Band Gap Engineering via Edge-Functionalization of Graphene Nanoribbons

Density functional calculations are used to perform a systematic study of the effect of edge-functionalization on the structure and electronic properties of graphene nanoribbons (GNRs). -H, -F, -Cl, -Br, -S, -SH, and -OH edge-functionalization of armchair, zigzag, and reconstructed Klein-type GNRs was considered. The most energetically favorable edge structure varies depending on the choice of functional group. It is shown, for the first time, that reconstructed Klein-type GNRs are important stable configurations for several edge-functional groups. Band gaps using three different exchange-correlation functionals are calculated. The band gap for armchair GNRs can be tuned over a range of similar to 1.2 eV by varying the edge-functional groups. In contrast, the band gaps of zigzag and reconstructed Klein edge GNRs are largely insensitive to the choice of edge-functional group, and ribbon width is instead the defining factor. Alternatively, the armchair GNR band gap can be controlled by varying the number of functional groups per opposing edge, altering the GNR effective width. Edge-functionalization design is an appropriate mechanism to tune the band gap of armchair GNRs.