Resonances in the photoemission cross section of a surface state: Results for Ag(111)

Abstract

We present a model to explain the resonances in the photoemission cross section of a surface state as a function of photon energy. The model is based on an extension of the direct-transition model for bulk states, and should be applicable to a surface state with a long decay length. Energy broadening of the final states and momentum broadening of the initial surface state are included in the consideration. Resonances in the surface-state photoemission cross section are expected to occur for photon energies corresponding to direct transitions from the surface state to final Bloch states. The cross section of a surface state in Ag(111) was measured over the photon energy range of 36--65 eV, and a resonance at 54 eV was observed. The data were compared with the theoretical results. The data for a similar surface state in Cu(111), studied previously by Louie et al. [Phys. Rev. Lett. 44, 549 (1980)] were reanalyzed in terms of the present model. The results for these two systems, Ag(111) and Cu(111), will be compared.