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 Ag 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.

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In this work, we compared formation and properties of heat-treated Ag nanoparticles in silica matrix synthesized by RFreactive magnetron cosputtering and sol-gel methods separately. The sol-gel and sputtered films were annealed at different temperatures in air and in a reduced environment, respectively. The optical UV-visible spectrophotometry have shown that the absorption peak appears at 456 and 400 nm wavelength indicating formation of silver nanoparticles in SiO 2 matrix for both the sol-gel and sputtering methods at 100 and 800• C, respectively. XPS measurements showed that the metallic Ag 0 nanoparticles can be obtained from both the techniques at these temperatures. According to XPS and AFM analysis, by increasing annealing temperature, the concentration of the Ag nanoparticles on the surface decreased and the nanoparticles diffused into the substrate for the sol-gel films, while for the films deposited by cosputtering method, the Ag surface concentration increased by increasing the temperature. Based on AFM observations, the size of nanoparticles on the surface were obtained at about 25 and 55 nm for sputtered and sol-gel films, respectively, supporting our optical data analysis. In comparison, the sputtering technique can produce Ag metallic nanoparticles with a narrower particle size distribution relative to the sol-gel method.

Silver nanocomposite coatings are prepared by the sol-gel method for the prevention of biofilm formation on the surface of medical implanted devices. High-temperature processing of such coatings can lead to diffusion of nanosilver and reduce the amount of available silver particles for long-term effects. Using a low-temperature sol-gel method, we have successfully prepared silane-based matrices, phenyltriethoxysilane (PhTEOS), containing different amounts of Ag nanoparticles. The incorporation of a silver salt into the sol-gel matrix resulted in a desired silver release rate, i.e. high initial release rate followed by a lower sustained release for more than 15 days, as determined by inductively coupled plasma mass spectrometry (ICP-MS). Scanning electron microscopy (SEM) has been employed to investigate the morphology of the film surfaces before and after immersion in a nutrient-rich bacterial suspension of approximately 10⁸ CFU ml⁻¹, which was incubated for up to 30 days at 37 °C. It was found that thin films containing 35 nm particles could prevent the formation of biofilm for over 30 days. The presence of surface silver before and after 3, 9 and 15 days immersion was confirmed by x-ray photoelectron spectroscopy (XPS).