Measurement of the surface density of states by field ionization

Abstract

It is shown that recent measurements of field ion energy distributions from clean tungsten surfaces probe the density of metal states in the vicinity of the surface. We find j( ω) = (2 π/ kh) Σ m | ∫ d 3 rψ m ( r) γ z | 2 δ( ω− ϵ m ), where j(ω) is the ion current a ω, ψ m and ϵ m are electronic metal eigenfunctions and eigenvalues in the presence of the external electric field used in field ionization and γ( z) is a function which is large near the noble gas atom. An explicit expression for γ( z) is given in the text. It is estimated that tungsten metal states with values of k ‖ at least as large as 0.5 Å −1 make an appreciable contribution to j(ω) where k ‖ is the electron momentum parallel to the surface.