Atomistic insight into the initial stage of graphene formation on SiC(0001) surfaces

Abstract

We present an atomistic insight into the processes leading to the formation of graphene on SiC(0001) surfaces by resorting to first-principles molecular dynamics empowered by free-energy sampling methods. Based on the experimental surface, consisting of terraces bordered by a sequence of steps, we find that Si atoms are dislodged from step edges and migrate toward more stable sites on the terrace, leaving behind C atoms carrying unsaturated chemical bonds. Our investigations reveal that subsequent Si atoms removal acts as a trigger to the formation of stable C-C bonds among these unsaturated C sites. This process eventually leads to the formation of C clusters which merge into larger structures with the typical pattern of graphene flakes. Specifically, a ${\mathrm{C}}_{6}$ ring formed during our simulations, assumes the typical hexagonal structure of graphene, becoming a precursor of larger graphene nanostructures. The characterization of the mechanisms and related free-energy landscapes provide an insight into the fundamental processes responsible for the realization of ordered C-based building blocks of graphene on the SiC(0001) surface.