Electron spectroscopic studies on the growth mechanism of oxide on aluminum surfaces exposed to water vapour.

摘要

The initial stages of the interaction of water vapour with polycrystalline aluminum surfaces at room temperature have been studied using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The effects of water vapour pressure on oxidation kinetics of aluminum have been examined in great detail in a pressure range from 1.0 × 10−6 to 6.5 × 10−4 Pa. The growth of thin oxide films on aluminum surfaces has been found to follow the Cabrera-Mott inverse logarithmic kinetics law at all pressures studied. The formation reaction of metal vacancies at the oxide film/gas interface is shown to be the rate determining process in the oxidation kinetics of aluminum. The formation of an aluminum hydride at the metal/oxide film interface is also found, which is associated with an oxidation process involving an incorporation of hydroxyl groups into the oxide structure. The pressure of water vapour is shown to have a major effect on initial stages of water adsorption and oxide nucleation as well as the oxide structure on aluminum surfaces.; The oxidation kinetics of Mg-, Si- and Fe-implanted aluminum have been studied at room temperature using the XPS technique with a view to better understanding the role of near-interface impurity in the oxidation process. These elements were implanted into high-purity aluminum at low ion doses ranging from 6.0 × 1012 to 3.6 × 1013 ions·cm −2. Increased surface concentration of Si and Mg implants causes an increase and a decrease, respectively, in the rate of initial oxide coalescence as well as in subsequent oxide growth. Implanted Fe does not cause any change in the oxidation rate of aluminum. The oxidation kinetics of implanted aluminum can be explained on basis of the metal vacancies as dominant defects in the oxide films.; The effects of energy and doses of Ar+ ion bombardment on oxidation kinetics have also been examined in the energy range 1–5 keV and ion dose ranging from 1.3 × 1016 to 3.8 × 1017 ions · cm−2 using AES and XPS. There is a threshold dose of Ar+ ions, above which the surface activity become significantly reduced, which is ascribed to a cluster formation blocking the surface diffusion pathway in the near-surface region. Finally, the oxidation kinetics of aluminum have been studied in a range of temperature from room temperature up to 573 K using the AES technique. As the temperature increases, the oxidation rate of aluminum decreases due to a decrease of sticking probability of water molecules as well as a decrease in the density of oxide islands. The temperature dependence of oxidation kinetics suggested a precursor mechanism for the water desorption. It has been also suggested that the growth of oxide islands in diameter is controlled by the diffusion of hydroxyl groups on aluminum surfaces.