Quasi-Freestanding Graphene via Sulfur Intercalation: Evidence for a Transition State

Sulfur intercalation of a carbon rich (63x63)R30 circle$(6\sqrt {3}\times 6\sqrt {3})R30\,<^>\circ$ reconstruction on silicon carbide, also known as buffer layer, is reported. In a two-zone furnace a sulfur rich precursor is heated and the gaseous species is transported for intercalation by an argon flow to the sample. Successful intercalation can be confirmed by X-ray photoelectron spectroscopy and low-energy electron diffraction. Angle-resolved photoelectron spectroscopy reveals a p-type doping of the intercalated samples. In some cases only partial intercalation appears with non-intercalated sulfur on top of the remaining buffer layer areas. Further annealing of such samples leads to a migration of the non-intercalated sulfur under the buffer layer areas, indicating that the sulfur bonded to the buffer layer constitutes a transition state. The formation of quasi-freestanding graphene by intercalation of sulfur under the (63x63)R30 circle$(6\sqrt {3}\times 6\sqrt {3})R30\,<^>\circ$ reconstruction layer (buffer layer) on silicon carbide is investigated. It is observed that the sulfur intercalation proceeds via a transition state, in which sulfur is strongly adsorbed on top of the buffer layer before it migrates to the interface.image