Structural properties of the graphene-SiC(0001) interface as a key for the preparation of homogeneous large-terrace graphene surfaces

We report on the interface between graphene and $4\mathrm{H}\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}(0001)$ as investigated by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). It is characterized by the so-called $(6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3})\mathrm{R}30\ifmmode^\circ\else\textdegree\fi{}$ reconstruction, whose structural properties are still controversially discussed but at the same time are crucial for the controlled growth of homogeneous high-quality large-terrace graphene surfaces. We discuss the role of three observed phases with periodicities $(6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3})\mathrm{R}30\ifmmode^\circ\else\textdegree\fi{}$, $(6\ifmmode\times\else\texttimes\fi{}6)$, and $(5\ifmmode\times\else\texttimes\fi{}5)$. Their LEED intensity levels and spectra strongly depend on the surface preparation procedure applied. The graphitization process imprints distinct features in the STM images as well as in the LEED spectra. The latter have the potential for an easy and practicable determination of the number of graphene layers by means of LEED.