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

Abstract

We report a chemically specific x-ray photoelectron diffraction (XPD) investigation using synchrotron radiation of the thermally induced growth of epitaxial graphene on the 6$H$-SiC(0001). The XPD results show that the buffer layer on the SiC(0001) surface is formed by two domain regions rotated by ${60}^{\ensuremath{\circ}}$ 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 $(6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3})R{30}^{\ensuremath{\circ}}$ 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 $s{p}^{2}$-to-$s{p}^{3}$ 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.