Calibration of XPS – energy scale for determination of the oxidation states of do** elements in SnO₂ powders

Abstract.

X-ray photoelectron spectroscopy (XPS) has been used to investigate the oxidation states of do** elements in doped SnO₂ powders. Because of low conductivity, however, charging and resulting peak shift is observed. To obtain the real peak position a suitable reference peak must be found in the XPS spectrum. In this study both internal (Sn3d_5/2 peak) and external references (Au4f_7/2 and C1 s) were examined. When external references were used a shift of all the peaks studied was observed; the extent of this depended on the do** element and the do** concentration. By do** with an element of valence >4 (Nb and Sb) we obtained peaks at binding energy (BE); do** with a trivalent element (In) led to peaks at values of the BE. This peak shift is connected with changes of Fermi level. In contrast, by using Sn3d_5/2 as reference we obtained results which enabled, for example, observation of the dependence of changes of the oxidation state of Sb on do** concentration.