SCANNING TUNNELING SPECTROSCOPY OF UNOCCUPIED SURFACE RESONANCES AT FREE-ELECTRON-LIKE METAL-SURFACES

We extend and detail a previously developed model for formation of ele ctronic resonances at free-electron-like metal surfaces, in order to c alculate scanning tunnelling (ST) spectra. The effect of the tip is mi micked by inclusion of an external field, self-consistently, in a jell ium description of the surface potential. The lattice-induced corrugat ion of the potential is included perturbatively via a pseudopotential. We compare our calculated ST spectra for Al(111) with experimental sp ectra for that surface and conclude that a peak occurring below the me tal vacuum level is a 'crystal-derived' resonance, in the sense that l attice effects are crucial for its manifestation.