SURFACE-PLASMON DISPERSION AND DAMPING ON AG(111)

Surface plasmon dispersion and damping on Ag(111) were studied by angl e-resolved electron-energy-loss spectroscopy. We find a positive dispe rsion, which can be described only assuming nonzero values for both li near 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. Su rface 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 o f surface plasmon damping. Beyond a critical q(parallel to) the linewi dth of the losses increases strongly with q(parallel to), as was the c ase also for Ag(001). The effect is ascribed to the opening of a decay channel involving the image potential state.