In the fully oxidized island the functional groups have been arranged in an ordered manner (similar to the chain-like structure described by Yan and Chou 40 ). In the second GO model, RGO, the positions of the functional groups have been chosen at random, where the oxidized and graphene-like regions intersect each other. Note that these two models present limiting situations and in principle a more elaborate model could include averaging with respect to variations in the specific arrangement of the functional groups (see, e.g., Ref. 25) or simultaneously occurring random and ordered regions.