Indirect bulk plasmon generation by electrons reflected above the solid surface

We demonstrate that the spatial dispersion of the dielectric response provides the mechanism to excite the bulk plasmon in a solid by incident electrons not penetrating into the bulk, which is the process inhibited in the nondispersive models. In this case the bulk plasmon generation is described by the surface energy-loss function, but not by the bulk one -Im[1/ε(q,ω)], while the latter must be used when the probing electrons do not penetrate the bulk. Comparison of the indirectly excited bulk plasmon, obtained for the surface of aluminum, with experimental spectrum shows that the effect is sufficiently strong to be accounted for in the interpretation of the reflection electron-energy-loss spectroscopy data of surface structures.