Detailed kinetic Monte Carlo simulations of graphene-edge growth

A new detailed chemical-kinetic Monte Carlo model of graphene-edge growth is presented. The model employs a fine-grained approach to chemically resolved species, allows for incorporation of five-member rings into growing structures, and links the stochastic kinetic steps to a geometry optimization, thereby properly accounting for curving of molecular structures. The evolving morphology is greatly affected by the rates of key reactions and hence by surface-site steric environment and gas-phase species concentrations. The evolving graphene morphology and growth rates seemingly reach "asymptotic" behavior, independent of the initial substrate. Most noteworthy, growing layers become significantly curved. The curvature occurs regardless of initial substrate at both 1500 and 2000 K with higher curvature occurring at the lower temperature. More intriguing is the observation that, at 2000 K, transition from planar to curved growth does not commence immediately but occurs at some later time, seemingly when the growing graphene reaches a size significantly larger than coronene. No curvature is produced in numerical simulations at 2500 K, indicating that high-energy environments cause the five-member-ring to be less stable, thus preventing them from forming.