ION-BEAM MODIFICATION OF FULLERENE

The response of thin films of fullerene (C-60) to energetic ion impact is investigated. The diagnostics employed include Fourier-transform i nfrared and Raman spectroscopies, cross-sectional transmission electro n microscopy, and atomic force microscopy. By combining the informatio n obtained from these diagnostics with that from the dependence of the conductivity on ion dose, it is concluded that each C-60 molecule com pletely disintegrates when hit by an energetic ion. The cross section for the destruction is about 6 x 10(-13) cm(2) for irradiation with 62 0-keV Xe ions. The disintegration occurs when C atoms are knocked out of the molecule either directly by the impinging ion or by an energeti c knock-on C atom within the damage cascade. This process is quite dif ferent from the Coulomb-explosion mechanism previously proposed in the literature. For very low ion doses (< 1 X 10(11) Xe/cm(2)) most of th e C-60 molecules remain intact; however this dose is sufficient to com pletely disrupt the ordering of the C-60 molecules in the van der Waal s bonded C-60 solid. Disruption of the lattice ordering at such low do ses is considered to be attributable to the weakness of the van der Wa als forces which bind the C-60 clusters together into the molecular so lid.