ON THE IMAGE-CONTRAST FROM DISLOCATIONS IN HIGH-ANGLE ANNULAR DARK-FIELD SCANNING-TRANSMISSION ELECTRON-MICROSCOPY

High-angle annular dark-field scanning-transmission electron microscop ic imaging of inclined dislocation segments revealed a number of chara cteristic contrast effects that have been shown to depend on the speci fic position of the dislocation in the foil.The dislocation contrast i s initially very dark at the entrant foil surface due to stress relaxa tion-induced scattering of the incident electrons. Below the entrant s urface of the foil, the dislocation exhibits oscillatory contrast whic h disappears for large incident beam divergence angles. Ultimately, th e dislocation contrast remains bright beyond a certain depth in the cr ystal towards the exit foil surface. A qualitative Bloch-wave scatteri ng description has been formulated to describe consistently the observ ed contrast features.