The initial oxidation of aluminum thin films at room temperature

Abstract

Thin film and ultra-high-vacuum techniques have been utilized in fabricating uncontaminated, atomically clean, aluminum surfaces in order to characterize the initial low temperature, low pressure oxidation kinetics of aluminum. The kinetics were followed gravimetrically by the quartz crystal microbalance technique and the aluminum-aluminum oxide surface was examined by utilizing electron microscopy and scanning electron microscopy techniques. It has been found that the kinetics of oxygen uptake associated with the initial oxidation stage cannot be adequately described by present chemisorption theory. An oxygen uptake model based on an “incorporation-chemisorption” transition is proposed to explain the “stable layer” associated with the aluminum oxygen reaction at room temperature. The kinetics of uptake associated with the incorporation reaction is characterized as a zero order reaction with an oxygen sticking coefficient of approximately 0.03. In contrast, the kinetics of the chemisorption range cannot distinguish between dissociative chemisorption or immobile molecular adsorption on adjacent vacant sites. The proposed “incorporation-chemisorption” model is consistent with low energy electron diffraction, resistivity and contact potential difference measurements previously reported in the literature and removes the apparent ambiguities regarding the interpretation of the initial oxygen uptake measurements.