Preparation and microstructure control of metal/oxide nano-composite thin films utilizing porous structure of oxide gels

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Silica coating films containing dispersed gold nanoporticles have been prepared by heat-treating the gel films obtained from tetraethoxysilane-water-ethanol-hydrochloric acid-chloroauric acid tetrahydrate solutions. It was found that the size and shape of the gold particles can be controlled by controlling the solution reaction time and amount of water in the starting solutions. In addition, aligned, elongated gold nenoparticles could be precipitated in coating films consisting of fibrous pseudoboehmite particles.Titania film electrodes containing dispersed gold or silver nanoparticles have been prepared by sol-gel method. It was found that photoresponse emerges in visible region when the metal particles are introduced to the titania photoanodes. The effect of the introduction of gold nanoparticles on the photoelectrochemical properties of dye-sensitized titania film photoanodes was also studied. The introduction of gold nanoparticles decreased the dye-induced photoresponse in the visible region, which was, however, found to be less when the overlap of the optical absorption of the gold particles and dyes was larger. This indicates that the dipole-dipole coupling between the gold particles and dye molecules dose exist, enhancing the photochemical processes occurring at the surface of the electrodes.In summary, it has been demonstrated that the size and shape of the metal nanoparticles can be controlled by controlling the microstructure of the gel matrices, where alignment of elongated metal nanoparticles is also possible. Possibility of development of new photoelectrodes with high energy conversion efficiencies was also investigated.