(190p) Investigation of the Hyperthermal Collisions of Atomic Oxygen with Graphene Using ReaxFF Reactive Force Field

We have investigated the hyperthermal collisions of atomic oxygen with a graphene sheet through molecular dynamic simulations using the ReaxFF reactive force field. A pristine sheet and a sheet with a single vacancy defect were considered in the study. Two different graphene sheet sizes, one with 24 atoms and the other with 600 atoms were studied in the simulations. The impinging oxygen atoms had a translational energy of 5eV. Since 5eV oxygen atoms are not sufficiently energetic to sputter a carbon atom from graphene, the sheet was functionalized with epoxides in order to observe various possible reactions. Interesting reactions observed include O₂ formation, epoxide formation, sheet damage and inelastic scattering of the impinging oxygen. The results of our simulations, in terms of the number of reactive events and reaction mechanisms, compared well with the DFT based results of Paci et al (J.Phys.Chem.A,2009,vol 113,pp 4677-4685) for the small sheet. In case of the larger sheet, the percentage of trajectories yielding oxygen atom scattering and epoxide formation were much higher while O₂ formation was much lower than that for the smaller sheet. This can be attributed to excessive artificial symmetry that makes the smaller sheet too stiff and may prohibit certain phonon modes. Thus size effects are important in studying the dynamics of these events.