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 t o) and that it is responsible for the anisotropy, the quadratic term b eing isotropic. The slopes are thereby considerably smaller than repor ted for Ag(001), confirming that the latter surface behaves abnormally . Surface plasmon damping is nearly q(parallel to)-independent for q(p arallel to) < 0.1 Angstrom(-1) and grows thereafter strongly in a face -and direction-dependent way. For Ag(110) surface plasmon damping depe nds linearly on crystal temperature T over the range 90 < 500 K. For A g(111), on the contrary, the dependence with T is linear only for T < 350 K and increases more rapidly thereafter. The effect is possibly re lated to the population depletion of the filled Shockley state near <( Gamma)over bar>. (C) 1997 Elsevier Science B.V.