Modelling the role of size, edge structure and terminations on the electronic properties of graphene nano-flakes

The addition of graphene nano-flakes to the suite of materials for graphene-based nanotechnology requires a complete understanding of the relationship between shape, structure, properties and property dispersion. Due to the large number of configurational degrees of freedom, this is a very challenging undertaking, particularly if morphological ensembles contain a reasonable array of sizes, shapes (edges and corners) and edge/corner terminations. We report results of density functional tight-binding simulations of zigzag (ZZ) and armchair (AC) hexagonal graphene nano-flakes, with unterminated, monoyhydride or dihydride terminated edges and corners. We find that hexagonal nano-flakes with AC edges are most likely to be achievable experimentally, providing that sufficient H is present during synthesis (or processing) to facilitate dihydride edge and corner passivation, forming a circumference of sp3 hybridized C atoms. This is significant, since the energy of the Fermi level and electronic density of states in the vicinity of the Fermi level are sensitive to the structural and chemical characteristics of the atoms around the circumference, which can be modified post-synthesis.