Electron stimulated oxidation of Al(111) in H2O vapor: Dipole orientation effects in the Al2O3 thin film

The electron stimulated oxidation of Al(111) using H2O(g) as a source of oxygen has been investigated at 300 K using near edge x-ray absorption fine structure (NEXAFS) and Auger electron spectroscopy. Irradiation with electrons (100 eV, 50 μA/cm2) produced thick Al2O3 film layers (up to 15 Å), compared to the films grown thermally (4 Å) by the same water exposure. A preferential normal orientation of the O–Al bonds was found for the films grown by the electron assisted process, causing the O K-edge NEXAFS spectra to depend on the incident angle of the polarized x-ray beam. In contrast, little polarization of the O–Al bonds was found for the case of Al2O3 films grown by thermal oxidation in H2O(g).