XPS investigations of surface segregation of doping elements in SnO2

Various doped tin oxide (dopants Sb, Nb, In) were prepared. By means of X-ray photoelectron spectroscopy (XPS) the dependence of the surface concentration on doping element, doping concentration and preparation technique was determined. Simultaneously, the electrical and morphological properties are strongly influenced even by low doping concentration. The dopant distribution was studied by XPS and SIMS depth profiling. A model for dopant distribution in the fine powders was proposed. At low concentrations, the doping element is build into the lattice of SnO2 partially and the residue substitutes Sn atoms in the topmost layer. Particles of the second phase are found at higher doping concentrations. Additionally, the analysis of Sb 3d3/2 peak position and shape in Sb doped samples shows a decrease of oxidation state of antimony with increasing doping concentration.