Test of dielectric-response model for energy and angular dependence of plasmon excitations in core-level photoemission

We compare experimental measurements of the loss structure appearing in the Si 2p and Si 1s photoemission lines for a large range of emission angles (between 0° and 82°) and kinetic energies (125-3660 eV) with calculations derived within a semiclassical dielectric-response formalism [A. Cohen Simonsen, F. Yubero, S. Tougaard, Phys. Rev. B 56 (1997) 1612]. It is found that this semi-classical dielectric description of the energy-loss processes reproduces the relative intensity of surface to bulk energy losses appearing in the lower kinetic energy side of the main photoelectron peaks as well as the relative intensity of the losses with respect to the zero-loss peak. The absolute ratio of intensity of the loss structure to the zero-loss is ∼25-35% lower compared to experiment using self-consistent inelastic mean free paths in the analysis.