Silver and gold nanoparticles were synthesized by the sol-gel process in SiO 2 , TiO 2 , and ZrO 2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag ؉ and Au 3؉ 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 H 2 atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO 2 film at 600°C and the TiO 2 and ZrO 2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO 2 and ZrO 2 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 TiO 2 and ZrO 2 films may hinder the growth of Ag and Au particles.

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Thin films of hafnium oxide have been prepared by using a dual ion beam sputtering system. A study of their physical properties is reported. In particular, structural and compositional characterization was performed by means of x-ray diffraction and x-ray photoelectron spectroscopy techniques, showing a mixture of amorphous and polycrystalline structure and a substoichiometric composition. The atomic force microscopy results have shown a crater-like morphology probably due to the deposition process. In addition the gas sensing characteristics were analyzed in the presence of carbon monoxide. The variations in the electrical resistance have shown the capability of the films to detect CO and then the possibility to use hafnium oxides as a new sensitive material in the field of gas sensors.

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