Plasmon damping and surface interband transitions on Ag(001) and (011)

Abstract

The dependence of surface-plasmon damping versus plasmon momentum and energy has been measured for the Ag(011) surface with angle-resolved electron energy loss spectroscopy. The data are compared with previous results obtained for Ag(001). At small transferred momenta, q‖, we observe a nearly linear dependence of the energy loss width with q‖ due to the growing phase space available for e-h pair creation. However the very efficient damping mechanism observed for q‖ beyond 0.10 Å−1 is not present for Ag(011). We demonstrate that it is due the onset of interband transitions between filled and empty surface states. Two such states are indeed present near the X point of Ag(001) as demonstrated by inverse photoemission experiments and electronic band structure calculations. The energy gap between the two bands can thus be determined by EELS with a greater precision than by photoemission.