220 keV Ag ion irradiation-induced surface plasmon resonance shift of gold nanoparticles in fullerene C60 matrix

Abstract

The effect of 220 keV Ag ion beam irradiation on the optical and structural properties of thermally co-deposited Au-C60 nanocomposite thin films on a quartz substrate is investigated by irradiating samples at different doses. To determine the exact gold (Au) concentration in the film and thickness of the film, Rutherford Backscattering Spectrometry (RBS) was utilized on the as-deposited film. The Surface Plasmon Resonance (SPR) of Au nanoparticles embedded into the fullerene C60 matrix was seen at 721 nm in the as-deposited sample. A ∼34 nm redshift in SPR wavelength was obtained at a dose of 1 × 1014 ions/cm2 which was mainly due to the increase in the size of Au nanoparticles with irradiation. At higher doses, a blue shift of ~67 nm was obtained at a dose of 1 × 1016 ions/cm2 which was due to the transformation of fullerene C60 matrix into amorphous carbon with a much lower dielectric constant at higher doses. The progressive transformation of fullerene C60 into amorphous carbon with increasing doses was confirmed by Raman spectroscopy. The size of Au nanoparticles in the highest dose irradiated sample was found to be ∼3.9 nm by High-Resolution Transmission Electron Microscopy (HRTEM) bright-field measurements. The size modifications of nanoparticles and SPR wavelength tuning of these nanoparticles are very much needed to use them in organic solar cell.