Formation of Carbon Clusters in the Initial Stage of Chemical Vapor Deposition Graphene Growth on Ni(111) Surface

To understand the nucleation of carbon atoms to form graphene on transition metal substrates during chemical vapor deposition (CVD) synthesis, carbon clusters supported on Ni(111) surfaces, namely C(N)@Ni(111) (where N <= 24), were explored systematically using density functional theory (DFT) calculations. Very different from the freestanding C clusters, on a Ni(111) surface, the C chain configuration is superior to the C ring formation and dominates the ground state until N > 12. A ground state structural transition from a one-dimensional C chain to a two-dimensional sp(2) network (or graphene island) occurs at N = 12. It is surprising that incorporating one to three 5-membered-rings (5MRs) or pentagons into a graphene island is required to achieve the energetically most stable structure. This deep insight into the supported C cluster formation is crucial for understanding the growth mechanism of graphene on a transition metal surfaces in CVD experiments and the experimental design of CVD graphene growth.