Ab initio calculations, combined with the nudged elastic band method, were used to study the diffusion of oxygen atoms on graphene. The most stable adsorption configuration was epoxy structure, and the diffusion barrier height for single epoxy oxygen was 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, the above results were compared with the diffusion of an oxygen atom on carbon nanotubes. 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 carbon nanotubes, the oxygen atoms would align along the tube axis (zig-zag direction). These facts suggest that the favored direction of oxygen alignment can be changed by the curvature of graphene.

Simulations for the Formation Dynamics and Electronic States of Carbon Nano Materials: Diffusion and Alignment of Oxygen Atoms on Graphene. T.Kawai, Y.Miyamoto: Current Applied Physics, 2011, 11[4], S50–