Controlling the motion of nanoscale building blocks on chemically contaminated or modified substrates was a bottleneck in bottom-up approaches to develop high performance nanoscale electro-mechanical systems. Nevertheless, how such modification of a substrate surface affects the mobility of an admolecule has not been well understood. Here, molecular dynamics simulations were used to study the surface diffusion of a C60 admolecule on both pure and hydrogenated graphene. By changing the temperature and hydrogen coverage, a diagram was obtained which clearly showed the existence of three distinct regimes in the surface diffusion of a C60 admolecule: superdiffusion, normal diffusion and sub-diffusion. Surprisingly, the simulations also showed that minute hydrogenation on graphene led to a giant reduction in molecular mobility. A theoretical model which takes into account the effects of both random traps and barriers was developed to predict the relation between the diffusion coefficient and the temperature and hydrogen coverage. The model predictions were in good agreement with the present molecular dynamics simulation results.

A Chemical Route to Control Molecular Mobility on Graphene. Jafary-Zadeh, M., Reddy, C.D., Zhang, Y.W.: Physical Chemistry Chemical Physics, 2012, 14[30], 10533-9