Adsorption and Diffusion of Oxygen on Single-Layer Graphene with Topological Defects

In this work, effects of oxygen adsorption and diffusion on the stability, morphology, and charge transfer in single-layer graphene with structural point defects were investigated by density functional theory, specifically for the experimentally characterized monovacancy, double-vacancy, 555-777, 5555-6-7777, and Stone-Wales defects. The theoretical analysis demonstrated strengthened oxygen adsorption on defective graphene as compared to pristine graphene, resulting in trapping of the oxygen onto defects. This was accompanied by significant charge transfer of up to 3e, unlike for pristine graphene. At the same time, atomic oxygen diffuses at different rates dependent on the local environment, however with relatively low barriers (mostly <1 eV), lower than for pristine graphene, thus, revealing an interplay between diffusion and adsorption in this case. Addition of a nonempirical correction to the exchange-correlation functional to take into account London dispersion demonstrated that the vdW-DF PBE functional does not change the overall trend in adsorption, structure and diffusion pathways, but the predicted adsorption energies and activation energy barriers are lower. Interestingly, following incorporation of oxygen within defects, the morphology has shown deformation from planarity of the nanostructure, particularly with higher coverage. This could explain, in part, initiation of budding and possibly the early stage of a tip-like structure in carbon nanotube growth on SiC(0001) in the presence of oxygen, as has been observed experimentally. Overall, the calculations on the effects of oxygen or other moiety adsorption on defective graphene provided a quantified basis for engineering defects in single-layer graphene, which are difficult to characterize experimentally.