Search

C60- ions were scattered from a gold surface at impact energies of 80–900 eV. The Cn- fragments abundance distribution (odd and even) and the sharp fragmentation threshold observed, point at a prompt shattering event. The measured angle and energy distributions of the Cn- fragments (n=2–12) provide clear evidence for a multifragmentation process where the superheated fullerenes leave the surface ‘intact’ and disintegrate away from the surface. [ABSTRACT FROM AUTHOR]

The collisional insertion of Cs[sup +] ions into surface adsorbed C[sub 60] molecules was studied by scattering Cs[sup +] ion beams from a C60 layer deposited on gold over the 35-220 eV impact energy range. Both Cs@C[sup +][sub 60] and C[sup +][sub 60] ions were ejected from the surface following the Cs[sup +] impact but each species was characterized by different impact energy dependent yields and internal temperatures. Clear evidence for the endohedral nature of the complex is given. Both the scattering dynamics (at impact energies up to ∼100 eV) and the instant rise of the Cs@C[sup +][sub 60] signal with the Cs[sup +] beam onset clearly demonstrate that the insertion/ejection process is basically a single collision event. The outgoing Cs@C[sup +][sub 60] and C[sup +][sub 60] ions fragment during their flight time, after leaving the surface, via sequential emission of C[sub 2] units down to Cs@C[sup +][sub 50] and C[sup +][sub 44], respectively. Relative impact energy dependent yields were measured for both parent species and for all fragments. The yield curves are kinetically shifted with respect to each other as expected. Comparing the impact energy dependent fragmentation patterns of C[sup +][sub 60] and Cs@C[sup +][sub 60] we conclude that the ejected Cs@C[sup +][sub 60] ion is much hotter than the C[sup +][sub 60] ion. The internal vibrational excitation for both species is reaching a maximal value around 90-110 eV impact energy and than gradually decreases with increase in impact energy. The integrated Cs@C[sup +][sub 60] yield is strongly peaked at around 80 ± 5 eV impact energy. At impact energies above 120 eV also a C[sup -][sub 60] signal is observed but no Cs@C[sup -][sub 60] could be detected. [ABSTRACT FROM AUTHOR]

Abstract: Yields of endohedral ions were measured under field-free conditions, following the impact of low energy (E o =40–200eV) Cs+ ions with a near-monolayer C60 molecules adsorbed on a gold surface. Under these conditions, we were able to apply model calculations and successfully simulate the experimental results. The simulation was carried out by integrating over calculated kinetic energy distributions (KEDs). Combined with former measurements and simulations of the KEDs, we arrive at a full and consistent description of both KEDs and impact energy dependent yields, reflecting the combined formation/ejection/decay dynamics of the ion. [Copyright &y& Elsevier]

We describe the formation and emission of endohedral fullerenes, Cs@C60+ and Cs@C70+, following a single collision of Cs+ ion with a sub-monolayer of C60 on gold and silicon surfaces and with a sub-monolayer of C70 on gold. A continuous low energy (E0=35–220 eV) Cs+ ion beam hit the C60 covered surface and the collisional formation and ejection of the endohedral Cs@C60+ complex, within a single Cs+/C60 collision, was observed and characterized. The steady state C60 coverage is shown to be in the sub-monolayer range. The instantaneous rise of the Cs@C60+ signal (by a factor of 103) 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@C60−2n+ (n=1–5) sequence and its termination at Cs@C50+. Similar experiments were carried out with nearly pure (98%) C70 sub-monolayer on gold. Both the Cs@C70−2n+ and C70−2n+ (n=0,1,2,…) fragmentation sequences were observed. Cs@C60+ and C60+ 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. [Copyright &y& Elsevier]