The reaction of O₂ with Al(1 1 0): A medium energy ion scattering study of nano-scale oxidation

We have used medium energy ion scattering to study oxygen transport and oxidation kinetics of Al(110) at elevated temperatures in dry oxygen. Oxidation results in the formation of a stable stoichiometric Al₂O₃ layer with fairly abrupt interfaces. The time dependence of the film growth follows inverse logarithmic law, in agreement with the Cabrera-Mott (field-assisted) oxidation mechanism. The dependence of the growth rate on pressure is parabolic. Microscopic details on oxidation mechanism are studied by re-oxidizing a thin oxide layer with isotopically labeled oxygen. The depth profiling of oxygen traces in the oxide shows that oxygen ions are mobile species transported via migration of oxide network defects. This migration across the film is the rate-limiting step controlling oxidation.