NOVEL DISLOCATION CONTRAST EFFECTS IN SCANNING-TRANSMISSION ELECTRON-MICROSCOPY

We present novel experimental results on the imaging of dislocations in HAADF-STEM. Images of inclined 60 degrees dislocation segments in Si exhibit a number of novel contrast effects which 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 and eventually exhibits oscillatory contrast at larger foil thicknesses. Ultimately, the dislocation contrast remains bright beyond a certain depth in the crystal towards the exit foil surface. A Bloch-wave scattering description has been formulated to consistently explain the observed contrast features.