INITIAL STEPS OF ALKALI-METAL-PROMOTED OXIDATION OF THE Al(111) SURFACE

Abstract

We investigate the initial Na-promoted oxidation of an Al surface at room temperature by core-level photoemission spectroscopy using synchrotron radiation. We bring the first evidence that, in the initial state, adsorbed oxygen atoms break the Na-Al bonds. This leads to the formation of an intermediate oxidation state involving both Na and Al sites with oxygen atom in a bridge-type site. This bonding configuration is shown to result from the Na/Al intermixing and appears as a precursor step playing a key role in the observed promoted oxidation. It is also likely to explain the formation, upon annealing, of Al oxides having a higher oxygen content than Al 2 O 3.