Surface excitation parameters of low-energy electrons crossing solid surfaces

The surface excitation parameter, which describes the influence of surface excitations by electrons for the vacuum side in electron spectroscopies, has been calculated for electrons of 200-2000 eV energies crossing surfaces of Cu, Ag, Au, Fe, Pd, Ni, MgO and SiO₂. These calculations were performed for both incident and escaping electrons by the use of dielectric response theory. Spatially varying differential inverse mean free paths for surface excitations as a function of electron distance from the surface were found. The results showed that small differences existed in the surface excitation parameter among different metals but large differences occurred between metals and semiconductors or insulators. Calculated surface excitation parameters were fitted very well to a simple formula, i.e. P_a = aE^-b, where P_a is the surface excitation parameter and E is the electron energy.