Ion irradiation (low & high energy ion) induced surface plasmon resonance in Cu(10%)C70 nanocomposite thin films

Abstract

Cu-C70 nanocomposite thin films were deposited on glass, silicon and TEM grids by thermal co-evaporation; the thin films were irradiated by 350 keV Ar ions and 120 MeV Ag ions at different fluences, ranging from 1 × 1013 to 3 × 1016 ions cm−2 in a high vacuum chamber. Rutherford backscattering (RBS) of pristine film verified that the thickness and copper content of thin films were 30 nm and ∼10 at%, respectively. The modifications in structure and optical properties of irradiated thin films were studied by UV-visible absorption spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS); the results were compared with those of pristine film. Raman spectroscopy gave evidence of transformation of fullerene C70 matrix into amorphous carbon after irradiation by 350 keV Ar ions at a fluence of 3 × 1014 ions cm−2. At 1 × 1015 ions cm−2 fluence, a surface plasmon resonance band due to Cu nanoparticles appeared at ∼627 nm in the visible absorption spectrum. This band was seen to undergo blue shift at higher fluence values. TEM confirmed that increasing fluence brings about the coarsening of Cu nanoparticles (from 2.4 to 6.6 nm). Moreover, XPS study ruled out the possibility of formation of any Cu compound due to irradiation. In contrast, irradiation by 120 MeV Ag ion led to amorphization of Cu (10%) C70 nanocomposite thin films at higher fluences. The SPR band intensity at 627 nm was appreciably enhanced at a fluence of 3 × 1013 ions cm−2. The amorphization of C70 due to irradiation by 120 MeV Ag ion at fluence 3 × 1013 ions cm−2 was confirmed by the appearance of D and G band in the concerned Raman spectra. Moreover, this brings about a small increase in particle size. Both particle coarsening and amorphization of C70 were responsible for the emergence of SPR band due to copper.