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 scattering formalism and its single scattering cluster, plane and spherical wave approximations are treated in detail. The simple direct methods exploiting low energy backscattering and high energy forward focusing, which can provide information on topmost crystal layers, are discussed. In general, one needs to compare experiment and theory via trial-and-error extensive multiple scattering calculations for a series of guessed test structures. Only structures explicitly taken into account in the analysis can be determined with certainty by these methods. Emission electron holographic approaches, of less resolving power than emission electron diffraction, are discussed in the second part of the paper. They are direct methods which can provide an approximate initial structure which is then to be refined by the multiple scattering approach. Ways to eliminate twins, self-hologram peaks and angular anisotropies, appearing in these approaches, are also discussed.