Electron-impact-induced oxidation of Al(111) in water vapor: Relation to the Cabrera-Mott mechanism

The oxidation of an A1(111) single-crystal surface induced by 100 eV electron bombardment in water vapor at room temperature has been studied using x-ray photoemission spectroscopy and electron-energy-loss spectroscopy. Electron bombardment significantly increases the growth rate and changes the observed growth-rare law in comparison to the oxidation without the electron beam, The aluminum oxide film grows with linear rather than parabolic time-dependent kinetics up to a thickness of about 25 Angstrom. After reaching this thickness, the growth rare slows down significantly. During oxidation the oxide film becomes electrically charged on its surface and the normal electric field in the oxide remains constant. The results are discussed in the framework of a Cabrera-Mott type oxidation mechanism.