Sol-Gel Synthesis and Characterization of Ag and Au Nanoparticles in SiO2, TiO2, and ZrO2 Thin Films

Silver and gold nanoparticles were synthesized by the sol- gel process in SiO2, TiO2, and ZrO2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag1 and Au31 ions in sol- gel systems. Various ligands of the metal ions were tested, and for each system it was possible to find a suitable ligand capable of stabilizing the metal ions and preventing gold precipitation onto the film surface. Thin films were prepared by spin-coating onto glass or fused silica substrates and then heat-treated at various temperatures in air or H2 atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO2 film at 600°C and the TiO2 and ZrO2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO2 and ZrO2 films, respectively. The films were characterized by UV-vis optical absorption spectroscopy and X-ray diffraction, for studying the nucleation and the growth of the metal nanoparticles. The results are discussed with regard to the embedding matrix, the temperature, and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO2 and ZrO2 films may hinder the growth of Ag and Au particles.