Sol-gel synthesis of metal nanoclusters-silica composite films

In a program on the development of metal nanoclusters in sol-gel derived thin films, attempts were made to synthesize pure and mixed metal clusters, control the cluster size and increase the volume fraction of the clusters. Thus, Ag, Cu and Ag-Cu nanoclusters were prepared in silica films using dip- and spin-coating techniques. The annealing of Ag/SiO2 films in different atmospheres (air, argon and 5% H-2-95% N-2 gas) caused modifications of Ag nanoclusters resulting in changes in their surface plasmon resonance (SPR) peak positions. The Cu and Ag-Cu codoped films were annealed in reducing atmosphere (5% H-2-95% N-2 gas). In order to prepare Cu nanoclusters of different sizes, the concentrations of Cu in Cu/SiO2 composite films were varied from 8 to 30 mol% and annealed at 800 degrees C for different times for growth. The size of the Cu nanoclusters was measured from the half band width of Cu SPR peak (appearing within 570-557 nm range) and X-ray diffraction. In this way Cu-nanoclusters of size ranges from about 3.5 to 10 nm (average diameters) were prepared. The Ag-Cu nanocluster-containing silica films show the existence of both Ag and Cu SPR peaks with some blue shifting in comparison with to their pure analogues depending on the Ag:Cu ratio.