Implanting atomic ions into surface adsorbed fullerenes: the single collision formation and emission of Cs@C 60+ and Cs@C 70+

Abstract

We describe the formation and emission of endohedral fullerenes, Cs@C 60 + and Cs@C 70 +, following a single collision of Cs + ion with a sub-monolayer of C 60 on gold and silicon surfaces and with a sub-monolayer of C 70 on gold. A continuous low energy ( E 0=35–220 eV) Cs + ion beam hit the C 60 covered surface and the collisional formation and ejection of the endohedral Cs@C 60 + complex, within a single Cs +/C 60 collision, was observed and characterized. The steady state C 60 coverage is shown to be in the sub-monolayer range. The instantaneous rise of the Cs@C 60 + signal (by a factor of 10 3) with the Cs + beam onset clearly demonstrate the single collision nature of the combined “atom penetration/endo-complex ejection” event. The fullerene molecule is actually being picked up off the surface by the penetrating Cs + ion. The evidence for the trapping of the Cs + ion inside the fullerene cage is given both by the appearance of the Cs@C 60−2 n + ( n=1–5) sequence and its termination at Cs@C 50 +. Similar experiments were carried out with nearly pure (98%) C 70 sub-monolayer on gold. Both the Cs@C 70−2 n + and C 70−2 n + ( n=0,1,2,…) fragmentation sequences were observed. Cs@C 60 + and C 60 + signals appeared strongly enhanced in these sequences. We believe that the experimental results presented here provide a first example of a single collision pick-up scattering (Eley–Rideal type) involving the formation and ejection of an endo-complex.