Vacancy Controlled Contact Friction in Graphene

We have demonstrated that, during the controlled oxidation in oxygen plasma and subsequent reduction induced by high energy photons, the contact friction in Chemical Vapor Deposition (CVD) grown graphene is dominated by the vacancies formed instead of the bonding with C-O based add-atoms and functional groups. Presence of vacancies can make graphene sheet more flexible to pucker at the contact edge, which increase the contact area and as a result leads to a larger contact friction. Modified graphene with large contact friction has a large density defects, but remains a good electrical conductor, in which the carrier transport is strongly affected by quantum localization effects even at room temperature.It is found that the oxidation process in graphene is substrate-sensitive. Comparing to monolayer graphene on SiO2 substrate, the oxidation process progresses much faster when the substrate is SrTiO3, while bilayer graphene exhibits great oxidation resistance on both substrates.