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We present a density functional study of graphene adhesion on a realisticSiO$_2$ surface taking into account van der Waals (vdW) interactions. TheSiO$_2$ substrate is modeled at the local scale by using two main types ofsurface defects, typical for amorphous silica: the oxygen dangling bond andthree-coordinated silicon. The results show that the nature of adhesion betweengraphene and its substrate is qualitatively dependent on the surface defecttype. In particular, the interaction between graphene and silicon-terminatedSiO$_2$ originates exclusively from the vdW interaction, whereas theoxygen-terminated surface provides additional ionic contribution to the bindingarising from interfacial charge transfer ($p$-type doping of graphene). Strongdoping contrast for the different surface terminations provides a mechanism forthe charge inhomogeneity of graphene on amorphous SiO$_2$ observed inexperiments. We found that independent of the considered surface morphologies,the typical electronic structure of graphene in the vicinity of the Dirac pointremains unaltered in contact with the SiO$_2$ substrate, which points to theabsence of the covalent interactions between graphene and amorphous silica. Thecase of hydrogen-passivated SiO$_2$ surfaces is also examined. In thissituation, the binding with graphene is practically independent of the type ofsurface defects and arises, as expected, from the vdW interactions. Finally,the interface distances obtained are shown to be in good agreement with recentexperimental studies.

Interfacial interactions between local defects in amorphous SiO$_2$ and supported graphene