Unoccupied states on Pd(110) and the surface potential barrier

Abstract

Inverse photoemission spectra on Pd(110) reveal bulk band-structure features, and surface-state features in the projected gaps centered at points Y\ifmmode\bar\else\textasciimacron\fi{} and X\ifmmode\bar\else\textasciimacron\fi{}. The energy dispersion of the bulk band-structure features is in agreement with direct-transition predictions. Surface-state energies and their dispersion are reproduced with a nearly-free-electron model and a surface-barrier model which places the image plane 2.3 a.u. beyond the outermost atomic layer. The experimentally determined energies of surface states are as follows: at point X\ifmmode\bar\else\textasciimacron\fi{}, 6.6 eV above ${E}_{F}$, designated ${S}_{0}^{+}$; at point Y\ifmmode\bar\else\textasciimacron\fi{}, 3.4 and 6.6 eV above ${E}_{F}$, designated ${S}_{0}^{+}$ and ${S}_{1}^{\mathrm{\ensuremath{-}}}$, respectively.