On the image contrast from dislocations in high-angle annular dark-field scanning transmission electron microscopy

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Abstract
High-angle annular dark-field scanning-transmission electron microscopic imaging of inclined dislocation segments revealed a number of characteristic contrast effects that have been shown to depend on the specific position of the dislocation in the foil. The dislocation contrast is initially very dark at the entrant foil surface due to stress relaxation-induced scattering of the incident electrons. Below the entrant surface of the foil, the dislocation exhibits oscillatory contrast which disappears for large incident beam divergence angles. Ultimately, the dislocation contrast remains bright beyond a certain depth in the crystal towards the exit foil surface. A qualitative Bloch-wave scattering description has been formulated to describe consistently the observed contrast features.