The development of Z-contrast imaging in the scanning transmission electron microscope has enabled dislocation core structures to be visualized with increasing detail. In single-component systems, core structures were generally found to be as expected from simple considerations or theoretical predictions. In more complex structures, however, cores were generally seen to take on configurations that were not previously anticipated, utilizing reconstructions or non-stoichiometry to lower the elastic strain field. An overview of these developments in a variety of materials was presented. Under suitable circumstances, impurity segregation sites were directly imaged at dislocation cores. More generally, electron energy loss spectroscopy gave detailed, atomic-resolution information on stoichiometry and impurity concentrations. These additional variables introduce additional degrees of freedom into the whole issue of structure/property relationships. Examples of an impurity-induced core structure transformation and a cooperative doping effect were shown. First-principles density functional calculations were used to link observed core structures to macroscopic properties. It was also shown that planar dislocation arrays were accurate descriptions of tilt grain boundaries, with the structural units geometrically equivalent to individual dislocation cores.

Direct Imaging of Dislocation Core Structures by Z-Contrast STEM. M.F.Chisholm, S.J.Pennycook: Philosophical Magazine, 2006, 86[29-31], 4699-725