187 research outputs found
GaN_Dislocations_1 EBSD Example data
No full text<p>EBSD Example data from a GaN sample, measured by Naresh Gunasekar. Data conversion by Aimo Winkelmann.</p>
Diffraction of backscattered electrons at crystal surfaces
No full textElectron backscatter diffraction (EBSD) has developed into a valuable tool for the analysis of materials in the scanning electron microscope (SEM) [1]. Pronounced improvements in applications of the EBSD method can be expected if it is possible to gain access to a quantitative description of not only the total number of backscattered electrons, but also to the fine-scale angular variations observed as diffraction patterns of these electrons. A complete simulation of the observed intensities, however, is only possible by applying electron diffraction theories that can properly include the multiple (dynamical) scattering of keV electrons in crystals [2,3].
I will discuss the application of many-beam dynamical theory to the simulation of experimental diffraction patterns of backscattered electrons. By energy-resolved measurements, the correlation between the energy loss of the scattered electrons and their diffraction effects can be investigated. First experimental results of corresponding angle-resolved reflection electron energy loss measurements are presented [4]. It is shown that under certain conditions, inelastically backscattered electrons can show more pronounced diffraction effects than the elastic electrons.
1. A.J. Schwartz, M. Kumar, B.L. Adams, D. P. Field (Eds.), Electron Backscatter Diffraction in Materials Science, 2nd edition, Springer, Berlin, 2009
2. A. Winkelmann, C. Trager-Cowan, F. Sweeney, A. P. Day, P. Parbrook, Ultramicroscopy 107, 414 (2007)
3. A. Winkelmann, Ultramicroscopy 108, 1546 (2008)
4. M. R. Went, A. Winkelmann, M. Vos, Ultramicroscopy 109, 1211 (2009
GaN Stripes EBSD
No full text<p>Raw EBSD Data for a GaN thin film sample with changing polarities and crystal structures as published in:</p>
<p>Point-Group Sensitive Orientation Mapping Using EBSD. Winkelmann A., Nolze G., Himmerlich M., Lebedev V., Reichmann A. (2016) In: Holm E.A. et al. (eds) Proceedings of the 6th International Conference on Recrystallization and Grain Growth (ReX&GG 2016). Springer. The data was measured by G.Nolze, the sample was provided by V. Lebedev and M. Himmerlich<br>
<a href="https://doi.org/10.1007/978-3-319-48770-0_41">https://doi.org/10.1007/978-3-319-48770-0_41</a></p>
<p>The data in <a href="https://zenodo.org/api/files/0f9f0014-75e7-4f63-bf8d-1636448101a8/static_bam_ef.txt?versionId=9ca597c9-edd1-486d-b542-00a5dd1edf72">static_bam_ef.txt </a> is a static EBSD background image (taken from a different experiment with the same detector)</p>
Nichtlineare Photoemission an Metalloberflächen unter Einfluss der Spin-Bahn-Kopplung
No full textDiese Arbeit beschäftigt sich mit der Untersuchung des Einflusses der Spin-Bahn-Wechselwirkung in der optischen Mehrphotonenanregung von spin-polarisierten Photoelektronen an nichtmagnetischen und magnetischen Metalloberflächen. In nichtlinearen Photoemissionsprozessen spielen die optisch angeregten Zwischenzustände eine große Rolle. Mehrphotonen-Photoemission bietet einen einzigartigen Zugang zu diesen Zuständen. Eine Vielzahl von Effekten in aktuell relevanten Forschungsrichtungen der Festkörperphysik wird direkt oder indirekt vom Elektronenspin beeinflusst. Dies macht die Wichtigkeit eines experimentellen Zugangs zum Elektronenspin in Festkörpern deutlich. Über die Kopplung des Spins eines Elektrons mit seiner Bahnbewegung im Mechanismus der Spin-Bahn-Kopplung kann ein indirekter Zugriff auf den Spinfreiheitsgrad über die Anregung der Elektronenorbitale erfolgen. Mittels zirkular polarisierter Strahlung können die Dipol-Auswahlregeln für optische Übergänge zwischen verschiedenen Elektronenzuständen genutzt werden, um gezielt Elektronen mit einer bestimmten Spinausrichtung aus einem insgesamt unpolarisierten Ensemble anzuregen.von Aimo Winkelman
EBSD Kikuchi Pattern Analysis, Silicon 15kV
No full textSupplementary Data and Images for Si EBSD pattern analysis as presented in
A. Winkelmann, T.B. Britton, G. Nolze "Constraints on the effective electron energy spectrum in backscatter Kikuchi diffraction", Physical Review B (2019
The Kikuchi bandlet method for the intensity analysis of the electron backscatter Kikuchi diffraction patterns
No full textThe present dissertation attempts to extend the application fields of the Electron Backscatter Kikuchi Diffraction technique (EBSD) by enabling the analysis of the intensity of the Electron Backscatter Kikuchi Diffraction patterns (EBSPs). It also presents an error analysis for the conventional method that retrieves the crystallographic orientation from an EBSP. The error analysis is performed on simulated patterns. An analytical, inferential statistics-based method for estimating the accuracy of a retrieved orientation and a retrieved misorientation of a real pattern is validated. The second part of this work introduces a method, which deconvolutes and reconstructs the individual Kikuchi bands, and thus, enables an accurate and automatic analysis of their intensity profiles. The method is termed the Kikuchi bandlet method. Two of this method's exemplary applications are also presented: (1) the quantification of the stored crystalline defects and (2) the improvement of the accuracy of the retrieved crystal orientation and the retrieved projection parameters of an EBSP. The method proposed for quantifying the stored defects through quantifying the individual Kikuchi band's sharpness is applied to a controlled experimental case of bending a micro-cantilever. It is shown that, using this method, for each reflector, the deviation of the atomic positions from equilibrium can be retrieved through the band sharpness, which, in effect, measures the incoherency of the diffracted beams. Linking the band sharpness to the underlying crystal structure is performed through the simulation of Kikuchi patterns resulting from a crystal structure containing a known defect, and subsequently, analysing the pattern with the Kikuchi bandlet method. The results shows that the dislocation is clearly visible on the planes that fulfil the criterion of diffraction, with being the dislocation's Burgers vector and being the reciprocal space vector of the reflector. They also show that the retrieved band sharpness correlates with the value.The intensity profile analysis of a reconstructed K-band reveals its characteristic hyperbolic features. Using these curves increases the accuracy of the estimated orientation and projection center. This is presented as the second application of the Kikuchi bandlet method. In the case studied here, for simulated pattern, an order of magnitude improvement in orientation accuracy and times improvement in projection center accuracy is achieved
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