Direct determination of interface structure and bonding with the scanning transmission electron microscope

The scanning transmission electron microscope is capable of forming an electron probe of atomic dimensions, allowing incoherent imaging and microanalysis to be achieved at atomic resolution. Images formed using elastically scattered electrons show strong atomic number ( Z ) contrast and reveal atomic column locations without the need for preconceived structure models. Column positions and scattering power can be directly retrieved by a maximum entropy analysis. The Z -contrast image also allows the probe to be positioned with atomic precision over selected atomic columns or planes, making possible atomic-resolution electron energy loss spectroscopy. Interfacial structure and bonding can both be determined directly from experimental data, often leading to unexpected insights. In SrTiO 3 , grain boundary structural units were identified, and found to be reconstructed, an efficient way to overcome the problem of like-ion repulsion in ionic materials. At a CdTe-GaAs [001] interface, 60° dislocations were directly identified to be of glide type, while in the case of Lomer dislocations, an unexpected core structure was found comprising a fourfold ring structure. With these techniques, dislocation core structure and impurity segregation may be studied experimentally at the atomic scale.