Effect of photoelectron mean free path on the photoemission cross-section of Cu(111) and Ag(111) Shockley states

The photoemission cross-section of Shockley states of Cu(111) and Ag(111) surfaces is studied over a wide range of photon energies. The constant initial-state spectra are very different for the two surfaces and show rich structure that does not follow the generally accepted nearly free electron model for the final state. Angle resolved photoemission data are interpreted within a one-step ab initio theory, revealing a multiple Bloch wave structure of photoemission final states. The inelastic scattering parameter-optical potential-is determined, and the energy dependence of the mean free path of the outgoing electron is calculated, which turns out to be the key for the understanding of the photoemission cross-section curve. These are essential steps for future exploration of wave function perturbations in the presence of surface nanostructures.