Final state band gap effects in UV photoemission from Cu(111)

The crystal momentum dependence of the final states involved in bulk photoemission from the sp-bands through a (111) surface of copper was investigated with a photon energy hν = 11.7 eV. Plane wave hybridization was observed and is described in terms of a 2-OPW model Hamiltonian with parameters determined to be V₀=7.1±0.1 eV for the inner potential and E_g = 1.6 ± 0.2 eV for the energy gap. The model is also shown to account for a rapid intensity variation with crystal momentum of the form |a_G(k)|², where a_G(k) is a plane wave amplitude of the final state wave function.