DAMAGING OF C60 FILMS BY MEV HEAVY-IONS

Thin films of C60 (99.99% purity) have been irradiated with 55 MeV I-127(10+) ions in a fluence range from 2.5 x 10(9) to 3 x 10(12) ions/cm2. Two methods have been employed to assess the modifications induced by the MeV ion irradiation: in situ plasma desorption mass spectrometry analysis and off-line micro-Raman spectroscopy. The yields of secondary low mass carbon cluster ions and intact C60 ions have been determined at different fluences. Damage cross-sections for the C60 molecules have been extracted from the ion yield curves as a function of MeV ion fluence. The secondary ion spectra of the C60 targets also show peaks corresponding to larger fullerenes with masses at least up to 2500 u. The evolution of the ion yields of these higher mass carbon clusters gives an evidence that they are not originally present in the target. They may be formed by coalescence reactions of C60 molecules as a result of an individual MeV ion impact.