Impact of C60 + ions onto an epitaxially grown crystalline fuilerite target is studied at a primary kinetic energy of 275 eV as a function of the angle of incidence. Scattered ions are investigated by velocity selective time-of-flight mass spectrometry at a fixed scattering angle of 140°. In addition to scattering of intact C6o + ions we also see desorbed C70 4 " as well as larger ions Cioo + to Ct3o + arising from reactive processes (fusion, coalescence). The velocity distribution of the receding C6o + ions reveals a range of processes from nearly elastic to fully inelastic. The angular dependence exhibits rich structure. This may be attributed to rainbow scattering, as confirmed by a simple classical trajectory calculation.PACS numbers: 79.20.Rf Buckminsterfullerene ion C6o + impact onto solid surfaces is a new and exciting field for experimental [1][2][3] and theoretical studies [4], Unique features have been observed: C6o suffers a substantial deformation in the encounter, however, it recovers its original shape after the interaction. For scattering from graphite in near normal incidence its final kinetic energy Ej was found to be only about 15 eV and nearly independent of its initial kinetic energy E m for up to 450 eV. Most of the energy is transferred into the target and into internal vibrational and rotational energy of the scattered molecule. Thus, the temperature of the scattered C6o + can be as high as 5000 K eventually leading to fragmentation after some j*s. In another kind of experiment, the reverse type of process has been observed: In laser desorption experiments of fuilerite from surfaces [5], aggregation of larger fullerenes by addition of C2 units to C60, and C70 has been seen. Complete fusion (coalescence) of small fullerenes (C6o,C7o) to large ones was found in a hot dense vapor generated by laser desorption of fullerenes [6] and recent studies of collisions between C6o + ions and thermal Ceo molecules gave direct evidence of Q20 formation in a bimolecular fusion reaction [7]. It is understood that such studies should provide essential elements for our basic understanding of the new field of fullerene chemistry. On the other hand, atomic-ion scattering from solid surfaces is a well developed field of research and has provided a wealth of information on the relevant interaction mechanisms. Rainbow scattering, for example, where one observes strongly enhanced scattering signals at particular deflection angles close to the minima and maxima of the classical deflection function, best known from optics and gas phase collisions, is a well understood effect also in ion/atom impact on surfaces, caused here by the periodicity of the interaction potential (see, e.g., a recent review [8]). Thus, a combination of surface scattering and C60-C60 interaction studies appears highly promising to improve our knowledge about C60 reactions and interaction processes. We therefore report in the present paper a first scattering experiment of C6o + ions from the well ordered solid surface of a crystalline C60 film, ...
Collisions of [Formula: see text] ions with surfaces of highly oriented pyrolytic graphite (HOPG), diamond (111) and heteroepitaxial fullerite films on mica in the impact energy range between 100 and 1500 eV are studied by mass, energy, and angle resolved time-of-flight mass spectrometry. For the graphite and diamond surfaces, highly inelastic scattering has been observed. The analysis of the velocity dependence of the scattered ions reveals that the normal and tangential component of the ion velocity have different significance for the collision dynamics. The normal component of the velocity appears to determine the amount of energy transferred into vibrational and deformational energy of the projectile and target. The final kinetic energy is independent of the impact energy for impact angles of ≈20° and impact energies between 140 and 450 eV. This observation can be explained by the existence of an upper bound of the final kinetic energy that is defined by the amount of energy stored in the deformed molecule without being deposited or destroyed. The tangential component is partially transformed into rotational energy of the [Formula: see text] in the collision with the surface, as may be explained by a simple rolling ball model. In contrast, scattering from heteroepitaxial fullerite films is nearly elastic for impact energies up to 230 eV and impact angles of about 20°. Additionally, the velocity distributions reveal a low velocity component. Its relative intensity increases with increasing impact energy and remains the only feature in the velocity distribution for impact energies higher than 290 eV. This component is due to sputtering of surface molecules. The angular dependent intensities of the fast ions exhibit a rich structure. This can be attributed to rainbow scattering, as confirmed by classical trajectory and molecular dynamics calculations with different levels of sophistication. These calculations also show that linear collision sequences along the closed packed rows of the fullerite surface may be generated as the result of the [Formula: see text] impact. A detailed study of these collision sequences by molecular dynamics calculations reveals that rainbow effects might be possible when these sequences are defocused due to thermal motion of the surface molecules. The contribution of this process to the measured velocity and angular distributions is discussed.
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