Surface plasmon dispersion and damping on Ag(111)

Surface plasmon dispersion and damping on Ag(111) were studied by angle-resolved electron-energy-loss spectroscopy. We find a positive dispersion, which can be described only assuming nonzero values for both linear and quadratic terms. The best-fit values are close to those of Ag(110) (1(1) over bar0$), confirming the similarity in the behavior of close-packed surfaces and close-packed directions on open surfaces. Surface plasmon damping depends weakly on momentum transfer, q(parallel to), for small q(parallel to), again in analogy to the case of Ag(110) (1 (1) over bar 0). This result demonstrates the existence of a link between surface plasmon dispersion and the q(parallel to) dependence of surface plasmon damping. Beyond a critical q(parallel to) the linewidth of the losses increases strongly with q(parallel to), as was the case also for Ag(001). The effect is ascribed to the opening of a decay channel involving the image potential state.