Graphene nucleation and growth on the transition metal surfaces: the role of pentagon, metal step and magic carbon clusters

The nucleation behavior of graphene on transition metal surfaces, either on a terrace or near a step edge, is systematically explored using density functional theory calculations. The supported carbon clusters, CN~(N=1$\sim $24), on the Ni(111) surface are carefully optimized [1,2]. A structural transformation from a C chain to a sp$^{2}$~C network at~C$_{12}$ and the most stable structures of sp$^{2}$ graphene islands contain one to three pentagons. In agreement with experimental observations, our calculations show that graphene nucleation near a metal step edge is superior to that on a terrace. Besides, ground state structures of supported CN (N = 16$\sim $26), clusters on four selected transition metal surfaces: (Rh(111), Ru(0001), Ni(111) and Cu(111)) are explored [3]. A core-shell structured of C$_{21}$ stands out as a magic cluster, which is one of the dominating carbon precursors in graphene CVD growth and has been observed in experimental STM images. The energy barrier of two C$_{21}$ clusters' coalescence is computed to illustrate their influence on the kinetics of graphene CVD growth at different temperatures. \\[4pt] [1] J. Gao, et al,. J. Am. Chem. Soc. 133, 5009 (2011). \\[0pt] [2] J. Gao, et al., J. Phys. Chem. C 115, 17695 (2011). \\[0pt] [3] Q. Yuan, et al., J. Am. Chem. Soc. (accepted).