Physical characteristics of heat-treated nano-silvers dispersed in sol-gel silica matrix

Silica films containing various concentrations of Ag nanoparticles were deposited on glass slides using a sol-gel process and then heat-treated in air at different temperatures. The films were analysed by using UV-visible spectrophotometry, atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) for their optical, Surface morphological as well as structural, and chemical properties. After heat-treatment, the optical absorption peaks of Ag nanoparticles show a blueshift and an intensity reduction due to particle size reduction and AgOx nanoparticle formation, respectively. The particle size reduction and Surface morphology changes in the films were observed by AFM and TEM as a function of heat-treatment temperature and A-concentration. Using AFM and XPS analyses, we have found that the Ag nanoparticles accumulated on the surface diffuse into the substrate as the heat-treatment temperature increases. XPS analysis also showed that the silver oxidation occurs during the heat-treatment, causing the reduction of absorption intensity. By controlling the Ag concentration and the heat-treatment temperature, we could change the silica structure, and tailor the average size of the silver nanoparticles down to less than 4 nm.