Nucleation and growth kinetics of graphene layers from a molten phase

Abstract

Nucleation and growth of graphene layers from Ni–C melts were investigated. It is shown that upon cooling of supersaturated liquids, graphite will grow either with flake or sphere morphology depending on the solidification rate and degree of supersaturation. At small solidification rates, graphite crystals are normally bounded by faceted low index basal and prismatic planes which grow by lateral movement of ledges produced by 2D-nucleation or dislocations. At higher growth rates, however, both interfaces become kinetically rough, and growth becomes limited by diffusion of carbon to growing interface. The roughening transition from faceted to non-faceted depends on the driving force and nature of growing plane. Due to high number of C–C dangling bonds in prismatic face, its roughening transition occurs in smaller driving force. As such, at intermediate rates, the prismatic interfaces become rough and grow faster while the basal plane is still faceted, leading to formation of flake graphite. At higher growth rates, both interfaces grow with a relatively similar rate leading to initiation of graphite sphere formation, which later grow by a multi-stage growth mechanism. An analytical model is developed to describe the size and morphology of graphite as a function of solidification parameters.