FULLERENE GENESIS BY ION-BEAMS

Clearly detectable quantities of molecular fullerene (C-60), the most recently discovered allotrope of carbon, have been observed in graphit e following irradiation with heavy projectile ions at energies of abou t 1 GeV using high pressure chromatography. Similar experiments using lower ion energies gave no corresponding signal, indicating an absence of fullerene. This clear difference suggests that there exists an ene rgy threshold for fullerene genesis. Beginning with a microscopic desc ription of deposition and transfer of energy from the ion to the targe t, a theoretical model is developed for interpretation of these and si milar experiments. An important consequence is a description of the fo rmation of large carbon clusters in the hot dense 'primeval soup' of s ingle carbon atoms by means of random 'sticky' collisions. The ion ene rgy threshold is seen as arising, physically. from a balance in the co mpetition between the rate of primary energy deposition and the rate o f system cooling. Rate equations for the basic clustering process allo w calculation of the time-dependent number densities for the different carbon clusters produced. An important consequence of the theory is t hat it is established that the region for the specific phase transitio n from graphite to fullerene lies in the same pressure regime on the p hase diagram as does the corresponding transition for graphite to diam ond.