Nanoporous Platinum Doped Cerium Oxides Thin Films Grown on Silicon Substrates: Ionic Platinum Localization and Stability

In this study, the characterization of nanostructured Pt-doped CeO2 films with low platinum content and porous structure is reported, deposited on silicon substrate by direct liquid injection chemical vapor deposition. The platinum localization and concentration in the nanocomposite are determined by scanning transmission electron microscopy associated with energy dispersive X-ray spectroscopy. Films are made of approximate to 3 nm diameter CeO2 particles and platinum is homogeneously dispersed through the layers. X-ray photoelectron spectroscopy (XPS) also shows that platinum is mainly in an ionic Pt2+ state. After diffusion through the preformed porous structure of ceria films, the platinum precursor decomposes at the surface of each ceria particle forming the films, producing a homogeneous platinum-doped CeO2 nanocomposite. This result is supported by synchrotron radiation XPS experiment, where the measured relative Pt concentration demonstrates that platinum is decomposed only at the surface of ceria particles. Finally, when the saturation of Pt2+ sites at the surface of ceria particles is reached, metallic nanoclusters are formed from platinum excess.