Changes due to the initial oxidation of A1(001) were determined from results of the first self-consistent thin-film calculations for the clean A1(001) surface as well as Al(001)-p(1×1)O. For clean A1(001), surface state-surface resonance bands obtained for a nine-layer slab were found to be in good agreement with photoemission measurements and our earlier non-self-consistent results; its work function (4.7 0.1 eV) is in good agreement with the Grepstad et al. experimental value (4.41 0.03 eV); no surface core-level shift was found in agreement with a recent photoemission measurement; finally, the absence of an increased broadening in the surface Al(2p) core level is discussed. For the nine-layer A1(001) plus O slab, the calculated reduction in the work function (0.6 eV) is in good agreement with the experimentally determined reduction (0.5-0.8 eV). Prominent O(2p) peaks in the surface layer density of states at - 8.0 and - 10.0 eV below EF are in good agreement with photoemission measurements. Structure at 1.0 and 1.8 eV above EF, due to O-induced surface resonance states, are related to interface states observed by surface soft-x-ray absorption spectroscopy. The overall bonding is found to be ionic in character with charge transfer onto the O atoms. A surface core-level shift of 1.5 eV to greater binding energy is found for the surface A1 atom, in excellent agreement with the Eberhardt and Kunz 1.4-eV Al(2p) shift. It is concluded that in the initial stages of oxidation a substantial number of O atoms are chemisorbed into coplanar, fourfold hollow sites, which is consistent with a recent extended-appearance-potential-fine-structure measurement for the Al-O bond length and an earlier self-consistent cluster calculation.
ASJC Scopus subject areas
- Condensed Matter Physics