Collective excitations on silver surfaces studied by photoyield

The surface electronic structure of Ag has been studied using angle and energy resolved photoyield (AERPY) using low photon energies (2.7-18 eV). The adlayer standing-wave-like bulk plasmon mode is clearly observed in Ag(1 1 1) and Ag(1 0 0) thin films. A feature at 3.7 eV, observed both on Ag adlayers and bulk crystal surface, is assigned to the multipole plasmon mode. No signature of the multipole plasmon is observed around 6.7 eV, which is in disagreement with the prediction of the s-d polarization model.