Relative stability of 6H-SiC(0001) surface terminations and formation of graphene overlayers by Si evaporation

We present density functional theory (DFT) calculations for 6H-SiC{0001} surfaces with different surface stackings, terminations and reconstructions. We compare the relative stability of different (0001) and different (000-1) surfaces in terms of their surface free energies. Removing surface and subsurface Si atoms, we simulate the formation of graphene and graphene-like overlayers by Si evaporation. We find that overlayers with a different nature of bonding are preferred at the two non-equivalent surface orientations. At (0001), a chemically bonded, highly strained and buckled film is predicted. At (000-1), a van der Waals (vdW) bonded overlayer is preferred. We quantify the vdW binding and show that it can have a doping effect on electron behavior in the overlayer