Doping of 20 MeV fullerene ion tracks in polyimide

Thin polyimide foils were irradiated with 20 MeV C-60(+) ions and subsequently doped with aqueous LiCl solution. The depth distributions of the dopant uptake were then recorded with the neutron depth profiling technique. In contrast to the doping of tracks of single-atomic ions or of small cluster ions, the dopant distribution extends far beyond the single-atomic ion range, indicating that some new secondary effects show up here. These may be attributed to the enhancement of cluster ion ranges in comparison to single-atomic ones [1,2], and additionally to the formation of micro- or nanocracks. The shapes of the dopant distributions are rather independent from the ion fluence, which indicates that the observed overrange effects are a peculiarity of individual fullerene ion tracks, and not just a high fluence effect for overlapping tracks. The total amount of dopant uptake increases with fluence, It scales with the total deposited energy density in a similar way as does the dopant uptake in tracks of single-atomic ions or of small cluster ions. First results with 30 MeV C-60(+) ions reconfirm these findings.