Study of sorption of oxygen on Al

Abstract

Uv photoemission study of oxygen sorbed on clean polycrystalline Al is reported. For small exposures of oxygen (0.5-3 L), a resonance level approximately 3 eV wide (FWHM) at 7.2 eV below $E_F$ was observed, and negligible work-function change was detected. These results disagree with recently reported calculation based on the atom-jellium model. We show that the origin of the disagreement is the fact that the model cannot accomodate the tendency of small, very electronegative adatoms such as oxygen to penetrate the metal surface. A generalized model allowing adatom penetration is seen to be consistent with the measurements. An independent model calculation of oxygen chemisorption on a small aluminum cluster based on the Hartree-Fock-Slater self-consistent-field method also confirms the penetration of the oxygen atom into the hole sites in between the aluminum surface atoms. Exposures beyond 3 L do not produce any shift in the resonance position and only a slight lowering of the work function.