222 Electron Reflection from Aluminium and Systematic Interaction

Energy dependence of electron diffraction from a bent wedge crystal of Al was investigated experimentally at energies from 100 KeV to 1 MeV as well as theoretically with particular interest in the systematic interaction. The (222) intensity at the crystal orientation for this reflection is remarkably reduced under observation at some 600 KeV where two dispersion sheets cross each other; furthermore the measured energy-dependence of a fine fringe appearing in the extinction contours agrees fairly well with our theoretical prediction. Around the orientation for (111) reflection the observed profile of (222) image-intensity includes a fringe synchronous to that in the (111) intensity, correspondingly to Vingsbo's observation for an MgO crystal (Proc. 6th International Congress for Electron Microscopy, Kyoto (1966), Vol. I 109.). As for (111) extinction distance, the present theoretical estimation gives a fringe-period shorter by 9% and 16% at 100 KeV and 1 MeV respectively than the simple two-ray approximation does.