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CP: Chemische Physik

CP 5: Große Moleküle an Oberflächen

CP 5.9: Talk

Tuesday, March 18, 1997, 12:45–13:00, Gl

Oxidation of Al(111) by Electron Impact on Adsorbed H₂O — •Hans D. Ebinger and John T. Yates Jr. — Surface Science Center, Dept. of Chemistry
University of Pittsburgh, PA 15260

The oxidation of Al(111) by low electron energy bombardment of adsorbed water layers has been studied with AES, XPS and ELS at 90K and 300K. Above an energy threshold of about 6 eV, which correlates with the lowest dissociative excitation energy for water in gas phase experiments, oxidation of the aluminum surface can be observed at 90K. At an electron energy of 100 eV a cross section of 2·10⁻¹⁶ cm² has been determined. We observe complete conversion from water into an oxidized state without significant desorption. While electron loss experiments with a primary energy of 460 eV show a loss feature close to the Alv₂O₃ bulk plasmon HREELS result rather suggests a highly disordered adlayer of incomplete stoichiometry. At 300K electron bombardment in water vapor supports the growth of a bulk oxide film with thickness limitation of about 30 Å. Charging phenomena can be observed.