Oxidation of ultrathin indium layers on W(1 1 0)--a core-level photoemission study

We have studied the reaction of ultrathin In overlayers on W(1 1 0) with molecular oxygen at 300 K. At a coverage of 0.25 monolayers (ML) oxygen first chemisorbs dissociatively at free tungsten sites and oxidation of In occurs with some delay. At an In coverage of 1.2 ML complete oxidation of the closed overlayer is observed. Layers of 3 ML thickness first show rapid transformation from In to an In₂O₃-like species until an oxide monolayer is formed. Further oxidation occurs at much reduced rate. No oxygen-induced restructuring is observed for In at 300 K, in contrast to the response of Ag monolayers deposited on W(1 1 0).