Oxygen adsorption on Graphene/GaN (0001) surface: A first-principles study

Abstract

Graphene or reduced-graphene-oxide are used in gallium nitride-based electronic devices because of similar properties such as transparency and high thermal conductivity. To date, there is not a detailed theoretical discussion of the oxygen adsorption on Graphene/GaN (0001) surface in the Literature. In this study, using the Density Functional Theory, we investigate the changes in the interactions between carbon and gallium atoms caused by the adsorption of oxygen atoms on the 3√3 × 3√3 graphene/ 4 × 4 GaN(0001) surface. Based on analysis of Electron Localization Function we have determined that the presence of covalent bonds between carbon and gallium atoms, in the surface without oxygen adsorbed, that produced a vertical buckling in graphene of 0.54 Å and 0.22 Å in the topmost gallium layer. The adsorption of oxygen on the surface caused the increment of the vertical buckling on both values; In this case, with 11 oxygen atoms adsorbed, it increases up to 1.01 Å in graphene and 0.38 Å in the topmost gallium layer. This effect causes a reordering of carbon-gallium bonds and modifies its bond length. Furthermore, based on the obtained formation energies, when the surface is exposed to oxygen-poor conditions, it remains without oxygen atoms adsorbed; in contrast, when the surface is exposed to rich oxygen conditions, it favors the adsorption of oxygen starting from 7 atoms. After this point, to increase the oxygen adsorption on the surface is required to apply energy to the system.