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

The three-way parallel factor analysis (PARAFAC) has been used to decompose a set of XPS (X-ray photoelectron spectroscopy) spectra which result durin g the oxidation of aluminium surfaces by water vapour. Al(2p) and O(1s) cor e-level photoelectron lines have been used to follow oxide film growth on c lean aluminium surfaces as a function of exposure time and pressure of wate r vapour. The PARAFAC solution provides new information on elemental proces ses in the very initial stages of oxidation kinetics, showing new component s in the XPS spectrum, as well as their evolution through the range of time and pressure variables. Reaction of H2O vapour with aluminium results in a ttenuation 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 fac tor is identified, which suggests the formation of an interface metal hydri de, with BE at 72.4(4) eV, as well as a concomitant oxide peak at 75.4(3) e V, At pressures above 1.3 x 10(-5) Pa this factor is diminished; this is pr esumably due to the increase in recombination of atomic hydrogen, (C) 1999 Elsevier Science B.V. All rights reserved.