C-60(- KINEMATICS AND DYNAMICS() IONS IN COLLISIONS WITH CRYSTALLINE SURFACES )

Collisions of C-60(+) 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. Fo r the graphite and diamond surfaces, highly inelastic scattering has b een observed. The analysis of the velocity dependence of the scattered ions reveals that the normal and tangential component of the ion velo city have different significance for the collision dynamics. The norma l component of the velocity appears to determine the amount of energy transferred into vibrational and deformational energy of the projectil e and target. The final kinetic energy is independent of the impact en ergy for impact angles of approximate to 20 degrees and impact energie s between 140 and 450 eV. This observation can be explained by the exi stence of an upper bound of the final kinetic energy that is defined b y the amount of energy stored in the deformed molecule without being d eposited or destroyed. The tangential component is partially transform ed into rotational energy of the C-60(+), in the collision with the su rface, 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 degrees. A dditionally, the velocity distributions reveal a low velocity componen t. Its relative intensity increases with increasing impact energy and remains the only feature in the velocity distribution for impact energ ies 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 co nfirmed by classical trajectory and molecular dynamics calculations wi th different levels of sophistication. These calculations also show th at linear collision sequences along the closed packed rows of the full erite surface may be generated as the result of the C-60(+) impact. A detailed study of these collision sequences by molecular dynamics calc ulations reveals that rainbow effects might be possible when these seq uences are defocused due to thermal motion of the surface molecules. T he contribution of this process to the measured velocity and angular d istributions is discussed.