Abstract
Thin films of TiO~2~โPt nanocomposites containing 4 at% Pt have been processed via spinโcoating. Film characterization involved XRD, Raman as well as XPS and scanning surface potential microscopy (SSPM). After annealing at 500 ยฐC the thin films consisted of nanocrystalline anatase and a few nm Pt nanoclusters. Annealing at 600 ยฐC resulted in the formation of a high volume fraction of rutile, โผ70%, and a coarsening of the microstructure, including Pt nanoparticles which attained a mean particle size of up to 11 nm. These results contrasted with those of pure TiO~2~ films obtained at 600 ยฐC which showed only a limited amount of rutile formation, namely 9%. Raman spectra of Ptโcontaining samples exhibited a fluorescence emission, as background to the Raman features, which was attributed to photoinduced luminescence from Pt nanoparticles supported by their surface plasmon resonance. Emission intensity being much higher in 600 ยฐC film indicated a difference between the two films in terms of the (Pt) particle size and crystallinity, in agreement with the XRD results. XPS investigations revealed different oxidation states of Pt at the surface and in the film interior. The spectra suggested a slight oxidation of Pt at the surface while mainly metallic Pt was revealed in the film interior. The morphology and distribution of the Pt nanoparticles in the films annealed at 600 ยฐC were investigated using SSPM. Discrete Pt nanoparticles, mainly distributed in the vicinity of TiO~2~ grain boundaries were revealed. Nanocomposite film formation, Pt distribution and morphology are explained in terms of the limited solubility of Pt in the TiO~2~ lattice and its higher surface energy in comparison to that of TiO~2~. Both effects are believed to lead to the formation of Pt nanoparticles at the (anatase or rutile) grain boundaries. (ยฉ 2008 WILEYโVCH Verlag GmbH & Co. KGaA, Weinheim)