Irradiation of swift heavy ions on thin films of C 60—a comparative study

Abstract

Thin films of C 60 were irradiated with swift heavy ions of Au (100 MeV) , Ni (110 MeV) and O (70 MeV) to study the irradiation effects. Films of C 60 with thickness ∼230 nm were deposited on quartz and float glass substrates. The samples irradiated by different fluences of ions were studied using optical absorption spectroscopy, in situ conductivity measurements and Raman spectroscopy. Obtained data indicate that swift ions at low fluences result in multiple molecular units like dimer or polymer. High fluence irradiation result in sub-molecular formations in amorphous semiconducting carbon network, indicating overall damage of the fullerene molecules. These sub-molecular units have been identified as nanocrystalline graphite. Observations with optical absorption spectroscopy of decrease in bandgap with increase in fluence, and with in situ resistivity measurements, are in conformity with understanding of structural changes from Raman spectroscopy. A comparison of changes produced by irradiation of these ions which have different electronic energy loss ( S e) values, is presented.