FORMATION OF FULLERENES IN MEV ION TRACK PLASMAS

MeV primary I-127(14+) ions from the Uppsala EN-tandem accelerator were used to bombard a polymer-poly(vinylidene difluoride). Positive ions of even numbered carbon clusters (C(n)+, n = 40-120) are ejected as a result of the interaction of fast MeV ions with the organic solid. The distribution of cluster sizes suggests that stable, closed carbon-cage structures-fullerenes-are formed. Initial radial velocity distributions of the desorbed carbon species are consistent with preferential ejection backward into the direction of the incoming MeV ions. Correlation between the directions of incoming particles and ejected clusters suggests that the latter (including C50+ and C60+) originate in the infratrack plasma produced by the fast primary ion's interaction with the sample. A main conclusion resulting from this study is that carbon cluster ions form as a result of a single primary ion impact and that they are ejected from an axially expanding infratrack plasma region.