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Insights into image contrast from dislocations in ADF-STEM
E Oveisi1, M C Spadaro2, E Rotunno3
1Interdisciplinary Centre for Electron Microscopy, École Polytechnique Fédérale de Lausanne (CIME-EPFL), Lausanne, Switzerland; Electron Spectrometry and Microscopy Laboratory, École Polytechnique Fédérale de Lausanne (LSME-EPFL), Lausanne, Switzerland.
Abstract:
Competitive mechanisms contribute to image contrast from dislocations in annular dark-field scanning transmission electron microscopy (ADF-STEM). A clear theoretical understanding of the mechanisms underlying the ADF-STEM contrast is therefore essential for correct interpretation of dislocation images. This paper reports on a systematic study of the ADF-STEM contrast from dislocations in a GaN specimen, both experimentally and computationally. Systematic experimental ADF-STEM images of the edge-character dislocations reveal a number of characteristic contrast features that are shown to depend on both the angular detection range and specific position of the dislocation in the sample. A theoretical model based on electron channelling and Bloch-wave scattering theories, supported by numerical simulations based on Grillo's strain-channelling equation, is proposed to elucidate the physical origin of such complex contrast phenomena.
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