We demonstrate the existence of a surface resonance below the vacuum level of a simple metal surface. Theoretical modeling of new scanning tunneling spectroscopy (STS) data from Al(111) shows that the mechanism for formation of this resonance is scattering from the bulk lattice. Correlation between the STS feature and structure seen in inverse photoemission (IPE) spectra from Al(111) suggests that the IPE feature is also attributed to this surface resonance, rather than a previously proposed matrix element effect.

• Received 2 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.849