Incremental oxidation of the surface of monolayer and bilayer graphene: A computational study

We report the binding energies for a monolayer and bilayer graphene sheet coated with up to 24 oxygen atoms added sequentially to one surface of a monolayer and bilayer. Our graphene/graphite system consists of an arrangement of 3 x 5 phenyl rings or 48 carbon atoms in the monolayer and 96 carbon atoms in the bilayer. Geometries were energy optimized using the RM1 semiempirical method employing Periodic Boundary Conditions (PBC) followed by single point PBE and HSE06, all with the 6-31g* basis and PBC. Results indicate that the first O atom bound to pure graphene has a binding energy 2.16 eV on the monolayer and 2.14 eV on the bilayer. As O atoms are added the binding energy increases to 2.61 eV when the surface coverage on the monolayer reaches 45.8% or 11 O atoms on the unit cell, and for the bilayer this maximum occurs with 45.8% coverage or 11 O atoms on the top of the bilayer. The binding energy then gradually declines to 2.41 eV for the monolayer and to 1.93 eV for the bilayer with 100% coverage or 24 O atoms covering the top of the surface. Oxygen atoms added in close proximity to one another have a greater binding energy than O atoms added with larger separations relative to the unit cell. The difference in O binding energy between the monolayer system and the bilayer system is on average 0.02 eV less for the bilayer, the second, and as the number of O atoms are increased, the binding energy between the graphene layers falls to zero after 45.8% coverage or with 11 O atoms. (C) 2014 Elsevier B.V. All rights reserved.