Multipole surface-plasmon-excitation enhancement in metals

We consider the energy losses undergone by an electron reflected inside the extended electron-density distribution at the surface of a metal. The random-phase approximation calculation of the dynamical response with a local-density approximation ground state reveals the dramatic enhancement of the multipole-plasmon intensity compared with the conventionally considered reflection in vacuum above the surface. Our calculations conciliate the theory and the electron-energy-loss spectroscopy experiment with regard to the multipole surface-plasmon intensity, which has been predicted by previous theories to be two orders of magnitude smaller than the experimental one. The influence of the nonzero electron density along the incident electron path on the surface and the bulk-plasmon generation is also discussed.