Unoccupied surface states on the (111) surface of silver: Evidence for broadening

We have studied Ag(111) with k-resolved inverse photoemission spectroscopy at hv=9.7 eV. In normal incidence we find image-state emission at Evac-(0.4±0.1) eV and the unoccupied part of an intrinsic surface-state band as a huge emission peak cut by EF. The energy dispersion of the intrinsic surface-state band and in particular its crossing of EF predicted by Ho et al. cannot be observed because of broadening effects as is shown by a theoretical simulation. The broadening is due to the vicinity of the surface state to the bulk continuum near EF as suggested by Kevan. © 1986 Springer-Verlag.