The oxidation kinetics of Mg-, Si- and Fe-implanted aluminum by using X-ray photoelectron spectroscopy

Abstract

The oxidation kinetics of Mg-, Si- and Fe- implanted aluminum has been studied at room temperature and a water vapour pressure of 2.0×10 −6 Pa using X-ray photoelectron spectroscopy. The elements Mg, Si and Fe were implanted into pure aluminum at low ion doses from 6.0×10 12 to 3.6×10 13 ions cm −2. Secondary ion mass spectrometry (SIMS) depth profiles have shown that the element distributions of Mg and Fe in aluminum are consistent with the theoretical depth profiles calculated using a TRIM program. The implanted elements are distributed in the near surface region with their maximum concentration at a depth of ∼50 nm. In the case of implanted Si, however, the SIMS depth profile shows no maximum concentration peak, and the near-surface concentration is much higher than that calculated. This is ascribed to diffusion of Si toward the surface during implantation. The oxidation kinetics of implanted aluminum have shown that surface concentrations of implanted Si, as low as 40 ppm, cause an increase in the Al oxidation rate compared to the pure metal. By contrast, equivalent concentrations of implanted Mg in aluminum result in a lowered oxidation rate until the oxide reaches a thickness of 3 monolayers, after which a rapid increase in oxidation occurs. Implanted Fe in the same concentration range does not cause any change in oxidation rate of aluminum. These oxidation kinetics can be explained on the basis of metal vacancies in the defect structure of aluminum thin oxide films. The effects of surface damage caused by ion beam during the implantation experiment were also determined by measurements of oxidation kinetics.