Three-fold diffraction symmetry in epitaxial graphene and the SiC substrate

The crystallographic symmetries and spatial distribution of stacking domains in graphene films on 6H-SiC(0001) have been studied by low-energy electron diffraction and dark-field imaging in a low-energy electron microscope. We find that the graphene diffraction spots from two and three atomic layers of graphene have three-fold symmetry consistent with AB (Bernal or rhombohedral) stacking of the layers. On the contrary, graphene diffraction spots from the buffer layer and monolayer graphene have apparent six-fold symmetry, although the three-fold nature of the satellite spots indicates a more complex periodicity in the graphene sheets.