Enhanced nonlinear optical absorption of Au/SiO2 nano-composite thin films

Nano metal-particle dispersed glasses are the attractive candidates for nonlinear optical material applications. Au/SiO₂ nano-composite thin films with 3~vol\% to 65~vol% Au are prepared by inductively coupled plasma sputtering. Au particles as perfect spheres with diameters between 10~nm and 30~nm are uniformly dispersed in the SiO₂ matrix. Optical absorption peaks due to the surface plasmon resonance of Au particles are observed. The absorption property is enhanced with the increase of Au content, showing a maximum value in the films with 37~vol% Au. The absorption curves of the Au/SiO₂ thin films with 3~vol\% to 37~vol% Au accord well with the theoretical optical absorption spectra obtained from Mie resonance theory. Increasing Au content over 37~vol% results in the partial connection of Au particles, whereby the intensity of the absorption peak is weakened and ultimately replaced by the optical absorption of the bulk. The band gap decreases with Au content increasing from 3~vol\% to 37~vol % but increases as Au content further increases.