In situ synthesis of noble metal nanoparticles in ultrathin TiO₂-gel films by a combination of ion-exchange and reduction processes

We have explored in situ synthesis of noble metal nanoparticles in ultrathin TiO₂-gel films, in view of the increasing importance of such nanoparticle-containing thin films. The two-step procedure consists of ion exchange in the ultrathin matrix and subsequent reduction of metal ions to nanoparticles by low-temperature H₂ plasma, by aqueous NaBH₄, and by UV irradiation. Smooth and transparent ultrathin TiO₂ films containing noble metal (Ag, Au, Pd, Pt) particles of 2-10 nm were readily obtained by this approach. The size and distribution of metal nanoparticles could be controlled by changing reaction conditions. The film thickness was precisely controlled by the cycle of film assembly. The low-temperature H₂ plasma treatment, first used for preparation of noble metal nanoparticles, showed interesting advantages over chemical and photoinduced reductions in fabrication of nanoparticle-containing inorganic thin films.