Role of Graphene Surface Ripples and Thermal Vibrations in Molecular Dynamics of C₆₀

Abstract

Nanocars are artificial molecular machines with chassis, axles, and wheels designed for nanoscale transport at materials' surfaces. Understanding the dependence of surface dynamics of nanocars on the substrate's physicochemical properties is critical to the design of the transport properties of such man-made nanoscale devices. Among the multitude of potential substrates for the nanotransporters, graphene exhibits intrinsic ripples on its surface, which may affect the surface dynamics of nanocars. In this work, we report our molecular dynamics study of motion of C 60 , a popular nanocar wheel, on the graphitic substrates with systematically controllable surface ripples. We find that surface ripples increase the amplitude of fullerene fluctuation in the direction normal to surface, which leads to decrease of the desorption temperature from 650 K on a double-layer graphite system with less ripples to 550 K on single-layer graphene with more ripples. The surface diffusion of C 60 follows the rare hops mechanism for temperatures up to 30 K. It switches to continuous semiballistic motion at 150 K. The surface ripples do not significantly affect the diffusion coefficients, but change the anomaly parameter, especially at low temperatures. The ripples exhibit no major effect on the rotational dynamics of C 60 , which is attributed to very small energy barriers for C 60 rotation on graphitic surfaces.

Locomotion of the C60-based nanomachines on graphene surfaces

“…As discussed in our previous study 53 the energy variation of sliding motion of a C 60 molecule on graphene is about 1.4 meV while the rolling of C 60 around the horizontal axis was as large as 40 meV. Comparing these energies clarifies that a C 60 tends to slide than to roll on graphene.…”

“…3 a), the Nanocar COM is mainly located 5.5 Å away from the surface. Due to the larger number of atoms and larger interaction energy in nanomachines as opposed to C 60 , the average distance is smaller for the former than for the latter, reported earlier to be 6.4 Å 32 , 53 . Already at this temperature, one may observe the signs of surface rippling as manifested in larger molecule height fluctuation for the flexible SLG as opposed to the FLG system with constraints on the motion of surface atoms.…”

“…The computed diffusion coefficient for Nanocar and Nanotruck on SLG is on the order of 5 Å 2 /ps at room temperature. This value is an order of magnitude less than the room-temperature diffusion coefficient (50 Å 2 / ps) for C 60 on a graphene sheet 53 . We attribute this difference to the greatly increased adsorbate/surface interaction energy for the NC or NT moving on graphene monolayer, as compared to a single C 60 molecule moving of such surface.…”

Temperature‐Dependent Adhesion in van der Waals Heterostructures

“…[25,26,35,36] The amplitudes increase with temperature due to thermal excitation of the vibrations, but also saturate at elevated temperatures, e.g., from 0.6 Å at room temperature to about 90% of the saturation level of 1 Å at 200 °C for freestanding graphene. [37] Saturation of the ripple amplitude may therefore explain the plateau observed in the adhesion measurements at around 90-120 °C.…”

Influence of Vacancies and Grain Boundaries on the Diffusive Motion of Surface Rolling Molecules

“…Martsinovich et al 37 studied C 60 motion on a silicone substrate forced by an AFM tip. Mofidi et al 38 studied the role of graphene surface ripples on the motion of C 60 .…”