Unoccupied electronic structure of Al(111)

The unoccupied electronic states of the Al(111) surface have been studied using k-resolved inverse-photoemission spectroscopy (KRIPES). In addition, a first-principles calculation of the bulk Al electronic structure has been performed to facilitate interpretation of the experimental data. The KRIPES spectra obtained along the [1¯10], [112¯], and [1¯ 1¯2] azimuths of the surface Brillouin zone are characterized by well-defined features 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 obtain a qualitative account of the bulk features, and semiquantitative agreement was obtained when excitation effects were considered. Dispersion of an unoccupied surface resonance along the [112¯] 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 [1¯12] direction is identified as an odd surface state occurring in a symmetry gap and may account for earlier electron-energy-loss data.