Epitaxial ultra-thin films of MgO were grown onto Ag(100) single crystals and were investigated using photo-electron spectroscopic and electron energy loss spectroscopic techniques. It was shown that the surface of MgO was non-stoichiometric, and contained a species which was identified spectroscopically as being MgO2. This was confined to the first monolayer. Photo-electron spectroscopic investigations were made of the sub-monolayer regime of MgO, where systematic peak shifts of the O 1s and Mg 1s emissions were found which were similar to those measured during the growth of thicker MgO layers. It was concluded that, by thermal activation, the metal/oxide interface could be oxidized to form Mg-O-Ag bonds preferentially. By depositing Mg layers and incompletely evaporating them, a monolayer with a large O deficiency could be produced. The electron energy loss spectroscopic data showed that this layer exhibited characteristic loss peaks at 2.1 and 3.3eV. These were attributed to color centers that were due to O vacancies.

Oxygen Surplus and Oxygen Vacancies on the surface of Epitaxial MgO Layers Grown onto Ag(100). D.Peterka, C.Tagenkamp, K.M.Schroder, W.Ernst, H.Pfnur: Surface Science, 1999, 431[1-3], 146-55