Scanning tunnelling spectroscopy of unoccupied surface resonances at free-electron-like metal surfaces

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Abstract
We extend and detail a previously developed model for formation of electronic resonances at free-electron-like metal surfaces, in order to calculate scanning tunnelling (ST) spectra. The effect of the tip is mimicked by inclusion of an external field, self-consistently, in a jellium description of the surface potential. The lattice-induced corrugation of the potential is included perturbatively via a pseudopotential. We compare our calculated ST spectra for Al(111) with experimental spectra for that surface and conclude that a peak occurring below the metal vacuum level is a 'crystal-derived' resonance, in the sense that lattice effects are crucial for its manifestation.