Processing and thin film formation of TiO2–Pt nanocomposites

Abstract

AbstractThin films of TiO2‐Pt nanocomposites containing 4 at% Pt have been processed via spin‐coating. Film characterization involved XRD, Raman as well as XPS and scanning surface potential microscopy (SSPM). After annealing at 500 °C the thin films consisted of nanocrystalline anatase and a few nm Pt nanoclusters. Annealing at 600 °C resulted in the formation of a high volume fraction of rutile, ∼70%, 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 TiO2 films obtained at 600 °C which showed only a limited amount of rutile formation, namely 9%. Raman spectra of Pt‐containing 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 °C 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 °C were investigated using SSPM. Discrete Pt nanoparticles, mainly distributed in the vicinity of TiO2 grain boundaries were revealed. Nanocomposite film formation, Pt distribution and morphology are explained in terms of the limited solubility of Pt in the TiO2 lattice and its higher surface energy in comparison to that of TiO2. Both effects are believed to lead to the formation of Pt nanoparticles at the (anatase or rutile) grain boundaries. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)