CHARACTERIZATION OF OXIDE LAYERS ON MG(0001) AND COMPARISON OF H2O ADSORPTION ON SURFACE AND BULK OXIDES

The composition, continuity, stoichiometry, and thickness of MgO thin films formed on the Mg(0001) surface were characterized by AES, ISS, UPS and XPS. The layer-by-layer mechanism of film growth was supported by comparison of the AES and ISS profiles for oxygen uptake, and by angle-resolved XPS results. Water was found to dissociate on both the thin film and the MgO(100) surfaces, forming surface hydroxyl groups upon adsorption of 200 K. The hydroxyls were characterized by an O(1s) peak at 533.1 eV in XPS and a valence band emission at 11.8 eV in UPS. The coverage of OH species determined by angle-resolved XPS measurements was ∼ 1 monolayer following adsorption at 210 K on a MgO(100) surface which had been sputtered but not annealed. Hydroxyl formation could be suppressed by annealing the sputtered MgO(100) surface prior to H2O exposure at room temperature. Thus sites of lower coordination number than those on the ideal MgO(100) surface are implicated in H2O dissociation. © 1990.