High-Resolution STEM and Related Imaging Techniques

Advances in electron optics have made it possible to form electron beams of sub-nanometer diameters, and these beams have enabled high-resolution imaging methods with incoherent scattering at high angles. The origin of this incoherence is discussed. Some practical issues of high-angle annular dark field imaging are presented, and the fortunate effect of electron channeling along ion cores is explained. One of the enabling technologies for this work is an aberration correction system. Methods of Cs correction are described, one in detail. The various higher-order aberrations are classified and enumerated. Some examples of atomic-scale imaging and chemical analysis of individual atoms are shown, with comments on future directions.