Nucleation and growth of $C60$ nanoparticles from the supersaturated vapor and from the undercooled liquid: A molecular simulation study

Using molecular simulation, we study the molecular mechanisms underlying the nucleation and growth of $C60$ nanoparticles from the supersaturated vapor and from the undercooled liquid. We show that in both cases, nucleation proceeds through the formation of small clusters composed of the metastable hexagonal close-packed (HCP) polymorph. This observation differs from the nucleation pathway of simple systems (e.g., modeled by Lennard-Jones potential) in which the nucleation proceeds through the metastable body-centered cubic polymorph. We rationalize this observation in terms of the relative steepness of the repulsion for the different potential models. Finally, we observe two different types of growth leading either to crystallites dominated by the metastable HCP polymorph or to crystallites whose structure is predominantly that of the stable face-centered cubic (FCC) polymorph. This finding is consistent with experiments on the crystallization of $C60$ from the vapor, which reported the formation of FCC and HCP crystals.