Effects of temperature and Ar⁺ ion bombardment on the initial oxidation stages of polycrystalline aluminium with water vapour

Abstract

The initial stages of oxide formation following the interaction of water vapour with polycrystalline aluminium surfaces have been studied using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Attenuation of the electron signal from the metallic substrate has been used to follow the oxidation kinetics of aluminium as a function of energy and dose of Ar + ion bombardment and temperature. The effects of energy and doses of Ar + ion bombardment on oxidation kinetics have been examined in the energy range 1-5 keV and ion dose ranging from 1.3 × 10 16 to 3.8 × 10 17 ions cm −2 . Although the increase in energy of Ar + ion bombardment slightly modified the oxidation kinetics, the effects of ion dose on oxidation kinetics are shown to be more complex. There is a threshold dose of Ar + ions above which the surface activity becomes significantly reduced; this is ascribed to cluster formation blocking the surface diffusion pathway in the near-surface region. The oxidation kinetics of aluminium also have been studied in a range of temperature from room temperature up to 573 K. As the temperature increases, the oxidation rate of aluminium decreases due to a decrease in the sticking probability of water molecules on the aluminium surfaces. The observed temperature dependence of the oxidation kinetics is likely to be due to a precursor mechanism of water desorption.