Simulations for the formation dynamics and electronic states of carbon nano materials: Diffusion and alignment of oxygen atoms on graphene

We performed ab initio calculations combined with the nudged elastic band method to study the diffusion of oxygen atoms on graphene. The most stable adsorption configuration is epoxy structure, and the diffusion barrier height for single epoxy oxygen is 0.9 eV. The calculated diffusion barrier of the second epoxy oxygen atom shows that the epoxy oxygen atoms tend to align along the armchair direction on a flat graphene surface. To estimate the curvature effect of a graphene sheet, we have compared above results with the diffusion of an oxygen atom on carbon nanotubes (CNTs). The curvature effect induces the stretching of the C–C bond beneath epoxy oxygen and reduces the internal strain due to the local curvature, which significantly lowers the total energy of the system. For the armchair CNT, the oxygen atoms would align along the tube axis (zigzag direction). These facts suggest that the favored direction of oxygen alignment can be changed by the curvature of graphene.