Doping of graphene adsorbed on the a-SiO$_2$ surface

TL;DR

This study uses ab initio calculations to show that graphene adsorbed on amorphous SiO$_2$ becomes n-type doped through van der Waals interactions, with charge transfer driven by oxygen atoms, affecting electronic mobility.

Contribution

It provides a detailed theoretical analysis of how amorphous SiO$_2$ induces doping and charge distribution changes in adsorbed graphene without chemical bonding.

Findings

Graphene adsorbs via van der Waals forces on a-SiO$_2$ surface.

Charge density becomes inhomogeneous, creating electron- and hole-rich regions.

Graphene becomes n-type doped due to charge transfer from oxygen atoms.

Abstract

We have performed an {\it ab initio} theoretical investigation of graphene sheet adsorbed on amorphous SiO$_2$ surface (G/a-SiO$_2$). We find that graphene adsorbs on the a-SiO$_2$ surface through van der Waals interactions. The inhomogeneous topology of the a-SiO$_2$ clean surface promotes a total charge density displacement on the adsorbed graphene sheet, giving rise to electron-rich as well as hole-rich regions on the graphene. Such anisotropic distribution of the charge density may contribute to the reduction of the electronic mobility in G/a-SiO$_2$ systems. Furthermore, the adsorbed graphene sheet exhibits a net total charge density gain. In this case, the graphene sheet becomes n-type doped, however, with no formation of chemical bonds at the graphene--SiO$_2$ interface. The electronic charge transfer from a-SiO$_2$ to the graphene sheet occurs upon the formation of a partially occupied level lying above the Dirac point. We find that such partially occupied level comes from the three-fold coordinated oxygen atoms in the a-SiO$_2$ substrate.