CHARGING AND MIXING EFFECTS DURING THE XPS ANALYSIS OF MIXTURES OF OXIDES

In this article we present an XPS analysis of mixtures of Al2O3 and TiO2 powders of different relative size in order to study differential charging effects. To illustrate some of the possible situations we have studied the behaviour of three different samples: (1) very large (microns) and porous particles of Al2O3 supporting TiO2 particles of relatively small size (300 angstrom); (2) Al2O3 and TiO2 particles of similar size (300 angstrom); and (3) very small particles (20-30 angstrom) of TiO2 dispersed in Al2O3 particles of 300 angstrom. The observed effects are then analysed by using Auger parameters and relative binding energies and discussed in terms of the different morphologies of the samples, as determined by TEM. The influence on charging of an electron flood gun and of Ar+ sputtering is also presented. In addition, ion-induced mixing effects have been clearly observed in the case of very small particles of TiO2 dispersed on alumina.