Insights into image contrast from dislocations in ADF-STEM

TL;DR

This paper provides a comprehensive analysis of the contrast mechanisms of dislocations in ADF-STEM imaging of GaN, combining experimental observations with theoretical modeling to improve interpretation accuracy.

Contribution

It introduces a detailed theoretical model supported by simulations to explain complex contrast features of dislocations in ADF-STEM images.

Findings

Contrast features depend on angular detection range and dislocation position.

Theoretical model based on electron channelling and Bloch wave scattering explains contrast.

Simulations validate the model's ability to predict contrast phenomena.

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 revealed 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 multislice simulations using Grillo s strain channelling equation, is proposed to elucidate the physical origin of such complex contrast phenomena.