Magic Carbon Clusters in the Chemical Vapor Deposition Growth of Graphene

Ground-state structures of supported C clusters, C_<i>N</i> (<i>N</i> = 16, ..., 26), on four selected transition metal surfaces [Rh(111), Ru(0001), Ni(111), and Cu(111)] are systematically explored by ab initio calculations. It is found that the core–shell structured C₂₁, which is a fraction of C₆₀ possessing three isolated pentagons and <i>C</i>_3<i>v</i> symmetry, is a very stable magic cluster on all these metal surfaces. Comparison with experimental scanning tunneling microscopy images, d<i>I</i>/d<i>V</i> curves, and cluster heights proves that C₂₁ is the experimentally observed dominating C precursor in graphene chemical vapor deposition (CVD) growth. The exceptional stability of the C₂₁ cluster is attributed to its high symmetry, core–shell geometry, and strong binding between edge C atoms and the metal surfaces. Besides, the high barrier of two C₂₁ clusters’ dimerization explains its temperature-dependent behavior in graphene CVD growth