Large shift in surface plasmon resonance wavelength with growth of embedded Au nanoparticles in fullerene C60 by Collision Cascades

Abstract

We report a 220 keV Ag ion beam irradiation-induced modifications of thin films of fullerene C60 containing gold (Au) nanoparticles. Nanocomposite thin films of Au-C60 were synthesized using a thermal co-deposition technique on a glass substrate. The as-deposited (pristine) thin films were irradiated by 220 keV Ag ion beam at different fluences ranging from 1 × 1013 ions/cm2 to 3 × 1016 ions/cm2 utilizing a low energy ion accelerator. The optical properties of pristine and irradiated thin films of Au-C60 were investigated using UV–visible spectroscopy. A redshift in the Surface Plasmon Resonance (SPR) wavelength from ~ 598–775 nm was obtained with increasing fluence up to 1 × 1014 ions/cm2, which indicated the growth of Au nanoparticles in the fullerene matrix due to ion irradiation. It was further confirmed by High-Resolution Transmission Electron Microscopy (HRTEM). With further increase in fluence, a blue shift from ~ 775–570 nm was obtained at a fluence of 1 × 1016 ions/cm2. The transformation of fullerene C60 into amorphous carbon (a:C) with increasing fluence of Ag ion beam was the main cause of this blue shift which was further confirmed by Raman spectroscopy. An increase in surface grain size with ion fluence was observed by Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscope (FESEM). The X-ray Photoelectron Spectroscopy (XPS) measurements were used for the chemical state analysis of the nanocomposite thin films before and after irradiation. The current-voltage measurements confirm the increase in the conductivity of the nanocomposite films with the fluence due to its transformation in carbon at higher fluences. The control on the size of Au nanoparticles and tuning of SPR wavelength by low energy ion irradiation may enhance the applicability of Au-C60 nanocomposite in organic solar cell.