Attractive curves: the role of deformations in adhesion and friction on graphene

Friction Force Microscopy measurements reveal a dramatic difference of a factor 3 between the friction forces experienced on single-monolayer graphene on top of oxidized and unoxidized copper substrates. We associate this difference with the strong and weak adhesion that the graphene experiences on these two substrates, respectively, but argue that it is too large to be ascribed either to a difference in contact area or to a difference in contact commensurability or even to a combination of these two effects. We use Density Functional Theory to show a significant increase in the chemical reactivity of graphene when it is curved.