Dispersion and intrinsic width of image resonances measured by resonant inelastic electron scattering: the ? 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 dominates the electron energy loss spectra of the ? phase of Pb/Ge(111) if the energy and the parallel momentum of the scattered electron are in the gap of the bulk bands projected onto the (1×1) surface Brillouin zone. The high energy and momentum resolution obtainable allows a detailed study of the interaction of these excited states with the substrate.