Calculated images of crystal lattices by axial illumination 1 MeV electrons

Multibeam (001) electron-microscope lattice-image (N = 3,5) properties are studied when axial illumination is used. Numerical calculations were particularly applied to (001)-oriented gold foils observed with 1 MeV electrons. Conditions for obtaining images showing no artificial periodicity are determined. It is shown that in a particular range of thickness (40-60 Å for three-beam interference or 70-120 Å for five-beam interference) and with the proper defocusing distance high-contrast images would be obtained: the exact projected atomic positions are directly visible on these images. The influence of departure from exact symmetry conditions, and of large variation of the lattice parameter, are also studied. These calculations suggest that it would be possible to observe direct lattice images of metals and to study their defects with actual 1 MeV electron microscopes.