Normal-incidence inverse photo-emission from Na(110)

The unoccupied states of Na(110) in the Gamma N direction have been studied with normal-incidence momentum-resolved inverse photo-emission (IPE). The isochromat spectra, although obscured over a small photon energy range by fluorescence photons produced following the excitation of Na 2p core electrons, suggest that sodium behaves like a nearly free-electron metal. No evidence is found in the authors' data for either a surface resonance above the Fermi level or a charge-density-wave-distorted band structure, two of the proposed explanations for the anomalous angle-resolved photo-emission reported for this surface.