Quantum mechanical simulation reveals the role of cold helium atoms and the coexistence of bottom-up and top-down formation mechanisms of buckminsterfullerene from carbon vapor

Abstract

After the discovery of the highly symmetric Buckminsterfullerene (BF), a major goal of the fullerene community has been to understand its formation mechanism. In the various mechanisms proposed in literature, BF forms by either a bottom-up only or a top-down only process. Here we present a comprehensive quantum mechanical molecular dynamics simulation study, that reports for the first time the observations of multiple icosahedral symmetric Ih-C60 cages formations at the atomic level. Our simulation results demonstrate that helium atoms can not only reduce the temperature of the carbon species, but more importantly they can dramatically influence the reaction dynamics and eventually the fullerene yield through thermal collisions with carbon species. The direct evidence for coexistence of both bottom-up and top-down mechanisms are shown. Interestingly, rather than ceasing magically at C60, a similar process also applies to the formation of larger or smaller fullerenes. Prolonged vacuum annealing simulations show a typical top-down process where shrinking and surface healing of defective cages can enhance the Ih-C60 yield. Our results shed new light on the fundamental BF formation process in graphite laser ablation, in carbon arc-discharge experiments, as well as in the interstellar space.