Graphene-substrate interaction on 6H-SiC(0001¯): A scanning tunneling microscopy study

International audienceThe early stage of graphene formation on the 6H-SiC 0001¯ surface is investigated by scanning tunneling microscopy. Islands made of a single graphitic plane form above regions of the substrate that show either a 2 2 C or a 3 3 reconstruction. The orientations of the single-layer domains present a broad distribution of rotation angles with respect to the substrate. The atomic structures of the 3 3 and 2 2 C substrate reconstructions are preserved under the first carbon layer. Low bias images reveal a graphitic structure, which indicates that the interaction between the first carbon plane and the SiC surface is comparatively much weaker on the C face than on the Si face of the substrate. The coupling is stronger on the 2 2 C surface reconstruction than on the 3 3 one, where an almost ideal graphene structure is found close to the Fermi level