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

The oxidation of iron films at {~}25 K and the reactive formation of iron oxides in a solid oxygen matrix is investigated using synchrotron-radiation-based photoemission. For O₂ 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 Fe₂{O}₃$-like phase. At higher iron coverages divalent FeO-like and metallic iron phases form because the supply of ${O}₂$ for the oxide-forming reaction decreases.