Bulk Plasmon Enhanced Photoemission from Nb(100) Surface Resonances.
Abstract:
The electronic properties of Nb100 are studied using angle-resolved photoemission. Several surface resonances are identified. One surface resonance exhibits significant enhancement of the photoemission cross section at the bulk plasma energy suggesting a novel probe of surface resonances having high degree of second-layer charge density. We report the observation of bulk plasmon enhanced photoemission from Nb100 surface resonances. This effect offers a sensitive direct probe of the spatial extent of surface states and surface resonances at metal surfaces in cases where a high degree of second-layer charge density exists in the two-dimensional Brillouin zone. A related enhancement effect has been recently reported by Drube and Himpsel for inverse photoemission. Photoemission cross section resonances associated with surface states which arise from final state effects have also been observed on silver and copper surfaces. However, these resonances are produced by a distinctly different mechanism than the one described in this paper.