Unconventional Near-equilibrium Nucleation of Graphene on Si-terminated SiC(0001) Surface.

The transfer-free character of graphene growth on Silicon Carbide (SiC) makes it compatible with state-of-the-art Si semi-conductor technologies for directly fabricating high-end electronics. Although significant progress has been achieved in epitaxial growth of graphene on SiC recently, the underlying nucleation mechanism remains elusive. Here, we present a theoretical study to elucidate graphene near-equilibrium nucleation on Si-terminated hexagonal-SiC(0001) surface. It is found that the ultra-large lattice mismatch between SiC(0001) surface and graphene and the highly localized electron distribution on SiC(0001) surface lead to a distinctive nucleation process: (i) Most of the magic carbon clusters on SiC(0001) show only C1 symmetry and are mainly composed of pentagonal rings; (ii) Two possible nucleation pathways are revealed, i.e, longitudinal and circular modes; (iii) Carbon clusters are more stable on flat terraces than near atomic step edges. Based on above findings, a graphene nucleation diagram on SiC(0001) is established and experimentally observed contradictories for graphene growth on SiC(0001) are answered. Our in-depth understanding on graphene nucleation on SiC(0001) extends nucleation mechanisms of 2D crystals and will benefit high-quality graphene growth on SiC(0001).