Self-energy in surface electron spectroscopy: II. Surface excitation on real metal surfaces

A scheme for calculating the complex self-energy of electrons moving in a real metal surface region is proposed. The approach is based on a quantum formula that uses a Drude-Lindhard model bulk dielectric function epsilon(q, omega) for describing free-electron metal. The experimental energy-loss function Im{-1/epsilon(omega)} is fitted to a finite sum of the modelled energy-loss functions and a corresponding expression for the complex self-energy is derived. Calculated differential inelastic scattering cross-section results are given for Mg, Ag and Au to show the surface and bulk excitation modes in these metals. The z-dependent inelastic mean free path and stopping power near a surface region are also obtained. The approach provides a practical scheme to be used in quantitative surface electron spectroscopy.