Ion beam co-sputtering deposition of Au/SiO2 nanocomposites

Transparent, light brownish, uniform SiO2 films embedded with spherical Au particles are fabricated on quartz substrates at room temperature by ion beam co-sputtering technique, and heated in an open furnace at different temperature from 500 to 900 °C with 100 °C step for 5 min (referred to as mode A). The as-deposited film is found to be a little oxygen deficient, and to have 2.59 at.% of Au, which is appreciably reduced only for the film heated at 900 °C. A Gaussian-type characteristic absorption peak at around 533 nm, originating from surface plasmon resonance (SPR) of the Au nanoparticles and dielectric confinement effects, occurs at 500 °C, evolves into two Gaussian-type peaks at higher temperature, and gradually has a redshift but also gets strong in intensity with increasing temperature, leading to that the film getting more intense in color with increasing temperature and finally looking ruby-red. This redshift arises from a size increase of Au particles due to diffusion-induced growth during heating, as evidenced from XRD spectra. The films are also heated in mode B, i.e., for different heating time at a fixed temperature of 700 °C, to compare the effect of heating ways on the growth of Au particles. It is also found that Au particle growth during heating is dependent on the exact heating ways. In mode A, a small fraction of Au nanoparticles grow faster and the rest are smaller in size distribution than in mode B. This difference, maybe as a result of different dependence of diffusion on time and temperature, suggests that a proper heating way should be considered to tailor nanoparticle size distribution.