Electronic structures of zigzag graphene nanoribbons with edge hydrogenation and oxidation

Using the ab initio density-functional theory method and local spin-density approximation, we calculated the electronic band structures of H or H2 edge-hydrogenated zigzag graphene nanoribbons (ZGNRs) as well as COH, CO, or C2O edge-oxidized ZGNRs. We found that the OH group yields almost the same band structure as the sp^2 hybridization of H edge, and that the ketone (CO) and ether (C2O) groups result in band structures similar to those of sp^3 hybridization of H2 edge. Compared to H passivation, edge oxidation by the ketone or the ether group is energetically more favorable, suggesting that the GNR's edges will be oxidized in the presence of oxidizing species. Edge oxidized GNRs show metallic band structures caused by the larger electronegativity of oxygen relative to carbon, and these findings raise a question about the physical origins of the experimental observations of semiconducting GNRs. Such discrepancy suggests that more realistic modeling of GNR edge structures will be necessary to understand the experimental findings.