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 Ti O2 powders of different relative size in order to study differential c harging effects. To illustrate some of the possible situations we have studied the behaviour of three different samples: (1) very large (mic rons) and porous particles of Al2O3 supporting TiO2 particles of relat ively small size (300 angstrom); (2) Al2O3 and TiO2 particles of simil ar size (300 angstrom); and (3) very small particles (20-30 angstrom) of TiO2 dispersed in Al2O3 particles of 300 angstrom. The observed eff ects are then analysed by using Auger parameters and relative binding energies and discussed in terms of the different morphologies of the s amples, as determined by TEM. The influence on charging of an electron flood gun and of Ar+ sputtering is also presented. In addition, ion-i nduced mixing effects have been clearly observed in the case of very s mall particles of TiO2 dispersed on alumina.