The effect of rotational degrees of freedom of C60 on the potential energy surface (PES). (a-e) Various configurations are used to examine the PES profiles. These configurations are named as: (a) Hex.-In Phase; (b) Hex.-Out Phase; (c) Pentagon; (d) Line-In Phase; and (e) Line-Out Phase. (f) Three-dimensional PES for the Hex.-In Phase configuration. (g) Contour plot representation of the PES in (f). The white arrow in (g) indicates the diffusion path with the lowest energy barrier. The arrangement of graphene atoms and their bonds is also illustrated in this figure. (h) and (i) show the PES profiles for the C60 with different facets, as shown in (a-e), during its translation along the  and  crystallographic directions of graphene, respectively.
Jafary-Zadeh et al. Nanoscale Research Letters 2012 7:148 doi:10.1186/1556-276X-7-148