Field Emission as a Probe of the Surface Density of States
David R. Penn, E. W. Plummer
Field-emission measurements of the total-energy distribution from a clean metal surface are shown to provide information about the density of states near the surface. Specifically, we find the field-emitted current per unit energy at energy ω to be given approximately by j(ω) (2hbar}/ m)Sλ-2 (ω)ΣmD02( Eperp}m) x |ψm(xm)|2δ (ω - εm), where D20 is the usual barrier-penetration probability with image potential corrections, Eperp}m= ω - hbar} 2k2||/2m, where k|| is the electron momentum parallel to the surface, |ψm(xm)| is the amplitude of the metal electron at the classical turning point (xm 1-2 Aring}), λ (ω) is a slowly varying function of ω, and S is the metal surface area. The D20 factor in j(ω) strongly weights electron states with small k|| and consequently j(ω) measures the density of states at xm arising from the component of the bulk band structure normal to the surface. Measurements of j(ω) for several single-crystal planes of tungsten will be presented and compared to the relevant photoemission data.
Physical Review B (Condensed Matter and Materials Physics)