Discrete valence-electron states for Na overlayers on Cu(111)

Abstract

A narrow peak close to the Fermi edge in photoemission spectra recorded normally to Cu(111) at high monolayer coverages of Na is explained in terms of one of a series of discrete states formed in the potential well between the Na vacuum barrier and the Cu(111) surface, which acts as a barrier for electrons with energies and wave vectors within the Cu s,p-band gap at the L point of the Brillouin zone. The discrete overlayer states have tails on the substrate side of the Cu(111)/Na interface. Using a phase-shift analysis we account for the coverage dependence of the energy of the observed state and estimate energies for higher members of the series. The lifetime broadening of the higher states is discussed.