Emission of velocity-correlated clusters in fullerene-solid single collision and diagnostics of the impact energized subsurface nanovolume.

Abstract

We have measured kinetic energy distributions (KEDs) of large clusters emitted from five different solid targets following a single impact of C60 - ion at 14 keV kinetic energy. It was found that all the large clusters emitted from a given target move with nearly the same velocity and that their KEDs can be described by a thermal distribution riding on a common center-of-mass velocity (shifted Maxwellian) of some precursor. This behavior is in sharp contrast to that observed when the incoming projectile ion is monoatomic. Different trends were observed when comparing the behavior of the KED families of group 5 early transition metal elements (Ta and Nb) with those of group 11 late transition metals (Cu, Ag, and Au). We propose a model for the initial phase of formation of the precursor and show that the measured KEDs can serve as both pressure and temperature probes for the impact excited, highly energized subsurface nanovolume, driving the ejection of the clusters. It is also shown that under the proposed impact scenario, thermally equilibrated conditions (of the atomic subsystem) can be established at the subsurface nanovolume on the early subpicosecond time scale relevant for the emission process. This conclusion is demonstrated both experimentally by the KEDs of the emitted large clusters (very high temperatures and center-of-mass velocity) and by molecular dynamics simulation of the temporal evolution of the thermal characteristics of the impact energized subsurface nanovolume.