Ion beam assisted formation of Ag nanoparticles in SiO 2 and their optical properties

Abstract

Ag nanoclusters in SiO 2 matrix were formed by magnetron co-sputtering followed by ion irradiation. The refractive index and optical extinction spectra of the films were studied. The SiO 2:Ag thin films exhibit a plasmon resonance in the visible region. In the as-deposited films the Ag nanoclusters are less then 0.5 nm in size. The intensity of the plasmon peak is low. After irradiation with 4.5 MeV Au ions the intensity of the peak increases and it becomes narrower. The FWHM of the plasmon peak corresponds to a mean radius increasing with the ion fluence. The method of the disappearing diffraction pattern was used for the refractive index determination. It is a critical angle method and is applicable for measurements of layers with thickness comparable with the used wavelength. Moreover it is insensitive to surface gradients of the real part of the refractive index and roughness, which disturb elipsometric data. The refractive index enhances with the increasing Ag concentration and irradiation ion fluence, as is expected from the light scattering theory.