Initial oxidation of the A1(001) surface: Self-consistent electronic structure of clean A1(001) andAl(001)−p(1×1)O

Abstract

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 $\mathrm{Al}\mathrm{}\left(001\right)\mathrm{}-p(1\mathrm{}\times 1)\mathrm{O}$. 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 $\mathrm{Al}\mathrm{}\left(2p\right)\mathrm{}$ 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 $\mathrm{O}\mathrm{}\left(2p\right)\mathrm{}$ peaks in the surface layer density of states at - 8.0 and - 10.0 eV below $E_F$ are in good agreement with photoemission measurements. Structure at 1.0 and 1.8 eV above $E_F$, 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 $\mathrm{Al}\mathrm{}\left(2p\right)\mathrm{}$ 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.