Surface photoemission in Ag(100)

Photoemission from the sp band of Ag(100) is significantly affected by surface effects. The dominant surface contribution at low-photon energies is derived from a ∇⋅A term in the optical-transition matrix element which gives rise to a significant amplitude for indirect transitions. This surface term interferes with the usual momentum matrix element for band-to-band transitions in the bulk, resulting in an asymmetric direct-transition peak. A line-shape analysis of spectra taken with various photon energies leads to a quantitative determination of this surface contribution. The results, as well as similar results for Ag(111) obtained over a different but adjoining range of photon energy, will be compared with the photon energy dependence of the dielectric function of Ag.