Atomic surface structure of graphene and its buffer layer on SiC(0001): A chemical-specific photoelectron diffraction approach

We report a chemically specific x-ray photoelectron diffraction (XPD) investigation using synchrotron radiation of the thermally induced growth of epitaxial graphene on the 6H-SiC(0001). The XPD results show that the buffer layer on the SiC(0001) surface is formed by two domain regions rotated by 60 degrees with respect to each other. The experimental data supported by a comprehensive multiple scattering calculation approach indicates the existence of a long-range ripple due the (6 root 3 x 6 root 3)R30 degrees. reconstruction, in addition to a local range buckling in the (0001) direction of the two sublattices that form the honeycomb structure of the buffer layer. This displacement supports the existence of an sp(2)-to-sp(3) rehybridization in this layer. For the subsequent graphene layer this displacement is absent, which can explain several differences between the electronic structures of graphene and the buffer layer. DOI: 10.1103/PhysRevB.87.081403