Oxidation of iron films at 25 K and the reactive oxidation of iron in solid oxygen

Abstract

The oxidation of iron films at \ensuremath{\sim}25 K and the reactive formation of iron oxides in a solid oxygen matrix is investigated using synchrotron-radiation-based photoemission. For ${\mathrm{O}}_{2}$ on Fe, the oxygen molecules dissociate and go into a chemisorbed state. At intermediate oxygen coverages, a disordered divalent FeO-like phase grows at the expense of the chemisorbed state. Further exposures of oxygen lead to the condensation of molecular oxygen on top of the oxide. Initial Fe depositions into a solid molecular oxygen film produce a trivalent ${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$-like phase. At higher iron coverages divalent FeO-like and metallic iron phases form because the supply of ${\mathrm{O}}_{2}$ for the oxide-forming reaction decreases.