EMISSION ELECTRON-DIFFRACTION AND HOLOGRAPHY - A THEORETICAL SURVEY

The first part of this article reviews emission electron diffraction, a very powerful tool for investigating short order surface structures. Within the standard single particle approach, the correct multiple sc attering formalism and its single scattering duster, plane and spheric al wave approximations are treated in detail. The simple direct method s exploiting low energy backscattering and high energy forward focusin g, which can provide information on topmost crystal layers, are discus sed. In general, one needs to compare experiment and theory via trial- and-error extensive multiple scattering calculations for a series of g uessed test structures. Only structures explicitly taken into account in the analysis can be determined with certainty by these methods. Emi ssion electron holographic approaches, of less resolving power than em ission electron diffraction, are discussed in the second part of the p aper. They are direct methods which can provide an approximate initial structure which is then to be refined by the multiple scattering appr oach. Ways to eliminate twins, self-hologram peaks and angular anisotr opies, appearing in these approaches, are also discussed.