Theoretical determination of the surface excitation parameter for Ti, Fe, Cu, Pd, Ag, and Au

The angular dependence of the surface excitation parameter (SEP) is theoretically determined for different materials (Ti, Fe, Cu, Pd, Ag, and Au) for angles to the surface normal between 10° and 70° and for energies between 300 and 3400 eV. The method is based on analysis of energy-differential inelastic electron scattering cross sections calculated from the dielectric function with the software QUEELS (quantitative analysis of electron energy losses at surfaces) valid for reflection-electron-energy-loss spectroscopy (REELS). The calculations presented here are closely related to a method previously developed [N. Pauly, S. Tougaard, F. Yubero, Surf. Interf. Anal. 37 (2005) 1151] for materials (like Al and Si) with a clear surface plasmon peak. However, for the materials studied here the excitations are broad and there is no clear visual distinction between surface and bulk excitations. It is therefore not possible, as in the previous studies of Al and Si, to isolate the intensity of the surface excitation directly. Therefore the volume component for an infinite medium is subtracted from the calculated cross section and in this way the surface excitation component of the cross section is determined and the SEP calculated.