SWIFT ATOMIC ION IRRADIATION OF C-60 FILMS - DEPENDENCE OF THE DAMAGECROSS-SECTION ON THE PRIMARY ION STOPPING POWER

Vacuum-sublimated C-60 films (around 1 mu m thick) are bombarded with fast atomic ions (He-4, C-12, O-16, S-32, Br-79; I-127) in the range f rom 2 to 80 MeV. The initial velocity of the primary ions is kept cons tant at 1.1 cm/ns, in order to maintain the same ion track size for al l impacting ions. Under these conditions the deposited energy density in the ion tracks is varied only due to changes in the stopping power, dE/dx, of the projectiles. Atomic force microscopy (AFM) and Fourier transform infrared absorption spectroscopy (FTIR) were used to charact erise the targets. AFM images indicate no major changes in topography and roughness of the irradiated samples. FTIR analyses of the irradiat ed samples give information on the changes in concentration of intact C, molecules as a function of primary ion fluence. From plots of the i ntensity of the C-60-specific IR absorption bands versus fluence, dama ge cross sections (a) for the C-60 molecules are extracted. For all an alysed bands, the values of a scale with the square of dE-/dx, i.e. th e deposited energy density in the ion tracks.