UNOCCUPIED ELECTRONIC-STRUCTURE OF AL(111)

The unoccupied electronic states of the Al(111) surface have been stud ied using k-resolved inverse-photoemission spectroscopy (KRIPES). In a ddition, a first-principles calculation of the bulk Al electronic stru cture has been performed to facilitate interpretation of the experimen tal data. The KRIPES spectra obtained along the [($) over bar 110], [1 1 $$($) over bar 2], and [($) over bar 1 $($) over bar$$ 12] azimuths of the surface Brillouin zone are characterized by well-defined featur es within 5 eV of the Fermi level, and broad, weak features at higher energies. In general, surface states and resonances appeared as strong spectral features while bulk transitions were weak for this surface. First-principles electronic-structure calculations were necessary to o btain a qualitative account of the bulk features, and semiquantitative agreement was obtained when excitation effects were considered. Dispe rsion of an unoccupied surface resonance along the [11 $$($) over bar 2] azimuth is consistent both with an occupied surface resonance found by an earlier photoemission study and with the predictions of surface electronic-structure calculations in the literature. A strong feature observed in the [($) over bar 112] direction is identified as an odd surface state occurring in a symmetry gap and may account for earlier electron-energy-loss data.