The interface structure of epitaxial graphene grown on 4H-SiC(0001)

We present a structural analysis of the graphene-4HSiC(0001) interface using surface x-ray reflectivity. We find that the interface is composed of an extended reconstruction of two SiC bilayers. The interface directly below the first graphene sheet is an extended layer that is more than twice the thickness of a bulk SiC bilayer (~1.7A compared to 0.63A). The distance from this interface layer to the first graphene sheet is much smaller than the graphite interlayer spacing but larger than the same distance measured for graphene grown on the (000-1) surface, as predicted previously by ab intio calculations.

Rotational stacking and its electronic effects on graphene films grown on 4H-SiC$(000bar{1})$

We examine the stacking order of multilayer graphene grown on the SiC$(000bar{1})$ surface using low-energy electron diffraction and surface X-ray diffraction. We show that the films contain a high density of rotational stacking faults caused by three types of rotated graphene: sheets rotated $30^circ$ and $pm 2.20^circ$ relative to the SiC substrate. These angles are unique because they correspond to commensurate phases of layered graphene, both with itself and with the SiC substrate. {it Ab intio} calculations show that these rotational phases electronically decouple adjacent graphene layers. The band structure from graphene at fault boundaries displays linear energy dispersion at the $K$-point (Dirac cones), nearly identical to that of a single graphene sheet.