017 (MC 2017), Lausanne (CH), 2017. [bibtex-key = Mueller-Caspary2017a]



303. Jan Mü�ener, Pascal Hille, Jörg Schörmann, Jörg Teubert, Bruno Gayral, Joel Bleuse, Eva Monroy, Tim Grieb, Andreas Rosenauer, and Martin Eickhoff. Bias-controlled optical transitions in GaN/AlN nanowire heterostructures. In Nanowire Week 2017, Lund (S), 2017. [bibtex-key = Muessener2017_conf]



304. Andreas Rosenauer, Florian F Krause, Marco Schowalter, Elias Goldmann, Frank Jahnke, Matthias Paul, Michael Jetter, Peter Michler, Marcus Müller, Peter Veit, Jürgen Christen, Tilman Schimpke, Adrian Avramescu, Martin Strassburg, and Jan-Philipp Ahl. Quantitative STEM: Comparative Studies of Composition and Optical Properties of Semiconductor Quantum Structures (Invited Talk). In Microscopy & Microanalysis 2017 Meeting (M&M 2017), St. Louis (USA), 2017. [bibtex-key = Rosenauer2017]



305. M. Schowalter, C. Carmesin, M. Lorke, D. Mourad, T. Grieb, K. Müller-Caspary, M. Yacob, J. P. Reithmaier, M. Benyoucef, A. Rosenauer, and F. Jahnke. The influence of morphology of InAs/InAlGaAs quantum dots emitting in the low-loss telecom wavelength range. In MC 2017, Lausanne (CH), 2017. [bibtex-key = Schowalter2017_conf]



306. Marco Schowalter, Beeke Geerken, Florian F. Krause, Tim Grieb, Knut Müller-Caspary, Christoph Mahr, Thorsten Mehrtens, Annick De Backer, Sandra Van Aert, and Andreas Rosenauer. A comparison of the simulation based and statistics based atomic counting techniques (Poster). In 4th Conference on Frontiers of Aberration Corrected Electron Microscopy (PICO 2017), Vaalsbroek (NL), 2017. [bibtex-key = Schowalter2017]



307. Marco Schowalter, Florian Fritz Krause, Tim Grieb, Knut Müller-Caspary, Thorsten Mehrtens, and Andreas Rosenauer. Influence of Microscope Imperfections and Detector Characteristics on Quantification of HAADF STEM images (Invited Talk). In 5th Annual Conference of AnalytiX (AnalytiX 2017), Fukuoka (J), 2017. [bibtex-key = Schowalter2017a]



308. K.H.W. van den Bos, N. Gauquelin, A. Beche, F.F. Krause, I. Lobato, S. Lazar, A. Rosenauer, S. Van Aert, and J. Verbeeck. Determining oxygen relaxations at an interface: A comparative study between transmission electron microscopy techniques (Talk). In Microscience Microscopy Congress 2017 (MMC 2017), Manchester (UK), 2017. [bibtex-key = Bos2017]



309. Marcos Alania, Annick De Backer, Ivan Lobato, Florian F. Krause, Dirk Van Dyck, Andreas Rosenauer, and Sandra Van Aert. How precise can atoms of a nanocluster be located in 3D from a tilt series of scanning transmission electron microscopy images? (Poster). In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Alania2016]



310. Tim Grieb, Florian F. Krause, Christoph Mahr, Knut Müller, and Andreas Rosenauer. Optimization of NBED simulations to predict experimental disc-detection measurements (Talk). In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Grieb2016]



311. A. Kirsch, M.M. Murshed, M. Schowalter, M. Curti, C.B. Mendive, and T. M. Gesing. Comparative band gap determinatio of photocatalytic active Bi2Fe4O9. In DGK 2016 conference in Stuttgart, Germany, 2016. [bibtex-key = Kirsch2016a]



312. F. F. Krause, A. Rosenauer, M. Schowalter, K. Müller-Caspary, T. Mehrtens, A. Beche, K.W.H. van den Bos, S. Van Aert, J. Verbeeck, and D. Van Dyck. Increased Resolution with the ISTEM mode (Talk). In Treffen des Arbeitskreises Hochauflösung (AKHREM) 2016, Berlin (D), 2016. [bibtex-key = Krause2016f]



313. Florian F. Krause, Marco Schowalter, Tim Grieb, Knut Müller-Caspary, Thorsten Mehrtens, and Andreas Rosenauer. Measurement of Diffraction Pattern Distortions for Quantitative STEM (Poster). In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Krause2016a]



314. Florian F. Krause, Marco Schowalter, Thorsten Mehrtens, Knut Müller-Caspary, Armand Beche, Karel W. H. van den Bos, Sandra Van Aert, Johan Verbeeck, and Andreas Rosenauer. ISTEM: A Realisation of Incoherent Imaging for Ultra-High Resolution TEM beyond the Classical Information Limit (Talk). In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Krause2016b]



315. Christoph Mahr, Knut Müller-Caspary, Tim Grieb, Florian F. Krause, Marco Schowalter, Anastasia Lackmann, Arne Wittstock, and Andreas Rosenauer. Measurement of strain in nanoporous gold using nano-beam electron diffraction. In European Microscopy Congress 2016 (EMC 2016), Lyon (F), [Poster IM06-352], 2016. [bibtex-key = Mahr2016c]



316. Christoph Mahr, Knut Müller-Caspary, Andreas Oelsner, Andreas Rosenauer, and Pavel Potapov. STEM strain measurement from a stream of diffraction patterns recorded on a pixel-free delay-line detector [Talk]. In EMAG conference 2016, Durham, UK, 2016. Abstract:

     Recent progress in nano-beam electron diffraction, ptychography and differential phase contrast microscopy [1] is based on the acquisition of a four-dimensional data set I(xp,yp,x,y) with (xp,yp) the position of the STEM probe, (x,y) a coordinate in the recorded image/diffraction pattern and intensity I. Since the speed of conventional charge-coupled devices is limited, a major challenge is the development of fast detectors. Here we present pilot experiments with a delay-line detector (DLD) mounted on an FEI Titan facility. Each electron impinging on the microchannel-plate stack of the DLD causes a cascade of secondary electrons. These electrons generate electrical pulses in two meandering wires. Depending on the incident position of the electron a characteristic time delay between the arrivals of the 2 conjunct pulses at the ends of each wire is measured, giving the coordinate of incidence perpendicular to the meander. By crossing two such delay-lines the point (x,y) and time Ï„ of incidence can be detected and thus an image can be reconstructed. We present strain measurements from convergent beam electron diffraction patterns [2] recorded at a STEM-raster of e.g. 100x100 pixels. Dwell times between 40 and 5ms have been used, corresponding to an acquisition of 10,000 diffraction patterns in 6.5 and 0.8min, respectively. In a GeSi-MOSFET we observe different strain regimes inside the GeSi-stressors owing to different Ge contents. Furthermore we show strain and rotation maps of catalytically interesting nanoporous gold, which has a sponge-like crystalline structure formed by the Au remaining from chemically corroded AuAg-alloys. Finally we show theoretical values [3] for precision and accuracy of the measured strain using nano-beam diffraction. As the precision of the measurement suffers from noise in the diffraction pattern, the precision degrades for shorter image integration times. On the other hand the precision can be increased using a precessing electron beam, as the diffraction discs are illuminated more homogeneously and hence their positions can be detected more precisely. In this way a compromise between precision and speed of the measurement has to be found.

     [bibtex-key = Mahr2016]



317. M. Müller, S. Metzner, T. Hempel, P. Veit, F. Bertram, F F Krause, T. Mehrtens, K. Müller-Caspary, A Rosenauer, T. Schimpke, A. Avramescu, M. Strassburg, and J. Christen. Optical, structural and compositional nano-scale characterization of InGaN/GaN core-shell microrod heterostructucom (Talk). In Proceedings of the Society of Photo-Optical Instrumentation Engineers Photonics West 2016 (SPIE Photonics West 2016) , San Francisco (USA), 2016. [bibtex-key = Mueller2016]



318. M. Müller, S. Metzner, T. Hempel, P. Veit, F. Bertram, F F Krause, T Mehrtens, K. Müller-Caspary, A Rosenauer, T. Schimpke, A. Avramescu, M. Strassburg, and J. Christen. Optical, structural and compositional nano-scale characterization of InGaN/GaN core-shell microrod heterostructures (Talk). In Society of Photo-Optical Instrumentation Engineers Photonics West 2016 (SPIE Photonics West 2016) , San Francisco (USA), 2016. [bibtex-key = Mueller2016a]



319. Knut Müller-Caspary, Florian F. Krause, Armand Béché, Martial Duchamp, Tim Grieb, Marco Schowalter, Stefan Löffler, Oliver Oppermann, Vadim Migunov, Florian Winkler, Heike Soltau, Lothar Strüder, Josef Zweck, Peter Schattschneider, Rafal Dunin-Borkowski, Johan Verbeeck, and Andreas Rosenauer. Momentum-resolved STEM: Measurement of atomic electric fields and angular multi-range analysis [Invited talk]. In The XXXVII Annual Meeting of the Electron Microscopy Society of India - International Conference on Electron Microscopy, 2016. Keyword(s): DPC, iris, picodiffraction, electric fields, ARSTEM. [bibtex-key = Mueller-Caspary2016c]



320. Knut Müller-Caspary, Florian F. Krause, Armand Béché, Martial Duchamp, Marco Schowalter, Stefan Löffler, Vadim Migunov, Florian Winkler, Martin Huth, Robert Ritz, Sebastian Ihle, Martin Simson, Henning Ryll, Heike Soltau, Lothar Strüder, Josef Zweck, Peter Schattschneider, Rafal Dunin-Borkowski, Johan Verbeeck, and Andreas Rosenauer. Measurement of Atomic Electric Fields by Scanning Transmission Electron Microscopy (STEM) Employing Ultrafast Detectors. In Microscopy and Microanalysis 2016, Columbus (OH/USA), [Invited Talk], volume 22, pages 484--485, July 24-28th 2016. Microscopy Society of America. Keyword(s): DPC, pnccd. Abstract:

     Contemporary aberration-corrected STEM enables to probe materials at a resolution of 50pm. This renders the mapping of electric fields at the subatomic scale possible which can give insight to charge densities, ionicity or polarization fields. Differential phase contrast (DPC) STEM as an established method to detect the field-induced angular deflection of the electron beam commonly employs segmented ring detectors [1,2] to record portions of the Ronchigram. This is usually assumed to be homogeneously filled and shifted as a whole in the presence of electric fields, causing characteristic signal differences in opposite segments. By multislice simulations for GaN the validity of these assumptions was checked [3]. With an aberration-corrected probe scanned over the Ga-N region as shown in Fig.1a, the Ronchigrams in Fig.1b have been obtained at 1.3nm specimen thickness. The dominant effect of atomic electric fields is hence a complex redistribution of intensity inside the Ronchigrams making segmented detector data difficult to quantify as to the deflection of the probe. By basic quantum mechanical arguments we take the complex intensity distribution in the Ronchigram into account. The diffraction plane shows the Fourier transform of the specimen exit wave, which corresponds to a transition from real to momentum space. The local diffracted intensity I(p) is hence proportional to the probability for the lateral momentum transfer vector p to occur. Consequently, the expectation value for the momentum transfer is calculated by a centre-of-gravity-type summation. This condenses the rich details of the Ronchigram to a single vector with fundamental physical meaning [3]. Fig.1c shows the vector field resulting from scanning over the GaN patch in Fig.1a, exhibiting atomic sites as sinks of momentum transfer whose magnitudes depend on the atomic number. To relate the electric field in the specimen to the observed momentum transfer, Ehrenfest’s theorem is applied. For thin specimens, is found to be proportional to the projection of the electric field along the optical axis, convolved with the intensity distribution of the incident STEM probe [3]. We demonstrate the potential of this approach in both simulation and experiment. For the GaN simulation in Fig.1c, we find the electric field depicted in Fig.1d. Atomic sites appear as sources of the field which has a magnitude of up to 1.5V/pm. As only the convolution of the true field with the probe intensity can be measured, the field strength decreases in the direct vicinity of atomic sites. In a first experiment, 20x20 Ronchigrams of SrTiO3 with a thickness of 2.5nm have been recorded on a conventional charge-coupled device (CCD), yielding momentum transfers and the electric field in Figs.2a,b.

     [bibtex-key = Mueller-Caspary2016a]



321. Knut Müller-Caspary, Thorsten Mehrtens, Marco Schowalter, Tim Grieb, Andreas Rosenauer, Florian F. Krause, Christoph Mahr, and Pavel Potapov. ImageEval. A software for the processing, evaluation and acquisition of (S)TEM images. In European Microscopy Congress 2016, Lyon (F), [Poster IM03-286], 2016. Abstract:

     Quantitative scanning or conventional TEM, as well as electron diffraction techniques usually require the processing of raw data, the comparison with simulated counterparts and a meaningful visualisation of results. Here we present ImageEval, a Matlab-based software which contains established techniques in a modularised manner with a graphical user interface. This enables the efficient, reproducible application of established techniques and assures both the access to and the transparent exchange of know-how among different groups after a pioneer methodical development. In the following we summarise central ImageEval features. The concept. ImageEval currently hosts 13 evaluation methods as separate modules. All modules can be used independently of each other but share a common data structure, so that results of one module can be further evaluated in another. Intermediate results, simulated reference or structural data are stored as meta data that is available for comparison or evaluation in all modules. The program reads Gatan (dm3) and FEI (emi/ser) file formats as well as common image formats. Large image series, e.g., 4-dimensional STEM data which often contain ~106 images and more, can be handled by pointers to files so as to load images into workspace only when to be processed. ImageEval is available as a standalone executable Version for Windows/Unix or as the Matlab source code directly, the latter option enabling the adaptation of evaluations for individual tasks. STEM Z-contrast. This module allows for the quantitative composition and/or thickness mapping based on (High-resolution, HR-) STEM images either on the atomic lattice or on a regular user-defined grid. To this end, STEM intensities extracted from a Voronoi segmentation are compared with simulations to be loaded as reference data [Ultram. 109, 1171 (2009)]. For complex unit cells, the comparison can be distinguished with respect to an arbitrary number of sublattices for the different atomic sites, and intensities extracted from different images (e.g. bright & dark field acquired simultaneously) may be used simultaneously. High-resolution strain state analysis. HR(S)TEM images can be evaluated by detecting atomic column positions (intensity maxima or minima) or lattice fringes with subpixel accuracy, e.g., by parabolian or Gaussian fits. Various filtering options are available, namely a Wiener noise filter which preserves the contrast of the high-resolution image. The vector field of the displacement from a regular lattice, its projection along a given direction and the local strain can be calculated [Optik 102, 63 (1996)]. Strain analysis by nano-beam electron diffraction (SANBED). Series of parallel- or convergent-beam electron diffraction patterns (CBED) are evaluated as to the positions of the reflections using centre of gravity computation (spot pattern) as well as radial gradient maximisation, edge detection or cross correlation methods [Micr. Microanal. 18, 995 (2012)]. Typically these are 3D or 4D data sets, corresponding to the acquisition of diffraction patterns on a STEM scan line or area. Differential Phase Contrast (DPC). This module calculates the centre of gravity (average momentum [Nat. Comm. 5, 5653 (2014)]), the signals of a segmented quadrant detector, bright- and annular bright field signals from a 3D or 4D data set, i.e. ronchigrams recorded at each position of the STEM probe. Tools for angle calibration and calculating the charge density are also available. COM interface. ImageEval can communicate with the common object model (COM) of the Microscope and the acquisition software. This enables the efficient implementation of individual experimental procedures such as acquiring a STEM image series while automically changing imaging parameters subsequently (e.g. acceptance angles of the ADF detector). Basic Tools. Routinely needed tools such as cross-correlation of images to correct for relative shifts, (inverse) Fourier transform, line profiling, calculation of rotational average/sum, applying circular, annular or polygon masks, binning and image rotation are collected here. Further methods include the analysis of angle-resolved STEM data, composition evaluation by lattice fringe analysis (CELFA, [Ultram. 72, 121 (1998)]) exploiting chemically sensitive imaging, geometric phase analysis (GPA (Ultram. 74, 131 (1998)]), data reduction in spot diffraction patterns, parametric fits ("atom counting" [Nature 470, 374 (2011)]), and processing of simulation results from the STEMsim software [Spr. Proc. Phys. 120, 169 (2007)] . [1] K. M-C. was supported by the Deutsche Forschungsgemeinschaft (DFG) under contract No MU 3660/1-1.

     [bibtex-key = Mueller-Caspary2016e]



322. Knut Müller-Caspary, Andreas Oelsner, and Pavel Potapov. STEM Strain Measurement From a Stream of Diffraction Patterns Recorded on a Pixel-Free Delay-Line Detector. In Microscopy and Microanalysis 2016, Columbus (OH/USA), [Poster], July 24-28th 2016. Abstract:

     Recent progress in nano-beam electron diffraction (NBED), ptychography and differential phase contrast microscopy [1] is based on the acquisition of a four-dimensional data set I(xp,yp,x,y) with (xp,yp) the position of the STEM probe, (x,y) a coordinate in the recorded image/diffraction pattern and intensity I. Since the speed of conventional charge-coupled devices is limited, a major challenge is the development of fast detectors. Here we present pilot experiments with a delay-line detector (DLD, [2]) mounted on an FEI Titan facility. As illustrated in Fig.1 the top of the DLD consists of a microchannel plate (MCP) stack that causes a cascade of secondary electrons for each 300keV electron impinging on the detector. The heart of the DLD are 2 meandering wires shown in blue and red in which each cascade causes electrical pulses travelling towards the ends of the wires. Depending on the incident position of the electron a characteristic time delay between the arrivals of the 2 conjunct pulses at the ends of a wire is measured with high accuracy, giving the coordinate of incidence perpendicular to the meander. By crossing two such delay-lines the point (x,y) and time t of incidence can be detected. Thus the DLD allows for both the recording of a continuous stream of single electron events processed by a time-to-digital converter (TDC) with a time precision in the picosecond range and the in-situ integration of the signal over a certain frame time to obtain conventional images. Note that no pixel raster is involved here. The two modes of operation are illustrated in the right part of Fig. 1. To characterise the DLD, we determined the quantum efficiency (QE) as a function of the incident intensity as shown in Fig. 2. The QE takes values between 50% for 0.5x106 and 22% for 17x106 electrons/second for a homogeneous illumination of the detector. Moreover, the modulation transfer function was determined to 0.1 at Nyquist frequency. Finally, we present strain measurements. An example is shown in Fig. 3 for a GeSi/Si MOSFET for the [001] and [110] direction at a STEM raster of 100x100 pixels. In particular we observe 2 strain regimes inside the GeSi stressors owing to different Ge contents of 25% and 37%, as has been verified by quantitative STEM Z-contrast evaluations. In Fig.3a, strain εyy in [001] direction was measured from the position of the 004 reflection [3] whereas the 220 reflection was used for the lateral strain measurement of εxx in Fig.3b. In between the stressors, the gate channel exhibits compressive strain of up to 3% laterally and an expansion below 1% along [001]. Dwell times between 40 and 5ms have been used, corresponding to an acquisition of 10,000 diffraction patterns in 6.5 and 0.8min, respectively.

     [bibtex-key = Mueller-Caspary2016b]



323. Knut Müller-Caspary, Andreas Oelsner, Pavel Potapov, and Thomas Schmidt. Analysis of strain and composition in GeSi/Si heterostructures by electron microscopy. In European Microscopy Congress 2016, Lyon (F), [Talk MS03-OP239], 2016. Abstract:

     Electronic properties of GeSi/Si-based metal oxide semiconductor field effect transistors (MOSFETs) are strongly influenced by the geometry, composition and strain state of the Ge containing source/drain stressor regions and the Gate channel in between. In the first part of our contribution, we hence present quantitative STEM Z-contrast evaluations of the Ge composition in MOSFETs with different stressor geometries and verify the results with energy-dispersive analyses of X-rays (EDX) using the chemiSTEM system mounted on an FEI Titan facility. To evaluate the strain distribution within the gate channel and the stressors, we used nano-beam electron diffraction employing a delay-line detector (DLD, [1]) which enhances the acquisition speed for the 4-dimensional data set (diffraction patterns as a function of the STEM raster position) to 10ms/image. As illustrated in Fig.1 the top of the DLD consists of a microchannel plate (MCP) stack that causes a cascade of secondary electrons for each 300keV electron impinging on the detector. The heart of the DLD are 2 meandering wires shown in blue and red in which each cascade causes electrical pulses travelling towards the ends of the wires. Depending on the incident position of the electron a characteristic time delay between the arrivals of the 2 conjunct pulses at the ends of a wire is measured with high accuracy, giving the coordinate of incidence perpendicular to the meander. By crossing two such delay-lines the point (x,y) and time τ of incidence can be detected. Thus the DLD allows for both the recording of a continuous stream of single electron events processed by a time-to-digital converter (TDC) with a time precision in the picosecond range and the in-situ integration of the signal over a certain frame time to obtain conventional images. Note that no pixel raster is involved here. The two modes of operation are illustrated in the right part of Fig. 1. An example for a MOSFET exhibiting 2 Ge regimes of 22% and 37% within the stressors is shown in Fig. 2 for the strain measurement along the [001] direction and in Fig. 3 for a measurement along the [110] direction. Here a STEM raster of 100x100 pixels was used with a dwell time of 40ms. Figure 2 was obtained by evaluating the position of the 004 CBED disc using the radial gradient maximisation method [2] whereas the 220 reflection was measured to obtain Fig.3. Two strain regimes are observed inside the GeSi stressors due to the different regimes of Ge contents. The gate channel exhibits compressive strain of up to 3% laterally and an expansion below 1% along [001]. Concerning the influence of the acquisition speed on strain precision, recording 10,000 diffraction patterns took 6.5min here, yielding a strain precision of 0.12% in terms of the standard deviation determined in unstrained Si regions. The same experiment at twice the scan speed (dwell time of 20ms) yields the same average strain distributions, however, at the precision of 0.18%. In the second part, we report a systematic study on the epitaxy of GeSi on Si (111) as a function of growth temperature. In particular, temperatures of 400, 450 and 550°C have been used and the strains along [111] and [1-11] have been measured. Using elasticity theory, composition maps were derived from the strain results, yielding the three Ge profiles in Fig.4. Obviously growth at 400 and 450°C leads to islands of pure Ge whereas the Ge content drops to 60% if the temperature is raised to 550°C. We finally discuss our results with respect to Si/Ge interdiffusion which causes a gradual change of composition at the interface. [1] K. Müller-Caspary, A. Oelsner, P. Potapov, Applied Physics Letters 107 (2015), 072110. [2] K. Müller and A. Rosenauer et al., Microscopy and Microanalysis 18 (2012), 995. [3] Funding: Deutsche Forschungsgemeinschaft (DFG) under contract MU3660/1-1.

     [bibtex-key = Mueller-Caspary2016g]



324. K. Müller-Caspary, O. Oppermann, T. Grieb, A. Rosenauer, F. F. Krause, M. Schowalter, T. Mehrtens, P. Potapov, A. Beyer, and K. Volz. Angle-resolved scanning transmission electron microscopy employing an iris aperture (Poster). In Electron Microscopy and Analysis Group Annual Conference (EMAG 2016), Durham (UK), 2016. [bibtex-key = Mueller-Caspary2016h]



325. Knut Müller-Caspary, Oliver Oppermann, Tim Grieb, Andreas Rosenauer, Marco Schowalter, Florian F. Krause, Thorsten Mehrtens, Pavel Potapov, Andreas Beyer, and Kerstin Volz. Angle-resolved Scanning Transmission Electron Microscopy (ARSTEM) for materials analysis. In European Microscopy Congress 2016, Lyon (F), [Poster IM06-350], 2016. Abstract:

     Many solid-state properties leave characteristic fingerprints in the angular dependence of electron scattering. STEM is dedicated to probe scattered intensity at atomic resolution, but it drastically lacks angular resolution due to detectors integrating over broad solid angles. By developing a setup which is capable of recording STEM images for dedicated acceptance angles of annular detectors, we firstly report the simultaneous measurement of specimen thickness, chemical composition and strain in a GaNxAs1-x/GaAs layer at atomic resolution. Our analysis exploits two angle ranges, namely A: 42-66 and B: 82-141mrad which exhibit different dependencies on nitrogen content x and specimen thickness as shown by the simulation in Fig.1a. To acquire images for dedicated angle settings, we developed a motorised, software-controlled iris aperture (Fig.2a) mounted above the Fischione 3000 ring detector in a Titan 80/300 (S)TEM, which is used to control the outer acceptance angle of the detector as depicted by the detector scans in the inset. Consequently, a STEM image formed by electrons scattered to the angular interval [α,β] is obtained by the difference I(β)-I(α) between 2 images taken at iris radii α and β. For GaNAs, we recorded four 2Kx2K high-resolution STEM (HRSTEM) images with iris radii 42, 66, 82 and 141 mrad, performed a Voronoi segmentation with respect to atomic columns and averaged the intensity within the Voronoi cells. By mapping the Voronoi intensity with respect to their cell index and correlating the images, specimen drift was compensated for. Subtracting respective images yields the data in Fig.1b,c for the desired angular ranges. The GaNAs layer is imaged with high contrast for the angular range of 42-66 mrad whereas it is invisible for a detector acceptance of 82-141 mrad. By simultaneously comparing Fig.1b,c with simulations [1], the local nitrogen content and specimen thickness were obtained as shown in Fig.1d,e. Hence our method overcomes the common problem to interpolate thickness from regions with known composition. Finally, profiles across the GaNAs layer (not shown) reveal an average N content of x=2.5% and a mean thickness of 186nm. The nitrogen content is verified by X-ray studies and strain state analysis in one of the HRSTEM images. The total acquisition took 5:40min here whereas a 1kHz camera would have needed 70min to obtain this data. Secondly, we imaged a GexSi1-x/Si field effect transistor using a dense sampling of the scattering angles between 16 and 255 mrad at two specimen thicknesses of 50 and 150 nm. Two different camera lengths with each 16 outer acceptance angles were used as shown in the radial sensitivity curves in Fig.2b, obtained by scanning the beam over the detector with iris aperture. Fig.2c exemplarily shows several images recorded at the larger camera length. The first image for the range [16,22 mrad] completely lacks chemical contrast in favour of strain-dominated intensity modulations in the vicinity of the Ge-containing source S and drain D stressors. Towards image 4 for [16,34 mrad] strain and the onset of Z-contrast determine the image contrast comparably, the latter caused by the 2 times larger atomic number of Ge compared to Si. In subsequent images Z-contrast dominates the signal revealing the two composition regimes of Ge with x=22% and x=37% which we determined using EDX with the chemiSTEM system. By subsequently subtracting the images we obtain the explicit angular dependence of scattered intensity for pure Si and the two Ge regimes in Fig.3a-c. Obviously the scattered intensity increases with both thickness and Ge content over the broad angle range covered here. Particular attention is to be drawn at the theoretical models included for comparison in Fig.3: δ denotes the exponent obtained for assuming the Rutherford model where intensity is proportional to Z^δ. The variety of δ values shows that there is no consistent trend as to a composition, thickness and angle-dependence, so that the Rutherford theory is inapplicable to our STEM data. Moreover, frozen-lattice multislice simulations for strain-relaxed (alloy) supercells are shown by the dashed lines. Although perfect agreement is found for angles above 35mrad, significant deviations are observed at smaller angles. This mismatch of contemporary simulations, which are fully elastic except for phonon scattering, is discussed in detail with respect to further inelastic scattering on the basis of the angular dependence measured from energy-filtered diffraction patterns. [1] Rosenauer and Schowalter: Springer Proceedings in Physics, Springer, 2007, 120, 169-172. [2] K. M.-C. is supported by the DFG under contract MU3660/1-1.

     [bibtex-key = Mueller-Caspary2016f]



326. A. Rosenauer, K. Müller-Caspary, M. Schowalter, T. Grieb, F. F. Krause, and T. Mehrtens. Analysis of composition and strain in semiconductor nanostructures by quantitative HAADF-STEM and imaging STEM. In PCSI 2016, Santa Barbara (US), 2016. [bibtex-key = Rosenauer2016_conf]



327. A. Rosenauer, K. Müller-Caspary, M. Schowalter, T. Grieb, F. F. Krause, T. Mehrtens, A. Beche, J. Verbeeck, V. Galioit, J. Zweck, Stefan Löffler, and Peter Schattschneider. Quantitative STEM - From composition to atomic electric fields (Invited Talk). In Electron Microscopy and Analysis Group Annual Conference (EMAG 2016), Durham (UK), 2016. [bibtex-key = Rosenauer2016]



328. Andreas Rosenauer, Knut Müller-Caspary, Marco Schowalter, Tim Grieb, Florian F. Krause, Thorsten Mehrtens, Armand Beche, Johan Verbeeck, Josef Zweck, Stefan Löffler, Peter Schattschneider, Marcus Müller, Peter Veit, Sebastian Metzner, Frank Bertram, Tilman Schimpke, Martin Strassburg, and Rafal Dunin-Borkowski. Quantitative STEM -- From composition to atomic electric fields [Invited Talk]. In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Rosenauer2016a]



329. Marco Schowalter, Beeke Geerken, Florian F. Krause, Tim Grieb, Knut Müller-Caspary, Christoph Mahr, Thorsten Mehrtens, Andreas Rosenauer, and Sandra Van Aert. Atom-counting in a non-probe corrected STEM (Poster). In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Schowalter2016a]



330. M. Schowalter, F. F. Krause, T. Grieb, K. Müller-Caspary, T. Mehrtens, and A. Rosenauer. Effects of instrument imperfections on quantitative scanning transmission electron Microscopy (Poster). In Electron Microscopy and Analysis Group Annual Conference (EMAG 2016), Durham (UK), 2016. [bibtex-key = Schowalter2016]



331. M. Schowalter, F. F. Krause, T. Grieb, K. Müller-Caspary, and T. Mehrtens A. Rosenauer. Effects of instrument imperfections on quantitative scanning transission electron microscopy. In PCSI 2016, Santa Barbara (US), 2016. [bibtex-key = Schowalter2016_conf]



332. Yi Wang, Dan Zhou, Wilfried Sigle, E. Suyolcu, Knut Müller-Caspary, Florian F. Krause, Andreas Rosenauer, and Peter A. van Aken. Precision and application of atom location in HAADF and ABF [Talk in IM05-II]. In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = Wang2016]



333. Dan Zhou, Knut Müller-Caspary, Wilfried Sigle, Florian F. Krause, Andreas Rosenauer, and Peter van Aken. Sample tilt effects on atom column position determination in ABF-STEM imaging. In Microscopy and Microanalysis Conference M&M 2016, Columbus (Ohio, USA), session A15.1, [Talk 19], July 24-28th 2016. Abstract:

     The determination of atom positions from atomically resolved transmission electron micrographs is fundamental for the analysis of crystal defects and strain. Annular bright-field (ABF) imaging in scanning transmission electron microscopy (STEM), has intrigued research interest in recent years due to its capability of direct visualisation of light elements, such as Li, N and O. The arrangement of light elements around heavy elements, such as the tilt of oxygen octahedra in complex oxides or the oxygen sub-lattice at complex-oxide hetero-interfaces, is accessible at the atomic-scale. To extract reliable atom positions directly from the images one has to assume that the maxima/minima positions in ABF images precisely correspond to the atom positions. In this work, we investigate the reliability of the atom column position determination in ABF-STEM imaging, with special emphasis on the influence of small specimen tilt from the zone axis. A glance of sample tilt effect on ABF/high-angle annular dark-field (HAADF) imaging is presented in Figure 1 which is the simulated results on cubic ZrO2. Small specimen tilt can occur by inaccurate tilting by the operator, but can also have intrinsic reasons such as in the case of static tilts of crystal planes or atom columns near crystal defects. Quantitative interpretation of both experimental HAADF and ABF images and simulation results reveals the complexity of the maxima/minima positions deviating from the supposed positions in HAADF/ABF images when a small amount of local sample tilt exists. The reasons leading to these results will be discussed with respect to basic imaging theory. Suggestions on how to improve the precision on the determination of the atom positions in ABF imaging will be proposed.

     [bibtex-key = Zhou2016a]



334. Karel H W van den Bos, Florian F. Krause, Armand Beche, Johan Verbeeck, Andreas Rosenauer, and Sandra Van Aert. Precise atomic column position measurements using ISTEM (Poster). In European Microscopy Congress 2016 (EMC 2016), Lyon (F), 2016. [bibtex-key = vandenBos2016]



335. Tim Grieb, Daniel Carvalho, Knut Müller-Caspary, Marco Schowalter, Christoph Mahr, Andreas Beyer, Andreas Hyra, T. Ben, F. M. Morales, R. Garcia, Kerstin Volz, B. Daudin, and Andreas Rosenauer. Quantitative nano-beam electron diffraction: Measuring strain and electric fields. In Microscopy Conference MC 2015, Göttingen (D), Session IM 2 [Talk], September 6-11th 2015. [bibtex-key = Grieb2015]



336. H.K. Grossmann, S. Schopf, T. Grieb, W. Li, A. Kuc, T. Heini, and L. Mädler. Flame made mixed metal oxide catalyst systems for the photo induced water splitting process. In Solar Fuels 2015, Uppsala (SE), 2015. [bibtex-key = Grossmann2015]



337. Florian F. Krause, Jan-Philipp Ahl, Darius Tytko, Pyuck-Pa Choi, Ricardo Egoavil, Marco Schowalter, Thorsten Mehrtens, Knut Müller-Caspary, Johan Verbeeck, Dierk Raabe, Joachim Hertkorn, Karl Engl, and Andreas Rosenauer. Homogeneity and Composition of MOVPE-Grown AlInGaN: A Nanostructure Multiprobe Study (Poster). In Proceedings of the Microscopy Conference 2015 (MC 2015), Göttingen (D), September 6-11th 2015. [bibtex-key = Krause2015e]



338. F F Krause, A Rosenauer, Müller K., M Schowalter, and T Mehrtens. Imaging STEM: A novel method for microscopy of semiconductors at ultra-high spatial resolution and precision (Talk). In Proceedings of Microscopy of Semiconducting Materials 2015 (MSM XIX), Cambridge (UK), volume Session 4b (Wed, April 1st), 2015. [bibtex-key = Krause2015c]



339. Florian Fritz Krause, Andreas Rosenauer, Knut Müller-Caspary, Marco Schowalter, and Thorsten Mehrtens. Conventional Transmission Electron Microscopy Imaging beyond the Diffraction and Information Limits. In Frontiers of Electron Microscopy in Materials Science (FEMMS) 2015, Lake Tahoe (CA/USA), [Invited Talk], September 13-18th 2015. Abstract:

     There are mainly two complementary imaging modes in transmission electron microscopy (TEM): Conventional TEM (CTEM) and scanning TEM (STEM). In the CTEM mode the specimen is illuminated with a plane electron wave, and the direct image formed by the objective lens is recorded in the image plane. STEM is based on scanning the specimen surface with a focused electron beam and collecting scattered electrons with an extended disk or ring-shaped detector. In our contribution we introduce ISTEM (imaging STEM), a new TEM imaging mode [1] which combines STEM illumination with CTEM imaging. We use a CCD camera to acquire images formed with the focused electron beam scanning over the specimen. As the acquisition time of the CCD camera is equal to the area scan time, the images corresponding to all the probe positions are summed up. The wave functions for different electron beam positions occur at different times, so that they cannot interfere and corresponding images are summed up incoherently. Thus, ISTEM exploits an improvement in resolution obtained by switching the spatially coherent illumination to highly incoherent illumination. The gain in resolution can easily be understood for the case of a completely incoherent illumination where the transfer function is given by the autocorrelation of the coherent transfer function, whereby the maximum spatial frequency transferred by the system is increased. In our contribution we will present a simulation study showing that ISTEM generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. We will also reveal by image simulation that this new TEM mode is more robust against chromatic aberration, which allows overcoming the conventional information limit of a microscope. These calculations are confirmed by experimental data for GaN along the [1-100] and [11-20] directions taken on our TITAN 80/300 microscope with a conventional information limit of 80 pm, where we resolved Ga and N columns at a distance of 63 pm. Thus, ISTEM combines advantages of STEM imaging such as improved point resolution with advantages of the CTEM imaging mode while avoiding disadvantages of STEM. In STEM, the precision for determining atom column positions is limited by scan noise which is caused by errors in positioning the electron probe, and the resolution is influenced by the finite source size effect. In contrast, ISTEM images do neither suffer from scan noise nor is the image resolution influenced by the finite source size. Furthermore, we will show by theoretical considerations that ISTEM is independent of lens aberrations of the probe forming system, but only depends on the radius of the probe forming aperture. Due to the principle of reciprocity, ISTEM can be made equivalent to annular bright field STEM using a ring-shaped condenser aperture, promising ultra-high resolution imaging of light elements by avoiding scan noise and source size effect. References: [1] A. Rosenauer, F.F. Fritz et al., Phys. Rev. Lett. 113 (2014) 096101

     [bibtex-key = Krause2015b]



340. F. F. Krause, A. Rosenauer, M. Schowalter, K. Müller-Caspary, and T. Mehrtens. ISTEM: A novel incoherent imaging mode for ultra-high resolution beyond the classical information limit (Talk). In Proceedings of the Microscopy Conference 2015 (MC 2015), Göttingen (D), September 6-11th 2015. [bibtex-key = Krause2015a]



341. Florian F. Krause, M. Schowalter, J.P. Ahl, J. Hertkorn, R. Egoavil, d. Tytko, P. P. Choi, T. Mehrtens, K. Müller-Caspary, D. Raabe, J. Verbeeck, K. Engl, and A. Rosenauer. Homogeneity and composition of MOVPE grown AlInGaN: a multiprobe nanostructure study. In Proceedings of Microscopy of Semiconducting Materials 2015 (MSM XIX), Cambridge (UK), 2015. [bibtex-key = Krause2015]



342. A. Krisch, M. M. Murshed, M. Schowalter, P. Gaczynski, K.-D. Becker, and T.M. Gesing. Nanoparticle precursor into polycrystalline Be2Fe4O9: structural, morphological and optical properties. In Proceedings of the NDDK2015 conference (talk), 2015. [bibtex-key = Krisch2015]



343. Johannes Ledig, Tilman Schimpke, Gregor Scholz, Florian F. Krause, Andreas Rosenauer, Martin Strassburg, Hergo-Heinrich Wehmann, and Andreas Waag. Comparison of electroluminescence and IV characteristics along a GaN based core-shell LED taken by point contacts inside a CL-SEM (Poster). In Proceedings of the Microscopy Conference 2015 (MC 2015), Göttingen (D), 2015. [bibtex-key = Ledig2015]



344. Christoph Mahr, Knut Müller, Marco Schowalter, Thorsten Mehrtens, Tim Grieb, Florian F. Krause, Daniel Erben, and Andreas Rosenauer. Analysis and improvement of precision and accuracy of strain measurements by convergent nano-beam electron diffraction (SANBED). In Microscopy of Semiconducting Materials 2015 (MSM XIX), Cambridge (UK) [Talk], volume Session 3b, Tue, March 31st, 2015. Abstract:

     The measurement of lattice strain is an important aspect in the characterisation of semiconductor nanostructures. As strain has large influence on the electronic band structure, methods for strain measurements with high precision, accuracy and spatial resolution are mandatory. In this contribution we present a study of precision and accuracy of the SANBED method proposed by M{\"u}ller et al. [1]. With this method we measure strain from distances between diffraction discs in convergent beam electron diffraction (CBED) patterns. As these distances depend on the local lattice parameters, according to Bragg’s law information about strain can be achieved simply by comparing the disc distances at different positions of the scanning electron probe. Rouviere et al. [2] demonstrated that using a precessing electron beam the precision of strain measurements from CBED patterns can reach 2x10-4 [2]. We show that this precision is also reached by our method. Nevertheless close to interfaces between parts of the specimen with different strain, the accuracy suffers from an effect that occurs in the recorded CBED patterns: In the scanning mode of a transmission electron microscope the incident electron wave can approximately be described as the Fourier transform of the condenser aperture. As a consequence the electron beam is not only focussed in one point and high spatial frequencies of the Fourier transformed aperture can pass through parts of the specimen with different strain, affecting the appearance of diffraction discs in the CBED patterns. In our contribution the influence of this effect on the accuracy of strain measurements will be discussed for the first time by evaluation of simulations. Furthermore we show how this interface effect can be minimised. [1] K. M{\"u}ller and A. Rosenauer et al., Microsc. Microanal. 18 (2012), p. 995. [2] J.-L. Rouviere et al., Appl. Phys. Lett. 103 (2013), p. 241913.

     [bibtex-key = Mahr2015b]



345. Christoph Mahr, Knut Müller-Caspary, Tim Grieb, Thorsten Mehrtens, Marco Schowalter, Florian F. Krause, Dennis Zillmann, and Andreas Rosenauer. Theoretical study of precision and accuracy of strain analysis by nano-beam electron diffraction (SANBED). In Microscopy Conference MC 2015, Göttingen (D), session MS 2, [Poster MS2.P023], September 6-11th 2015. [bibtex-key = Mahr2015a]



346. Thorsten Mehrtens, Marco Schowalter, Jakob Borchardt, Max Grimme, Knut Müller-Caspary, Lars Hoffmann, H. Jönen, U. Rossow, A. Hangleiter, and Andreas Rosenauer. Temperature dependence of HAADF intensity: Influence of disorder. In Microscopy Conference MC 2015, Göttingen (D), session IM 2, [Poster IM2.P049], September 6-11th 2015. [bibtex-key = Mehrtens2015]



347. Knut Müller, Florian F. Krause, Armand Béché, Marco Schowalter, Vincent Galioit, Stefan Löffler, Johan Verbeeck, Josef Zweck, Peter Schattschneider, and Andreas Rosenauer. A quantum mechanical approach to electron picodiffraction reveals atomic electric fields. In Materials Research Society Spring Meeting 2015 (MRS 2015), San Francisco (USA) [Talk], volume Symposium ZZ, Talk 2.02, 2015. Abstract:

     Contemporary aberration-corrected scanning transmission electron microscopy (STEM) enables to probe material properties at a resolution of 80pm and below. However, mapping of atomic electric fields in nanoelectronics remains a challenge. Progress in this field relies on the differential phase contrast (DPC) technique which uses segmented detectors to detect the field-induced angular deflection of the STEM beam via a shift of the central part of the diffraction pattern (the 'ronchigram'), causing a characteristic asymmetry in opposite segments (Nature Phys. 8, 611 (2012); Ultramicroscopy 2, 251 (1977)). The established interpretation of DPC relies on the assumptions that the ronchigram is homogeneously filled and shifted as a whole. First we focus on the validity of these assumptions. In simulation and experiment we show that ronchigrams neither exhibit homogeneous intensity even for thinnest specimens (1-5nm), nor are they shifted as a whole. Contrary, the effect of electric fields is a complex redistribution of intensity inside the ronchigram which needs to be captured by pixelated detectors such as CCD cameras. Second, we present a simple but stringent quantum mechanical interpretation: In recording the 2D intensity distribution in the diffraction pattern, we detect the squared modulus of the specimen exit wave function in momentum space. Hence the intensity I(px,py) in a certain pixel of the CCD is proportional to the probability that the corresponding momentum (px,py) is observed. Thus the centre-of gravity-type summation =∫ I(px,py) dpxdpy yields the expectation value for the momentum, independently of the complexity of the diffraction pattern. We demonstrate how the momentum transfer can be related to the electric field convolved with the intensity of the STEM probe in thin specimens. In exploiting Maxwell's equations, we show how our method can pave the way to mapping charge and electron densities. Third, we present case studies for GaN and SrTiO3 to demonstrate the applicability of this concept. In a simulation study for GaN a set of 80x80 ronchigrams (corresponding to the raster of the STEM probe) has been simulated using the multislice method. These data allow for determining , the electric field, charge- and electron density, and for a comparison with the density functional theory based counterparts. In an experimental study of SrTiO3, a unit cell was rastered with an aberration-corrected STEM probe at 20x20 pixels, and ronchigrams have been recorded for each raster position. Using this 4D data set, we demonstrate the experimental applicability of our method by quantitatively determining both momentum transfer and electric field within the SrTiO3 unit cell. By calculating the divergence of the electric field, we furthermore show the ability to image light atoms such as O, while mapping charge densities is currently hindered by experimental constraints such as scan noise.

     [bibtex-key = Mueller2015b]



348. Knut Müller, Florian F. Krause, Armand Béché, Marco Schowalter, Vincent Galioit, Stefan Löffler, Johan Verbeeck, Josef Zweck, Peter Schattschneider, and Andreas Rosenauer. Quantum mechanical interpretation of electron picodiffraction reveals atomic electric fields. In Microscopy of Semiconducting Materials 2015 (MSM XIX), Cambridge (UK) [Talk], volume Session 4b (Wed, April 1st), 2015. Abstract:

     A prominent scanning TEM (STEM) technique for studying atomic-scale electric fields is differential phase contrast (DPC) microscopy. Conventionally, segmented ring detectors are utilised to record portions of the ronchigram [1], which is assumed to be homogeneously filled and shifted as a whole in presence of electric fields in the specimen. We firstly investigate the reliability of these assumptions by showing that electron ronchigrams exhibit rich intensity variations already for thinnest specimens (1-2nm), and that the dominant effect of atomic electric fields on aberration-corrected probes is a complex redistribution of intensity inside ronchigrams. This explains why segmented DPC detectors yield high contrast at atomic sites whereby a quantification of electric fields in terms of ronchigram shifts is prone to errors. Then we give a quantum mechanical interpretation of DPC: The ronchigram is recorded in the diffraction plane, showing the Fourier transform of the specimen exit wave. According the axioms of quantum mechanics, the local ronchigram intensity I(p) is thus proportional to the probability for the lateral momentum vector p to occur. Hence the expectation value for the momentum is calculated by a centre-of-gravity-type summation, relating the rich details of the ronchigram to a single vector with fundamental physical meaning in a direct and simple manner. To put this into practice, we use a pixelated detector in experiment. Finally Ehrenfest's theorem is applied to relate the electric field to the momentum transfer via a proportionality factor. In a comprehensive simulation study of GaN, we demonstrate the capability of our method by calculating momentum transfer, electric field and charge-/electron densities from simulated ronchigrams. We then prove the experimental applicability by mapping the electric field in an SrTiO3 unit cell quantitatively and verify these results by simulations [2]. [1] Shibata et al., Nat.Phys. 8, p611 (2012) [2] M{\"u}ller et al., Nat.Comm. 5, p5653, (2014)

     [bibtex-key = Mueller2015c]



349. M. Müller, S. Metzner, T. Hempel, P. Veit, F. Bertram, F. F. Krause, T. Mehrtens, K. Müller-Caspary, A. Rosenauer, T. Schimpke, M. Strassburg, and J. Christen. Nanoscale Characterization of InGaN/GaN core-shell microrods: Correlation of the optical properties and the composition of the InGaN single quantum well (Talk). In Proceedings of the International Conference on Nitride Semiconductors 2015 (ICNS 11), Peking (CHN), 2015. [bibtex-key = Mueller2015]



350. Knut Müller, Andreas Oelsner, Andreas Rosenauer, and Pavel Potapov. STEM strain measurement from a stream of diffraction patterns recorded on a pixel-free delay-line detector. In Microscopy of Semiconducting Materials 2015 (MSM XIX), Cambridge (UK) [Poster], volume Poster Session 2, Poster P 2.5 (Tue, March 31st), 2015. Abstract:

     Recent progress in nano-beam electron diffraction (NBED), ptychography or differential phase contrast microscopy is based on the acquisition of a four-dimensional data set I(x,y,p,q) with (x,y) the position of the STEM probe, (p,q) a coordinate in the diffraction pattern and intensity I. Since the speed of conventional charge-coupled devices is limited, a major challenge is the development of fast detectors. Here we present pilot experiments with a delay-line detector (DLD) mounted on an FEI Titan facility. The top of the DLD consists of a microchannel plate (MCP) stack that causes a cascade of secondary electrons for each 300keV electron impinging on the detector. The heart of the DLD is a meandering wire in which each cascade causes electrical pulses travelling towards the end of the wire. Depending on the incident position of the electron a characteristic time delay between the arrivals of the 2 conjunct pulses at the wire ends is measured with high accuracy, giving the coordinate of incidence perpendicular to the meander. By crossing two such delay-lines coupled to a time-to-digital converter the incident point (p,q) and time is measured for each detected electron, with a time precision in the picosecond range. To characterise the DLD, we determined the quantum efficiency as a function of the incident intensity to be between 50\% for 0.5x10^6 and 22\% for 17x10^6 electrons/second for a homogeneous illumination of the detector. Moreover, the modulation transfer function was determined to 0.1 at Nyquist frequency. Finally, we present strain measurements in a GeSi/Si MOSFET for the [001] and [110] direction at a STEM raster of 100x100 pixels by recording the 004 and 220 CBED discs on the DLD. Dwell times between 40 and 5ms have been used, corresponding to an acquisition of 10,000 diffraction patterns in 6.5 and 0.8min, respectively.

     [bibtex-key = Mueller2015a]



351. K. Müller-Caspary, F. F. Krause, A. Béché, M. Schowalter, V. Galioit, S. L[öffler, J. Verbeeck, J. Zweck, P. Schattschneider, and A. Rosenauer. Quantum mechanical interpretation of electron picodiffraction reveals atomic electric fields. In Microscopy Conference MC 2015, Göttingen (D), session IM 5, [Talk], September 6-11th 2015. [bibtex-key = Mueller-Caspary2015c]



352. Knut Müller-Caspary, Florian F. Krause, Armand Béché, Marco Schowalter, Vincent Galioit, Stefan Löffler, Oliver Oppermann, Tim Grieb, Andreas Oelsner, Pavel Potapov, Johan Verbeeck, Josef Zweck, Peter Schattschneider, and Andreas Rosenauer. Quantum mechanical interpretation of electron picodiffraction reveals atomic electric fields. In Frontiers of Electron Microscopy in Materials Science (FEMMS) 2015, Lake Tahoe (CA/USA), [Invited Talk], September 13-18th 2015. Abstract:

     A prominent scanning TEM (STEM) technique for studying atomic-scale electric fields is differential phase contrast (DPC) microscopy. Conventionally, segmented ring detectors are utilised to record portions of the ronchigram [1], which is assumed to be homogeneously filled and shifted as a whole in presence of electric fields in the specimen. We investigate the reliability of these assumptions by showing that electron ronchigrams exhibit rich intensity variations already for thinnest specimens (1-2nm), and that the dominant effect of atomic electric fields on aberration-corrected probes is a complex redistribution of intensity inside ronchigrams. This explains why segmented DPC detectors yield high contrast at atomic sites whereby a quantification of electric fields in terms of ronchigram shifts is prone to errors. Then we give a quantum mechanical interpretation of DPC: The ronchigram is recorded in the diffraction plane, showing the Fourier transform of the specimen exit wave. According the axioms of quantum mechanics, the local ronchigram intensity I(p) is thus proportional to the probability for the lateral momentum vector p to occur. Hence the expectation value for the momentum is calculated by a centre-of-gravity-type summation, relating the rich details of the ronchigram to a single vector with fundamental physical meaning in a direct and simple manner. To put this into practice, we use a pixelated detector in experiment. Theoretically Ehrenfest's theorem is applied to relate the electric field to the momentum transfer via a proportionality factor. In a comprehensive simulation study of GaN, we demonstrate the capability of our method by calculating momentum transfer, electric field and charge-/electron densities from simulated ronchigrams. We then prove the experimental applicability by mapping the electric field in an SrTiO3 unit cell quantitatively and verify these results by simulations [2]. This contribution finally addresses practical aspects of multidimensional STEM, especially ultrafast data acquisition employing, e.g., delay-line detectors as well as the current state of momentum-resolved STEM beyond electric field mapping. References: [1] Shibata et al., Nat.Phys. 8, 611 (2012). [2] M{\"u}ller et al., Nat.Comm. 5, 5653, (2014).

     [bibtex-key = Mueller-Caspary2015b]



353. K. Müller-Caspary, Andreas Oelsner, Andreas Rosenauer, and Pavel Potapov. STEM strain measurement from a stream of diffraction patterns recorded on a pixel-free delay-line detector. In Microscopy Conference MC 2015, Göttingen (D), session IM 1, [Poster IM1.P029], September 6-11th 2015. [bibtex-key = Mueller-Caspary2015]



354. Andreas Rosenauer, Florian F. Krause, Knut Müller, Marco Schowalter, and Thorsten Mehrtens. Conventional Transmission Electron Microscopy Imaging beyond the Diffraction and Information Limits. In Materials Research Society Spring Meeting 2015 (MRS 2015), San Francisco (USA) [Talk], volume Symposium ZZ, Talk 2.02, 2015. Abstract:

     There are mainly two complementary imaging modes in transmission electron microscopy (TEM): Conventional TEM (CTEM) and scanning TEM (STEM). In the CTEM mode the specimen is illuminated with a plane electron wave, and the direct image formed by the objective lens is recorded in the image plane. STEM is based on scanning the specimen surface with a focused electron beam and collecting scattered electrons with an extended disk or ring-shaped detector. In our contribution we introduce ISTEM (imaging STEM), a new TEM imaging mode [Phys. Rev. Lett. 113 (2014) 096101] which combines STEM illumination with CTEM imaging. We use a CCD camera to acquire images formed with the focused electron beam scanning over the specimen. As the acquisition time of the CCD-camera is equal to the area scan time, the images corresponding to all the probe positions are summed up. The wave functions for different electron beam positions occur at different times, so that they cannot interfere and corresponding images are summed up incoherently. Thus, ISTEM exploits an improvement in resolution obtained by switching the spatially coherent illumination to highly incoherent illumination. The gain in resolution can easily be understood for the case of a completely incoherent illumination where the transfer function is given by the autocorrelation of the coherent transfer function, whereby the maximum spatial frequency transferred by the system is increased by a factor of two. In our contribution we will present a simulation study showing that ISTEM generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. We will also reveal by image simulation that this new TEM mode is more robust against chromatic aberration, which allows overcoming the conventional information limit of a microscope. These calculations are confirmed by experimental data for GaN along the [1-100] and [11-20] directions taken on our TITAN 80/300 microscope with a conventional information limit of 80 pm, where we resolved Ga and N columns at a distance of 63 pm. Thus, ISTEM combines advantages of STEM imaging such as improved point resolution with advantages of the CTEM imaging mode while avoiding disadvantages of STEM. In STEM, the precision for determining atom column positions is limited by scan noise which is caused by errors in positioning the electron probe, and the resolution is influenced by the finite source size effect. In contrast, ISTEM images do neither suffer from scan noise nor is the image resolution influenced by the finite source size. Furthermore, we will show by theoretical considerations that ISTEM is independent of lens aberrations of the probe forming system, but only depends on the radius of the probe forming aperture. Due to the principle of reciprocity, ISTEM can be made equivalent to annular bright field STEM using a ring-shaped condenser aperture, promising ultrahigh resolution imaging of light elements by avoiding scan noise and source size effect.

     [bibtex-key = Rosenauer2015b]



355. A. Rosenauer, K. Müller-Caspary, M. Schowalter, T. Grieb, F. F. Krause, and T. Mehrtens. Analysis of composition and strain in semiconductor nanostructures by quantitative STEM using HAADF intensity, angular multi-range analysis and imaging STEM. In Microscopy Conference MC 2015, Göttingen (D), Session MS 2 [Invited Talk], September 6-11th 2015. [bibtex-key = Rosenauer2015]



356. A. Rosenauer, K. Müller-Caspary, M. Schowalter, T. Grieb, F.F. Krause, T. Mehrtens, A. Béché, J. Verbeeck, V. Galioit, J. Zweck, Stefan Löffler, and Peter Schattschneider. Quantitative STEM. In Proceedings of the International Workshop on Advanced and In-situ Microscopies of Functional Nanomaterials and Devices 2015 (IAMNANO 2015) [Invited Talk], Hamburg (D), 2015. [bibtex-key = Rosenauer2015a]



357. H. Ryll, M. Simson, C. Boothroyd, R. E. Dunin-Borkowski, C. Dwyer, R. Hartmann, M. Huth, s. Ihle, V. Migunov, K. Müller-Caspary, A. Rosenauer, J. Schmidt, H. Soltau, and L. Strüder. The wave-particle duality of electrons demonstrated with sub-pixel resolution by recording off-axis electron holograms on a pnCCD direct detector. In Microscopy Conference MC 2015, Göttingen (D), Session IM 1 [Invited Talk], September 6-11th 2015. [bibtex-key = Ryll2015]



358. Marco Schowalter, Florian F. Krause, Tim Grieb, Knut Müller-Caspary, Thorsten Mehrtens, and Andreas Rosenauer. Effects of Instrument Imperfections on Quantitative Scanning Transmission Electron Microscopy (Poster. In Proceedings of the Microscopy Conference 2015 (MC 2015), Göttingen (D), September 6-11th 2015. [bibtex-key = Schowalter2015b]



359. Marco Schowalter, Florian F. Krause, Tim Grieb, Knut Müller-Caspary, Thorsten Mehrtens, and Andreas Rosenauer. Investigation of detector characteristics for quantification of HAADF-STEM images (Poster). In Proceedings of Microscopy of Semiconducting Materials 2015 (MSM XIX), Cambridge (UK), 2015. [bibtex-key = Schowalter2015a]



360. M. Schowalter, A. Rosenauer, K. Müller-Caspary, T. Grieb, and T. Mehrtens. Quantitative STEM. In EAgLE workshop on high-resolution transmission electron microscopy - from sample preparation to interpretation, 21.-25. September 2015, Warsaw, Poland (invited talk), 2015. [bibtex-key = Schowalter2015]



361. M. C. Sequeira, M. B. Lourenco, A. Redondo-Cubero, N. Franco, E. Alves, M. Sousa, T. C. Esteves, J. Rodrigues, N. Ben Sedrine, M. J. Soares, A. J. Neves, M. R. Correia, T. Monteiro, P. R. Edwards, K. P. O'Donnell, M. Bockowski, C. Wetzel, D. Carvalho, T. Ben, F.M. Morales, R. Garcia, T. Grieb, A. Rosenauer, P. Kluth, and K. Lorenz. Quantum Well Intermixing in InGaN/GaN Structures. In ICDS 2015, Espoo (FI), 2015. [bibtex-key = Sequeira2015_conf]



362. M. Simson, H. Banba, R. Hartmann, M. Huth, S. Ihle, L. Jones, Y. Kondo, K. Müller, P. D. Nellist, H. Ryll, R. Sagawa2, J. Schmidt, H. Soltau, L. Strüder, and H. Yang. 4D-STEM imaging with the pnCCD (S)TEM-Camera. In Microscopy and Microanalysis (M&M, Portland, USA) [Talk], 2015. [bibtex-key = Simson2015b]



363. M. Simson, R. E. Dunin-Borkowski, C. Dwyer, R. Hartmann, M. Huth, S. Ihle, P. Kotula, V. Migunov, K. Müller-Caspary, A. Rosenauer, H. Ryll, J. Schmidt, H. Soltau, L. Strüder, and M. Wollgarten. The pnCCD (S)TEM Camera - A Pixelated, Fast and Direct Detector for TEM and STEM. In PICO conference 2015: Frontiers of aberration-corrected electron microscopy, Kasteel Vaalsbroek (The Netherlands) [Poster], 2015. [bibtex-key = Simson2015a]



364. Martin Simson, Henning Ryll, R. Hartmann, Martin Huth, Sebastian Ihle, Lewis Jones, Y. Kondo, Knut Müller, Peter D. Nellist, R. Sagawa, J. Schmidt, Heike Soltau, Lothar Strder, and Hao Yang. Fast STEM imaging with the pixelated pnCCD (S)TEM-camera. In Microscopy Conference MC 2015, Göttingen (D), session IM 1, [Poster IM1.P012], September 6-11th 2015. [bibtex-key = Simson2015]



365. M. Teck, H. K. Grossmann, T. Grieb, T. Hartmann, L. M�dler, and Th. M Gesing. PDF-refinement of crystalline & nanocrystalline Bi2WO6. In DGK 2015, G�ttingen (DE), 2015. [bibtex-key = Teck2015_conf]



366. Dan Zhou, Knut Müller-Caspary, Wilfried Sigle, Florian F. Krause, Andreas Rosenauer, and Peter van Aken. Effects of small sample tilt on atomic column position determination in ABF-STEM imaging. In Microscopy Conference MC 2015, Göttingen (D), session IM 2, [Poster IM2.P055], September 6-11th 2015. [bibtex-key = Zhou2015]



367. Josef Zweck, Knut Müller, Florian F. Krause, Armand Béché, Marco Schowalter, Vincent Galioit, Stefan Löffler, Johan Verbeeck, Peter Schattschneider, and Andreas Rosenauer. Exploring the space between atoms: Interatomic electric fields imaged by STEM-DPC. In Multinational Congress on Microscopy (MCM) 2015, Eger (Hungary) [Invited talk], 2015. Abstract:

     Traditionally, differential phase contrast is a technique which measures the deflection of the electron probe by intrinsic electric or magnetic fields, using a position sensitive detector, most commonly a four quadrant detector. For homogeneous fields, the recorded beam shift may be directly converted to a local field value within the specimen, provided that the specimen's thickness is known. Recently, it has been shown [1], that the traditional approach can be refined for the case of very thin (2-3 nm) specimens using an aberration-corrected scanning transmission microscope (STEM), where the electron probe can be focussed to a diameter of 70 pm, and a position sensitive ("pixelated") detector. Then, two important modifications have to be taken into account. Firstly, when the beam probes the specimen, it remains no longer a mere homogeneously bright zero order beam disk, as it is required for traditional DPC imaging. Instead, the beam's intensity distribution forms a focussed spot on the specimen, illuminating not only the central area but also the surrounding atomic sites, giving rise to a complicated diffraction pattern. Secondly, it has been shown that - again in contrast to traditional DPC imaging - the beam disk does not shift, but changes its inner structure along with the beam's position when moved on a 70 pm length scale. So the task is now to interpret the intensity patterns within the diffraction disk (see Fig. 1 a) to gain information on the electric fields probed by the beam, causing the diffraction pattern. This obviously implies the use of a multi-segmented detector, in our case a CCD camera. From the diffraction pattern we obtain the averaged lateral momentum (Fig. 1 b) transferred to the electrons passing through the specimen as described in [1] which is used to derive a local electric field distribution (Fig. 1 c) and (using Gau{\ss}'s law) the charge distribution. This greatly enhances the visibility of light atoms, such as oxygen in SrTiO 3, shown in Fig. 2. The work presented clearly shows the usefulness of DPC for (sub-)atomic scale imaging of not only the position of atoms but also the electrostatic fields and charge densities associated with the atoms. It also demonstrates the necessity to move towards a quantum mechanical interpretation of the diffraction patterns in STEM mode. This work was co-supported by grants from the European Research Council, the Hercules fund from the Flemish Government, the Deutsche Forschungsgemeinschaft (DFG) and the Austrian Science Fund (FWF).

     [bibtex-key = Zweck2015]



368. Jan-Philipp Ahl, Joachim Hertkorn, Anna Nirschl, Michael Benedikt, Bernhard Holländer, Florian F. Krause, Pyuck-Pa Choi, Dierk Raabe, and Andreas Rosenauer. On the possibility to use quaternary AlInGaN for polarization engineering (Talk). In Proceedings of the International Conference on Metalorganic Vapor Phase Epitaxy 2014 (ICMOVPE 17), Lausanne (CH), 2014. [bibtex-key = Ahl2014]



369. Manuel Dries, Simon Hettler, Björn Gamm, Erich Müller, Wilfried Send, Dagmar Gerthsen, Knut Müller, and Andreas Rosenauer. A Nanocrystalline Hilbert Phase Plate for Phase Contrast Transmission Electron Microscopy. In Microscopy and Microanalysis (M&M) 2014, Hartford (USA) [], 2014. [bibtex-key = Dries2014a]



370. T Grieb, Müller K., Mahr C., Cadel E., Beyer A., Talbot E., Schowalter M., Volz K., and Rosenauer A.. A Method to Analyse the Chemical Composition in (InGa)(NAs) based on Evaluation of HAADF Intensity in STEM. In 18th International Microscopy Congress (IMC) [Talk IT-2-O-2414], 2014. [bibtex-key = Grieb2014a]



371. H.K. Grossmann, T. Grieb, and L. Mädler. Tailor made multi-component oxide nanaoparticles produced by double flame spray pyrolysis and their application for photocatalytic water splitting. In ICONN 2014, Adelaine (AU), 2014. [bibtex-key = Grossmann2014_conf]



372. H.K. Grossmann, T. Grieb, and S. Schopf, Y.H. Ng, R. Amal, and L. Mädler. Flame made oxide heterojunctions for efficient charge separation in photocatalytic applications. In IPS conference 2014, Berlin (DE), 2014. [bibtex-key = Grossmann2014_confD]



373. H.K. Grossmann, T. Grieb, and S. Schopf, Y.H. Ng, R. Amal, and L. Mädler. Flame made oxide heterojunctions for photocatalytic water splitting. In ProcessNet Jahrestagung (2014), Aachen (DE), 2014. [bibtex-key = Grossmann2014_confB]



374. H.K. Grossmann, A. Gröhn, T. Grieb, F. Meierhofer, U. Fritsching, K. Wegner, and L. Mädler. Size and composite controlled synthesis of multi oxide nanoparticles using double flame spray pyrolysis. In ProcessNet Jahrestagung (2014), Aachen (DE), 2014. [bibtex-key = Grossmann2014_confC]



375. H. Kauko, T. Grieb, A. M. Munshi, K. Mller, A. Rosenauer, B. O. Fimland, and A. T. J. van Helvoort. The Outward Diffusion of Sb during Nanowire Growth Studied by Quantitative High-Angle Annular Dark Field Scanning Transmission Electron Microscopy. In Nanowires 2014, Eindhoven (NL), volume 20, pages 186--187, 8 2014. [bibtex-key = Kauko2014_conf]



376. F. F. Krause, Müller K., D. Zillmann, J. Jansen, M. Schowalter, and A. Rosenauer. Comparison of intensity and absolute contrast of simulated and experimental high-resolution transmission electron microscopy images for different multislice simulation methods (Poster). In Proceedings of the 18th International Microscopy Congress (IMC), Prag (CZ), 2014. [bibtex-key = Krause2014]



377. M.B. Lourenco, A. Redondo-Cubero, N. Franco, E. Alves, M. Sousa, T.C. Esteves, J. Rodrigues, N. Ben Sedrine, M.J. Soares, A.J. Neves, M.R. Correia, T. Monteiro, P.R. Edwards, K.P. O'Donnell, M. Bockowski, C. Wetzel, D. Carvalho, T. Ben, F.M. Morales, R. Garcia, T. Grieb, A. Rosenauer, and K. Lorenz. High thermal stability of InGaN/GaN quantum wells. In Vacuum conference (2014), Aveiro (PT), 2014. [bibtex-key = Lourenco2014]



378. Christoph Mahr, Knut Müller, Daniel Erben, Marco Schowalter, Josef Zweck, Kerstin Volz, and Andreas Rosenauer. Strain Analysis by Nano-Beam Electron Diffraction (SANBED) in semiconductor nanostructures. In 18th International Microscopy Congress (IMC) [Poster IT-9-P-3029], 2014. Abstract:

     The measurement of lattice strain is an important aspect in the characterisation of semiconductor nanostructures. As strain has large influence e.g. on the mobility of charge carriers, methods for accurate strain measurement with high precision are mandatory. In the present work [1] we measure strain from the positions of diffraction discs in convergent-beam electron diffraction (CBED) patterns using dedicated algorithms. Large one- and two-dimensional series of CBED-patterns (~3000) in semiconductor nanostructures have been recorded at an FEI Titan facility in STEM mode. Contrary to parallel illumination in conventional Nano-beam electron diffraction (NBED), we show that focusing the beam with a semi-convergence of 2.6 mrad increases the spatial resolution drastically by a factor of 5 to be 0.5 - 0.7nm. We determined the precision of this method to be 0.07\%. The rich inner structure of CBED-discs causes a big challenge to recognize their positions accurately. In particular, three different algorithms have been developed: As shown in figure 1, the first algorithm detects edges around each disc and iteratively deselects erroneous edges by circle-fitting. In this way the fit converges to the disc boundary. A disadvantage of this parameter-free method is a long computation time. An improvement of speed by a factor of 15 is achieved with the Radial Gradient Maximisation method. This method positions two sets of rings around the initially estimated disc position, one set of rings with smaller radii than estimated and one with larger radii, as illustrated in figure 2. Disc position and radius are determined by maximising the difference between the integrated intensity on inner and outer rings. The third method is a cross-correlation with different masks. As it is nearly a factor of 100 faster than the edge detection algorithm it is capable for in-situ strain measurement during CBED pattern acquisition. The left part of figure 3 shows two different masks. Mask A assumes fully illuminated CBED-discs, whereas with mask B the inner structure of the diffraction discs has less influence on the result. The right part of figure 3 shows the change in the correlation function if the disc is shifted. The disc position can be determined from the shift between mask and experiment. We compare the precision of the three different algorithms among each other and with respect to former approaches [e.g. 2, 3]. Finally we show by application, that specimen cooling, zero-loss energy filtering and aberrations of the projection system only weakly affect the measured strain. [1] K. M{\"u}ller and A. Rosenauer et al., Microsc. Microanal. 18 (2012), p. 995. [2] F. Uesugi et al., Ultramicroscopy 111 (2011), p.995. [3] A. Béché et al., Appl. Phys. Lett. 95 (2009), p. 123114.

     [bibtex-key = Mahr2014]



379. Thorsten Mehrtens, Marco Schowalter, Darius Tytko, Pyuck-Pa Choi, Dierk Raabe, Lars Hoffmann, Holger Jönen, Uwe Rossow, Andreas Hangleiter, and Andreas Rosenauer. Temperature dependence of Z-contrast in InGaN. In 18th International Microscopy Congress (IMC), Prague (Czech Republic) [Poster presentation], 2014. [bibtex-key = Mehrtens2014]



380. Knut Müller, Henning Ryll, Ivan Ordavo, Sebastian Ihle, Martin Huth, Martin Simson, Josef Zweck, Kerstin Volz, Heike Soltau, Pavel Potapov, Lothar Strüder, Marco Schowalter, Christoph Mahr, Daniel Erben, and Andreas Rosenauer. Strain Analyisis by Nano-Beam Electron Diffraction using millisecond frames of a direct electron pnCCD detector. In 18th International Microscopy Congress (IMC) [Talk MS-8-O-3268], 2014. [bibtex-key = Mueller2014b]



381. Knut Müller, Henning Ryll, Ivan Ordavo, Sebastian Ihle, Martin Huth, Martin Simson, Josef Zweck, Kerstin Volz, Heike Soltau, Andreas Rosenauer, Pavel Potapov, Marco Schowalter, Lothar Strüder, Christoph Mahr, and Daniel Erben. Strain Analysis from Nano-beam Electron Diffraction Patterns Recorded on Direct Electron Charge-coupled Devices. In Microscience Microscopy Congress, MMC 2014, Manchester (UK), July, 2014 [invited talk PS3.1.4], 2014. Abstract:

     Central properties of crystalline specimen are closely connected with local lattice strain. We present a method to measure strain in crystalline specimen from series of electron diffraction patterns acquired by scanning transmission electron microscopy (STEM). 3 algorithms were developed to detect the positions of convergent-beam electron diffraction (CBED) discs which are converted to strain via Bragg's equation. With a spatial resolution of 0.5nm our method improves the performance of nano-beam electron diffraction (NBED) approximately by a factor of 5 [1] while still exhibiting a strain precision of 0.07\%. To allow for 2D strain mapping with high spatial sampling, we replaced the slow-scan CCD of the microscope by a direct electron pnCCD detector [2,3,4] with ultrafast (>1kHz) readout hardware. We demonstrate the application of strain analysis by NBED (SANBED) to semiconductor nanostructures, such as GaAs-based stacks of quantum layers and Si-based metal-oxide semiconductor field effect transistors (MOSFETs). Traditionally, SANBED experiments use parallel illumination [1] with 2.5nm being the current limit for spatial resolution. In contrast, we use a focused probe with a convergence angle of 2.5-3mrad to achieve probe diameters of 0.5nm. This requires robust algorithms to detect CBED discs exhibiting a rich interior intensity variations. The Selective Edge Detection (SE) algorithm uses Prewitt's edge detection and subsequently fits circles to edge pixels while erroneous edges are ruled out. The Radial Gradient Maximisation (RG) algorithm optimises the centre of a rotational average such that the intensity gradient near the disc border is maximum. Thirdly, Cross-Correlation (CC) can determine the position of a reflection by cross-correlation with ring-shaped masks. The difference between the 3 algorithms is the speed as RG and CC are 15x and 75x faster than SE, respectively. With a duration of 10ms per image, CC is suitable for in-situ strain evaluation [5]. The algorithms have been applied to a series of 800 CBED patterns recorded on a scan over the quantum layer stack shown in the Z-contrast image top left in Fig.1. The sequence of InxGa1-xNyAs1-y/GaAs layers with different compositions x and y exhibits a complex strain profile with alternating compressive and tensile strain, leading to the SANBED measurement in black. In this case, data was recorded on Gatan slow-scan CCD. All three algorithms, SE, RG and CC, yield the same strain profile within the respective precisions being σ=0.07-0.08\%, despite the fact that the inner CBED disc structure varied drastically. In practice, SANBED must be able to map strain at a scale of 100x100nm2 in 2D, e.g., in MOSFETs. With 0.5nm sampling, a series of 40,000 diffraction patterns must hence be recorded in a few minutes. Noise characteristics, detection quantum efficiency (DQE) and read-out speed of conventional CCDs lead to min. acquisition times of approximately 200ms per scan point. To increase acquisition speed, we used a prototype scintillator-free pnCCD camera operated at rates up to 1kHz. A series of 40,000 diffraction patterns can thus be acquired in less than one minute. The pnCCD detector is very radiation-hard as it had been developed for satellite missions originally. We first investigated the same layers as above at 200ms frame time. As depicted bottom left in Fig.1, the above profile and precision are reproduced. Using millisecond frames, we obtain the strain profile shown top right in Fig.1 which not only demonstrates that operation of the pnCCD is possible at 1kHz but also yields reliable data reflecting the former strain profile again. The precision of σ=0.1\% is slightly worse than before but tolerable for most applications [6]. Secondly, we recorded a series using the very weak 008 reflection being extremely sensitive to strain to exploit the high DQE of the pnCCD. The resulting strain profile bottom right in Fig.1 shows that precision can be nearly doubled this way up to σ=0.035\% [7]. First 2D maps for strain along [110] and [001] in a GeSi/Si MOSFET are shown in Fig.2. Here, CBED patterns were recorded on a Gatan CCD at a low sampling of 45x60 scan points with 200ms CCD frame time. Although the action of the GeSi stressors S/D on the Si below gate G can be measured (compression along [110], elongation along [001]), a higher sampling is desirable. We therefore scanned the MOSFET with 256x256=65536 scan points and recorded diffraction patterns on the pnCCD detector with 1kHz readout recently and will show the strain result at the conference.

     [bibtex-key = Mueller2014a]



382. Andreas Rosenauer, Knut Müller, Thorsten Mehrtens, Marco Schowalter, Timo Aschenbrenner, Carsten Kruse, Detlef Hommel, Lars Hoffmann, Andreas Hangleiter, Pyuck-Pa Choi, and Dierk Raabe. Measurement of the indium concentration in high-indium content InGaN layers by scanning transmission electron microscopy and atom probe tomography. In SPIE Photonics West OPTO, San Francisco (USA) [Invited Talk], 2014. Abstract:

     In this contribution we demonstrate measurement of indium concentration in InGaN by scanning transmission electron microscopy using a high angle annular dark field detector. It is based on comparison of experimental images with image simulation, for which we use the frozen lattice approximation. Results are compared with atom probe tomography using InGaN layers with high In concentration of approximately 30 \% as applied in green semiconductor laser diodes. The results of the STEM measurement are in excellent agreement with composition profiles obtained by atom probe tomography. As example of application we demonstrate existence of quantum dots in InGaN layers.

     [bibtex-key = Rosenauer2014]



383. Andreas Rosenauer, Knut Müller, Thorsten Mehrtens, Marco Schowalter, Moritz Tewes, Timo Aschenbrenner, Carsten Kruse, Detlef Hommel, Pyuck-Pa Choi, Dierk Raabe, and Pavel Potapov. Measurement of Composition with Quantitative STEM. In EMSI-2014, Delhi (India) [Invited Talk], 2014. [bibtex-key = Rosenauer2014a]



384. U. Rossow, L. Hoffmann, H. Bremers, R. Buss, F. Ketzer, T. Langer, T. Mehrtens, M. Schowalter, A. Rosenauer, and A. Hangleiter. Indium incorporation processes investigated by pulsed and continuous growth of ultrathin InGaN quantum wells. In ICMOVPE XVII, Lausanne (Switzerland) [Poster presenation], 2014. [bibtex-key = Rossow2014]



385. I.V. Rozhdestvenskaya, M. Czank, M. Schowalter, E. Mugnaioli, and W. Depmeier. New data of denisovite and the model of the structure according to HAADF images. In Abstracts of XVIII International conference „Crystalchemistry, XRPD and spectroscopy of minerals“ (2014), Ekaterinburg, 160-161. (in Russian), 2014. [bibtex-key = Rozhdestvenskaya2014]



386. Henning Ryll, Robert Hartmann, Martin Huth, Sebastian Ihle, Knut Müller, Andreas Rosenauer, Julia Schmidt, Martin Simson, Heike Soltau, and Lothar Strüder. New Operation Modes with the PNCCD TEM Camera for Versatile, Direct Electron Imaging in Transmission Electron Microscopy Applications. In Microscience Microscopy Congress, MMC 2014, Manchester (UK), July, 2014 [Poster 1051], 2014. Abstract:

     Recently, the pnCCD has been introduced as a directly detecting electron imager in transmission electron microscopy to meet the requirements of challenging experiments and applications [1, 2]. The currently used physical pixel size is 48x48μm² with 264x264 pixels. Up to 1000 full frames per second can continuously be recorded. The radiation hard pnCCD is suitable for detection of TEM electrons with energies ranging from 300keV down to 20keV. Back illumination through a thin entrance window enables imaging of such low keV TEM electrons. The key benefits of the pnCCD TEM camera are its high readout speed, its radiation hardness and the low keV imaging capabilities as well as the single electron detection capability. Besides that the camera has the advantage that operation parameters can be changed by the user easily to adapt to the specific needs of the application. Additionally, raw data can be stored and analyzed: For instance, the analog amplifiers can be programmed to adapt to the energy of the incoming TEM electrons. Thus it is possible to detect single electrons in the energy range between 300 keV and 20 keV with the same high signal to noise ratio (Figure 1). This single electron detection capability enables further data analysis of the imaged TEM electrons. A subpixel resolution with up to 1320x1320 pixels can be achieved this way, increasing the imaging resolution especially for TEM energies below 120 keV [1]. Errors due to vibration or drift of the sample can also be corrected for due to the fast readout. The application specific configuration approach is further supported by new operation modes that were developed for the pnCCD. Mainly, these new modes increase the number of detectable TEM electrons per image. TEM electrons scatter in the detector bulk and create a number of electron-hole pairs depending on the energy of the TEM electron. The electrons that are thus generated are eventually collected in the potential wells that make up the pixels. These potential wells can hold a limited number of electrons, before excess electrons spill over into neighboring pixels. This effect is usually called blooming and can distort the imaging (Figure 2a). The number of collectable TEM electrons is increased by a factor of 3-4 in the high charge handling capacity mode (HCHC mode) (Figure 2b). Consequently, with a readout rate of 1000 fps and a TEM energy of 80 keV, 16000 TEM electrons can be collected in one pixel during a one second acquisition. This number can be further increased with faster readout in windowing or binning mode. The blooming effect is prevented in the anti-blooming mode (AB mode) (Figure 2c). Excess charge is drained out of the detector before it is collected in neighboring pixels, though the number of collectible electrons is not as high as in the HCHC mode. In the same image, spots with very high and very low electron doses (down to single electrons) can be recorded with the AB mode. The third new mode, called XPLUS mode, combines the features of increased charge handling capacity and prevented blooming (Figure 2d). The characteristics of the different operation modes will be explained in the presentation with the help of the example application of fast diffraction pattern imaging [2]. Benefits of the pnCCD camera for TEM applications will be illustrated with additional measurements taken at energies from 300 keV to 20keV.

     [bibtex-key = Ryll2014]



387. T. Schimpke, M. Binder, B. Galler, J. Hartmann, A. Waag, F. F. Krause, T. Mehrtens, A. Rosenauer, M. Müller, S. Metzner, P. Veit, F. Bertram, J. Christen, and H-J. Lugauer M. Strassburg1. Control of emission wavelength gradient along the m-plane facet of high aspect-ratio core-shell InGaN/GaN microrod LED structures (Talk). In Proceedings des Arbeitskreistreffens der Deutsche Gesellschaft für Kristallwachstum und Kristallzüchtung e.V. Arbeitskreis Epitaxie von III-V-Halbleitern 2014(AK III-V DGKK 29), Magdeburg (D), 2014. [bibtex-key = Schimpke2014]



388. M. Schowalter, F. Krause, T. Grieb, T. Mehrtens, K. Müller, and A. Rosenauer. Position resolved single electron response of the HAADF-STEM detector and improved method for intensity normalisation. In 18th International Microscopy Congress (IMC) [Talk IT-2-O-3292], 2014. [bibtex-key = Schowalter2014b]



389. Marco Schowalter, Thorsten Mehrtens, Jokob Borchard, Max Grimme, Knut Müller, and Andreas Rosenauer. Influence of disorder on the temperature dependence of the HAADF intensity. In EMSI-2014, Delhi (India) [Talk], 2014. [bibtex-key = Schowalter2014a]



390. M Simson, R. Hartmann, M. Huth, S. Ihle, K. Müller, A. Rosenauer, H. Ryll, J. Schmidt, H. Soltau, and L. Strüder. New Operation Modes with the direct detecting pnCCD-camera in Transmission Electron Microscopy. In 18th International Microscopy Congress (IMC) [Poster IT-8-P-1696], 2014. [bibtex-key = Simson2014]



391. D. Zhou, W. Sigle, K. Müller, A. Rosenauer, C. Zhu, M. Kelsch, Maier J., and P. van Aken. Contrast Investigation of Annular Bright-Field Imaging in Scanning Transmission Electron Microscopy of LiFePO4. In 18th International Microscopy Congress (IMC) [Poster IT-2-P-2042], 2014. [bibtex-key = Zhou2014]



392. Kristian Frank, Andre Wichmann, Arne Wittstock, Marcus Bäumer, Lutz Mädler, and Andreas Rosenauer. Investigation of a Nanoporous Gold / TiO2 Catalyst by Electron Microscopy and Tomography. In Symposium V - Geometry and Topology of Biomolecular and Functional Nanomaterials, volume 1504 of MRS Proceedings, 1 2013. [bibtex-key = Frank2013]



393. Tim Grieb, Knut Müller, Emanuel Cadel, Rafael Fritz, Nils Neugebohrn, Etienne Talbot, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. Chemical composition analysis of dilute GaNAs and InGaNAs by high-angle annular dark field STEM. In International Conference on Electron Microscopy and XXIV Annual Meeting of the Electron Microscope Society of India (EMSI) 2013, Kolkata (India) [Talk], 2013. Abstract:

     InxGa1-xNyAs1-y is of technological interest as both, In and N lower the semiconductor's band gap, allowing either to emit or to absorb in the infra-red, so that InGaNAs can either be used for laser diodes in telecommunication at wavelengths of 1.3 and 1.55 mm where glass fibres show optimum transmission, or as part of multi-junction solar cells. Quantitative chemical analysis by evaluating high-angle annular dark field (HAADF) micrographs recorded in high-resolution (HR) scanning transmission electron microscopy (STEM) with simulations was shown for e.g. for InGaN [1]. For this purpose, experimental STEM images are compared with image simulations. HAADF-STEM images of (In)GaNAs obtained in [100] zone axis show an enhanced intensity due to Huang scattering at static atomic displacements (SADs). SADs are distortions of the atomic lattice due to different covalent radii of In and Ga as well as As and N. Especially in the case of GaNAs scattering at N-induced SADs dominates thermal diffuse scattering (TDS) [2]. In consequence, the image contrast does not show the common Z-contrast behavior in which heavier elements exhibit higher intensity in the HAADF regime - instead, GaNAs layers occur brighter in HAADF images compared to GaAs. In this contribution we determine the N concentration in ternary GaNAs with y<0.05 by comparing the HAADF intensities to simulated intensities. We further expand this method to simultaneously determine both, the In and the N concentration from quaternary InGaNAs. For this, two sources of information are extracted on atomic scale: on the one hand the distances of atomic columns are measured which allows for a strain state analysis (SSA), on the other hand the characteristic HAADF intensity is evaluated by a comparison with simulated intensities. For the simulations, the frozen-lattice multislice approach is used in the STEMsim software [3], taking scattering at SADs and TDS into account. We compute the SADs by relaxing the supercells with the LAMMPS [4] package using Keating's valence force field model [5]. Figure 1 shows the ratio of the simulated HAADF intensity of InGaNAs and GaAs as a function of specimen thickness for different compositions (see legend of Figure 1.). The high concentration-dependent contrast allows for an accurate determination of the chemical composition. We characterise five GaNAs/GaAs quantum wells and two InGaNAs/GaAs quantum wells with different concentrations grown in [001] direction by MOVPE. Figure 2 shows the N concentration map (2.a) and profile (2.b, from averaging along [010]-direction) for a GaNAs quantum well with a nominal concentration y=0.03. The N concentrations of all quantum wells were in good agreement with results obtained from SSA of the STEM images. Figure 3 shows the concentration profiles for In (red) and N (green) for an InGaNAs quantum well with nominal concentrations of x=0.32 and y=0.02. The yellow curve shows the indium concentration obtained by atom-probe tomography (APT). [1] A. Rosenauer, T. Mehrtens, K. M{\"u}ller, K. Gries, M. Schowalter, P. V. Satyam, S. Bley, C. Tessarek, D. Hommel, K. Sebald, M. Seyfried, J. Gutowski, A. Avramescu, K. Engl, S. Lutgen, Ultramicroscopy 111 (2011) 1316. [2] T. Grieb, K. M{\"u}ller, R. Fritz, M. Schowalter, N. Neugebohrn, N. Knaub, K. Volz and A. Rosenauer, Ultramicroscopy 117 (2012), 15. [3] A. Rosenauer and M. Schowalter, Springer Proceedings in Physics 120 (2007), 169. [4] S. Plimpton, J. Comput. Phys. 117 (1995), 1. [5] P. N. Keating, Phys. Rev. 145 (1966), 637. [6] This work was supported by the German Research Foundation (DFG) under contract number SCHO 1196/3-1 and RO 2057/8-1-3008074.

     [bibtex-key = Grieb2013c]



394. T. Grieb, K. Müller, E. Cadel, R. Fritz, E. Talbot, M. Schowalter, K. Volz, and A. Rosenauer. Determination of In and N concentration in (InGa)(NAs) quantum wells using HAADF STEM and investigation of annealing effects. In Proceedings of the Microscopy Conference 2013 (MC 2013, Regensburg) Germany [Poster], volume 1: Instrumentation and Methods, pages IM.1.P024, 2013. [bibtex-key = Grieb2013b]



395. T. Grieb, K. Müller, R. Fritz, V. Grillo, M. Schowalter, K. Volz, and A. Rosenauer. Avoiding surface strain field induced artifacts in 2d chemical mapping of dilute GaNAs quantum wells by HAADF STEM. In Proceedings of the Microscopy Conference 2013 (MC 2013, Regensburg) Germany [Poster], volume 1: Instrumentation and Methods, pages IM.1.P008, 2013. [bibtex-key = Grieb2013a]



396. Dominik Heinz, Mohamed Fikry, Timo Aschenbrenner, Marco Schowalter, Tobias Meisch, Manfred Madel, Florian Huber, Matthias Hocker, Ingo Tischer, Thorsten Mehrtens, Knut Müller, Manuel Frey, Julian Jakob, Benjamin Neuschl, Detlef Hommel, Andreas Rosenauer, Klaus Thonke, and Ferdinand Scholz. Ga(In)N micro- and nanostructures for optical gas sensing. In Statusworkshop Kompetenznetz Funktionelle Nanostrukturen [Poster], 2013. [bibtex-key = Heinz2013]



397. L. Hoffmann, Uwe Rossow, Heiko Bremers, R. Buss, F. Ketzer, T. Langer, T. Mehrtens, M. Schowalter, A Rosenauer, and A. Hangleiter. Indium incorporation into thin and ultrathin InGaN layers with high indium content for long wavelength applications. In 15th European Workshop on Metalorganic Vapour Phase Epitaxy (EWMOVPE XV), 2013. [bibtex-key = Hoffmann2013]



398. Florian F. Krause, Knut Müller, Dennis Zillmann, Jacob Jansen, Marco Schowalter, and Andreas Rosenauer. Comparison of intensity and absolute contrast of simulated and experimental high-resolution transmission electron microscopy images for different multislice simulation methods (Poster). In Proceedings of the Microscopy Conference 2013 (MC 2013), Regensburg (D), volume 1: Instrumentation and Methods, pages IM.1.P022, 2013. [bibtex-key = Krause2013]



399. Christoph Mahr, Knut Müller-Caspary, Andreas Rosenauer, Marco Schowalter, Daniel Erben, Josef Zweck, and Pavel Potapov. Effect of lens aberrations on strain measurements from Convergent Beam Electron Diffraction patterns. In DPG Frühjahrstagung 2013, Regensburg, March, 2013 [Talk MM2.3], 2013. [bibtex-key = Mahr2013]



400. Thorsten Mehrtens, Marco Schowalter, Darius Tytko, Pyuck-Pa Choi, Dierk Raabe, Lars Hoffmann, Holger Jönen, Uwe Rossow, Andreas Hangleiter, and Andreas Rosenauer. Measuring composition in InGaN from HAADF-STEM images and studying the temperature dependence of Z-Contrast. In Microscopy of Semiconducting Materials 2013 (MSM XVIII),Oxford (UK) [Talk], 2013. [bibtex-key = Mehrtens2013]



401. Knut Müller, Henning Ryll, Ivan Ordavo, Marco Schowalter, Josef Zweck, Heike Soltau, Sebastian Ihle, Lothar Strüder, Kerstin Volz, Pavel Potapov, and Andreas Rosenauer. STEM strain analysis at sub-nanometre scale using millisecond frames of a direct electron read-out CCD camera. In Microscopy of Semiconducting Materials 2013 (MSM XVIII),Oxford (UK) [Talk], volume G: Scanning Electron and Ion Beam Techniques, 2013. [bibtex-key = Mueller2013b]



402. K. Müller, H. Ryll, I. Ordavo, D. Zillmann, M. Schowalter, J. Zweck, H. Soltau, S. Ihle, L. Strüder, K. Volz, P. Potapov, and A. Rosenauer. Strain Analysis by Nano-Beam Electron Diffraction (SANBED): Present performance and future prospects. In Proceedings of the Microscopy Conference 2013 (MC 2013, Regensburg) Germany [Talk], volume 1: Instrumentation and Methods, pages IM.1.004, 2013. [bibtex-key = Mueller2013]



403. M. Qi, W. A. O'Brien, C. A. Stephenson, V. Patel, N. Cao, B. J. Thibeault, T. Kosel, M. Schowalter, A. Rosenauer, V. Protasenko, H. Xing, and M. A. Wistey. Stability study of highly tensile strained Ge for optical device appliations. In Conf. Proceeding. 55th electronic material conference (EMC 2013), 2013. [bibtex-key = Qi2013]



404. Andreas Rosenauer. Introduction to STEM and the Multislice Method. In Advanced School on Transmission Electron Microscopy (2013) March 4-8 2013, Institute of Physics, Bhubaneswar, India [invited talk], 2013. [bibtex-key = Rosenauer2013a]



405. Andreas Rosenauer. Simulation of STEM images. In Advanced School on Transmission Electron Microscopy (2013) March 4-8 2013, Institute of Physics, Bhubaneswar, India [invited talk], 2013. [bibtex-key = Rosenauer2013c]



406. A. Rosenauer, K. Müller, T. Mehrtens, M. Schowalter, A. Würfel, T. Aschenbrenner, C. Kruse, D. Hommel, L. Hoffmann, A. Hangleiter, Pyuck-Pa Choi, and D. Raabe. Quantitative Methods in TEM and STEM. In , 2013. [bibtex-key = Rosenauer2013]



407. H. Ryll, K. Müller, S. Ihle, H. Soltau, I. Ordavo, A. Liebel, R. Hartmann, A. Rosenauer, and L. Strüder. A new direct electron imaging camera for transmission electron microscopy based on an ultrafast pnCCD. In Proceedings of the Microscopy Conference 2013 (MC 2013, Regensburg) Germany [poster], volume 1: Instrumentation and Methods, pages IM.1.P029, 2013. [bibtex-key = Ryll2013]



408. H. Ryll, K. Müller, S. Ihle, H. Soltau, I. Ordavo, A. Liebel, R. Hartmann, A. Rosenauer, and L. Strüder. Results of a pnCCD Based Ultrafast Direct Single Electron Imaging Camera for Transmission Electron Microscopy. In Proceedings of the Microscopy and Microanalysis Conference 2013 (MandM 2013, Indianapolis) USA [Talk], volume A14.04: New Instrumentation at the Limits: Characteristics and Applications, 2013. [bibtex-key = Ryll2013a]



409. Marco Schowalter, Ingo Stoffers, Florian Krause, Thorsten Mehrtens, Knut Müller, Malte Fandrich, Timo Aschenbrenner, Detlef Hommel, and Andreas Rosenauer. Composition determination using HAADF-STEM in AlGaN/GaN heterostructures revisited. In Microscopy Conference 2013 (MC 2013, Regensburg) [Poster Presentation], volume 1: Instrumentation and Methods, pages IM.1.P028, 2013. [bibtex-key = Schowalter2013]



410. Ingo Stoffers, Marco Schowalter, Florian Krause, Thorsten Mehrtens, Knut Müller, Malte Fandrich, Timo Aschenbrenner, Detlef Hommel, and Andreas Rosenauer. Composition quantification from HAADF-STEM in AlGaN/GaN heterostructures revisited. In Microscopy of Semiconducting Materials 2013 (MSMX VIII),Oxford (UK) [Poster Presentation], 2013. [bibtex-key = Stoffers2013]



411. Moritz Tewes, Florian Krause, Knut Müller, Pavel Potapov, Marco Schowalter, Thorsten Mehrtens, and Andreas Rosenauer. Quantitative Composition Evaluation from HAADF-STEM in GeSi/Si Heterostructures. In Microscopy of Semiconducting Materials 2013 (MSM XVIII),Oxford (UK) [Talk], 2013. [bibtex-key = Tewes2013a]



412. Timo Aschenbrenner, Heiko Dartsch, Elahe Zakizadeh, Carsten Laurus, Stephan Figge, Alexander Würfel, Thorsten Mehrtens, Andreas Rosenauer, and Detlef Hommel. Enhanced Carrier Confinement in InGaN Quantums Dots by Al(In,Ga)N Barrier Layers. In ICMOVPE - XVI Busan, (Korea) [Talk], 2012. [bibtex-key = Aschenbrenner2012]



413. Stephanie Bley, Thorsten Mehrtens, Parlapalli Venkata Satyam, and Andreas Rosenauer. Optimierung der Präparation von GaN-basierten Proben mittels Niedrigenergie-Ionendünnung für (S)TEM. In DPG Frühjahrstagung, Berlin (Germany) [Talk], number HL 64.7, pages 240, 2012. [bibtex-key = Bley2012]



414. Malte Fandrich, Timo Aschenbrenner, Stephan Figge, Thorsten Mehrtens, Andreas Rosenauer, and Detlef Hommel. AlInN/GaN-heterostructures for sensing applications. In Verhandlungen der DPG, number HL 73.1, pages 245, 2012. [bibtex-key = Fandrich2012a]



415. Malte Fandrich, Timo Aschenbrenner, Thorsten Klein, Stephan Figge, Carsten Kruse, Thorsten Mehrtens, Andreas Rosenauer, and Detlef Hommel. Nitride Based Heterostructures with Ga- and N-Polarity for Sensing Applications. In ICMOVPE - XVI [Talk], 2012. [bibtex-key = Fandrich2012]



416. S. Figge, T. Aschenbrenner, K. Morosov, E. Zakizadeh, C. Kruse, A Rosenauer, T. Mehrtens, S. Kremling, S. Höfling, L. Worschech, L. Forchel, and D. Hommel. Enhanced carrier confinement in InGaN quantum dots. In International Workshop on Nitride Semiconductors 2012 [Talk], 2012. [bibtex-key = Figge2012]



417. T. M. Gesing, M. Schowalter, C. Weidenthaler, M. M. Murshed, A. Rosenauer, J.C. Buhl, H. Schneider, and R. X. Schneider. Mullite-type dibismuth nonaoxometallates-(III): the effect of Strontium doping. In European crystallographic meeting, July 29 - September 11, 2012 Bergen, Norway, 2012. [bibtex-key = Gesing2012]



418. Tim Grieb, Knut Müller, Rafael Fritz, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. A method to avoid strain field induced artifacts in 2D chemical mapping of dilute GaNAs by HAADF STEM. In Microscopy and Microanalysis [Talk 595], volume 18, pages 1028--1029, 2012. Abstract:

     Scanning transmission electron microscopy (STEM) using a high-angleannular dark field (HAADF) detector can be used to investigate the chemical composition of ternary semiconductors as the scattering intensity highly depends on the specimen's chemical properties. In Ref. [1] a method for the evaluation of the indium concentration in InGaN quantum wells was suggested which is based on a comparison of experimental image intensities with simulations carried out with the frozen lattice approximation. We recently showed [2] that this approximation can also be used to compute the image intensity for GaNAs quantum wells embedded in GaAs. In GaNAs electron scattering is predominated by Huang scattering at static atomic displacements which has the effect that, under the applied imaging conditions, GaNAs quantum wells appear brighter in HAADF STEM images compared to GaAs. Quantitative analysis of the nitrogen concentration of GaNAs layers pseudomorphically grown in a GaAs matrix is also hindered by the surface strain fields that occur in vicinity of the interfaces. These strain fields decrease the image intensity thus leading to dark stripes in the GaAs regions that are running parallel to the interfaces. This effect of strain fields on STEM imaging of interfaces was explained in Ref. [3] for InGaAs and in Ref. [4] for InGaNAs and leads to artifacts in the evaluation of chemical composition. In this contribution we suggest a method combining two STEM images taken under different camera lengths to render full 2d-mapping of the nitrogen concentration possible. The HAADF STEM image in Fig. 1 a) was taken with detection angles between 36 and approximately 218 mrad corresponding to a camera length of 196 mm at our Titan 80/300 TEM. One can clearly see that the intensity close to the quantum well is decreased. As a consequence, the evaluated concentration profile shown in Fig. 2 a) contains two dips on each side of the quantum well where the nitrogen concentration is artificially negative. The concentration in the center of the well is not affected by the strain fields and was checked by high-resolution X-ray diffraction measurements and strain state analysis from the STEM image. We confirm by multislice simulations that GaAs shows less scattering intensity in regions affected by surface strain at high scattering angles, whereas the intensity increases in the low-angle regime. Using an inner detector radius of about 14 mrad, the increase at low angles balances the decrease of the intensities at high angles so that the dips disappear. For this reason the STEM image in Fig. 1 b) was taken with lower detection angles between 14 and approximately 87 mrad (camera length of 478 mm) directly after taking the image in Fig. 1 a). ...

     [bibtex-key = Grieb2012b]



419. Tim Grieb, Knut Müller, Rafael Fritz, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. A new method for true 2d chemical mapping: strain-field unaffected evaluation of dilute GaNAs by HAADF STEM. In Microscopy and Microanalysis (M&M) conference 2012, Phoenix (USA) [Poster], 2012. [bibtex-key = Grieb2012c]



420. Tim Grieb, Knut Müller, Andreas Hyra, Rafael Fritz, Marco Schowalter, Nicolai Knaub, and Andreas Rosenauer. Chemical analysis of InGaNAs quantum wells using HAADF STEM. In EMC 2012 [Poster], Session PS1.2: Thin films, Coatings and Interface, Manchester (UK), 2012. [bibtex-key = Grieb2012a]



421. Lars Hoffmann, Heiko Bremers, Holger Jönen, Uwe Rossow, Thorsten Mehrtens, Marco Schowalter, Andreas Rosenauer, and Andreas Hangleiter. STEM and XRD investigations of ultra thin GaInN/GaN quantum wells with high indium content. In Verhandlungen der DPG, number HL 64.6, pages 240, 2012. [bibtex-key = Hoffmann2012a]



422. L. Hoffmann, H. Bremers, H. Jönen, U. Rossow, T. Mehrtens, M. Schowalter, A. Rosenauer, and A. Hangleiter. STEM and XRD investigations of ultra-thin GaInN/GaN quantum wells with high indium content. In International Workshop on Nitride Semiconductors 2012 [Talk], 2012. [bibtex-key = Hoffmann2012]



423. H. Kauko, T. Grieb, A. Rosenauer, and A. T. J. van Helvoort. Studying Sb distribution in heterostructured GaAs/GaAsSb nanowires with quantitative HAADF-STEM. In EMC 2012, Manchester (UK), 2012. [bibtex-key = Kauko2012_conf]



424. T. Mehrtens, M. Schowalter, D. Tytko, P.-P. Choi, D. Raabe, L. Hoffmann, A. Hangleiter, and A. Rosenauer. Temperature dependence of Z-Contrast for InGaN. In Microscopy & Microanalysis, Phoenix (USA) [Talk], 2012. [bibtex-key = Mehrtens2012]



425. Knut Müller, Andreas Rosenauer, Marco Schowalter, Josef Zweck, Rafael Fritz, and Kerstin Volz. Strain analysis by nano-beam electron diffraction (SANBED) in semiconductor nanostructures [Invited talk]. In The XXXIII Annual Meeting of the Electron Microscopy Society of India, pages 36, 2012. Keyword(s): SANBED. Abstract:

     In this contribution, we present a method to measure lattice strain from a series of convergent-beam electron diffraction (CBED) patterns [1] acquired in scanning TEM (STEM). The fundamental but simple Bragg law is exploited to measure strain with a precision of 7·10−4 and a spatial resolution of 0.5−0.7 nm directly from CBED disc positions. In particular, we present 3 different algorithms for pattern recognition to measure CBED reflection positions accurately: The first detects edges in a patch around each disc in a raw diffraction pattern and iteratively finds all edge points which lie on the disc boundary by circle fitting. This method is rather slow but exact in the sense that it is parameter-free. The second takes a rotational average in the patch with logarithmically scaled intensities and maximises the gradient in radial direction by optimising the centre of the rotational average. This approach speeds up the strain measurement by a factor of 15. The third method exploits cross-correlations between each reflection patch and different types of masks. It profits from high-speed Fourier transforms and is nearly a factor of 100 faster than the edge detection algorithm. By application to a 350 nm wide quantum layer stack with a highly complex strain profile of alternating compressive/tensile strain state, it is shown that all three approaches lead to identical strain results. Artefacts caused by the varying inner disc structure throughout the quaternary InGaNAs as well as ternary GaNAs and InGaAs quantum wells buried in GaAs are eliminated. A methodological comparison with former approaches [e.g. 2,3] is also given with respect to accuracy and precision. Besides applications to Ge/Si systems, we present prospects for the operation and acquisition hardware of a TEM, directly deduced from the three algorithms above to allow for fast strain map acquisition in-situ at the microscope. Here, we operated an FEI Titan (S)TEM microscope in STEM mode to record a series of energy filtered CBED patterns on CCD. [1] K. M{\"u}ller and A. Rosenauer et al., Strain measurement in semiconductor heterostructures by scanning transmission electron microscopy, Accepted for publication in Microscopy and Microanalysis (Apr. 26th, 2012). [2] F. Uesugi et al., Ultramicroscopy 111, 995-998 (2011). [3] A. Béché et al., Applied Physics Letters 95, 123114 (2009).

     [bibtex-key = Mueller2012b]



426. Knut Müller, Andreas Rosenauer, Marco Schowalter, Josef Zweck, Rafael Fritz, and Kerstin Volz. Strain measurement in semiconductor nanostructures by convergent electron nanoprobe diffraction [Talk]. In Verhandlungen der Deutschen Physikalischen Gesellschaft, volume 47, pages 312, 2012. Abstract:

     The fundamental but simple Bragg law is exploited to measure lattice strain with a precision of 7·10−4 and a spatial resolution of 0.5−0.7 nm directly from convergent beam electron diffraction (CBED) patterns. In particular, we present 3 different algorithms for pattern recognition to measure CBED reflection positions accurately: The first detects edges in a patch around each CBED disc and iteratively finds all edge points which lie on the disc boundary by circle fitting. The second takes a rotational average in the patch and maximises the gradient in radial direction by optimising the centre of the rotational average. The third and fastest method exploits cross-correlations between each reflection patch and different types of masks. Besides results for a 350 nm wide InxGa1−xNyAs1−y/GaAs highly strained quantum layer stack with alternating compressive/tensile strain, we present prospects for the operation and acquisition hardware of a TEM, directly deduced from the three algorithms above to allow for a fast strain map acquisition directly at the microscope in future. For the present study we operated an FEI Titan (S)TEM microscope in STEM mode to record a series of energy filtered CBED patterns on CCD.

     [bibtex-key = Mueller2012a]



427. A. Rosenauer, K. Mller, T. Mehrtens, M. Schowalter, A. Würfel, T. Aschenbrenner, C. Kruse, D. Hommel, L. Hoffmann, A. Hangleiter, P.-P. Choi, and D. Raabe. Measurement of composition in InGaN nanostructures using scanning transmission electron microscopy. In International Workshop on Nitride Semiconductors 2012, Sapporo (Japan) [Invited Talk], 2012. [bibtex-key = Rosenauer2012e]



428. A. Rosenauer, K. Müller, T. Mehrtens, M. Schowalter, T. Aschenbrenner, C. Kruse, D. Hommel, K. Sebald, and J. Gutowski. TEM investigation of InGaN quantum dots. In First German-Korean Symposium on Nano-optics and Nano-technology, Hanse-Wissenschaftskolleg, Delmenhorst, (Germany) December 14, 2012, [Invited talk], 2012. [bibtex-key = Rosenauer2012d]



429. Andreas Rosenauer, Knut Müller, Thorsten Mehrtens, Marco Schowalter, Rafael Fritz, and Kerstin Volz. Measurement of Composition and Strain by Scanning Transmission Electron Microscopy. In Microscopy and Microanalysis, Phoenix (USA) [Invited talk], 2012. [bibtex-key = Rosenauer2012c]



430. Andreas Rosenauer, Knut Müller, Thorsten Mehrtens, Marco Schowalter, Alexander Würfel, Timo Aschenbrenner, Carsten Kruse, Detlef Hommel, Lars Hoffmann, Andreas Hangleiter, S. A. Gerstl, Pyuck-Pa Choi, and Dirk Raabe. Measurement of composition and strain in InGaN quantum dots by STEM [Plenary talk]. In The XXXIII Annual Meeting of the Electron Microscopy Society of India, EMSI2012, Bengaluru (Indien), July 4, 2012 [invited talk], pages 25, 2012. Abstract:

     In this contribution we demonstrate methods for measurement of composition and strain by scanning transmission electron microscopy (STEM). STEM combined with a high angle annular dark field detector allows Z-contrast imaging with high material contrast that can be used for quantification of composition. The suggested method is based on comparison of experiment with image simulation [1,2,3], which yields the local specimen thickness and the indium concentration for each atomic column. Image simulations are performed with the STEMsim program [4] in the frozen lattice approximation taking into account static atomic displacements (SAD), which occur due to the different covalent radii of In and Ga atoms. Results of this method will be compared with results obtained by atom probe tomography. A variation of local lattice parameter can be investigated by strain state analysis in STEM with two different methods. First, high-resolution STEM (HRSTEM) images can be used to investigate the positions of atomic columns. Second, acquisition of a series of several hundreds of diffraction patterns along a STEM line scan allows strain analysis by nano beam electron diffraction (SANBED) from evaluation of distances between diffracted discs. These methods were applied to investigate InGaN quantum dots grown by metal organic vapour phase expitaxy on sapphire and on GaN substrates. In both cases the uncapped InGaN layers show in-rich islands with a lateral size of a few tens of nanometers on the surface. For sapphire substrates, all threading dislocations are decorated with such islands. In between these islands, the surface contains InGaN islands with a meander like structure and a height of a few atomic layers. The large In-rich islands disappear during overgrowth with GaN and form additional InGaN layers on top of the quantum dot layer. Composition and strain state of these layers were investigated with quantitative STEM Z-contrast imaging as well as strain state analysis using HRSTEM and SANBED. [1] A. Rosenauer et al., Ultramicroscopy 109 (2009) 1171. [2] J.M. LeBeau and S. Stemmer, Ultramicroscopy 108 (2008) 1653. [3] A. Rosenauer et al., Ultramicroscopy 111 (2011) 1316-1327 [4] A. Rosenauer and M. Schowalter, Springer Proceedings in Physics 120 (2007) 169.

     [bibtex-key = Rosenauer2012b]



431. A. Rosenauer, K. Müller, T. Mehrtens, M. Schowalter, J. Zweck, R. Fritz, and K. Volz. Measurement of Composition and Strain by STEM. In International Conference on Extended Defects in Semiconductors, EDS 2012, Thessaloniki (Greece) [Invited Talk], 2012. [bibtex-key = Rosenauer2012]



432. Andreas Rosenauer, Knut Müller, Thorsten Mehrtens, Marco Schowalter, Josef Zweck, Rafael Fritz, and Kerstin Volz. Measurement of composition and strain by STEM. In Microscopy and Microanalysis 2012 (M&M2012), Phoenix, Arizona, July 29-August 2 [Invited talk], volume 18, pages 1804--1805, 2012. Abstract:

     In this contribution we demonstrate methods for measurement of composition and strain by scanningtransmission electron microscopy (STEM). On the one hand, STEM combined with a high angle annular dark field detector allows Z-contrast imaging with high material contrast that can be used for quantification of composition. The suggested method is based on comparison of experiment with image simulation [1], facilitated by normalizing the intensity with respect to the incident electron beam [2,1]. As an example, Fig. 1a shows a part of a high-resolution STEM image of an InGaN quantum well buried in GaN. First, we apply a Wiener filter for noise reduction, being followed by detecting the positions of the atomic columns (Fig. 1b). Then the original image is segmented into Voronoi cells (Fig. 1c), for which we compute the mean normalized intensity (Fig. 1d). Comparison with image simulations yields the local specimen thickness (Fig. 1e) and the indium concentration for each atomic column (Fig. 1f). Image simulations were performed with the STEMsim program [3] in the frozen lattice approximation and taking into account static atomic displacements (SAD), which occur due to the different covalent radii of In and Ga atoms. For the calculation of SADs we used the LAMMPS code [4] and Stillinger-Weber empirical potentials with parameters published by Lei et al.[5]. As a critical issue we also address a possible structural degradation of InGaN layers during illumination with electrons. As an example, Smeeton et al. [6] observed a clustering of indium after afew minutes irradiation time if parallel beam illumination was applied. In contrast, we could not detect any significant change of image contrast or composition during acquisition of 32 images with 80 s exposure time corresponding to a total irradiation time of 42 minutes. The high stability of the InGaN layers can be explained by the significantly smaller electron dose in our STEM experiments compared to that given in reference [6]. Acquisition of a series of several hundreds of diffraction patterns along a STEM line scan, on the other hand, can be used for evaluation of strain profiles. We tested three different algorithms in the field of (circular) pattern recognition that are able to detect diffracted disc positions accurately, fromwhich the strain in growth direction is calculated. Although the three approaches are very different as one is based on edge detection, one on rotational averages and one on cross-correlation with masks, it is found that identical strain profiles (Fig. 2b) result for the InxGa1xNyAs1 y/GaAs heterostructure shown in Fig. 2(a) consisting of five compressively and tensile strained layers. We achieve a precision of strain measurements of 7-9 · 10^-4 and a spatial resolution of 0.5 0.7 nm over the whole width of the layer stack which was 350 nm.

     [bibtex-key = Rosenauer2012a]



433. Uwe Rossow, Andreas Kruse, Holger Jönen, Lars Hoffmann, Fedor Ketzer, Torsten Langer, Ronald Buss, Heiko Bremers, Andreas Hangleiter, Thorsten Mehrtens, Marco Schowalter, and Andreas Rosenauer. Optimizing the Growth Process of the Active Zone in GaN Based Laser Structures for the Long Wavelength Region. In ICMOVPE - XVI [Talk], 2012. [bibtex-key = Rossow2012]



434. Alexander Würfel, Thorsten Mehrtens, Christian Tessarek, Timo Aschenbrenner, Detlef Hommel, and Andreas Rosenauer. Untersuchung von InGaN-basierten Quantenpunktsystemen mittels STEM Z-Kontrast. In Verhandlungen der DPG, number HL 25.15, pages 223, 2012. [bibtex-key = Wuerfel2012]



435. Heiko Dartsch, Christian Tessarek, Stephan Figge, Timo Aschenbrenner, Carsten Kruse, Marco Schowalter, Andreas Rosenauer, and Detlef Hommel. Electroluminescence from InGaN quantum dots in a monolithically grown GaN/AlInN cavity. In DPG Frühjahrstagung, Dresden (Germany) [Talk], 2011. [bibtex-key = Dartsch2011]



436. S. Figge, H. Dartsch, C. Tessarek, T. Aschenbrenner, C. Kruse, D. Hommel, K. Sebald, M. Seyfried, J. Kalden, J. Gutowski, M. Schowalter, K. Müller, A. Rosenauer, M. Florian, and F. Jahnke. Enhancing the Collection-Efficiency of InGaN Quantum Dots in Single Photon Emitters. In poster PC1.17 ICNS 9 Glasgow, U.K. 2011, [Poster], volume PC1.17, 2011. [bibtex-key = Figge2011]



437. K. Frank, A. Rosenauer, A. Wittstock, B. Neumann, and M. Bäumer. STEM - tomography of nanoporous gold. In poster IM3.P144 MC 2011, Kiel, Germany [poster], 2011. [bibtex-key = Frank2011]



438. R. Fritz, A. Beyer, W. Stolz, O. Rubel, T. Grieb, K. Müller, M. Schowalter, A. Rosenauer, I. Häusler, A. Mogilatenko, H. Kirmse, W. Neumann, and K. Volz. HAADF-STEM in a JEOL 2200FS for quantitative analysis of composition in compound III/V semiconductor materials. In W. Jäger, W. Kaysser, W. Benecke, W. Depmeier, S. Gorb, L. Kienle, M. Mulisch, D. Häussler, and A. Lotnyk, editors, Proceedings of the Microscopy Conference 2011 (MC 2011, Kiel), volume 1: Instrumentation and Methods, pages IM2.P130, 2011. DGE - German Society for Electron Microscopy. [bibtex-key = Fritz2011a]



439. Rafael Fritz, Andreas Beyer, Wolfgang Stolz, Kerstin Volz, Knut Müller, Marco Schowalter, Andreas Rosenauer, Ines Häusler, Anna Mogilatenko, Holm Kirmse, and Wolfgang Neumann. Quantitative analysis of chemical composition using HAADF -STEM in a JEOL 2200FS. In Microscopy of semiconducting materials, Cambridge (UK) [Talk], 2011. [bibtex-key = Fritz2011]



440. T. M. Gesing, M. Schowalter, C. Weidenthaler, M. M. Murshed, A. Rosenauer, J.C. Buhl, H. Schneider, and R. X. Schneider. Strontium incorporation in Mullite-type Bi2M4O8. In Presented at IUCR conference in Madrid, 2011. [bibtex-key = Gesing2011]



441. T. Grieb, K. Müller, O. Rubel, R. Fritz, C. Gloistein, N. Neugebohrn, M. Schowalter, K. Volz, and A. Rosenauer. Determination of Nitrogen concentration in dilute GaNAs by STEM HAADF Z-contrast imaging. In MSM 2011 Cambridge, U.K. [talk] talk D13, 2011. [bibtex-key = Grieb2011c]



442. Tim Grieb, Knut Müller, Oleg Rubel, Rafael Fritz, Marco Schowalter, Kerstin Volz, and Andreas Rosenauer. Determination of nitrogen concentration in dilute GaNAs by STEM HAADF Z-contrast imaging. In DPG Frühjahrstagung, Dresden (Germany) [Talk], 2011. [bibtex-key = Grieb2011a]



443. T. Grieb, K. Müller, O. Rubel, R. Fritz, M. Schowalter, K. Volz, and A. Rosenauer. STEM strain state analysis in combination with HAADF intensity evaluation to determine chemical composition of GaNAs quantum wells. In W. Jäger, W. Kaysser, W. Benecke, W. Depmeier, S. Gorb, L. Kienle, M. Mulisch, D. Häussler, and A. Lotnyk, editors, Proceedings of the Microscopy Conference 2011 (MC 2011, Kiel), volume 1: Instrumentation and Methods, pages IM2.P120, 2011. DGE - German Society for Electron Microscopy. [bibtex-key = Grieb2011]



444. V. Grillo, K. Müller, C. Frigeri, K. Volz, F. Glas, and A. Rosenauer. Strain, composition and disorder in ADF imaging of semiconductors. In MSM 2011 Cambridge, U.K. [talk] talk D10, 2011. [bibtex-key = Grillo2011b]



445. L. Hoffmann, H. Bremer, H. Jönen, U. Rossow, J. Thalmair, J. Zweck, M. Schowalter, A. Rosenauer, and A. Hangleiter. Strain Relaxation Mechanisms in Green Emitting GaInN/GaN Laser Diode Structures. In ICNS 9 Glasgow, U.K., 2011 [talk] talk B4.3, 2011. [bibtex-key = Hoffmann2011a]



446. Lars Hoffmann, Heiko Bremers, Holger Joenen, Uwe Rossow, Johannes Thalmair, Josef Zweck, Marco Schowalter, Andreas Rosenauer, and Andreas Hangleiter. Strain Relaxation Mechanisms in Green Emitting GaInN/GaN Laser Diode Structures. In DPG Frühjahrstagung, Dresden (Germany) [Talk], 2011. [bibtex-key = Hoffmann2011]



447. Robert Imlau, Knut Müller, Marco Schowalter, Rafael Fritz, Kerstin Volz, and Andreas Rosenauer. Untersuchung struktureller und optischer Eigenschaften von getemperten InGaNAs-Trögen mittels TEM-Dreistrahlabbildung. In DPG Frühjahrstagung, Dresden (Germany) [Talk], 2011. [bibtex-key = Imlau2011a]



448. R. Imlau, K. Müller, M. Schowalter, O. Rubel, R. Fritz, K. Volz, and A. Rosenauer. Investigation of optical and concentration profile changes of InGaNAs/GaAs heterostructures induced by thermal annealing. In MSM 2011 Cambridge, U. K. [poster] poster 2.16, 2011. [bibtex-key = Imlau2011]



449. H. Kauko, T. Grieb, A. Rosenauer, R. Bjørge, M. Munshi, H. Weman, and A. T. J. van Helvoort. Composition analysis of heterostructured GaAs nanowires with quantitative HAADF-STEM. In Nanolab Meeting 2011, Trondheim (NO),, 2011. [bibtex-key = Kauko2011_conf]



450. G.T. Martinez, S. Van Aert, J. Verbeeck, S. Bals, and A. Rosenauer. Quantitative interface characterization using model-based HAADF STEM. In poster IM2.P116 MC 2011, Kiel, Germany [poster], 2011. [bibtex-key = Martinez2011]



451. Thorsten Mehrtens, Stephanie Bley, Marco Schowalter, Kathrin Sebald, Moritz Seyfried, Jürgen Gutowski, Stephan S. A. Gerstl, Pyuck-Pa Choi, Dierk Raabe, Adrian Avramescu, and Andreas Rosenauer. A (S)TEM and Atom Probe Tomography Study of InGaN. In DPG Frühjahrstagung, Dresden (Germany) [Talk], number 62.3, 2011. [bibtex-key = Mehrtens2011a]



452. Thorsten Mehrtens, Stephanie Bley, Marco Schowalter, Kathrin Sebald, Moritz Seyfried, Jürgen Gutowski, Stephan S. A. Gerstl, Pyuck-Pa Choi, Dierk Raabe, Adrian Avramescu, and Andreas Rosenauer. A (S)TEM and atom probe tomography study for InGaN. In MSM 2011 Cambridge, U.K. [talk] talk D7, 2011. [bibtex-key = Mehrtens2011c]



453. Thorsten Mehrtens, Stephanie Bley, Marco Schowalter, Kathrin Sebald, Moritz Seyfried, Jürgen Gutowski, Stephan S. A. Gerstl, Pyuck-Pa Choi, Dierk Raabe, Adrian Avramescu, and Andreas Rosenauer. Determination of composition in InGaN/GaN heterostructures using (S)TEM, Atom Probe Tomography and Photoluminescence. In E-MRS Spring Meeting 2011, Nice (France) [Talk], 2011. [bibtex-key = Mehrtens2011b]



454. K. Müller, T. Grieb, O. Rubel, M. Schowalter, R. Fritz, D. Z. Hu, D. Schaadt, M. Hetterich, K. Volz, and A. Rosenauer. Conventional and Scanning TEM of InGaNAs: Comparison of theory and experiment. In W. Jäger, W. Kaysser, W. Benecke, W. Depmeier, S. Gorb, L. Kienle, M. Mulisch, D. Häussler, and A. Lotnyk, editors, Proceedings of the Microscopy Conference 2011 (MC 2011, Kiel) Germany [poster] Best poster award, volume 1: Instrumentation and Methods, pages IM2.P132, 2011. DGE - German Society for Electron Microscopy. [bibtex-key = Mueller2011d]



455. Knut Müller, Marco Schowalter, Andreas Rosenauer, Dongzhi M. Hu, Daniel Schaadt, Michael Hetterich, Philippe Gilet, Oleg Rubel, Rafael Fritz, and Kerstin Volz. Annealing in InGaNAs studied by TEM three-beam imaging. In DPG Frühjahrstagung, Dresden (Germany) [Talk], 2011. [bibtex-key = Mueller2011b]



456. K. Müller, M. Schowalter, O. Rubel, D. Z. Hu, D. M. Schaadt, M. Hetterich, P. Gilet, R. Fritz, K. Volz, and A. Rosenauer. TEM 3-beam study of annealing effects in InGaNAs using ab-initio structure factors for strain-relaxed supercells. In MSM 2011 Cambridge, U. K. [Talk] talk B4, 2011. [bibtex-key = Mueller2011a]



457. Andreas Rosenauer. Composition mapping in InGaN with Quantitative STEM and comparison with atom probe measurements. In Invitied talk B2.1 ICNS 9 Glasgow, U.K. 2011 [invited talk], 2011. [bibtex-key = Rosenauer2011g]



458. A Rosenauer, T. Mehrtens, K. Müller, K. Gries, M. Schowalter, S. Bley, P. V. Satyam, A. Avramescu, K. Engl, and S. Lutgen. 2D-composition mapping in InGaN without electron beam induced clustering of indium by STEM HAADF Z-contrast imaging. In MSM 2011 Cambridge, U.K. [poster] poster 2.18, 2011. [bibtex-key = Rosenauer2011f]



459. A. Rosenauer, T. Mehrtens, K. Müller, K. Gries, M. Schowalter, S. Bley, P. V. Satyam, A. Avramescu, K. Engl, and S. Lutgen. Composition mapping in InGaN using HAADF STEM imaging. In W. Jäger, W. Kaysser, W. Benecke, W. Depmeier, S. Gorb, L. Kienle, M. Mulisch, D. Häussler, and A. Lotnyk, editors, Proceedings of the Microscopy Conference 2011 (MC 2011, Kiel), volume 1: Instrumentation and Methods, pages IM2.P113, 2011. DGE - German Society for Electron Microscopy. [bibtex-key = Rosenauer2011d]



460. Andreas Rosenauer, Thorsten Mehrtens, Knut Müller, Katharina Gries, Marco Schowalter, Stephanie Bley, Parlapalli Vencata Satyam, Christian Tessarek, Detlef Hommel, Kathrin Sebald, Moritz Seyfried, Jürgen Gutowski, Adrian Avramescu, Karl Engl, and Stephan Lutgen. Quantitative STEM: Composition mapping in InGaN. In DPG Frühjahrstagung, Dresden (Germany) [Invited talk], 2011. [bibtex-key = Rosenauer2011c]



461. A. Rosenauer, T. Mehrtens, K. Müller, K. Gries, M. Schowalter, P. V. Satyam, S. Bley, C. Tessarek, D. Hommel, K. Sebald, M. Seyfried, J. Gutowski, S. S. A. Gerstl, P. P. Choi, and D. Raabe. Composition mapping in InGaN with quantitative STEM Z-contrast imaging. In ICNS Glasgow 2011 [Invited talk], 2011. Abstract:

     Special interest in chemical mapping of composition in InGaN quantum well structures by transmission electron microscopy (TEM) was raised more than ten years ago when experiments pointed towards the existence of composition fluctuations, theoretically supported by the predictions of miscibility gaps. However, the reliability of TEM for the investigation of composition fluctuations was called into question, when it was found that illumination of a specimen with a parallel electron beam can lead to formation of indium rich regions already after a few minutes [1]. In this contribution we show that electron beam induced clustering of indium can be strongly reduced in the case of scanning transmission electron microscopy (STEM). The suggested method [2] uses STEM imaging with a high-angle annular dark field detector. In this mode, the analyzed intensity chiefly is caused by thermal diffuse scattering and static atomic displacements due to the different covalent radii of gallium and indium atoms. The analysis procedure is based on a comparison of the experimentally recorded intensity with accurate image simulation carried out with the STEMsim [3] program. As an application of the method we demonstrate examples of InGaN layers with fluctuations similar to the expected random alloy fluctuations. As the STEM measurements can only give composition values averaged along the electron beam direction, these results will be compared with atom probe analyses, from which a three dimensional information of the composition distribution was deduced. We also investigated InGaN layers that show quantum dot (QD) emission in micro-photoluminescence experiments [4]. These layers reveal fluctuations of the indium concentration that clearly exceed the random alloy fluctuations. We found pronounced, approximately 5 nm large regions with increased indium concentration, which most probably lead to the QD emission in the photoluminescence experiments.

     [bibtex-key = Rosenauer2011b]



462. A. Rosenauer, K. Müller, and M. Schowalter. STEMSIM-a software tool for simulation of STEM ADF Z-contrast imaging. In invited talk in the Workshop W4 Simulation for TEM and STEM MC 2011, Kiel, Germany [invited talk], 2011. [bibtex-key = Rosenauer2011]



463. P.V. Satyam, J. K. Dash, A. Rath, R. R. Juluri, P. Santhana Raman, K. Müller, M. Schowalter, R. Imlau, and A. Rosenauer. Shape transformation of SiGe structures on ultra clean Si (5 5 7) and Si(5 5 12) surfaces. In MSM 2011 Cambridge, U.K. [poster] poster P2.2, volume P2.2, 2011. [bibtex-key = Satyam2011a]



464. P. V. Satyam, A. Rosenauer, J. Dash, A. Rath, J. Raghava, M. Schowalter, Tim Grieb, K. M�ller, T. Mehrtens, and Robert Imlau. Compositional analysis of nanostructures with STEM Z-contrast imaging. In EM50, Hyderabad (India) [Talk], 2011. [bibtex-key = Satyam2011]



465. M. Schowalter, J. Fischer, A. Rosenauer, and R.E. Dunin-Borkowski. A theoretical assessment of the reported increase in the mean inner potential of Au clusters with decreasing particle size. In poster IM2.P129 MC 2011, Kiel, Germany [poster], 2011. [bibtex-key = Schowalter2011b]



466. M. Schowalter, K. Müller, and A. Rosenauer. Density Functional Theory simulations for quantitative transmission electron microscopy. In CECAM-HQ-EPFL workshop 2011, Lausanne, Switzerland [invited talk], 2011. [bibtex-key = Schowalter2011a]



467. M. Schowalter, M. Tewes, K. Frank, R. Imlau, A. Rosenauer, H.S. Lee, O.G. Rastelli, M. Schmidt, M. Tavast, T. Leinonen, and M. Guina. Investigation of diffusion in AlAs/GaAs distributed Bragg reflectors using HAADF STEM imaging. In MSM 2011 Cambridge, U.K. [poster] poster P2.12, 2011. [bibtex-key = Schowalter2011]



468. W. Van den Broek, S. Van Aert, A. Rosenauer, and D. Van Dyck. Atomic resolution tomographic reconstruction algorithm for particles of nanometer size. In poster IM3.P146 MC 2011, Kiel [poster], 2011. [bibtex-key = VandenBroek2011]



469. T. Volkenandt, E. Müller, T. Mehrtens, A. Rosenauer, and D. Gerthsen. Quantitative analysis of InGaN thin layers by scanning transmission electron microscopy at low electron energies. In W. Jäger, W. Kaysser, W. Benecke, W. Depmeier, S. Gorb, L. Kienle, M. Mulisch, D. Häussler, and A. Lotnyk, editors, Proceedings of the Microscopy Conference 2011 (MC 2011, Kiel, Germany) [poster], volume 1: Instrumentation and Methods, pages IM2.P114, 2011. [bibtex-key = Volkenandt2011]



470. K. Volz, R. Fritz, A. Beyer, W. Stolz, K. Müller, M. Schowalter, A. Rosenauer, I. Haeusler, A. Mogilatenko, H. Kirmse, and W. Neumann. Quantitative analysis of chemical composition using HAADF-STEM in a JEOL 2200FS. In talk D11 MSM 2011 Cambridge, U.K. [talk], 2011. [bibtex-key = Volz2011]



471. T. Aschenbrenner, G. Kunert, W. Freund, S. Figge, C. Kruse, M. Schowalter, C. Vogt, A. Rosenauer, J. Kalden, K. Sebald, J. Gutowski, and D Hommel. High quality GaN nanorods: from catalyst free growth to an LED. In presented at IWN 2010, 2010. [bibtex-key = Aschenbrenner2010]



472. Stephanie Bley, Thorsten Mehrtens, and Andreas Rosenauer. Präparation von GaN-basierten Proben mittels Niedrigenergie-Ionendünnung für Transmissionselektronenmikroskopie. In DPG Frühjahrstagung, Regensburg, number HL 34.33, 2010. [bibtex-key = Bley2010]



473. M. Dries, B. Gamm, K. Schultheiss, A. Rosenauer, R.R. Schröder, and D. Gerthsen. Object-wave Reconstruction by Carbon-Film-Based Zernike- and Hilbert-Phase Plate Microscopy: A Theoretical Study Not Restricted to Weak Phase Objects. In Microscopy and Microanalysis 2010, 2010. [bibtex-key = Dries2010a]



474. S. Figge and A. Rosenauer. The guideways for InGaN quantum dot formation - Stranski-Krastanov and spinodal decomposition (2010):. In IWN2010 - 19-24 September , Tampa, Florida, USA, 2010. [bibtex-key = Figge2010]



475. M. Florian, F. Jahnke, A. Pretorius, A. Rosenauer, H. Dartsch, C. Kruse, and D. Hommel. Influence of growth imperfections on optical properties of nitride pillar VCSEL microcavities. In DPG Frühjahrstagung, Regensburg (Germany), 2010. [bibtex-key = Florian2010]



476. Kristian Frank, Marco Schowalter, Andreas Rosenauer, Wojciech Pacuski, Carsten Kruse, and Detlef Hommel. Quantitative Untersuchung von ZnTe-basierten optoelektronischen Heterostrukturen mittels Transmissionselektronenmikroskopie. In DPG Frühjahrstagung in Regensburg, 2010. [bibtex-key = Frank2010]



477. Rafael Fritz, Andreas Beyer, Oleg Rubel, Wolfgang Stolz, Kerstin Volz, Knut Müller, Marco Schowalter, Andreas Rosenauer, Ines Häusler, Anna Mogilatenko, Holm Kirmse, and Wolfgang Neumann. Quantitative analysis of chemical composition in Ga(AsP)-heterostructures using HAADF-STEM in a JEOL 2200FS. In International Microscopy Congress (IMC17) Rio de Janeiro (Brazil) [Poster presentation], 2010. [bibtex-key = Fritz2010]



478. D. Gerthsen, H. Blank, D Litvinov, R. Schneider, A. Rosenauer, T. Passow, A. Grau, P. Feinäugle, H. Kalt, C. Klingshirn, and M. Hetterich. On the incorporation of indium in InAs-based quantum structures. In Journal of Physics: Conference Series 209, 012006, 2010. [bibtex-key = Gerthsen2010]



479. T. M. Gesing, M. Schowalter, C. Weidenthaler, A. Rosenauer, H. Schneider, and R.X. Fischer. Synthesis and properties of Mullite-type Bi(1-x)Sr(x)2M1 4OM2 9-x/2 (M=Al, Ga,Fe). In presented at BMEA, Taiwan (2010), 2010. [bibtex-key = Gesing2010a]



480. Claas Gloistein, Knut Müller, Marco Schowalter, Andreas Rosenauer, and Jacob Jansen. Computation and measurement of atomic mean square displacements for quantitative evaluation of high angle annular dark field images. In International Conference on Advances in Electron Microscopy and Related Techniques/XXXI Annual Meeting of EMSI, Mumbai (India) [Invited talk], 2010. [bibtex-key = Gloistein2010]



481. K Gries, F. Heinemann, A. Ziegler, A. Rosenauer, and M. Fritz. The influence of the insoluble and soluble matrix on the growth of calcium carbonate crystals. In Gordons Research Conference, Biomineralization, New London (NH, USA), 2010 [poster], 2010. [bibtex-key = Gries2010a]



482. Katharina Gries, Malte Launspach, Meike Gummich, Tanja Dodenhof, Andreas Rosenauer, and Monika Fritz. New functional ceramic composits through biomineralisation?. In DPG Frühjahrstagung, Regensburg (Germany), 2010. [bibtex-key = Gries2010]



483. Vincenzo Grillo, Frank Glas, Knut Müller, and Andreas Rosenauer. Simulation of STEM-HAADF microscopy images for the chemical quantification in InGaAsN alloys. In Transnational Access Meeting (TAM), Helsinki (Finland) [Poster presentation], 2010. [bibtex-key = Grillo2010]



484. C. Kruse, W. Pacuski, T. Jakubczyk, M. Florian, K. Frank, T. Kazimierczuk, A. Golnik, J. A. Gaj, F. Jahnke, A. Rosenauer, and D. Hommel. High-quality ZnTe-based micropillars containing CdTe quantum dots. In ICPS 2010, 2010. [bibtex-key = Kruse2010]



485. Thorsten Mehrtens, Marco Schowalter, Knut Müller, Dongzhi Hu, Daniel M. Schaadt, and Andreas Rosenauer. Measuring of segregation profiles from HAADF -STEM images. In International Microscopy Congress (IMC17), Rio de Janeiro (Brazil) [Poster presentation], 2010. [bibtex-key = Mehrtens2010]



486. K. Müller, M. Schowalter, A. Rosenauer, J. Jansen, K. Tsuda, J. Titantah, and D. Lamoen. Refinement of chemically sensitive structure factors using parallel and convergent beam electron nanodiffraction. In MSM XVI, Oxford 2009, 16.-20. März Journal of Physics: Conference Series, 209 (2010) 012025, 2010. [bibtex-key = Mueller2010c]



487. Knut Müller, Marco Schowalter, Oleg Rubel, Kerstin Volz, Michael Hetterich, Dongzhi Hu, Daniel Schaadt, and Andreas Rosenauer. Dual compositional mapping in InGaNAs using a single TEM lattice fringe image. In International Microscopy Congress (IMC17), Rio de Janeiro (Brazil) [Poster presentation], 2010. [bibtex-key = Mueller2010]



488. S. Pokhrel, K. Grossmann, J. Birkenstock, J.I. Flege, J. Falta, M. Schowalter, A. Rosenauer, N. Barsan, U. Weimar, and L. Mädler. Aerosol made Sn doped In2O3 (ITO) nanoparticles for gas sensing application. In presented at IAC conference (2010), 2010. [bibtex-key = Pokhrel2010]



489. A. Rosenauer, K. Gries, K. Müller, M. Schowalter, A. Pretorius, A. Avramescu, K. Engl, and S. Lütgen. Measurement of Composition Profiles in III-Nitrides by Quantitative Scanning Transmission Electron Microscopy. In MSM XVI, Oxford 2009, 16.-20. März Journal of Physics: Conference Series, 209 (2010) 012009, 2010. [bibtex-key = Rosenauer2010b]



490. Andreas Rosenauer, Thorsten Mehrtens, Stephanie Bley, Knut Müller, Katharina Gries, Marco Schowalter, Christian Tessarek, Detlef Hommel, Kathrin Sebald, Moritz Seyfried, and Jürgen Gutowski. Composition mapping in InGaN quantum wells and quantum dots using high resolution STEM imaging. In International Microscopy Congress (IMC17), Rio de Janeiro (Brazil) [Poster presentation], 2010. [bibtex-key = Rosenauer2010a]



491. Andreas Rosenauer, Knut Müller, Katharina Gries, Marco Schowalter, Angelika Pretorius, Adrian Avramescu, Karl Engl, and Stephan Lutgen. Towards Quantitative Scanning Transmission Electron Microscopy: Measurement of Composition in III Nitrides. In International Conference on Advances in Electron Microscopy and Related Techniques/XXXI Annual Meeting of EMSI, Mumbai (India) [Invited talk], 2010. [bibtex-key = Rosenauer2010]



492. M. Schowalter, T. Aschenbrenner, C. Kruse, D. Hommel, and A. Rosenauer. TEM characterization of catalyst- and mask-free grown GaN nanorods. In MSM XVI, Oxford 2009, 16.-20. März Journal of Physics: Conference Series, 209 (2010) 012020, 2010. [bibtex-key = Schowalter2010a]



493. Marco Schowalter, Thorsten Mehrtens, and Andreas Rosenauer. The effect of strain on mean square displacement in wurtzite InGaN. In International Microscopy Congress (IMC17), Rio de Janeiro (Brazil) [Poster presentation], 2010. [bibtex-key = Schowalter2010]



494. Moritz Speckmann, Thomas Schmidt, Jan Ingo Flege, Inga Heidmann, Andre Kubelka, Locatelli A., T. O. Mentes, M. A. Nino, Knut Müller, Andreas Rosenauer, and Jens Falta. Facets, mazes, slabs, and nanowires: silver-mediated germanium growth on silicon surfaces. In 37th International conference on Vacuum Ultraviolet and X-ray Physics (VUVX), Vancouver (Canada) [Talk], 2010. Abstract:

     The adsorption of surfactant materials on Si surfaces has a strong impact on the subsequent growth of Ge nanostructures. Due to the modulation of surface properties, like morphology and surface free energy, suppressed or enhanced 3D growth as well as less defects in the Ge structures and a reduced intermixing between Ge and the Si substrate can be observed. Hereby, we will show that Ag is an extremely versatile tool for these purposes. Depending on the substrate orientation and the Ag-induced reconstruction and morphology, either a suppressed or an enhanced 3D growth of the Ge structures can be generated. On the (√3x√3)-Ag reconstruction on Si(111), huge flat islands are observed with in-situ LEEM. For a growth temperature of about 500°C, the LEEM data indicate that these islands coalesce and form a continuous film at a Ge coverage of about 15 nm. XPEEM experiments give evidence for the suppression of intermixing as only a very low Si content is found in the islands. The formation of a periodic misfit dislocation network and a twin formation are observed, using GIXRD and TEM. A completely different behaviour is found for the Si(113) surface. In this case, Ag induces the formation of a regular pattern of nanofacets along the [1-10] direction. Subsequently grown Ge forms small anisotropic nanoislands with a wire-like geometry at an aspect ratio of about 4:1. These nanowires are aligned along the Ag-induced faces.

     [bibtex-key = Speckmann2010]



495. J. Titantah, D. Lamoen, M. Schowalter, and A. Rosenauer. Ab initio based atomic scattering amplitudes and 002 electron structure factor of GaInAs/GaAs quantum wells. In MSM XVI, Oxford 2009, 16.-20. März Journal of Physics: Conference Series, 209 (2010) 012040, 2010. [bibtex-key = Titantah2010]



496. Timo Aschenbrenner, Gerd Kunert, Carsten Kruse, Stephan Figge, Joachim Kalden, Kathrin Sebald, Knut Müller, Marco Schowalter, Jürgen Gutowski, Andreas Rosenauer, and Detlef Hommel. Catalyst- and mask-free grown GaN nanocolumns. In E-MRS Fall Meeting 2009, Warsaw (Poland) [Invited talk], 2009. [bibtex-key = Aschenbrenner2009]



497. B. Butz, R. Schneider, D. Gerthsen, M. Schowalter, and A. Rosenauer. Chemical instability as reason for degradation of ionic conductivity in 8.5 mol% Y03-doped ZrO. In W. Grogger, F. Hofer, and P. Pölt, editors, MC2009, Graz (Austria) Vol. 3: Materials science, pages 201--302, 2009. [bibtex-key = Butz2009]



498. M. Dries, B. Gamm, K. Schultheiss, A. Rosenauer, R.R. Schröder, and D. Gerthsen. Object wave reconstruction by carbon-film-based Zernike- and Hilbert-phase plates. In MC2009 Graz (Austria), 2009. [bibtex-key = Dries2009]



499. B. Gamm, M. Dries, K. Schultheiss, H. Blank, A. Rosenauer, R.R. Schr�er, and D. Gerthsen. Object wave reconstruction by phase plate transmission electron microscopy. In MC2009 Graz (Austria), 2009. [bibtex-key = Gamm2009]



500. K. Gries, M. Fritz, and A. Rosenauer. Detection of calcium ions in the mantle epithelium of the abalone Haliotis laevigata. In MC2009 Graz (Austria) Vol.2: Life Sciences, pp297 - 298, 2009, 2009. [bibtex-key = Gries2009b]



501. Thorsten Mehrtens, Knut Müller, Marco Schowalter, Nils Neugebohrn, Andreas Rosenauer, Dongzhi Hu, and Daniel Schaadt. Towards a quantitative concentration analysis in InGaAs-heterostructures using HAADF-STEM. In G. Kothleitner and M. Leisch, editors, MC2009, Graz (Austria) Vol. 1: Instrumentation and Methodology, pages 219--220, 2009. [bibtex-key = Mehrtens2009a]



502. Thorsten Mehrtens, Marco Schowalter, Knut Müller, Andreas Rosenauer, Dongzhi Hu, and Daniel Schaadt. Analysis of segregation profiles in InGaAs quantum wells via TEM and STEM. In Verhandlungen der DPG, number HL 1.6, 2009. [bibtex-key = Mehrtens2009]



503. Knut Müller, Marco Schowalter, Andreas Rosenauer, Jacob Jansen, Kenji Tsuda, John Titantah, and Dirk Lamoen. Measurement of structure factors by parallel and convergent beam electron nanodiffraction. In G. Kothleitner and M. Leisch, editors, MC2009, Vol. 1: Instrumentation and Methodology [Poster], pages 293--294, 2009. [bibtex-key = Mueller2009a]



504. Knut Müller, Marco Schowalter, Andreas Rosenauer, Wolfgang Stolz, and Kerstin Volz. Simultaneous measurement of In and N concentration maps and profiles in InGaNAs from a single TEM lattice fringe image. In W. Grogger, F. Hofer, and P. Pölt, editors, MC2009, Graz (Austria) Vol. 3: Materials science, pages 45--46, 2009. [bibtex-key = Mueller2009]



505. S. Pokhrel, M. Schowalter, A. Rosenauer, and L. Mädler. New precursors leading to single crystalline WO3 nanospheres. In presented at AICHE annual meeting (2009), 2009. [bibtex-key = Pokhrel2009]



506. A. Rosenauer, M. Schowalter, A. Pretorius, A. Avramescu, K. Engl, and S. Lutgen. Quantitative measurement of composition profiles at interfaces in semiconductor nanostructures by HRSTEM. In PSI2009, Puri, India, February 2009, 2009. [bibtex-key = Rosenauer2009]



507. Marco Schowalter, Thorsten Mehrtens, Kristian Frank, Knut Müller, and Andreas Rosenauer. Analysis of semiconductor interfaces and surface segregation using the composition evaluation by lattice fringe analyis (CELFA) method. In Physics at surfaces and Interfaces (PSI), Puri (India) [Talk], 2009. [bibtex-key = Schowalter2009b]



508. V. Srivastava, K.B. Surreddi, S. Scudino, M. Schowalter, V. Uhlenwinkel, A. Schulz, J. Eckert, A. Rosenauer, and H.-W. Zoch. Novel microstructural characteristics and properties of spray formed Al-RE-TM based alloys. In Proceedings of the 4th International conference on spray deposition and melt atomization SDMA2009 and 7th international conference on spray forming ICSF7 held at University of Bremen during September 07-09, 2009, 2009. [bibtex-key = Srivastava2009a]



509. John T. Titantah, Dirk Lamoen, Marco Schowalter, Andreas Rosenauer, and Knut Müller. Ab initio based atomic scattering amplitudes and 002 electron structure factor of GaInAsN / GaAs quantum wells. In 32nd International Symposium on Dynamical Properties of Solids, Antwerp (Belgium) [Poster presentation], September 2009. [bibtex-key = Titantah2009]



510. T. Aschenbrenner, S. Figge, D. Hommel, M. Schowalter, and A. Rosenauer. MOVPE-growth of a-plane InGaN quantum wells on GaN buffer layers on r-plane sapphire substrates. In IC-MOVPE, 1.-6. June 2008, 2008. [bibtex-key = Aschenbrenner2008a]



511. H. Dartsch, S. Figge, T. Aschenbrenner, A. Pretorius, A. Rosenauer, and D. Hommel. Strain compensated AlGaN/GaN-Bragg-reflectors with high Al content grown by MOVPE. In IC-MOVPE, 1.-6. June 2008, 2008. [bibtex-key = Dartsch2008]



512. P. Galindo, J. Pizarro, A. Rosenauer, A. Yanez, E. Guerrero, and S. Molina. HAADF-STEM image simulation of large scale nanostructures. In M. Luysberg, K. Tillmann, T. Weirich (Eds.): EMC 2008, Instrumentation and Methods, volume 1, pages 111--112, 2008. [bibtex-key = Galindo2008]



513. K. Gries, R. Kröger, C. Kuebel, M. Fritz, and A. Rosenauer. Electron microscopic investigations of the polymer/mineral composite material nacre. In S. Richter, A. Schwedt (Eds.): EMC 2008, Vol. 2: Materials Science, pp. 733-734, DOI: 10.1007/978-3-540-85226-1_367, 2008. [bibtex-key = Gries2008]



514. Katharina Gries, Roland Kröger, Christian Kuebel, Monika Fritz, and Andreas Rosenauer. Elektronenmikroskopische Untersuchung des Polymer-Mineral-Verbundmaterials Perlmutt. In DPG Frühjahrstagung, Berlin (Germany), 2008. [bibtex-key = Gries2008a]



515. M. Monville, S. Bonnany, M. Schowalter, C. Birgot, B. Lombardet, and C. Belouet. Proceedings of Carbon conference. In , 2008. [bibtex-key = Monville2008]



516. Knut Müller and Katharina Gries. Advanced Methods in Transmission Electron Microscopy. In Tutorial held at the workshop of the Institute for solid state physics in Riezlern, Austria. A handout of the 30 minutes talk is available at http://www.ifp.uni-bremen.de, 2008. [bibtex-key = Mueller2008c]



517. Knut Müller, Marco Schowalter, Andreas Rosenauer, Jacob Jansen, John Titantah, and Dirk Lamoen. Measurement of 002 structure factors for GaAs from electron spot diffraction patterns. In Verhandlungen der DPG [Talk], number HL 33.2, pages 376, 2008. [bibtex-key = Mueller2008b]



518. Knut Müller, Marco Schowalter, Andreas Rosenauer, Dirk Lamoen, John Titantah, Jacob Jansen, and Kenji Tsuda. Measurement of GaAs structure factors from the diffraction of parallel and convergent electron nanoprobes. In M. Luysberg, K. Tillmann, and T. Weirich, editors, EMC 2008, Vol. 1: Instrumentation and methods [Poster], pages 215--216, 2008. [bibtex-key = Mueller2008a]



519. Knut Müller, Marco Schowalter, Andreas Rosenauer, John Titantah, Dirk Lamoen, Jacob Jansen, and Kenji Tsuda. Measurement of 002 structure factors for GaAs using parallel and convergent beam electron diffraction. In Meeting of the Arbeitskreises Hochauflösende Elektronenmikroskopie der Deutschen Gesellschaft für Elektronenmikroskopie, Bremen [Vortrag (Talk)], 2008. [bibtex-key = Mueller2008]



520. A. Pretorius, T. Aschenbrenner, H. Dartsch, S. Figge, D. Hommel, and A. Rosenauer. Transmission electron microscopical investigation of AlGaN/GaN distributed Bragg reflectors. In IWN 2008, 6-10 Oktober, Montreaux, Schweiz Physica Status Solidi C 6, S680-S683, 2008. [bibtex-key = Pretorius2008c]



521. A. Pretorius, A. Rosenauer, T. Aschenbrenner, H. Dartsch, S. Figge, and D. Hommel. TEM analyses of microstructure and composition of Al(x)Ga(1-x)N/GaN distributed Bragg reflectors. In S. Richter, A. Schwedt (Eds.): EMC 2008, Vol. 2: Materials Science, pp. 81-82, DOI: 10.1007/978-3-540-85226-1_41, 2008. [bibtex-key = Pretorius2008a]



522. A. Rosenauer, M. Schowalter, J. Titantah, and D. Lamoen. A novel emission potential multislice method to calculate intensity contributions for thermal diffuse scattering in plane wave illumination TEM. In M. Luysberg, K. Tillmann, T. Weirich (Eds.): EMC 2008, Vol. 1: Instrumentation and Methods, pp. 147-148, DOI: 10.1007/978-3-540-85156-1_74, 2008. [bibtex-key = Rosenauer2008a]



523. M. Schowalter, A. Rosenauer, J. Titantah, and D. Lamoen. Computation and parametrization of Debye-Waller temperature factors for sphalerite type II-VI, III-V and group IV semiconductors. In M. Luysberg, K. Tillmann, T. Weirich (Eds.): EMC 2008, Vol. 1: Instrumentation and Methods, pp. 153-154, DOI: 10.1007/978-3-540-85156-1_77, 2008. [bibtex-key = Schowalter2008]



524. R. Kroeger, T. Paskova, A. Rosenauer, D. Hommel, B. Monemar, P. Fini, B. Haskell, J. Speck, and S. Nakamura. On the mechanism of dislocation and stacking fault formation in a-plane GaN films grown by hydride vapor phase epitaxy. In Physics of Semiconductors, 28th International Conference. Vienna, Austria. 24-28 July 2006. AIP-Conference-Proceedings. 2007; 893: 341-2, 2007. [bibtex-key = Kroeger2007]



525. R. Kröger, T. Paskova, D. Hommel, A. Rosenauer, P. Fini, B. Haskell, J. Speck, S. Nakamura, and B. Monemar. Defects in a-plane GaN films on r-plane sapphire. In Springer Proceedings in Physics: MSM(2007), 2007. [bibtex-key = Kroeger2007b]



526. D. Litvinov, D. Gerthsen, A. Rosenauer, M. Schowalter, T. Passow, and M. Hetterich. The role of segregation in InGaAs heteroepitaxy. In presented at THERMEC, Advanced thin films and nanomaterials (2006) Materials Science Forum Vols. 539-543 (2007) 3540-3545, 2007. [bibtex-key = Litvinov2007a]



527. D. Litvinov, D. Gerthsen, A. Rosenauer, M. Schowalter, T. Passow, and M. Hetterich. The role of segregation in InGaAs heteroepitaxy. In Materials Science Forum, 539-543, (2007), 3540, 2007. [bibtex-key = Litvinov2007]



528. R. Popescu, E. Müller, D. Gerthsen, M. Wanner, M. Schowalter, A. Rosenauer, and A. Böttcher. Mean Inner Coulomb Potential of Au Clusters Analyzed by Transmission Electron Holography. In Proceedings of Microscopy and Microanalysis Conference (2007, 2007. [bibtex-key = Popescu2007b]



529. R. Popescu, E. Müller, D. Gerthsen, M. Wanner, M. Schowalter, A. Rosenauer, A. Böttcher, D. Löffler, and P. Weis. Increase of the Mean Inner Coulomb Potential of Au in Au Clusters Induced by Surface Tension. In MC 2007, Saarbrücken, Germany, September 2-7, 2007 Microsc. Microanal. 13 (Suppl. 3), 2007, 138 DOI: 10.1017/S1431927607080695, 2007. [bibtex-key = Popescu2007a]



530. A. Pretorius, T. Yamaguchi, K. Müller, R. Kröger, D. Hommel, and A. Rosenauer. Concentration Measurement In Free-Standing InGaN Nano-Islands With Transmission Electron Microscopy. In MC 2007, Saarbrücken, Germany, September 2-7, 2007 Microsc. Microanal. 13 (Suppl. 3), 2007, 312, 2007. [bibtex-key = Pretorius2007]



531. A. Rosenauer. A Local Absorptive Potential Multislice Approximation to Calculate Intensity Contributions from Thermal Diffuse Scattering in Conventional TEM. In MC 2007, Saarbrücken, Germany, September 2-7, 2007 Microsc. Microanal. 13 (Suppl. 3), 2007, 024 DOI: 10.1017/S1431927607080129, 2007. [bibtex-key = Rosenauer2007c]



532. Andreas Rosenauer and Marco Schowalter. STEMSIM-a new software tool for simulation of STEM HAADF Z-contrast imaging. In A. G. Cullis and P. A. Midgley, editors, Springer Proceedings in Physics, volume 120, pages 169--172, 2007. Springer. [bibtex-key = Rosenauer2007b]



533. Andreas Rosenauer, Marco Schowalter, Knut Müller, John Titantah, and Dirk Lamoen. Ab-inito Methods as Tools for Quantitative High-Resolution Transmission Electron Microscopy. In MRS Fall Meeting, Boston (USA) [Invited talk], 2007. [bibtex-key = Rosenauer2007a]



534. A. Rosenauer, M. Schowalter, K. Müller, J. Titantah, D. Lamoen, P. Kruse, and D. Gerthsen. Ab-inito Methods as Tools for Quantitative High-Resolution Transmission Electron Microscopy. In MRS Autumn Meeting 2008 Symposium C: Quantitative Electron Microscopy for Materials Science SESSION C21: HRTEM and Quantitative Comparison of Experiment and Theory II, 2007. [bibtex-key = Rosenauer2007]



535. M. Schowalter, A. Rosenauer, J. Titantah, and D. Lamoen. Calculation of Debye-Waller temperature factors for GaAs. In Springer Proceedings in Physics: MSM(2007), 2007. [bibtex-key = Schowalter2007a]



536. M. Schowalter, A. Rosenauer, J. Titantah, and D. Lamoen. Temperature dependence of Debye-Waller Factors of sphalerite III-V Semiconductors calculated from Ab Initio Force Constants. In MC 2007, Saarbrücken, Germany, September 2-7, 2007 Microsc. Microanal. 13 (Suppl. 3), 2007, 128 DOI: 10.1017/S1431927607080646, 2007. [bibtex-key = Schowalter2007]



537. J. T. Titantah, D. Lamoen, M. Schowalter, and Rosenauer. Bond length variations in InGaAs crystals fom Tersoff potential. In Springer Proceedings in Physics: MSM(2007), 2007. [bibtex-key = Titantah2007b]



538. D. Litvinov, D. Gerthsen, A. Rosenauer, M. Schowalter, T. Passow, P. Feinäugle, and M. Hetterich. Transmission Electron Microscopy Study of In-Segregation and Critical Floating-Layer Content of Indium for Island Formation in InGaAs. In Proceedings of the International Microscopy Conference 16, Sapporo, Japan (2006), 2006. [bibtex-key = Litvinov2006a]



539. A. Pretorius, M. Schowalter, N. Daneu, R. Kröger, A. Recnik, and A. Rosenauer. Structural analysis of pyramidal defects in Mg-doped GaN. In ICNS-6, August / September 2005, Bremen Phys. stat. sol c, 3 (2006), 1803, 2006. [bibtex-key = Pretorius2006b]



540. A. Pretorius, M. Siebert, T. Schmidt, R. Kroeger, T. Yamaguchi, D. Hommel, J. Falta, and A. Rosenauer. Indium Concentration Measurements in Nano-Sized InGaN Islands Using High Resolution Transmission Electron Microscopy.. In Proceedings of the 16th International Microscopy Congress, Sapporo, Japan, 1454, 2006, 2006. [bibtex-key = Pretorius2006a]



541. A. Pretorius, T. Yamaguchi, C. Kuebel, R. Kröger, D. Hommel, and A. Rosenauer. TEM analyses of wurtzite InGaN islands grown by MOVPE and MBE. In ICNS 6, August / September 2005, Bremen Phys. stat. sol c, 3 (2006), 1679-1682, 2006. [bibtex-key = Pretorius2006]



542. A. Rosenauer, A. Pretorius, M. Schowalter, K. Müller, T. Yamaguchi, D. Hommel, D. Litvinov, and D. Gerthsen. Composition determination of semiconductor nanostructures. In NVvM - BSM Joint Meeting Lunteren, NL, November 26-28, 2006, 2006. [bibtex-key = Rosenauer2006a]



543. A. Rosenauer, M. Schowalter, F. Glas, and D. Lamoen. Ab initio computation of 002 structure factors for electron scattering in strained InGaAs. In Proceedings of DFTEM, Vienna (2006), 2006. [bibtex-key = Rosenauer2006]



544. E. Roventa, G. Alexe, M. Schowalter, R. Kroeger, D. Hommel, and A. Rosenauer. Anisotropic Spatial Correlation of CdSe/Zn(S)Se Quantum dot Stacks Grown by MBE. In Presented at 12th International Conference on II-VI Compounds, September 12-16, Warsaw, Poland Phys. Stat. Sol.-C, 3 (2006) 887-890, 2006. [bibtex-key = Roventa2006]



545. M. Schowalter, A. Rosenauer, D. Litvinov, and D. Gerthsen. Investigation of segregation by quantitative transmission electron microscopy. In Optica Applicata 36 (2006) 297-309, 2006. [bibtex-key = Schowalter2006a]



546. M. Schowalter, A. Rosenauer, J. Titantah, D. Lamoen, P. Kruse, and D. Gerthsen. Computation of the mean inner Coulomb potential of technological important semiconductors, gold and amorphous carbon. In Proceeding of DFTEM, Vienna (2006), page 11, 2006. [bibtex-key = Schowalter2006]



547. T. Yamaguchi, S. Einfeldt, S. Gangopadhyay, A. Pretorius, A. Rosenauer, J. Falta, and D. Hommel. Two to three dimensional transitions of InGaN and the impact of GaN overgrowth. In ICNS 6, August / September 2005, Bremen Phys. stat. sol c, 3 (2006), 1396-1399, 2006. [bibtex-key = Yamaguchi2006]



548. M. Beer, K. Engl, J. Zweck, A. Able, M. Wegscheider, M. Schowalter, and A. Rosenauer. Quantative TEM Analysis of the composition of InGaN/AlGaN layers: Selection of the proper imaging conditions. In Presented at Microscopy Conference Davos (2005), 2005. [bibtex-key = Beer2005]



549. D. Litvinov, D. Gerthsen, A. Rosenauer, T. Passow, M. Grün, C. Klingshirn, and M. Hetterich. In-distribution in InGaAs Quantum Wells and Quantum Islands. In Presented at MCMXIV, Oxford, 2005. [bibtex-key = Litvinov2005]



550. E. Müller, P. Kruse, D. Gerthsen, A. Rosenauer, M. Schowalter, D. Lamoen, R. Kling, and A. Waag. Measurement of the mean inner potential of ZnO nanorods by transmission electron holography. In Springer Proceedings in Physics 107, 233 (2005), ISBN: 3.540-31914-X, 2005. [bibtex-key = Mueller2005c]



551. E. Müller, P. Kruse, D. Gerthsen, A. Rosenauer, M. Schowalter, D. Lamoen, R. Kling, and A. Waag. Measurement of the mean inner potential of ZnO nanorods by transmission electron holography. In Presented at E-MRS 2005 Spring Meeting Strassbourg (2005), 2005. [bibtex-key = Mueller2005b]



552. A. Pretorius, T. Yamaguchi, R. Kroeger, C. Kuebel, D. Hommel, and A. Rosenauer. Investigation of In(x)Ga(1-x)N islands with electron microscopy. In Springer Proceedings in Physics 107, 17 (2005), ISBN: 3.540-31914-X, 2005. [bibtex-key = Pretorius2005]



553. A. Rosenauer, M. Schowalter, F. Glas, and D. Lamoen. First-principles calculations of 002 structure factors for electron diffraction in strained In(x)Ga(1-x)As. In Springer Proceedings in Physics 107, 151 (2005), ISBN: 3.540-31914-X, 2005. [bibtex-key = Rosenauer2005a]



554. M. Schowalter, A. Rosenauer, D. Lamoen, P. Kruse, and D. Gerthsen. Ab initio computation of the mean inner coulomb potential of technologically important semiconductors. In Springer Proceedings in Physics 107, 233 (2005), ISBN: 3.540-31914-X, 2005. [bibtex-key = Schowalter2005a]



555. T. Torunski, O. Rubel, W. Stolz, K. Volz, P. Kruse, D. Gerthsen, M. Schowalter, and A. Rosenauer. Annealing Behaviour of N Containing III/V-Semiconductors. In presented at Electronics Materials Conference (EMC) , Santa Barbara (USA), 22.06.-24.06, 2005. [bibtex-key = Torunski2005]



556. D. Litvinov, D. Gerthsen, A. Rosenauer, B. Daniel, and M. Hetterich. Investigation of the growth and composition of ZnMnSe heterostructures by transmission electron microscopy Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 2, 451-452. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 2, 451-452, 2004. [bibtex-key = Litvinov2004c]



557. D. Litvinov, D. Gerthsen, A. Rosenauer, P. Gilet, and L. Grenouillet. Measurement of the nigrogen-concentration profile in GaInN/GaAs heterostructures by quantitative high-resolution transmission electron microscopy Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 127-128. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 127-128, 2004. [bibtex-key = Litvinov2004b]



558. E. Piscopiello, A. Rosenauer, A. Passaseo, and G. Van Tendeloo. Segregation in InGaAs/GaAs quantum wells grown by MOCVD Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 123-124. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 123-124, 2004. [bibtex-key = Piscopiello2004]



559. A. Rosenauer and D. Gerthsen. Optimum imaging conditions for strain state analysis of InGaN/GaN heterostructures. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 103-104, 2004. [bibtex-key = Rosenauer2004]



560. M. Schowalter, P. Kruse, D. Lamoen, A. Rosenauer, and D. Gerthsen. First principles calculation of the mean inner Coulomb potential for cubic II/VI and hexagonal III/V semiconductors. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 195-196, 2004. [bibtex-key = Schowalter2004b]



561. M. Schowalter, A. Rosenauer, D. Lamoen, and D. Gerthsen. Strain state analysis of InGAAs/GaAs heterostructures: Elastic relaxation in cross section and cleaved specimen,. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 1, 129-130, 2004. [bibtex-key = Schowalter2004]



562. T. Torunski, K. Volz, W. Stolz, P. Kruse, D. Gerthsen, M. Schowalter, and A. Rosenauer. Quantification of N distribution in Ga(Nas)/GaAs multi-quantum well structures. In Proceedings of the 13th European Microscopy Congress, Antwerp, Belgium, August 22-27, 2004, Vol. 2, 441-442, 2004. [bibtex-key = Torunski2004]



563. D. Gerthsen, E. Hahn, V. Potin, A. Rosenauer, B. Kuhn, J. Off, F. Scholz, A. Dussaigne, B. Damilano, and N. Grandjean. In distribution in InGaN quantum wells: influence of phase separation, In segregation and In desorption. In Microcopy of Semiconducting Materials 2003, Cambridge, UK, 31 March-3 April 2003, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2003), 2003. [bibtex-key = Gerthsen2003]



564. P. Kruse, A. Rosenauer, and D. Gerthsen. Determination of the mean inner potential in III-V semiconductors by electron holography. In Microcopy of Semiconducting Materials 2003, Cambridge, UK, 31 March-3 April 2003, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2003), 2003. [bibtex-key = Kruse2003a]



565. D. Litvinov, A. Rosenauer, D. Gerthsen, P. Kratzert, M. Rabe, and F. Henneberger. Influence of ZnSe cap layer growth on the morphology and Cd distribution in CdSe/ZnSe quantum dot structures. In Proceedings of the SPIE - The Internation Society for Optical Engineering 5023 (2003) 42-4, 2003. [bibtex-key = Litvinov2003]



566. M. Melzer, Marco Schowalter, Andreas Rosenauer, D. Gerthsen, and J. P. Reithmaier. Untersuchung der Segregation von In in InAs/AlAs Heterostrukturen. In DPG Frühjahrstagung, Dresden (Germany) Verhandl. DPG (VI) 38, 1, 186, 2003. [bibtex-key = Melzer2003]



567. A. Rosenauer, D. Gerthsen, D. Van Dyck, S. Van Aert, and A.J. Den Dekker. Present state of the composition evaluation of ternary semiconductor nanostructures by lattice fringe analysis,. In Microcopy of Semiconducting Materials 2003, Cambridge, UK, 31 March-3 April 2003, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2003), 2003. [bibtex-key = Rosenauer2003a]



568. A. Rosenauer, M. Melzer, M. Schowalter, D. Gerthsen, E. Piscopiello, A. Passaseo, R. Cingolani, R. Reithmaier, J. P. amd Krebs, A. Forchel, and G. Van Tendeloo. Segregation in InGaAs/GaAs Quantum Wells: MOCVD versus MBE. In Microscopy Conference MC2003, International Forum for Advanced Microscopy, September 7-12, 2003, Dresden, Germany Micrsocopy and Microanalysis 9 (2003) 230-1, 2003. [bibtex-key = Rosenauer2003]



569. M. Schowalter, M. Melzer, A. Rosenauer, D. Gerthsen, R. Krebs, J. P. Reithmaier, A. Forchel, M. Arzberger, M. Bichler, G. Abstreiter, M. Grau, M.-C. Amann, R. Sellin, and D. Bimberg. Segregation in III-V semiconductor heterostructures studied by transmission electron microscopy,. In Microcopy of Semiconducting Materials 2003, Cambridge, UK, 31 March-3 April 2003, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2003), 2003. [bibtex-key = Schowalter2003c]



570. M. Schowalter, A. Rosenauer, D. Gerthsen, M. Grau, and M.-C. Amann. Quantitative investigation of Sb distribution in GaSb/GaAs heterostructures,. In Microcopy of Semiconducting Materials 2003, Cambridge, UK, 31 March-3 April 2003, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2003), 2003. [bibtex-key = Schowalter2003b]



571. M. Schowalter, A. Rosenauer, D. Gerthsen, R. Sellin, and D. Bimberg. Structure factors for the composition determination of InGaAs/GaAs quantum wells with the 002 beam: Isolated atom approximation versus density function theory. In Microscopy Conference MC2003, International Forum for Advanced Microscopy, September 7-12, 2003, Dresden, Germany Microscopy and Microanalysis 9 (2003), 234-5, 2003. [bibtex-key = Schowalter2003]



572. M. Efremov, V. Volodin, V.A. Sachkov, V. Preobrazhenskii, B. Semyagin, N. Ledentsov, V. Ustinov, I. Soshnikov, D. Litvinov, A. Rosenauer, and D. Gerthsen. RAMAN study of GaAs quantum wires grown with partial filling of corrugated (311)A AlAs surfaces. In Microelectron. J. 33, 535-40, 2002. [bibtex-key = Efremov2002]



573. E. Hahn, Andreas Rosenauer, Dagmar Gerthsen, J. Off, and F. Scholz. In-Verteilung beim MOVPE-Wachstum von GaInN-Quantenfilmen. In DPG Frühjahrstagung, Regensburg (Germany) Verhandl. DPG (VI) 37,1, 195, 2002. [bibtex-key = Hahn2002]



574. P. Kruse, A. Rosenauer, and D. Gerthsen. Determination of the mean inner potential in III-V semiconductors by electron hologrpahy. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, 2002. [bibtex-key = Kruse2002]



575. E. Kurtz, B. Dal Don, M. Schmidt, H. Kalt, C. Klingshirn, D. Litvinov, A. Rosenauer, and D. Gerthsen. CdSe quantum islands in ZnSe: a new approach. In Thin Solid Films 412, 89-95, 2002. [bibtex-key = Kurtz2002a]



576. D. Litvinov, A. Rosenauer, D. Gerthsen, and H. Preis. Transmission electron microscopy investigation of CdSe/ZnSe quantum dot structures. In Phys. Stat. Solidi B 229 (1), 523-527, 2002. [bibtex-key = Litvinov2002a]



577. V. Potin, E. Hahn, M. Schowalter, A. Rosenauer, D. Gerthsen, B. Kuhn, and F. Scholz. Quantitative analysis of the In-distribution in InGaN/GaN-heterostructures. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, 2002. [bibtex-key = Potin2002a]



578. A. Rosenauer and D. Gerthsen. Composition evaluation of ternary semiconductor nanostructres by lattice fringe analysis. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, p. 195, 2002. [bibtex-key = Rosenauer2002b]



579. A. Rosenauer, D. Gerthsen, D. Van Dyck, M. Arzberger, G. Böhm, and G. Abstreiter. Compositional analysis of semiconductor nanostructures based on electron holography and a chemically sensitive reflection. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, p. 291, 2002. [bibtex-key = Rosenauer2002a]



580. A. Rosenauer, D. Gerthsen, D. Van Dyck, M. Arzberger, G. Böhm, and G. Abstreiter. Quantification of segregation and mass transport in InGaAs/GaAs quantum dot structrues. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, p. 59, 2002. [bibtex-key = Rosenauer2002]



581. Marco Schowalter, Andreas Rosenauer, Dagmar Gerthsen, M. Arzberger, M. Bichler, and G. Abstreiter. Untersuchung der Segregation von In in InAs/AlAs Heterostrukturen. In DPG Frühjahrstagung, Regensburg (Germany) Verhandl. DPG (VI) 37, 1, 163, 2002. [bibtex-key = Schowalter2002b]



582. M. Schowalter, A. Rosenauer, D. Gerthsen, M. Grau, and M.-C. Amann. Influence of growth interruptions on the composition of GaSb/GaAs quantum wells. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, p. 53, 2002. [bibtex-key = Schowalter2002a]



583. M. Schowalter, A. Rosenauer, D. Gerthsen, R. Sellin, and D. Bimberg. Segregation in MBE and MOCVD: A comparison. In International Conference on Electron Microscopy (ICEM) 15, Durban, 1-6 September 2002, p. 113, 2002. [bibtex-key = Schowalter2002]



584. K. Chinyama, K. O'Donnell, A. Rosenauer, and E. Kurtz. Composition of self-assembled quantum dots in CdSe-ZnSe quantum well structures. In Microcopy of Semiconducting Materials 2001, Oxford, UK, 25-29 March 2001, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2001), 2001. [bibtex-key = Chinyama2001]



585. Dagmar Gerthsen and Andreas Rosenauer. Halbleiter-Quantenpunkte: Welche Informationen kann die Elktronenmikroskopie liefern?. In DPG Frühjahrstagung, Hamburg (Germany) [Talk] Plenarvortrag, Frühjahrstagung des Arbeitskreises Festkörperphysik 2001, Hamburg, Verhandl. DPG (VI) 36, 1/(2001), 62, 2001. [bibtex-key = Gerthsen2001]



586. E. Kurtz, M. Schmidt, D. Litvinov, B. Dal Don, R. Dianoux, H. Zhao, H. Kalt, A. Rosenauer, D. Gerthsen, and C. Klingshirn. Correlation in vertically stacked CdSe based quantum islands. In Phys. Stat. Solidi B 229 (1), 519-522, 2001. [bibtex-key = Kurtz2001]



587. D. Litvinov, D. Gerthsen, A. Rosenauer, H. Preis, E. Kurtz, and C. Klingshirn. Cd distribution and defects in single and multilayer CdSe/ZnSe quantum dot structures,. In International Conference on Semiconductor Quantum Dots (QD 2000). - 31 July-3 Aug. 2000 Phys. Status Solidi B 224, 147-51, 2001. [bibtex-key = Litvinov2001b]



588. D. Litvinov, A. Rosenauer, D. Gerthsen, and H. Preis. Cd-Verteilung und Defekte in CdSe/ZnSe Quantenpunktstrukturen,. In DPG Frühjahrstagung, Hamburg (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 2001, Hamburg, Verhandl. DPG (VI) 36, 1/(2001), 158, 2001. [bibtex-key = Litvinov2001a]



589. V. Potin, E. Hahn, A. Rosenauer, and D. Gerthsen. Determination of indium composition fluctuation in InGaN/GaN quantum wells by quantitative high resolution electron microscopy. In Microcopy of Semiconducting Materials 2001, Oxford, UK, 25-29 March 2001, Inst. Phys. Conf. Ser. 169, 25-28 Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2001), 2001. [bibtex-key = Potin2001]



590. A. Rosenauer, D. Gerthsen, D. Van Dyck, M. Arzberger, G. Böhm, and G. Abstreiter. Atomic-scale composition analysis of semiconductor quantum dots by transmission electron microscopy,. In 7th International Symposium on Advanced Physical Fields „Fabrication and Characterization of Nanostructured Materialsâ€�, 12-15.11.2001 Tsukuba, 2001. [bibtex-key = Rosenauer2001b]



591. A. Rosenauer, D. Gerthsen, D. Van Dyck, M. Arzberger, G. Böhm, and G. Abstreiter. Compositional analysis based upon electron holography and a chemically sensitive reflection, (invited talk). In Microcopy of Semiconducting Materials 2001, Oxford, UK, 25-29 March 2001, Inst. Phys. Conf. Ser. 169, 33-36 Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2001), 2001. [bibtex-key = Rosenauer2001a]



592. A. Rosenauer, D. Van Dyck, D. Gerthsen, M. Arzberger, G. Böhm, and G. Abstreiter. Structural and chemical investigation of InAs/GaAs nanostructures by transmission electron microscopy,. In International Conference on Semiconductor Quantum Dots (QD 2000). - 31 July-3 Aug. 2000 Phys. Status Solidi B 224, 213-16, 2001. [bibtex-key = Rosenauer2001]



593. S. Schaefer, D. Litvinov, A. Rosenauer, D. Gerthsen, M. Bartels, and D. Schikora. HRTEM-Untersuchung von CdZnSe/GaAs(100) Inselstrukturen. In DPG Frühjahrstagung, Hamburg (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 2001, Hamburg, Verhandl. DPG (VI) 36, 1/(2001), 180, 2001. [bibtex-key = Schaefer2001]



594. M. Schowalter, B. Neubauer, A. Rosenauer, D. Gerthsen, O. Schön, and M. Heuken. MOCVD growth of Ga(Al)N/InGaN/Ga(Al)N-Heterostructures: Influence of the Buffer Layer Al-Concentration an d Growth Duration on the In-Incorporation in InGaN. In MRS spring meeting 2001, San Francisco, 2001. [bibtex-key = Schowalter2001b]



595. M. Schowalter, P. Pfundstein, B. Neubauer, A. Rosenauer, D. Gerthsen, T. Stephan, H. Kalt, A. Allam, B. Schneller, O. Schön, and M. Heuken. Composition of InGaN:In distribution and influence of lattice strain. In Microcopy of Semiconducting Materials 2001, Oxford, UK, 25-29 March 2001, Inst. Phys. Conf. Ser. 169, 273-276 Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (2001), 2001. [bibtex-key = Schowalter2001a]



596. M. Strassburg, A. Hoffmann, R. Heitz, U. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, D. Gerthsen, D. Schikora, and K. Lischka. High-excitation properties and time-resolved behaviour of three-dimensional CdSe/ZnSe islands. In DPG Frühjahrstagung, Hamburg (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 2001, Hamburg, Verhandl. DPG (VI) 35, 4/(2000), 587, 2001. [bibtex-key = Strassburg2001]



597. D. Gerthsen, E. Hahn, B. Neubauer, A. Rosenauer, O. Schön, M. Heuken, and A. Rizzi. Composition fluctuations in InGaN analized by transmission electron microscopy,. In 216. WE-Heraeus Seminar on Nitrogen in Solids and at Solid Surfaces: Present Status and Future Trends. - 30 May-2 June 1999. Status Solidi A 177, 145-55, 2000. [bibtex-key = Gerthsen2000a]



598. D. Gerthsen, A. Rosenauer, D. Litvinov, and N. Peranio. Structural and chemical analysis of CdSe islands in a ZnSe matrix by transmission electron microscopy. In II-VI Compounds 1999. Ninth International Conference, 1-5 Nov. 1999 J. Cryst. Growth 214-215, 707-11, 2000. [bibtex-key = Gerthsen2000]



599. N. N. Ledentsov, I. L. Krestnikov, M. Strassburg, R. Engelhardt, S. Rodt, R. Heitz, U.W. Pohl, A Hoffmann, D. Bimberg, A. V. Sakharov, V. Lundin, A. S. Usikov, Z. Alferov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Quantum dots formed by ultrathin insertions in wide-gap matrices,. In Third International Workshop on Molecular Beam Epitaxy- Growth Physics and Technology (MBE-GPT). - 23-28 May 1999. Thin Solid Films 367, 40-7, 2000. [bibtex-key = Ledentsov2000]



600. D. Luerssen, R. Bleher, H. Kalt, H. Richter, T. Schimmel, A. Rosenauer, D. Litvinov, A. Kamilli, D. Gerthsen, B. Jobst, K. Ohkawa, and D. Hommel. Localization of excitons in pairs of natural dots induced by stacking faults in ZnSe quantum wells. In 6th International Meeting on Optics of Excitons in Confined Systems (OECS-6). - 30 Aug.-2 Sept. 1999 Phys. Status Solidi A 178, 189-92, 2000. [bibtex-key = Luerssen2000a]



601. D. Luerssen, R. Bleher, H. Kalt, H. Richter, T. Schimmel, A. Rosenauer, D. Litvinov, A. Kamilli, D. Gerthsen, B. Jobst, K. Ohkawa, and D. Hommel. Stacking-fault-induced pairs of localizing centers in ZnSe quantum wells,. In II-VI Compounds 1999. Ninth International Conference, 1-5 Nov. 1999 J. Cryst. Growth 214-215, .634-8, 2000. [bibtex-key = Luerssen2000]



602. B. Neubauer, A. Rosenauer, D. Gerthsen, O. Schön, and M. Heuken. Influence of the growth duration on the In concentration in epitaxial InGaN layers,. In 12th European Congress on Electron Microscopy (EUREM 12), July 9-14 2000, Brno, Czech Republic, Proceedings, Volume II, P 281, 2000. [bibtex-key = Neubauer2000]



603. A Rosenauer and D. Van Dyck. The effect of strain on chemically sensitive imaging with the (002) reflection in sphalerite type crystals. In 12th European Congress on Electron Microscopy (EUREM 12), July 9-14 2000, Brno, Czech Republic, Proceedings, Volume III, I 121, 2000. [bibtex-key = Rosenauer2000]



604. D. Schikora, S. Schwedhelm, I. Kudryashov, K. Lischka, D. Litvinov, A. Rosenauer, D. Gerthsen, M. Strassburg, A. Hoffmann, and D. Bimberg. Investigations on the formation kinetics of CdSe quantum dots,. In II-VI Compounds 1999. Ninth International Conference, 1-5 Nov. 1999 J. Cryst. Growth 214-215, 698-702, 2000. [bibtex-key = Schikora2000]



605. E. Schomburg, S. Brandl, S. Winnerl, K.F. Renk, N. N. Ledentsov, V. Ustinov, A. Zhukov, P.S. Kopev, H.W. Hubers, J. Schubert, H.P. Roser, A. Rosenauer, D. Litvinov, D. Gerthsen, and J.M. Chamberlain. Miniband transport in a GaAs/AlAs superlattice with submonolayer barriers in a static and THz electric field,. In Ninth International Conference on Modulated Semiconductor Structures. MSS9 / Japan Soc. Appl. Phys. Physica E 7, 814-18, 2000. [bibtex-key = Schomburg2000]



606. M. Strassburg, T. Deniozou, A. Hoffmann, S. Rodt, V. Turck, R. Heitz, U.W. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, D. Gerthsen, S. Schwedhelm, I. Kudryashov, K. Lischka, and D. Schikora. Optical identification of quantum dot types in CdSe/ZnSe structures. In II-VI Compounds 1999. Ninth International Conference, 1-5 Nov. 1999 J. Cryst. Growth 214-215,756-60, 2000. [bibtex-key = Strassburg2000a]



607. M. Strassburg, A. Hoffmann, R. Heitz, U.W. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, D. Gerthsen, I. Kudryashov, K.. Lischka, and D. Schikora. Resonant gain in ZnSe structures with stacked CdSe islands grown in Stranski-Krastanov mode,. In Third International Symposium on Blue Laser and Light Emitting Diodes (ISBLLED 2000). - 5-10 March 2000 Phys. Status Solidi A 180, 281-5, 2000. [bibtex-key = Strassburg2000]



608. R. Bleher, H. Kalt, A. Kamilli, A. Rosenauer, D. Gerthsen, K. Ohkawa, and D. Hommel. Erhöhte bandkantennahe Lumineszenzausbeute verknüpft mit Frank-Defekten in ZnSe-Quantenfilmen. In DPG Frühjahrstagung, Münster (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1999, Münster, Verhandl. DPG (VI) 34, 1999, 768, 1999. [bibtex-key = Bleher1999]



609. I. L. Krestnikov, M. Strassburg, M. Caesar, V. Shchukin, A. Hoffmann, U. W. Pohl, D. Bimberg, N. N. Ledentsov, V.G. Malyshkin, P.S. Kop'ev, Z. Alferov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Vertical arrangement and wavefunction control in structures with 2D quantum dots (invited). In Proceedings ICPS24, Jerusalem, August 2-7, 1998, D. Gershoni, Ed. (World Scientific, 1999), pp. 70-77, 1999. [bibtex-key = Krestnikov1999]



610. D. Litvinov, A. Rosenauer, and D. Gerthsen. Struktur und Zusammensetzung von CdSe/ZnSe-Quantenpunkten,. In DPG Frühjahrstagung, Münster (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1999, Münster, Verhandl. DPG (VI) 34, 1999, 722, 1999. [bibtex-key = Litvinov1999]



611. B. Neubauer, E. Hahn, A. Rosenauer, and D. Gerthsen. Investigation of Composition Fluctuations in InxGa1-xN,. In Microcopy of Semiconducting Materials 1999, Oxford, UK, 22-25 March 1999, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (1999), 1999. [bibtex-key = Neubauer1999a]



612. B. Neubauer, A. Rosenauer, D. Gerthsen, O. Ambacher, M. Stutzmann, M. Albrecht, and H.P. Strunk. Analysis of composition fluctuations in Al(x)Ga(1-x)N. In E-MRS 1998 Spring Meeting, Symposium L: Nitrides and Related Wide Band Gap Materials. - 16-19 June 1998 Mater. Sci. Eng. B 59, 182-5, 1999. [bibtex-key = Neubauer1999]



613. W. Oberst, A. Rosenauer, D. Gerthsen, and A. Förster. Quantitative transmissionselektronenmikroskopische Untersuchung von InGaAs/GaAs-Quantenpunktstrukturen. In DPG Frühjahrstagung, Münster (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1999, Münster, Verhandl. DPG (VI) 34, 1999, 768, 1999. [bibtex-key = Oberst1999]



614. N. Peranio, A. Rosenauer, and D. Gerthsen. Strukturelle und chemische Analysen an CdSe/ZnSe-Quantenpunktstrukturen. In DPG Frühjahrstagung, Münster (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1999, Münster, Verhandl. DPG (VI) 34, 1999, 769, 1999. [bibtex-key = Peranio1999]



615. A. Rosenauer, W. Oberst, D. Gerthsen, and A. Förster. Atomic scale analysis of the indium distribution in InGaAs/GaAs(001) heterostructures: segregation, lateral indium redistribution and the effect of growth interruptions,. In MRS Fall Meeting 1998, Symposium: Growth Instabilities and Decompostion DuringHeteroepitaxy. Thin Solid Films 357, 18-21, 1999. [bibtex-key = Rosenauer1999a]



616. A. Rosenauer, N. Peranio, and D. Gerthsen. Investigation of CdSe/ZnSe Quantum Dot Structures by Composition Evaluation by Lattice Fringe Analysis,. In Microcopy of Semiconducting Materials 1999, Oxford, UK, 22-25 March 1999, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (1999), 1999. [bibtex-key = Rosenauer1999]



617. M. Strassburg, R. Engelhardt, R. Heitz, U.W. Pohl, S. Rodt, V. Turck, A. Hoffmann, D. Bimberg, I. L. Krestnikov, N. N. Ledentsov, Z. Alferov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Quantum dots formed by ultrathin CdSe-ZnSe insertions. In Proceedings of the 7th International Symposium Nanostructures: Physics and Technology, Ioffe Institute, St. Petersburg, Russia, June 14-18, 1999, p.13-19, 1999. [bibtex-key = Strassburg1999b]



618. M. Strassburg, I. L. Krestnikov, A. Göldner, V. Kutzer, A. Hoffmann, N. N. Ledentsov, Z. Alferov, D. Litvinov, A. Rosenauer, and D. Gerthsen. Excitonic gain in CdSe/ZnSe quantum dot structures. In Proceedings ICPS24, Jerusalem, August 2-7, 1998, D. Gershoni, Ed. (World Scientific), 1999. [bibtex-key = Strassburg1999]



619. U. Fischer, A. Rosenauer, T. Remmele, D. Gerthsen, and A. Förster. HRTEM-Untersuchung von InGaAs/GaAs(001) - Inselstrukturen. In DPG Frühjahrstagung, Regensburg (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1998, Regensburg, Verhandl. DPG (VI) 33, 1998, 728, 1998. [bibtex-key = Fischer1998]



620. I. L. Krestnikov, S. V. Ivanov, P. Kop'ev, N. N. Ledentsov, M. Maximov, A. V. Sakharov, S. V. Sorokin, A. Rosenauer, D. Gerthsen, C.M. Sotomayor Torres, D. Bimberg, and Z. Alferov. RT exciton waveguiding and lasing in submonolayer CdSe-(Zn, Mg)(S, Se) structures. In Second International Conference on Low Dimensional Structures and Devices. Lisbon, Portugal, 19-21 May 1997 Materials Science & Engineering B (Solid-State Materials for Advanced Technology) B51, 26-29, 1998. [bibtex-key = Krestnikov1998]



621. Ch. Märkle, W. Petri, M. Grün, U. Woggon, C. Klingshirn, A. Wurl, U. Fischer, A. Rosenauer, D. Gerthsen, T. Kümmell, G. Bacher, and A. Forchel. Kubische CdS/ZnS-Quantentrogstrukturen. In DPG Frühjahrstagung, Regensburg (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1998, Regensburg, Verhandl. DPG (VI) 33, 1998, 684, 1998. [bibtex-key = Maerkle1998]



622. A. Rosenauer, D. Gerthsen, and A. Förster. Composition evaluation of In(x)Ga(1-x)As island structures by lattice fringe analysis and strain state analysis,. In Electron Microscopy 1998, paper presented at ICEM14, Cancun, Mexico, 31 August to 4 Septermber 1998, Symposium S, Volume I , 613-14, 1998. [bibtex-key = Rosenauer1998]



623. A. Wurl, A. Rosenauer, D. Gerthsen, B. Hahn, and W. Gebhardt. Frühstadien des Wachstums von ZnTe Epitaxieschichten auf (100)- und (111)-GaAs Substraten. In DPG Frühjahrstagung, Regensburg (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1998, Regensburg, Verhandl. DPG (VI) 33, 1998, 682, 1998. [bibtex-key = Wurl1998]



624. A. Rosenauer, T. Remmele, U. Fischer, A. Förster, and D. Gerthsen. Strain determination in mismatched semiconductor heterostructures by the digital analysis of lattice images,. In Microcopy of Semiconducting Materials 1997, Oxford, UK, 7-10 April 1997, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (1997), 39-42, 1997. [bibtex-key = Rosenauer1997a]



625. T.H. Walter, A. Rosenauer, D. Gerthsen, F. Fischer, R. Gall, Th. Litz, A. Waag, and G. Landwehr. Transmission electron microscopy investigations of an epitaxial beryllium-chalcogenide-based superlattice,. In Microcopy of Semiconducting Materials 1997, Oxford, UK, 7-10 April 1997, Proceedings of the Royal Microscopical Society Conference, Editors A.G. Cullis, J.L. Hutchison, Institute of Physics Publishing (1997), 315-318, 1997. [bibtex-key = Walter1997]



626. M. J. Kastner, D. Brunhuber, B. Hahn, A. Rosenauer, and W. Gebhardt. Untersuchungen zum Gitterrelaxationsverhalten von MOVPE gewachsenen ZnSSe-Schichten. In DPG Frühjahrstagung, Münster (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1996, Regensburg, Verhandl. DPG (VI) 31, 1996, 1434, 1996. [bibtex-key = Kastner1996a]



627. T. Reisinger, S. Lankes, M. Kastner, A. Rosenauer, F. Franzen, M. Meier, and W. Gebhardt. Growth, Structural and Optical Characterization of MBE ZnCdSe/ZnSe QWs,. In 7th International Conference II-VI Compounds and Devices. Edinburgh, UK, 13-18 Aug 1995, J. Cryst. Growth 159, 510-513, 1996. [bibtex-key = Reisinger1996]



628. W. Gebhardt, T. Reisinger, B. Hahn, and A. Rosenauer. Growth of Large Gap II-VI Semiconductors by MBE and MOVPE: A Comparative Study,. In International Conference on Semiconductor Heteroepitaxy, Monpellier, France, July 4th to 7th, World Scientific, 1995, 51-58, 1995. [bibtex-key = Gebhardt1995]



629. M. Grün, M. Hetterich, C. Klingshirn, A Rosenauer, and W. Gebhardt. Decrease of the Phase Stability in II-VI Epitaxial Layers Due to Strain,. In II-VI Compounds and Semimagnetic Semiconductors. Third European Workshop on II-VI Compounds and Fourth International Workshop on Semimagnetic (Diluted Magnetic) Semiconductors. Linz, Austria, 26-28 Sept 1994, Materials Science Forum Vols. 182-184, 235-238, 1995. [bibtex-key = Gruen1995]



630. T. Reisinger, A. Rosenauer, F. Franzen, and W. Gebhardt. In-Situ Growth Control of ZnSe/GaAs and ZnCdSe Quantum Wells,. In International Conference on Semiconductor Heteroepitaxy, Monpellier, France, July 4th to 7th, World Scientific, 1995, 118-121, 1995. [bibtex-key = Reisinger1995]



631. A. Rosenauer, T. Reisinger, E. Steinkirchner, J. Zweck, and W. Gebhardt. Bestimmung der Diffusion von Cd in CdSe/ZnSe Quantentrogstrukturen. In DPG Frühjahrstagung, Berlin (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1995, Berlin, Verhandl. DPG (VI) 30, 1995, 1212, 1995. [bibtex-key = Rosenauer1995b]



632. A. Rosenauer, G. Schütz, T. Reisinger, H. Preis, F. Franzen, and W. Gebhardt. TEM Investigation of Plastic Relaxation in ZnSe/GaAs(001), International Conference on Semiconductor Heteroepitaxy, Monpellier, France, July 4th to 7th,. In World Scientific, 1995, 114-117, 1995. [bibtex-key = Rosenauer1995]



633. N. Schnellinger, A. Rosenauer, J. Zweck, and A. Hoffmann. Investigations on Preparation Artefacts in Au/Si Cross-Sectioned Samples,. In ICEM 13 Paris 17.-22.7.1995, 1021-1022, 1995. [bibtex-key = Schnellinger1995]



634. G. Schütz, Rose., T. Reisinger, and W. Gebhardt. TEM-Untersuchung der Spannungsrelaxation in MBE ZnSe/GaAs(001). In DPG Frühjahrstagung, Berlin (Germany) Frühjahrstagung des Arbeitskreises Festkörperphysik 1995, Berlin, Verhandl. DPG (VI) 30, 1995, 1213, 1995. [bibtex-key = Schuetz1995]



635. D. Gerthsen, T. Walther, and A. Rosenauer. Quantitative High-Resolution Electron Microscopy of Semiconductor Heterostructures,. In 9. Japan-Germany Forum on Information Technology, Oita (Japan), 8.-11.11.1994, 1994. [bibtex-key = Gerthsen1994]



636. M. Grün, M. Hetterich, C. Klingshirn, A. Rosenauer, and W. Gebhardt. Strain-Relief in Wurtzite-Type CdS and CdSe Epitaxial Films,. In 22nd International Conference on The Physics of Semiconductors, Vol. 3, Vancouver, Canada, August 15-19, 1994 World Scientific 3, (1995) 2665, 1994. [bibtex-key = Gruen1994a]



637. A. Rosenauer, H. Stanzl, K. Wolf, S. Bauer, M. Kastner, M. Grün, and W. Gebhardt. Spatial Confinement of Misfit Dislocations at the Interfaces of Epitaxial CdSe/GaAs(111) and ZnTe/GaAs(111) Studied by TEM,. In 17th International Conference on Defects in Semiconductors. Gmunden, Austria, 18-23 July 1993, Materials Science Forum vols. 143-147, 567-572, 1994. [bibtex-key = Rosenauer1994]



638. H. Stanzl, A. Rosenauer, K. Wolf, M. Kastner, B. Hahn, and W. Gebhardt. MOVPE Growth of ZnSeTe on (111) and (001) GaAs Substrates,. In SPIE 2140 Epitaxial Growth Processes, Los Angeles (USA), 138-147, 1994. [bibtex-key = Stanzl1994]



639. A. Naumov, K. Wolf, H. Stanzl, A. Rosenauer, S. Lankes, and W. Gebhardt. Exciton spectra of ZnSeTe epilayers and ZnTe/ZnSeTe/ZnTe SQWs grown by MOCVD. In DPG Frühjahrstagung, Münster (Germany) 13th General Conference of the Condensed Matter Division (European Physical Society) in conjunction with Arbeitskreis Festkörperphysik (Deutsche Physikalische Gesellschaft), Europhysics Conference Abstracts 17A, 1436, 1993. [bibtex-key = Naumov1993]



640. H. Stanzl, A. Rosenauer, K. Wolf, A. Naumov, S. Lankes, M. Kastner, F. Gilg, G. Hirmer, T. Starke, and W. Gebhardt. MOVPE Growth and Characterization of ZnTeSe-Epilayers and ZnTe/ZnTeSe SQWs. In DPG Frühjahrstagung, Münster (Germany) 13th General Conference of the Condensed Matter Division (European Physical Society) in conjunction with Arbeitskreis Festkörperphysik (Deutsche Physikalische Gesellschaft), Europhysics Conference Abstracts 17A, 1425, 1993. [bibtex-key = Stanzl1993]



641. S. Bauer, A. Rosenauer, J. Skorsetz, W. Kuhn, H.P. Wagner, J. Zweck, and W. Gebhardt. Investigation of Strained ZnTe Epilayers by High Resolution Electron Microscopy,. In Fifth international conference on II-VI-compounds, Tamano, Japan, 8-13 Sept 1991, J. Cryst Growth 117, 297-302, 1992. [bibtex-key = Bauer1992]



642. Dennis Marquardt. Strukturelle Analyse von Methylammoniumbleibromid Perowskiten auf Muskovit Mica. Master's thesis, Fachbereich Physik und Elektrotechnik der Universität Bremen, 2016. [bibtex-key = BacchelorDennisMarquardt]



643. Knut Müller-Caspary. Applications and limitations of momentum-resolved STEM [Talk at the Meeting of the AK-HREM on High-resolution TEM, TU Berlin, Berlin(Germany)], April 2016. [bibtex-key = Mueller-Caspary2016i]



644. Knut Müller-Caspary. Probing electric fields by STEM [Lecture], June 2015. [bibtex-key = Mueller-Caspary2015e]



645. Knut Müller-Caspary and Andreas Rosenauer. STEM and TEM Simulation [Tutorial], June 2015. [bibtex-key = Mueller-Caspary2015f]



646. Christoph Mahr. Bestimmung von Präzision und Genauigkeit bei Verzerrungsmessungen mittels konvergenter Elektronenbeugung. Master's thesis, Universität Bremen, Otto-Hahn-Allee 1,28359 Bremen, Germany, September 2014. [bibtex-key = Mahr2014a]



647. Knut Müller. Evaluation of STEM images with the ImageEval software [Tutorial], January 2014. [bibtex-key = Mueller2014h]



648. Knut Müller. Nanowires, quantum wells, MOSFETs: Scanning and conventional TEM characterisation of structure and composition [Invited talk], October 2014. [bibtex-key = Mueller2014d]



649. Knut Müller. Practice of quantitative STEM [Lecture], January 2014. [bibtex-key = Mueller2014f]



650. Knut Müller. Quantitative analysis of (S)TEM images using the ImageEval software [Tutorial], October 2014. [bibtex-key = Mueller2014j]



651. Knut Müller. Simulation of STEM images [Lecture], January 2014. [bibtex-key = Mueller2014e]



652. Knut Müller. Simulation of STEM images with the STEMsim software [Tutorial], January 2014. [bibtex-key = Mueller2014g]



653. Knut Müller, Thorsten Mehrtens, Florian Krause, Marco Schowalter, and Andreas Rosenauer. Simulation of STEM images [Invited talk], February 2014. [bibtex-key = Mueller2014c]



654. Knut Müller and Andreas Rosenauer. Quantitative STEM simulation/Evaluation [Tutorial], September 2014. [bibtex-key = Mueller2014i]



655. Moritz Tewes. Quantitative STEM-Untersuchung von Germanium-Silizium-Heterostrukturen (Quantitative STEM investigations of germanium-silicon heterostructures). Master's thesis, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany, February 2013. Abstract:

     In dieser Arbeit habe ich mich mit der Bestimmung von Germanium-Konzentration in Germanium-Silizium-Gemischen besch{\"a}ftigt. Die Untersuchung der chemischen Zusammensetzung erfolgte mittels HAADF-STEM. Bei dieser Messmethode wird ein Elektronenstrahl auf die Probe fokussiert und nur Elektronen in einem bestimmten Streuwinkelbereich werden detektiert. Die gemessene Intensit{\"a}t ist unter anderem abh{\"a}ngig von der Kernladungszahl Z und somit chemisch sensitiv. Die Auswertung erfolgt durch Vergleich mit simulierten Daten, denn wie LeBeau et al. [6] gezeigt haben, ist eine quantitive Auswertung mit normierten Intensit{\"a}ten m{\"o}glich. In dieser Arbeit wurden Simulationsdaten f{\"u}r die Zonenachse [100] und [110] berechnet. Die Simulation erfolgte mit dem Multislice-Verfahren mit dem Frozen Lattice-Ansatz unter Verwendung des STEMsim-Programms [16]. Statische Atomverschiebungen (SADs) wurden bei den Simulationen durch ein empirisches Potential [36] und die LAMMPS Software [9] ber{\"u}cksichtigt. Au{\ss}erdem wurde gezeigt, wie gro{\ss} die Superzellen f{\"u}r die Simulationen gew{\"a}hlt werden m{\"u}ssen, sowie dass bei den Fozen Lattice-Simulationen {\"u}ber wenigstens 10 Konfigurationen gemittelt werden muss um verl{\"a}ssliche Ergebnissen zu erhalten. Es wurde simuliert, wie sich die STEM-Intensit{\"a}t f{\"u}r Silizium {\"a}ndert, wenn das Silizium in Wachstumsrichtung verzerrt wird. In dieser Arbeit wurde gezeigt, dass es m{\"o}glich ist radial gespeicherte Simulationsdaten zur Auswertung zu nutzen. Im experimentellen Teil der Arbeit wurden drei Proben untersucht. Anhand einer Keilprobe aus Silizium sollten {\"u}ber Messungen der Probendicke die Simulationen f{\"u}r reines Silizium {\"u}berpr{\"u}ft werden. Als Referenzmessung wurde eine Dunkelfeldmessung herangezogen. Mittels Blochwellenrechnung wurde die Strahlintensit{\"a}t in Abh{\"a}ngigkeit von der Probendicke bestimmt. Die beiden erhaltenen Ergebnisse stimmen mit Abweichungen von 5-10 nm {\"u}berein. Es wurde au{\ss}erdem eine TEM-Kalibrierungsprobe auf SiGe-Basis untersucht. Diese Probe besitzt Quantentr{\"o}ge mit nominell 19\% Germanium eingebettet in Silizium. Mittels STEM wurde eine vom Hersteller nicht beschriebene Unterstruktur entdeckt. Die gemessene Konzentration schwankt in den STEM-Messungen aufgrund der Unterstruktur zwischen (13+/-3)\% und (19+/-3)\%. Die als Referenzmessung durchgef{\"u}hrte Verzerrungsmessung stimmt mit den gemessenen STEM-Werten {\"u}berein, der Fehler der Messung ist allerdings zu gro{\ss} um die STEM-Werte zu best{\"a}tigen. Die dritte untersuchte Probe ist eine MOSFET-Probe zur Verf{\"u}gung gestellt von GlobalFoundaries. Diese Probe soll nominell Bereiche mit 27\% Ge und 19\% Ge enthalten. Zuerst wurde die Probe mit EDX untersucht um die Bereiche mit Germanium zu lokalisieren. Dabei wurde die Germaniumkonzentration der beiden Bereiche mit 23-25\% bzw. 17-19\% bestimmt. In STEM-Messungen wurden Konzentrationen von (29 33) 4\% Ge bzw. (20 ô€€€ 25)  3\% Ge f{\"u}r die beiden Bereiche gemessen. Diese Werte liegen etwas {\"u}ber den nominellen Werten. Au{\ss}erdem wurden bei der Untersuchung der MOSFET-Probe Artefakte in der STEM-Intensit{\"a}t festgestellt, die das Messen einer Ge-Konzentration in den Siliziumbereichen verursachten. Diese Artefakte werden vermutlich von Oberfl{\"a}chenverzerrungen hervorgerufen, denn die in dieser Arbeit simulierte Verzerrung von Silizium in Wachstumsrichtung ist nicht ausreichend um die Abnahme in der STEM-Intensit{\"a}t zu erkl{\"a}ren. Zusammenfassend kann gesagt werden, dass sich die Methode HAADF-STEM zur quantitativen Untersuchung von Silizium-Germanium-Strukturen eignet. Es gibt noch einige M{\"o}glichkeiten zur weiteren Untersuchung, von denen nachfolgend die wichtigsten genant werden sollen. Notwendig ist eine Wiederholung der Verzerrungsmessung zur Bestimmung des Germanium-Gehalts in den Quantentr{\"o}gen der untersuchten Kalibrierungsprobe, um die Simulationen zu best{\"a}tigen. Es wurden zwar auch in der MOSFET-Probe Konzentrationen gemessen, die nahe denen des Herstellers sind, allerdings treten bei dieser Messung Verzerrungseekte auf, die die Dickenbestimmung m{\"o}glicherweise beeinflussen, sodass sie sich nicht zum Verifizieren der Simulationen eignet. Weitere Fortsetzungen zeigen sich in dem Untersuchen m{\"o}glicher Oberfl{\"a}chenverzerrungen. Es m{\"u}sste eine Simulation durchgef{\"u}hrt werden, in der eine GeSi-Schicht eingebettet in Silizium mittels empirischen Potentials relaxiert wird und {\"u}berpr{\"u}ft werden, ob Artefakte, wie in dieser Arbeit beobachtet, auftreten. Au{\ss}erdem w{\"a}re die Untersuchung der Probe bei anderen Kameral{\"a}ngen m{\"o}glich, sodass der Detektor einen anderen Winkelbereich abdeckt. Grieb et al. [46] haben gezeigt, dass es Winkelbereiche gibt, wo keine Artefakte durch Oberfl{\"a}chenverzerrungen in der STEM-Intensit{\"a}t auftreten. Die f{\"u}r die Auswertung in einem anderenWinkelbereich ben{\"o}tigte CT-Matrix k{\"o}nnte anhand der in dieser Arbeit simulierten radialen Daten mit relativ wenig Aufwand durchgef{\"u}hrt werden.

     [bibtex-key = Tewes2013b]



656. Knut Müller. Practice and Application of quantitative STEM [Lecture], March 2013. [bibtex-key = Mueller2013d]



657. Knut Müller. Strain Analysis by Nano-Beam Electron Diffraction (SANBED) [Lecture], August 2013. [bibtex-key = Mueller2013e]



658. Knut Müller and Andreas Rosenauer. Simulation of STEM images with the STEMsim software [Tutorial], March 2013. [bibtex-key = Mueller2013f]



659. Knut Müller, Andreas Rosenauer, Marco Schowalter, Josef Zweck, Kerstin Volz, Heike Soltau, Pavel Potapov, and Karl Engl. Strain Analysis by Nano-Beam Electron Diffraction [Invited talk], 2013. [bibtex-key = Mueller2013c]



660. Daniel Erben. Verspannungsmessungen in SiGe-basierten Feldeffekttransistoren mittels konvergenter Elektronenbeugung (Strain measurements in SiGe-based field effect transistors using convergent electron diffraction), August 2012. [bibtex-key = Erben2012]



661. Patrick Karasch. Messung von Verspannungen und piezoelektrischen Feldern in InGaN/GaN Quantentrögen mittels Elektronenbeugung (Measurement of strain and piezoelectric fields in InGaN/GaN quantum wells by electron diffraction), August 2012. [bibtex-key = Karasch2012]



662. Christoph Mahr. Einfluss von Linsenfehlers auf Verspannungsmessungen aus CBED-Bildern im TEM (Impact of lens aberrations on strain measurements from CBED images in a TEM), July 2012. [bibtex-key = Mahr2012]



663. Dennis Zillmann. Bestimmung der Modulationstransferfunktion einer CCD-Kamera und Kontrasttransfer in der Transmissionselektronenmikroskopie (Determination of the modulation transfer function of a CCD camera and contrast transfer in the field of transmission electron microscopy). Master's thesis, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany, October 2011. Abstract:

     Im Rahmen dieser Arbeit wurde sich schwerpunktm{\"a}{\ss}ig mit der Bestimmung der Szintillator-MTF der Gatan UltraScan1000 CCD-Kamera besch{\"a}ftigt. Der zweite Teil befasste sich mit dem Einfluss der thermisch diffusen Streuung (TDS) auf den Kontrast in HRTEM-Aufnahmen. In Kap. 4 wurde zun{\"a}chst die Methode von Thust zur Bestimmung der Szintillator-MTF dargelegt [11]. Mit einem darauf basierenden und in MatlabTM selbst implementierten Auswertungsprogramm konnte die Szintillator-MTF der CCD-Kamera anhand von Kantenbildern des im Mikroskop integrierten Beamblankers bis zur Nyquist-Frequenz kN bestimmt werden. Die Verwendung eines Edelstahlblechs, das mit der Geometrie eines Dreisegment-Siemens-Sterns zugeschnitten war, erm{\"o}glichte es, alternative Kantenbilder aufzunehmen. Dies geschah mittels eines im Mikroskop eingebauten Bildspeicherplattenstapels, der so modifiziert wurde, dass er mit der CCD-Kamera gleichzeitig in das Mikroskop gefahren werden konnte. Anhand der Kantenbilder konnte eine verl{\"a}ssliche Bestimmung der MTF bis zu einer Frequenz von sqrt(2)*kN erreicht werden. An der Sterngeometrie wurde {\"u}berdies der Einfluss des Aliasings n{\"a}her untersucht, wobei sich kein signifikanter Einfluss des Aliasings aus den Ergebnissen ableiten lie{\ss}. Dies steht im Widerspruch zu den Berichten von Kirkland, Ruijter und Thust, nach denen sich das Aliasing verf{\"a}lschend auf die MTF auswirkt. Ferner konnten die gefundenen Resultate mit einer alternativen Bestimmungsmethode von Van den Broek et al. {\"u}bereinstimmend verifiziert werden. Schlussendlich stimmten die Ergebnisse auch mit der von Thust ermittelten und vergleichbaren MTF-Kurve gut {\"u}berein, wobei sich geringe Abweichungen mit der individuellen Beschaffenheit der Phosphorszintillatoren und mit Unterschieden in der Implementierung erkl{\"a}ren lie{\ss}en [11]. Kapitel 5 wurde der Betrachtung des Kontrasts anhand des Stobbs-Faktors gewidmet [7]. Aus diesem Grund wurde der Kontrast aus HRTEM-Aufnahmen einer GaAs-Probe mit einem keilf{\"o}rmigen Dickenprofil bestimmt. Es wurden drei Probenstellen unterschiedlicher Dicke bei Verwendung verschiedener Objektivaperturen untersucht. F{\"u}r jede der drei Probenstellen f{\"u}hrte ein steigender Aperturradius zu einer Kontrastsenkung. Eine Aussage {\"u}ber die Dickenabh{\"a}ngigkeit des Kontrasts konnte jedoch nicht getroffen werden. Eine der untersuchten Stellen wurde dabei mit energiegefilterten Elektronen aufgenommen, so dass an Plasmonen gestreute Elektronen ausgeschlossen wurden. Auch wenn sich die experimentell untersuchten Probenstellen aufgrund der teilweise unbekannten Defoki nicht miteinander vergleichen lie{\ss}en, so ergaben sich mit den energiegefilterten HRTEM-Aufnahmen deutlich h{\"o}here Kontrastwerte von beispielsweise 0,7 f{\"u}r die kleinste Apertur (von 6, 8 nm−1) gegen{\"u}ber den anderen beiden Stellen. Dies lie{\ss} sich nicht ausschlie{\ss}lich mit einem siginifikanten Dickenunterschied erkl¨aren. Daher sollten k{\"u}nftige TDS-Untersuchungen mit energiegefilterten Aufnahmen durchgef{\"u}hrt werden. Insgesamt st{\"u}tzten die Ergebnisse die Annahme von Van Dyck, dass der Stobbs-Faktor teilweise auf die im Beugungsbild enthaltenen, thermisch diffus gestreuten Elektronen zur¨uckzuf¨uhren ist. In Kapitel 6 wurden mit den aus Kap. 5 ermittelten Gr{\"o}{\ss}en HRTEM-Bilder von GaAs simuliert. Die Simulationen erfolgten mit dem STEMsim-Programm [30], in dem der Ansatz der inkoh{\"a}renten Summierung von Van Dyck implementiert war. Insgesamt wurden Simulationen f{\"u}r sechs Probendicken zwischen 20 nm und 150 nm mit jeweils variierendem Aperturradius durchgef{\"u}hrt, um analog zu Kap. 5 die Kontrastabh{\"a}ngigkeiten zu untersuchen. Dabei ging in die Simulationen die in Kap. 4 bestimmte MTF ein. Alle simulierten Dicken ergaben eine Kontrastabnahme mit steigendem Aperturradius. Ein direkter Kontrastvergleich zwischen Experiment und Simulation war allerdings nur f{\"u}r die Probendicke von 30 nm m{\"o}glich und ergab bei der kleinsten Apertur von 6, 8 nm−1 einen Stobbs-Faktor von 1,44 und ohne Apertur 1,80. Verglichen mit dem Stobbs-Faktor von 1,72 f{\"u}r die kleinste Apertur, bestimmt aus den Simulationen mit den Inkoh{\"a}renzenveloppen des Transmissionskreuzkoeffizienten (TCC), resultierten f{\"u}r die inkoh{\"a}rente Summierung plausiblere Ergebnisse. Dies dr{\"u}ckte sich insbesondere im Vergleich der absoluten Kontraste, bei TCC ohne/mit MTF 0,57/0,31 und inkoh{\"a}rente Summierung 0,41/0,26, aus. Damit blieben die mit der inkoh{\"a}renten Summierung gefundenen Stobbs-Faktoren von 1,44 und 1,80 unter den bislang berichteten von drei bis f{\"u}nf, und waren ferner vergleichbar mit denen von Hochmeister et al. gefundenen zwischen 1,5 bis 2,3. Eine genauere Untersuchung kleiner Blenden lieferte zudem einen stark blendenabh{\"a}ngigen Kontrast, was mit der dynamischen Beugung und der Pendell{\"o}sung bei Mehrfachstreuung zusammenh{\"a}ngt, weil dann bei einer gr{\"o}{\ss}eren Blende zus{\"a}tzliche Beugungsreflexe zum HRTEM-Bild beitragen. So f{\"u}hrte ein Blendenwechsel von 6, 8 nm−1 auf 7, 4 nm−1 zu einem drastischen Kontrastverlust von 0,44 auf 0,28. Dieses Verhalten zeigte sich f{\"u}r nahezu alle simulierten Dicken, bis auf die Dicke von 30 nm. Da Dicken von 20 nm oder 40 nm auch diesen starken Kontrastabfall verzeichneten, konnte der kleinste Faktor von 1,44 f{\"u}r 30 nm aufgrund der experimentellen Dickenungenauigkeit von ±15 nm nicht sicher ermittelt werden. {\"U}berdies konnte zwar eine tendenzielle, aber keine grunds{\"a}tzliche Kontrastabnahme mit zunehmender Probendicke festgestellt werden, da auch hier die dynamische Beugung weiterhin einen starken Einfluss auf den Kontrast hat. Zusammenfassend l{\"a}sst sich sagen, dass die Ber¨ucksichtigung der MTF im Diffraktogramm einen deutlichen Kontrastverlust in den simulierten HRTEM-Bildern hervorruft und daher den Stobbs-Faktor bei dicken Proben teilweise erkl{\"a}rt. Demzufolge muss die MTF in den Simulationen von HRTEM-Bildern einbezogen werden. Weiter gaben die experimentellen Kontrastuntersuchungen und die angekn{\"u}pften Simulationen klare Hinweise darauf, dass auch die TDS eine weitere Ursache f{\"u}r den Stobbs-Faktor in HRTEM-Aufnahmen sein k{\"o}nnte. Eine stichhaltige Belegung daf{\"u}r macht allerdings weitere Untersuchungen notwendig. Vergleichende Kontrastuntersuchungen des Stobbs-Faktors m{\"u}ssen demnach mit energiegefilterten HRTEMAufnahmen durchgef{\"u}hrt werden, die den Einfluss von Plasmonen ausschlie{\ss}en. Auch die Untersuchung an anderen Keilproben, aus beispielsweise Silizium mit amorphen Siliziumdioxid-Bereichen, ist denkbar, wobei die amorphen Bereiche zur Bestimmung des Defokus ausgenutzt werden k{\"o}nnen.

     [bibtex-key = Zillmann2011]



664. Thorsten Mehrtens. Bestimmung von Segregationsprofilen in InGaAs/GaAs-Quantentrögen mittels konventioneller und Rastertransmissionselektronenmikroskopie. Master's thesis, Universität Bremen, 2009. Abstract:

     Mit der erstmaligen optischen Abbildung mittels Eletronen durch Max Knoll und Ernst Ruska in den Drei{\ss}iger Jahren des vorigen Jahrhunderts ist die Grundlage f{\"u}r die Entwicklung des Transmissionselektronenmikroskops (TEM) geschaffen worden [1]. Dieses stellt f{\"u}r die Physik ein wichtiges Instrument dar, da moderne aberrationskorrigierte Transmissionselektronenmikroskope durch die extrem kurze Wellenl{\"a}nge der Elektronen in der Lage sind, selbst Nanostrukturen bis zu 0,08nm aufzul{\"o}sen. Heutzutage steht dabei die Gewinnung von quantitativen Ergebnissen immer mehr im Mittelpunkt der Untersuchungen. Diese werden zum Beispiel dazu ben{\"o}tigt, um Aussagen {\"u}ber die Struktur und die chemische Zusammensetzung von Nanostrukturen treffen zu k{\"o}nnen, wie sie bei der Entwicklung von neuartigen, auf Halbleitern basierenden optischen Bauelementen, wie Lasern extsuperscript{1} oder Leuchtdioden (LED extsuperscipt{2}s), ben{\"o}tigt werden. Die genaue Kenntnis des Wachstumsprozesses, bei dem der Effekt der Segregation eine wichtige Rolle spielt, ist dabei essentiell. Bei der Segregation kommt es dadurch, dass nicht alle Atomsorten mit gleicher Effizienz in die gewachsene Kristallstruktur eingebaut werden, zu unscharfen Grenzen zwischen Bereichen unterschiedlichen Materials bzw. unterschiedlicher chemischer Komposition, da nicht in den Kristall eingebaute Atome w{\"a}hrend des Wachstums in benachbarte Schichten segregieren. Die Segrationsprofile mittels Molekularstrahlepitaxie (MBE extsuperscript{3}) gewachsener Strukturen haben dabei eine charakteristische Form, welche durch Modelle von Moison et al. [2] und Muraki et al. [3] theoretisch beschrieben wird. Muraki et al. f{\"u}hren dabei die sogenannte Segregationseffizienz R ein, welche ein Ma{\ss} f{\"u}r die St{\"a}rke der Segregation ist. In dieser Arbeit wird die Segregationseffizienz in heterogenen In extsubscript{x}Ga extsubscript{1-x}As/GaAs Quantenschichtsystemen untersucht, welche mittels MBE gewachsen wurden. Es wird der Einfluss einer kurzen Temperaturerh{\"o}hung der Probe (sogenannter "Flash-Off") vor dem Wachstum der InGaAs-Schichten auf die Segregation ermittelt um Segregation von Gallium aus den GaAs-Bereichen der Probe in die InGaAs-Quantentr{\"o}ge zu vermeiden. Dazu werden Konzentrationsprofile mittels zwei verschiedener quantitativer TEM-Methoden bestimmt. Die erste Methode ist Composition Evaluation by Lattice Fringe Analysis (CELFA), bei welcher ausgenutzt wird, dass in der Zinkblende-Struktur, in der InGaAs kristallisiert, die Amplitude des gebeugten (002)-Strahls von der chemischen Zusammensetzung der Probe abh{\"a}ngt. Die zweite Methode ist ein quantitatives Rastertransmissionselektronenmikroskopieverfahren (STEM extsuperscript{4}). Hierbei wird die Probe mit einem stark fokussierten Strahl abgerastert und es werden mittels eines Ringdetektors (HAADF extsuperscript{5}-Detektor) nur die Elektronen detektiert, welche unter im Vergleich zur Abbildung in der konventionellen TEM gro{\ss}en Winkeln gestreut werden. Segregationsprofile k{\"o}nnen hier dadurch bestimmt werden, dass die Gr{\"o}{\ss}e der gestreuten Intensit{\"a}t von der Kernladungszahl Z der streuenden Atome abh{\"a}ngt (Z-Kontrast). Im folgenden Teil dieser Arbeit werden die zwei Methoden n{\"a}her erl{\"a}utert und es werden die Ergebnisse der Messungen vorgestellt, wobei der Schwerpunkt in der HAADF-STEM-Methodik liegt, welche sich noch am Anfang ihrer Entwicklung befindet. Die CELFA-Auswertungen dienen daher als Referenz um die Genauigkeit der HAADF-STEM-Ergebnisse absch{\"a}tzen zu k{\"o}nnen. Die Pr{\"a}sentation der Ergebnisse erfolgt in f{\"u}nf Kapiteln, wobei im ersten Kapitel die notwendigen theoretischen Grundlagen zum Verst{\"a}ndnis dieser Arbeit geliefert werden. Darauf folgt das Kapitel "Probenwachstum und Segregation", welches den Herstellungsprozess der analysierten Probe mittels MBE und den damit eng verbundenen Prozess der Segregation beschreibt. Im Anschluss daran werden verschiedene Verfahren zum Simulieren von Referenzdaten pr{\"a}sentiert. Bloch-Wellen-Rechnungen werden zur Erzeugung der CELFA-Referenzdaten und Multislice extsuperscript{6}-Rechnungen zur Auswertung der HAADF-STEM-Messungen ben{\"o}tigt. Anschlie{\ss}end wird der experimentelle Teil dieser Arbeit vorgestellt. Hierbei wird zuerst auf die verschiedenen Arten der verwendeten Probenpr{\"a}parationsmethoden eingegangen, bevor die experimentellen Details der Messungen erl{\"a}utert werden. Einen Schwerpunkt dieser Arbeit bilden Mutlislice-Simulationen und die Bestimmung von geeigneten Simulationsparamtern zur Erzeugung der Referenzdaten f{\"u}r die HAADF-STEM-Auswertung. Auf Grund des immensen Rechenaufwandes der Simulationen m{\"u}ssen hier Paramter gefunden werden, die gleichzeitig den Rechenaufwand minimieren und ausreichend genaue Referenzwerte liefern. Dieses und die CELFA- bzw. HAADF-STEM-Auswertung werden im Kapitel "Auswertung der experimentellen Daten" dargestellt. Schlie{\ss}lich werden in diesem Kapitel die mit beiden Methoden bestimmten Segregationskoeffizienten miteinander in Abh{\"a}ngigkeit von der "Flash-Off"-Temperatur verglichen. Zum Schluss folgt eine Zusammenfassung der Ergebnisse und ein Ausblick auf m{\"o}gliche Fortsetzungen der Untersuchungen. 1Engl. Light Amplification by Stimulated Emission of Radiance. 2Engl. Light Emitting Diode. 3Engl. Molecular Beam Epitaxy. 4Engl. Scanning Transmission Electron Microscopy. 5Engl. High Angle Annular Dark-Field. 6Dt. Vielschicht.

     [bibtex-key = Mehrtens2009b]



665. Claas Gloistein. Messung von Debye-Waller-Faktoren für Galliumarsenid mittels Elektronenbeugung (Measurement of Debye-Waller-factors for gallium arsenide by electron diffraction), May 2009. [bibtex-key = Gloistein2009]



666. Nils Neugebohrn. Quantitative Untersuchung der Temperatur- und Dickenabhängigkeit des STEM-Dunkelfeldsignals von Zinkblende-Halbleitern (Quantitative investigation of the temperature and thickness dependence of the STEM dark field signal of zinc blende semiconductors), July 2009. [bibtex-key = Neugebohrn2009]



667. Knut Müller. Measurement of 002 structure factors for GaAs using parallel and convergent beam electron diffraction [Talk], April 2008. [bibtex-key = Mueller2008d]



668. Knut Müller. Bestimmung von Strukturfaktoren für Galliumarsenid mittels Elektronenbeugung - Entwicklung und Test einer Messmethode (Determination of structure factors for gallium arsenide by electron diffraction - development and test of a measurement method). Diplomarbeit, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany, September 2007. Abstract:

     In dieser Arbeit wurde eine Methodik f{\"u}r die Transmissionselektronenmikroskopie entwickelt, mit der aus Beugungsbildern Strukturfaktoren gemessen werden k{\"o}nnen. Motiviert wurde diese Arbeit sowohl durch ein allgemeines physikalisches Interesse, da Strukturfaktoren eine grundlegende Gr{\"o}{\ss}e in der Festk{\"o}rperphysik darstellen, als auch durch die Anwendung in der modernen Halbleiterphysik der Nanostrukturen. Insbesondere die quantitative Analyse der lokalen chemischen Zusammensetzung dieser Strukturen mittels CELFA ist auf die genaue Kenntnis von Strukturfaktoren angewiesen. Der Messmethode liegen Refinementprozeduren zu Grunde, die Beugungsbilder unter Verwendung ebener Wellen simulieren. Der Frage, inwieweit diese Situation experimentell realisiert werden kann, wurde in dieser Arbeit gro{\ss}e Priorit{\"a}t einger{\"a}umt. Dazu wurden die wichtigsten Informationen {\"u}ber Linsen, Blenden und deren Anordnung f{\"u}r die Mikroskope der CM-Serie (Philips) zusammengetragen und erl{\"a}utert. Die Einfl{\"u}sse verschiedener Parameter wie die Beschaffenheit der Elektronenquelle, die Gr{\"o}{\ss}e der Kondensorblende, die sph{\"a}rischen Aberrationen der Kondensorlinsen sowie ein Defokus der C2-Linse wurden anhand von Simulationen im Hinblick auf Gr{\"o}{\ss}e und Profil des Spots untersucht. Mittels FIB-Pr{\"a}paration wurden Kondensorblenden mit Durchmessern von wenigen Mikrometern hergestellt, so dass Spotgr{\"o}{\ss}en von unter 10\,nm bei nahezu paralleler Beleuchtung experimentell realisiert werden konnten. Die Auswertungsprozedur der entwickelten Methodik besteht im Wesentlichen aus zwei Schritten. Erstens werden aus einer Beugungsbildserie unter Einbeziehung des Programmpakets ELSTRU die Orientierungen, Probendicken und Debye-Parameter f{\"u}r jedes Beugungsbild unter Verwendung des Refinementprogramms MSLS bestimmt. Dieses Refinement basiert auf dem Vergleich von simulierten und experimentellen Bragg-Intensit{\"a}ten. Letztere k{\"o}nnen mit Hilfe des Programms GREED bestimmt werden, das dazu eine Subtraktion des diffusen Hintergrundes im Beugungsbild vornimmt. Zweitens werden die Ergebnisse dieses Refinements als Basis f{\"u}r Blochwellen-Simulationen zur Anpassung des gesuchten Strukturfaktors benutzt. Die zu Grunde liegende Theorie dieser Simulationen wurde ausf{\"u}hrlich dargestellt und in das MATLAB-Programm Bloch4TEM umgesetzt. Neben Refinementaufgaben kann dieses Programm zur Simulation von Beugungsbildern bei paralleler und konvergenter Beleuchtung, Dispersionsfl{\"a}chen, Dickenabh{\"a}ngigkeiten von Amplituden, Phasen und Intensit{\"a}t abgebeugter Wellen sowie hochaufl{\"o}senden Abbildungen unter dem Einfluss von Linsenfehlern verwendet werden. Zur Beurteilung der Zuverl{\"a}ssigkeit der Refinementergebnisse wurden GaAs Beugungsbilder in der Zonenachse $\langle010\rangle$ mit der Frozen-Phonon-N{\"a}herung simuliert und auf die beschriebene Weise ausgewertet. Dabei zeigte sich, dass der Fehler f{\"u}r den 002-Strukturfaktor am Ende der Auswertungskette klein genug ist, um die aus DFT-Rechnungen erwartete Modifikation des Strukturfaktors durch Elektronenumverteilung aufgrund der chemischen Bindung nachweisen zu k{\"o}nnen. Zur Interpretation der Refinementergebnisse von MSLS wurde das Konzept der Debye-Waller Karten motiviert. Diese bedeuten die Darstellung der Ergebnisse von einer Vielzahl von Refinements in Abh{\"a}ngigkeit von den Startwerten f{\"u}r die Debye-Parameter von Gallium und Arsen. Es wurden Kriterien zusammengestellt, mit deren Hilfe das Regime mit den richtigen Refinementergebnissen f{\"u}r Debye-Parameter und Probendicke gefunden werden kann. Die Messungen an experimentellen Bildern gestaltete sich schwieriger. F{\"u}r f{\"u}nf Beugungsbildserien konnten jeweils Debye-Parameter mittels MSLS bestimmt werden. Der Vergleich mit verschiedenen Literaturwerten zusammen mit der Absch{\"a}tzung der Probentemperaturen f{\"u}hrte zu der Erkenntnis, dass die ermittelten Debye-Parameter nicht allein den Einfluss der thermischen Bewegung der Atome repr{\"a}sentieren, sondern innerhalb der Refinementprozedur allgemein ein Ma{\ss} f{\"u}r die St{\"o}rung der strengen Periodizit{\"a}t des Kristallpotentials sind. Das zum 002-Strukturfaktor proportionale 002-Kristallpotential konnte in zwei F{\"a}llen mittels Bloch4TEM bestimmt werden. Beide Messungen erscheinen im Sinne des Refinements etwa gleich plausibel und spiegeln jeweils einen der Literaturwerte in wider. Im Hinblick auf die Verifizierung des Konzeptes der MASAs konnte diese Messung noch keine Klarheit schaffen, da zun{\"a}chst ein Fehler von der Gr{\"o}{\ss}enordnung der erwarteten Modifizierung des Kristallpotentials angenommen werden muss. Die Betrachtung dieser Messungen im Zusammenhang mit der Tatsache, dass es sich um die ersten Resultate einer neuen Methode handelt, ist vielversprechend, da die Messergebnisse in ein Intervall fallen, dessen Grenzen durch zwei theoretische Vorhersagen verschiedener Quellen begrenzt ist. Der letzte Beitrag, den diese Arbeit zum Vorhaben der pr{\"a}zisen Messung des 002-Struk\-tur\-fak\-tors von GaAs und weiteren Verbindungshalbleitern der Zinkblendestruktur leisten m{\"o}chte, kann nur ausblickender Art sein. Neben weiteren Messungen in der oben beschriebenen Weise erscheinen folgende Erg{\"a}nzungen der beschriebenen Methodik vielversprechend: Erstens kann die Sicherstellung paralleler Beleuchtung bei Verwendung eines Kondensorlinsensystems aus drei Linsen besser gew{\"a}hrleistet werden als beim System aus zwei Linsen, das in dieser Arbeit verwendet wurde. Sogenannte K{\"o}hler-Beleuchtung w{\"a}re ideal. Zweitens ist eine genauere Bestimmung der Bragg-Intensit{\"a}ten zu erwarten, wenn energiegefilterte Bilder aufgenommen werden. Ein Nachteil besteht dabei darin, dass Bildspeicherplatten in den meisten Mikroskopen dann nicht zur Aufzeichnung verwendet werden k{\"o}nnen. Drittens kann die in dieser Arbeit angewandte Methodik durch weitere erg{\"a}nzt werden. Insbesondere sollte versucht werden, das simultane Refinement von Debye-Parametern und Probendicken zu vermeiden, indem die Dicken separat gemessen werden. Eine geeignete Methode stellt z.B. die Elektronenholographie dar. Die experimentelle Schwierigkeit besteht dabei darin, bei zwei v{\"o}llig verschiedenen Einstellungen des Mikroskops Beugungsbild und Hologramm von derselben Probenstelle zu erhalten. Viertens kann ein Probenhalter mit Heiz- bzw. K{\"u}hlvorrichtung bei der Bestimmung der Debye-Parameter hilfreich sein, da die Probentemperatur dann genauer bekannt ist als in dieser Arbeit. Dadurch kann leichter entschieden werden, ob die gemessenen Debye-Parameter unter starkem Einfluss nicht-thermischer St{\"o}rungen der Periodizit{\"a}t des Potentials stehen. Durch die Aufnahme von Beugungsbildserien bei verschiedenen Temperaturen kann evtl. auf den Verlauf der Debye-Parameter als Funktion der Temperatur geschlossen werden. Modernste Mikroskope wie etwa die Titan-Serie der Firma FEI sind mit entsprechenden Vorrichtungen ausger{\"u}stet oder ausr{\"u}stbar.

     [bibtex-key = Mueller2007]



669. Knut Müller. Quantitative Analyse von InGaN-Inseln mittels Hochauflösungs-Transmissionselektronenmikroskopie (Quantitative analysis of InGaN-islands by high-resolution transmission electron microscopy), June 2006. [bibtex-key = Mueller2006]

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