Kinetic aspects of the formation of aluminium oxide by use of a microwave-induced plasma
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The oxidation of thin aluminium layers in a microwave plasma has been investigated to determine the kinetics of oxide growth.
Thin Al-coatings were oxidized by means of a variety of gas mixtures, characterized by different partial pressures of oxygen, in microwave-induced plasmas of different power. To study the whole kinetic process the Al-metal and the oxide formed were investigated by means of a combination of grazing incidence X-ray reflectometry (GIXR) and grazing incidence X-ray diffractometry (GIXRD). XPS and FTIR spectroscopy confirmed the formation of stoichiometric Al2O3 . The alumina formed is X-ray amorphous. Quantitative description of oxide formation was achieved indirectly by determination of the decrease in the integrated intensity of the Al(111)-peak and the total thickness of the whole coating. These values enabled calculation of kinetic data.
It was found that oxide growth was a combination of two simultaneous processes – diffusion and sputter processes. The diffusion coefficient D (cm2 s–1) and the sputter rate S (nm s–1) were determined. The effect of the composition of the gas mixture, microwave power, and concentration of activated oxygen species on the oxidation process will be discussed. For calculation of the activation energy, EA, of this plasma-enhanced diffusion process the temperature-dependence of D was investigated.
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