IMAGING ELASTIC STRAINS IN HIGH-ANGLE ANNULAR DARK-FIELD SCANNING-TRANSMISSION ELECTRON-MICROSCOPY

High-angle annular dark field (HAADF) imaging in a dedicated scanning transmission electron microscope (STEM) has been applied to the study of imperfect crystals. Firstly, a study of B-doped layers in Si has revealed significantly stronger contrast and of opposite sign relative to simple atomic number contrast (Z-contrast) predictions. It is shown that misfitting substitutional B atoms act as point defect sites in a Si matrix which enhance scattering to high angles via a static Debye-Waller effect. Multi-beam Bloch-wave theory has been used to quantitatively predict experimental contrast levels. Secondly, HAADF-STEM imaging of inclined dislocation segments revealed a number of novel contrast effects which depend on the specific position of the dislocation in the foil. Unlike conventional diffraction contrast from dislocations, HAADF dislocation contrast is neither similar nor complementary at the entrant and exit surfaces of the specimen. A qualitative Bloch-wave scattering description has been developed consistently to describe the dislocation contrast features.