Application of parallel factor analysis and X-ray photoelectron spectroscopy to the initial stages in oxidation of aluminium

Abstract

The three-way parallel factor analysis (PARAFAC) has been used to decompose a set of XPS (X-ray photoelectron spectroscopy) spectra which result during the oxidation of aluminium surfaces by water vapour. Al(2p) and O(1s) core-level photoelectron lines have been used to follow oxide film growth on clean aluminium surfaces as a function of exposure time and pressure of water vapour. The PARAFAC solution provides new information on elemental processes in the very initial stages of oxidation kinetics, showing new components in the XPS spectrum, as well as their evolution through the range of time and pressure variables. Reaction of H 2O vapour with aluminium results in attenuation of the metallic peak, binding energy (BE) at 72.87±0.05 eV, and increase of the oxidic peak, BE at 75.80±0.05 eV. An additional factor is identified, which suggests the formation of an interface metal hydride, with BE at 72.4(4) eV, as well as a concomitant oxide peak at 75.4(3) eV. At pressures above 1.3×10 −5 Pa this factor is diminished; this is presumably due to the increase in recombination of atomic hydrogen.