ELS-LEED study of electronic excitations on Ag(110) and Ag(111)

An energy loss spectroscopy-low-energy electron diffraction (ELS-LEED) study of the electronic excitation spectrum of Ag(110) and Ag(111) is presented. We find that for both surfaces, the linear term dominates surface plasmon dispersion at small transferred momentum, q(parallel to) and that it is responsible for the anisotropy, the quadratic term being isotropic. The slopes are thereby considerably smaller than reported for Ag(001), confirming that the latter surface behaves abnormally. Surface plasmon damping is nearly q(parallel to)-independent for q(parallel to) < 0.1 Angstrom(-1) and grows thereafter strongly in a face-and direction-dependent way. For Ag(110) surface plasmon damping depends linearly on crystal temperature T over the range 90 < 500 K. For Ag(111), on the contrary, the dependence with T is linear only for T < 350 K and increases more rapidly thereafter. The effect is possibly related to the population depletion of the filled Shockley state near <(Gamma)over bar>.