Initial stages of oxidation of Mg(0001) and the role of co-adsorbed alkalimetals

Soft X-ray Mg 2p photoemission using synchrotron radiation at moderate spec tral resolution has been used to investigate the early stages of oxidation of Mg(0001) with and without preadsorbed Na or K. On the alkali-free surfac e, some evidence is found for a state characterized by a chemical shift int ermediate between that of the metallic and oxidic states, but the limited r esolution and overlapping spin-orbit split surface and bulk metallic compon ents precludes more thorough characterization. Preadsorbed Na or K enhance the initial rate of oxidation by approximately a factor of two. It is sugge sted that the mechanism is an enhancement of the rate of oxygen dissociatio n. (C) 1999 Elsevier Science B.V. All rights reserved.