Computer simulation of high resolution images of crystal defects

Abstract

During the last two years, the cores of several lattice defects in elemental Si and Ge have been directly imaged by high resolution electron microscopy The 3Å resolution images necessary for such work are even more sensitive to microscope defocus, astigmatism and other imaging parameters, and the specimen thickness and orientation, than the 4Å resolution images of complex oxides. Comparison of experimental results with computer-simulated images is therefore essential. The need for matching with theoretical simulations will increase for the coming generation of the 1-2Å point-to-point resolution microscopes.The presently used image simulation programs are based on the multi-slice formulation of the dynamical scattering theory. They are very adequate for thin specimens and a few hundred beams but at larger specimen thicknesses and a greater number of beams the computation times required to simulate one image may be an hour or more.We are therefore investigating the suitability of alternative computational approximations and formalisms such as neglecting diffuse-diffuse scattering in the multi-slice method and the matrix diagonalization formulation of the dynamical scattering theory.