First-principles investigation of graphene fluoride and graphane

Different stoichiometric configurations of graphane and graphene fluoride are investigated within density-functional theory. Their structural and electronic properties are compared, and we indicate the similarities and differences among the various configurations. Large differences between graphane and graphene fluoride are found that are caused by the presence of charges on the fluorine atoms. A configuration that is more stable than the boat configuration is predicted for graphene fluoride. We also perform GW calculations for the electronic band gap of both graphene derivatives. These band gaps and also the calculated Young’s moduli are at variance with available experimental data. This might indicate that the experimental samples contain a large number of defects or are only partially covered with H or F.

Figure 1

(Color online) Four different configurations of hydrogen/fluorine-graphene: (a) chair, (b) boat, (c) zigzag, and (d) armchair configurations. The different colors (shades) represent adsorbates (H or F) above and below the graphene plane. The supercell used to calculate the elastic constants is indicated by the dashed box.

Figure 2

(Color online) Fluorographene in the (a) zigzag and (c) armchair configurations. The nearest-neighbor bonds of one F atom are indicated with dotted lines to show the symmetry of the superlattices [as shown in (b) and (d)]. (b) The hexagonal superlattice which is formed in case of chair and zigzag configurations. (d) The cubic superlattice which is formed in case of boat and armchair configurations.

Figure 3

(Color online) The electronic band structure and the corresponding density of states (GGA) for the chair configuration of (a) graphane and (b) fluorographene. The valence-band maximum has been used as the origin of the energy scale.