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

Three-way parallel factor analysis (PARAFAC) has been used to decompose a s et 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 PARA FAC. The PARAFAC solution provides new information on elemental processes i n 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 pre ssure variables. As expected, the reaction of water vapour with aluminium r esults 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. Howeve r, 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 ox ide 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 x 10(-5) Pa this factor is diminished: in the case of higher pre ssure, this is ascribed to an increase of the recombination of atomic hydro gen. Copyright (C) 1999 John Wiley & Sons, Ltd.