Figure 2.

Effect of temperature on the diffusion coefficient and kinetic friction of the C₆₀/graphene system. (a) The Arrhenius analysis of the surface diffusion coefficient, D, of the C₆₀ indicates the existence of two diffusive regimes with a crossover around 75 K. The inset of (a) illustrates that the friction coefficient decreases from 1.3 ps^-1 to a value in the order of 0.01 ps^-1 when the temperature is increased from 25 to 200 K. (b) Mean square displacement (MSD) of C₆₀ motion as a function of time at 50 and 125 K. Note that at 50 K, the MSD grows linearly with time, consistent with quasi-continuous Brownian motion. At 150 K, the MSD is initially parabolic for time shorter than 1/η, consistent with ballistic-like Brownian motion.