Work function changes during low pressure oxidation of aluminum at room temperature

The oxidation kinetics of clean bulk aluminum surfaces exposed to low oxygen pressures (10^?8 to 2 × 10^?6 torr) at room temperature were followed by measurement of work function changes. The interaction of oxygen with aluminum resulted in a decrease in the work function, indicating that the chemisorbed surface oxygen was unstable and incorporation into the subsurface region took place even at very small surface coverages. A “stable layer” of constant work function was finally formed on the aluminum surface. The limiting work functio nchange (work function change to form the “stable layer”) became less negative with increase in oxygen pressure. It was not possible to explain these results on the basis of previously published oxygen uptake models. A new model based on a pressure dependent limiting amount of outer surface and incorporated oxygen is proposed to explain the pressure dependence of the limiting work function change.