Modifications in Fullerene C70 Thin Film induced by Dense Ionization and Thermal Treatment

Abstract

This study presents the comparative modifications in optical, structural and morphological properties of fullerene C70 thin film induced by swift heavy ion irradiation and thermal annealing. Fullerene C70 thin films are prepared by resistive heating method on quartz substrates. One set of the films are irradiated with 125 MeV Au ions at different fluences varying from 1×1012 to 3×1013 ions/cm2 and second set of the films are annealed at temperatures varying from 50 to 350 ̊C for 30 minutes. The UV-visible spectroscopy and Raman spectroscopy are performed on pristine, irradiated and annealed films to investigate the modification in optical and structural properties after irradiation and annealing. UV-visible spectra show that the optical band gap of fullerene C70 film decrease with increasing fluence and temperature. The experiment using Raman scattering exhibits the transformation of fullerene C70 into amorphous carbon at higher fluences and higher temperatures as well. This transformation is evidenced by the presence of D and G bands of amorphous carbon in irradiated and annealed films. Atomic force microscopy is performed to observe the variation in surface roughness of films variation with irradiation and temperature. Swift ion irradiation induces the cylindrical zone so called “ion track” made of amorphous materials with in the fullerene C70 thin films. The damage cross-section and radius of cylindrical zone is calculated to be 2.8 ×10-13 cm2 and 3.0 nm respectively using the kinetics of damage of fullerene C70.