Sub-angstrom imaging of dislocation core structures: how well are experiments comparable with theory?

Abstract

During the past 50 years, transmission electron microscopy (TEM) has evolved from an imaging tool to a quantitative method that approaches the ultimate goal of understanding the atomic structure of materials atom by atom in three dimensions both experimentally and theoretically. Today's TEM abilities are tested in the special case of a Ga-terminated 30° partial dislocation in GaAs:Be where it is shown that a combination of high-resolution phase contrast imaging, scanning TEM (STEM), and local electron energy loss spectroscopy (EELS) allows for a complete analysis of dislocation cores and associated stacking faults. We find that it is already possible to locate atom column positions with picometre precision in directly interpretable images of the projected crystal structure and that chemically different elements can already be identified together with their local electronic structure. In terms of theory, the experimental results can be quantitatively compared with ab initio electronic structure total energy calculations. By combining elasticity theory methods with atomic theory, an equivalent crystal volume can be addressed. Therefore, it is already feasible to merge experiments and theory on a picometre length scale. Whereas current experiments require the utilization of different, specialized instruments, it is foreseeable that the rapid improvement of electron optical elements will soon generate a next generation of microscopes with the ability to image and analyze single atoms in one instrument with deep sub-angstrom spatial resolution and an energy resolution better than 100 meV.

Acknowledgements

The authors acknowledge support of the National Center for Electron Microscopy, Lawrence Berkeley Lab, which is supported by the US Department of Energy under Contract #DE-AC02-05CH11231. This research is supported by the National Energy Research Scientific Computing Center and by the Directorate, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy. D.C.C. acknowledges the support of the Miller Institute for Basic Research.