MODELS FOR TERMINATION OF CRYSTAL BOUNDARIES IN THE THEORY OF TRANSMISSION ELECTRON-DIFFRACTION AND COMPARISON WITH EXPERIMENTAL-DATA

Calculations of electron diffraction intensities in transmission elect ron microscopy commonly assume a model representing surfaces and inter faces in crystals as flat boundaries (flat-boundary model, FBM). It is shown that the independent-atom model (IAM) representing the crystal potential as a superposition of spherical atomic potentials leads to i mproved boundary conditions. Intensities calculated from the two model s at large deviation from the Bragg peak in weak reflections (e.g. 200 in InGaAs) differ significantly. Results from both types of calculati on are compared with an experimental diffraction pattern recorded usin g energy-filtered large-angle convergent-beam electron diffraction fro m an In0.53Ga0.47/InP bicrystal. It is shown that calculations using t he IAM give a better agreement with experiment.