Diffusion of a graphene flake on a graphene layer was analyzed and a diffusion mechanism was proposed for the system under consideration. According to this mechanism, rotational transition of the flake from commensurate to incommensurate states takes place with subsequent simultaneous rotation and translational motion until the commensurate state was reached again, and so on. The molecular dynamics simulations and analytic estimates based on ab initio and semi-empirical calculations demonstrated that the proposed diffusion mechanism was dominant at temperatures T∼ (1-3)Tcom, where Tcom corresponded to the barrier for transitions of the flake between adjacent energy minima in the commensurate states. For example, for the flake consisting of ∼40, 200 and 700 atoms the contribution of the proposed diffusion mechanism through rotation of the flake to the incommensurate states exceeded that for diffusion of the flake in the commensurate states by one to two orders of magnitude at 50 to 150K, 200 to 600K and 800 to 2400K, respectively. The possibility to experimentally measure the barriers to relative motion of graphene layers based upon the study of diffusion of a graphene flake was considered. The results obtained were also relevant for understanding of dynamic behavior of polycyclic aromatic molecules on graphene and should be qualitatively valid for a set of commensurate adsorbate-adsorbent systems.

Fast Diffusion of a Graphene Flake on a Graphene Layer. Lebedeva, I.V., Knizhnik, A.A., Popov, A.M., Ershova, O.V., Lozovik, Y.E., Potapkin, B.V.: Physical Review B, 2010, 82[15], 155460