Layers of different thickness of CeO2 doped by Pt were prepared by magnetron sputtering on different substrates: Si (1 0 0) and a graphite foil. The structure and chemical composition of the Pt-CeO2 catalysts have been investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HAXPES). SEM showed that the layers prepared on different substrates had very different morphology. XPS and HAXPES studies demonstrated that Pt was dispersed only in Pt2+ and Pt4+ oxidation states in CeO2. Intensity of Pt2+- and Pt4+-peaks was affected by the plasma substrate interaction effects showing that carbon substrate played an active role by determining the film structure. The Pt2+/Pt4+ and Ce3+/Ce4+ ratios depend on the layer thickness and increases in the case of the graphite substrate. The reduced character of porous layer was explained by a general effect of formation of defects and oxygen vacancies at oxide edges and steps, and oxygen reaction with carbon which is responsible of formation of oxygen deficient cerium oxide at the interface. (C) 2012 Elsevier B. V. All rights reserved.