Dispersion and intrinsic width of image resonances measured by resonant inelastic electron scattering: The alpha phase of Pb/Ge(111)

Evidence of image states on semiconductor surfaces has been very scanty so far. We find that resonant scattering through image resonances totally domi nates the electron energy loss spectra of the alpha phase of Pb/Ge(111) if the energy and the parallel momentum of the scattered electron are in the g ap of the bulk bands projected onto the (1 x 1) surface Brillouin zone. The high energy and momentum resolution obtainable allows a detailed study of the interaction of these excited states with the substrate.