π-Bonding-dominated energy gaps in graphene oxide

The chemical bonding in graphene oxide with oxygen concentrations from 50% to 1% is investigated using first-principle calculations. The energy gaps are mainly determined by the competition of the orbital hybridizations in the C-C, O-O, and C-O bonds. They are very sensitive to changes in the oxygen concentration and distribution. Five types of π-bonding exist on moving from full to vanishing adsorption, namely complete termination, partial suppression, 1D bonding, deformed planar bonding, and the well-behaved type. They can account for the finite and gapless characteristics, corresponding to O-concentrations of >25% and <3%, respectively. The feature-rich chemical bonding dominates the band structures and density of states, leading to diverse electronic properties.