Formation of a Buffer Layer for Graphene on C-face SiC{0001}

Graphene films prepared by heating the SiC ̅ surface (the C-face of the {0001} surfaces) in a Si-rich environment are studied using low-energy electron diffraction (LEED) and low-energy electron microscopy (LEEM). Upon graphitization, an interface with √ × √ -R±7.6 symmetry is observed by in situ LEED. After oxidation, the interface displays √ × √ -R30 symmetry. Electron reflectivity measurements indicate that these interface structures arise from a graphene-like “buffer layer” that forms between the graphene and the SiC, similar to that observed on Si-face SiC. From a dynamical LEED structure calculation for the oxidized Cface surface, it is found to consist of a graphene layer sitting on top of a silicate (Si2O3) layer, with the silicate layer having the well-known structure as previously studied on bare SiC ̅ surfaces. Based on this result, the structure of the interface prior to oxidation is discussed.