Experimental Study of Inelastic Process at the Crystal Surface in Angle Resolved Low-Energy Electron Energy Loss Spectroscopy

Angle-intensity profiles of inelastically scattered electrons were measured around several diffraction spots for the energy loss less than 20 eV. Peak structures were observed near diffraction spots. The energy loss dependence and the incident energy dependence of the peak position are discussed on the basis of the two step inelastic diffraction model, which suggests three characteristics in electron energy loss processes at a surface: (1) maximum probability of surface electronic excitation occurs at the momentum transfer parallel to the surface, (2) peaks due to loss before diffraction process dominate for grazing incidence and (3) a part of inelastic electrons due to surface electronic excitations have coherency as well as the incident electron according to the spot-like distribution of inelastic electrons.