Unexpected surface sensitivity at high energies in angle-resolved photoemission

Abstract

Angle-resolved photoemission data from Al(001) taken with photon energies up to several hundred electron volts show an unexpected surface sensitivity at high energies. The surface state at the center of the surface Brillouin zone can be clearly observed up to photon energies higher than 700 eV. The surface to bulk intensity ratio appears to increase with photon energy, despite the longer inelastic mean-free path of the electrons and the increased vibrational amplitude at the surface. We explain this surprising behavior by considering the effect of phonon excitation in the photoemission event.