Low-energy EELS investigation of surface electronic excitations on metals

Recent progress in experimental and theoretical investigations of surface electronic excitations of metals is reviewed with an emphasis on surface plasmon dispersion. The experimental methods applied to these studies are critically discussed, highlighting present limitations and possible future developments. Available data on the dependence of surface plasmon frequency, dispersion and damping on crystal temperature and of surface plasmon damping on parallel momentum and energy are collected. Surface plasmon dispersion and Mie resonance shift as a function of cluster size are compared when possible. The implications of surface plasmon dispersion for the position of the centroid of the induced charge at the surface and in general for the optical surface properties are presented and discussed.