Influence of Boundary Conditions and of Electronic and Vibrational Surface Phenomena on Low-Energy-Electron Diffraction from the Low-Index Faces of Aluminum

Abstract

An overlapping-atomic-charge-density model is used to construct muffin-tin potentials of surface ion cores on the (100), (110), and (111) faces of aluminum. When applied to bulk ion cores, this model leads to potentials whose associated elastic-low-energy electron diffraction (ELEED) intensities are indistinguishable from those predicted by a "correct" self-consistent muffin-tin potential. Moreover, the alterations in the ELEED intensities wrought by the differences between the surface and bulk potentials are small relative to those caused by plausible variations of the vacuum-solid boundary conditions among those commonly used by the various theoretical groups specializing in intensity calculations. The enhanced vibrations of the surface ion cores relative to those in the bulk, however, can lead to substantial changes in the ELEED intensities at fixed temperature as well as in the temperature dependence of these intensities. When their consequences are incorporated into the model, excellent correspondence with experimental ELEED spectra on Al(111) is achieved, but the comparable correspondence for Al(100) is poor. The absolute intensities of ELEED spectra from a planar Al(100) surface can be described by the model only if surface-plasmon loss processes are regarded as extending the inelastic collision damping about one lattice spacing in front of the outermost layer of ion cores.