Tuning the Energy Band Structures and Optical Properties of Armchair Graphene Nanoribbons Using Oxygen Adsorption

The electronic properties and optical properties of bare and H-terminated armchair graphene nanoribbons (AGNRs), with adsorption of single and double oxygen atoms, are investigated using density functional theory. Our results suggest that the number of adsorbed atoms and modification of atomic edge configuration cause an indirect-to-direct band gap and a metal-to-semiconductor transition. In addition, our results demonstrate that a change in the number of adsorbed atoms leads to N-semiconductor-to-P-semiconductor transition in H-terminated AGNRs. Single oxygen atom adsorption on the bare AGNRs results in an indirect-band-gap semiconductor with an energy gap of 0.212 eV. The band structures near the Fermi level are mainly dominated by C-2s, 2p and O-2s, 2p electronic states, which are strongly hybridized in the conduction and valence bands. We also find that H-terminated AGNRs with single O adsorption and double O adsorption become n-type and p-type semiconductors, respectively. By increasing adsorption of O atoms and modifying the edge H atoms, the peaks of the optical absorption tend to be redshifted. Furthermore, the number of peaks is reduced as edge H atom concentration is modified, for the same number of adsorbed atoms. Electron energy loss spectroscopy (EELS) is redshifted for single and double O atoms adsorbed on bare and H-terminated AGNRs.