Temperature induced surface plasmon resonance in Au/a-C nanocomposite thin film

Nanocomposite thin film containing Au nanoparticles in carbon matrix is developed using co-sputtering method in a high vacuum chamber (<10^-6 torr). The atomic concentration of Au metal (6 at. %) is kept low so that the properties of matrix are not deteriorated much by the presence of metal. In order to enhance the growth of Au nanoparticles to an appreciable size, thermal annealing is performed on the as-deposited films at increasing temperatures from 100 to 500 °C in an inert atmosphere (continuous flow of Ar gas is maintained during heating and cooling). Annealing is performed for 1 hr on each sample. Growth of the Au nanoparticles and evolution of carbon matrix by thermal treatment is understood through TEM and Raman spectroscopy. TEM images of the as-deposited sample taken at different areas of the sample clearly indicate the spherical-shaped Au nanoparticles with an average diameter of ∼1.5 nm which is further increased up to ∼15.3 nm at the temperature of 500 °C. The results of Raman spectroscopy confirm the increase in the intensity of characteristic D and G bands of amorphous carbon with temperature. Surface plasmon resonance is successfully induced by temperature treatment at a wavelength of ∼548 nm at 400 °C, which is further enhanced at 500 °C. The growth of Au nanoparticles is also confirmed by X-ray diffraction study.