Graphene is a 2D sheet of carbon atoms arranged in the honeycomb lattice. Figure (a) shows the model of the graphene 4x4 supercell. Figure (b) shows an STM image of the Graphene lattice grown on 6H-SiC(0001) with the 4x4 supercell shown in green. The large, bright spots form the corrugation pattern 6√3 x 6√3 due to the coincidence between the Graphene and the SiC(0001) lattices.
M. Hupalo, S. Binz, and M. C. Tringides, J. Phys. Condens. Matter 23, 045005 (2011). "Strong metal adatom–substrate interaction of Gd and Fe with graphene"