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 re vealed significantly stronger contrast and of opposite sign relative t o 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-W aller effect. Multi-beam Bloch-wave theory has been used to quantitati vely predict experimental contrast levels. Secondly, HAADF-STEM imagin g of inclined dislocation segments revealed a number of novel contrast effects which depend on the specific position of the dislocation in t he foil. Unlike conventional diffraction contrast from dislocations, H AADF dislocation contrast is neither similar nor complementary at the entrant and exit surfaces of the specimen. A qualitative Bloch-wave sc attering description has been developed consistently to describe the d islocation contrast features.