STRUCTURAL EFFECTS IN SINGLE-CRYSTAL PHOTOELECTRON, AUGER-ELECTRON, AND KIKUCHI-ELECTRON ANGULAR DIFFRACTION PATTERNS

The full-hemisphere diffraction patterns of primary photoelectrons, photoemission Auger electrons, and Kikuchi electrons are reported for single-crystal surfaces of Cu(100), Cu(111), Cu(110), Ir(111), and Ag(100), to test models for direct structure determinations from angle-dependent final-state diffraction patterns. Our measurements show a simple correlation between the low-index crystallographic directions of the substrate and local intensity maxima in the electron angular distributions. We find that the angular anisotropy can be qualitatively explained in all cases studied by final-state elastic forward scattering. The strong forward scattering features in photoemission diffraction patterns are used to measure bond angles and determine the structure of Cu ultrathin films on Ir(111). In addition, a radial image function based on a holographic Fourier-transform algorithm is evaluated for the determination of bond lengths from three-dimensional images reconstructed from the two-dimensional diffraction pattern.