Ab initio cluster study of the chemisorption of oxygen on an aluminium (111) surface

Abstract

The results of an ab initio all-electron Hartree-Fock study of the interaction of oxygen with Al₁₀ and Al₃ clusters are reported. These clusters model the closepacked Al(111) surface. The Al₁₀ cluster has seven atoms in the first layer and three in the second; the Al₃ cluster has only three atoms in the first layer. The chemisorption of atomic oxygen at the f.c.c. sites of Al(111) has been studied by means of calculations on Al₁₀O₃, Al₁₀O and Al₃O. The Al₁₀O₃ cluster was chosen to provide the opportunity of incorporating part of the possible influence of oxygen-oxygen interactions on the chemisorption properties.

A stable phase of oxygen has been found to be chemisorbed just outside the surface, with a vertical distance between oxygen and the first A1 plane of ∼0.6 Å. The calculated vibrational energy of the oxygen motion in a direction normal to the surface in the harmonic approximation is ∼50 meV. The results are consistent with the coexistence of oxygen in overlayer and underlayer configurations. No significant influence of oxygen-oxygen interaction on the calculated properties has been found. Finally, the calculation of the chemical shift of surface Al(2p) ionization is discussed.