Gold nanoparticle thin films

The optical properties of Au@SiO2 particle films have been analysed as a function of the particle volume fraction, which is controlled through the silica shell thickness. The surface plasmon peak position is accurately predicted by the Maxwell–Garnett (MG) model, but very poorly by the Bruggeman model. A simple, analytical approximation for the plasmon band shift is also presented. The films exhibit uniform, transmitted colours, and display metallic reflection at low angles of incidence, even at low volume fractions. The specular reflectance spectra of the films are also in agreement with MG theory. The results demonstrate that it is possible to synthesize composite materials with optical properties that lie anywhere between those of transparent glass and those of metallic gold.