PLASMA DESORPTION MASS-SPECTROMETRY IN STUDIES OF FORMATION AND SPUTTERING OF FULLERENES BY MEV ATOMIC IONS

An account is presented on plasma desorption mass spectrometry (PDMS) studies of different carbon-containing organic solids utilizing megaelectronvolt (MeV) atomic ions from the Uppsala EN-tandem accelerator. Positive ions of even-numbered carbon clusters (C-n(+), n = 40 to >200) are ejected as a result of the interaction of the fast MeV ions with the target. The distribution of cluster sines suggests that stable, closed carbon-cage structures - fullerenes - are formed. Among the investigated materials that produce carbon clusters are poly(vinylidenefluoride) and fluorinated fullerenes - C60F2m. For comparison purposes data from C-60 targets have been also collected and analyzed. PDMS has been used for the in situ assessment of the damaging of C-60 films by MeV heavy ions. Results on delayed electron emission from C-60(-) sputtered by MeV ions from C-60 fullerene targets are also presented. A model of fullerene formation as a result of MeV ion interactions with the organic solid, including the yield dependence on primary ion charge state, is summarized. Both the data and the model suggest that fullerenes are formed as a result of a single primary ion impact and that they are ejected from an axially expanding infratrack plasma region. Results on different types of coalescence reactions in synthetic C-60 fullerene targets and in blends of pure (synthetic) C-60 With polystyrene leading to ejection of higher mass positive fullerene ions (C-k(+), K from 60 to more than 200) are also reported. The coalescence reactions are induced by the interaction of a single MeV ion with the solid. We argue that our data contribute to elucidating some general patterns of the fullerene formation mechanism.