Effect of Ag nanoparticle size on the plasmonic photocatalytic properties of TiO2 thin films

Photocatalytic TiO2 films combined with Ag nanoparticles (NPs) embedded-SiO2 films were fabricated by means of a RF magnetron sputtering and subsequent rapid thermal annealing (RTA). X-ray diffraction results show that the TiO2 films have anatase phase when annealed at 500 °C. The Ag NPs were formed by deposition and subsequent annealing at 600 °C. Scanning electron microscopy (SEM) results show that the density of the NPs decreases with increasing Ag film thickness. For example, the average NP diameter varies from ~ 19.3 to ~ 55.9 nm as the film thickness increases from 2 to 12 nm. Transmittance measurements show that as the Ag NP size decreases, the plasmonic peaks shift towards the shorter-wavelength region and become narrower. It is further shown that under UV-illumination (352 nm), all the TiO2 films with the Ag NPs show higher methylene blue decomposition rates compared to the TiO2 only films and the TiO2 films with Ag NP (a 7 nm-thick Ag film) show the best decomposition rate among the samples possibly due to the combined effects of optimized localized field amplification and radiative efficiency.