The plasma oxidation mechanism of Al coatings on Si substrates

In this study, the plasma oxidation mechanism of aluminium (Al) coatings was studied by experimental and theoretical methods. Two alumina coatings prepared by thermal oxidation or plasma oxidation treatment were characterised by the energy-dispersive X-ray spectroscopy line-scan analysis. It was found that the sample treated by plasma oxidation had a peak curve of the O²⁻ ions at a depth of 0·7 μm. This phenomenon indicated that high-energy O²⁻ ions could be injected into the inner part of the coatings. The distribution and diffusion of O²⁻ ions in Al coatings were investigated by computer simulation using the Stopping and Range of Ions in Matter (SRIM) software and the first principles of molecular dynamics-based calculations. The experimental results of the distribution of O²⁻ ions agreed with those calculated by the SRIM software, which proved that the range of O²⁻ ion concentrations in the Al coatings was proportional to the energy of the O²⁻ ions. Through simulations of the Vienna Ab-Initio Simulation Package, it was shown that the inserted O²⁻ ions moved back and forth nearby the original location if there were no other Al vacancies available and the diffusion mechanism of oxygen was vacancy diffusion.