ELECTRONIC SPUTTERING OF FULLERENES AND THE INFLUENCE OF PRIMARY ION CHARGE-STATE

Even-numbered positive ion carbon clusters, fullerenes (C2n, n = 20, 2 1, . . . ), are formed and ejected as a result of the interaction of s wift atomic ions with a solid film of organic polymer - poly(vinyliden e difluoride), PVDF. Studies of that phenomenon including the dependen ce of fullerene yield on the incident MeV ion's stopping power and ini tial radial velocity distributions of ejected ions, have been reported earlier [G. Brinkmalm et al., Chem. Phys. Lett. 191 (1992) 345; Phys. Rev. B 47 (1993) 7560]. In this paper, the dependence of the yield of the ejected cluster ions from PVDF as a function of the charge state of the incident MeV ion is reported. Swift 72.3 MeV I-127 ions in char ge states ranging from + 13 to + 25 from the Uppsala EN-tandem acceler ator are used in the experiments, and the secondary ion yield is measu red in a time-of-flight mass spectrometer, equipped with an electrosta tic ion mirror. The results are compared to data for secondary ions, e jected by the same primary ions, from samples of synthetic fullerenes (C60 and C70). No dependence of the yield on the charge state of the i ncoming ion is observed for the high mass even-numbered carbon cluster s from PVDF, while yields of C60 and C70 ions from synthetic fullerene targets show a weak charge state dependence. This finding indicates t hat excited polymer material from layers deeper than the MeV ion charg e equilibration length in the solid contributes to the formation of ej ected carbon cluster ions ejected from PVDF.