Symmetry breaking in graphene layers on SiC-substrate—an ab-initio study

A comprehensive detailed ab-initio study of the electronic structure of 1–7 graphene layers on the polar SiC (0 0 0 1) substrate systems has been performed for the first time. We observe a symmetry-breaking in all the graphene–SiC (0 0 0 1) substrate systems leading to an opening of band gap in contrast to the existence of zero band gap seen in the isolated graphene layer. The planar lattice parameter in graphene–SiC system decreases with the number of graphene layers from 3.051 Å to 2.948 Å showing an overall decrease of 3.5% and it approaches toward the bulk graphite. The electronic structure of the graphene layer-SiC system depends crucially on the planar lattice parameter and both the band gap and the location of the Dirac point are affected drastically. The band gap and the depth of the Dirac point below the Fermi level decrease with the number of graphene layers in conformity with the recent ARPES experiments of Zhou et al. The present results in some graphene–SiC systems are seen to be different from the earlier theoretical results reported in the literature.