Application of parallel factor analysis and x-ray photoelectron spectroscopy to the initial stages in oxidation of aluminium. I. The Al 2p photoelectron line

Abstract

Three-way parallel factor analysis (PARAFAC) has been used to decompose a set of x-ray photoelectron spectroscopy (XPS) spectra that result during the oxidation of aluminium surfaces. The Al 2p 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. In this paper, a fine peak structure of the XPS Al 2p spectrum has been extracted using PARAFAC. 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 a range of time and pressure variables. As expected, the reaction of water vapour with aluminium results in attenuation of the metallic peak at binding energy (BE) 72.87±0.05 eV and an increase of the oxidic peak at BE 75.80±0.05 eV. However, an additional factor is also identified, which suggests the formation of an interfacial metal hydride at BE 72.4(4) eV, as well as a concomitant oxide peak at 75.4(3) eV. Both are ascribed to products of the hydrolysis of adsorbed water molecules at the aluminium interface. At pressures above and below 1.3×10−5 Pa this factor is diminished; in the case of higher pressure, this is ascribed to an increase of the recombination of atomic hydrogen. Copyright © 1999 John Wiley & Sons, Ltd.