Fine Structure of Electron Diffraction Beams from a Gold Crystal and from a Silver Film on a Gold Crystal

Abstract

A study of the diffraction of low-speed electrons from a gold crystal has been made under the same conditions as those previously used for a silver crystal to determine the extent to which the previously observed fine structure characteristics depend on the nature of the atoms composing the crystal. For normal incidence there are many differences in the positions, structure, and relative intensities of the corresponding beams from the two crystals. Intensity measurements as a function of angle of incidence show some similarities in these characteristics for the two crystals, but there are many more differences. Results for a thin silver film on a gold crystal are in general the same as those for a massive silver crystal so that the different results for the two crystals appear to be real and not due to differences in surface irregularities. Differences are noted in the deviations from the surface grating formula during growth and decay of diffraction beams from the gold crystal and from the silver film on the gold crystal. This makes it appear unlikely that the number of atom lines in the elementary grating is the only determining factor. Beams which deviate from the surface grating formula may follow one of two depth grating formulas. Some dependence of this characteristic on angle of incidence is noted. Since no beams characteristic of a surface gas lattice on the gold crystal were observed when gas was known to be present, the gas layer must be noncrystalline.