Plasmon excitation by charged particles interacting with metal surfaces

Recent experiments (R.A. Baragiola and C.A. Dukes, Phys. Rev. Lett. 76 (199 6) 2547) with slow ions incident at grazing angle on metal surfaces have sh own that bulk plasmons are excited under conditions where the ions do not p enetrate the surface, contrary to the usual statement that probes exterior to an electron gas do not couple to the bulk plasmon. We here use the quant ized hydrodynamic model of the bounded electron gas to derive an explicit e xpression for the probability of bulk plasmon excitation by external charge d particles moving parallel to the surface. Our results indicate that for e ach q (the surface plasmon wave vector) there exists a continuum of bulk pl asmon excitations, which we also observe within the semi-classical infinite -barrier (SCIB) model of the surface. (C) 1999 Elsevier Science B.V. All ri ghts reserved.