Friction and mobility of carbon nanoparticles on a graphene sheet

TL;DR

This study uses molecular dynamics to analyze how carbon nanoparticles move on graphene sheets, revealing two friction regimes—diffusion and ballistic—and how temperature and normal force influence their mobility.

Contribution

It introduces a detailed molecular dynamics analysis of nanoparticle friction on graphene, distinguishing between diffusion and ballistic regimes and their temperature dependencies.

Findings

Friction depends on temperature and particle size.

Ballistic friction increases with temperature, diffusion friction decreases.

Normal force increases nanoparticle friction.

Abstract

It is shown using the method of molecular dynamics that the motion of carbon nanoparticles (rectangular graphene flakes, spherical fullerenes of size $L<10$ nm) on the surface of a thermalized graphene sheet lying on a flat substrate can be described as the motion of particles in a viscous medium with a constant coefficient of friction, the value of which depends on the temperature and particle size. It has been shown that there are two types of effective friction: diffusion and ballistic. In ballistic regime of motion (at velocities $v>100$ m/s), deceleration occurs due to the interaction of moving nanoparticles with thermal out-of-plane bending vibrations of a graphene sheet. Because of this, with the increasing temperature, the coefficient of friction monotonically increases. In the diffusion regime of motion (at $v<10$ m/s), friction arises due to the need for the particle to overcome local energy barriers, therefore it decreases with increasing emperature. The difference between ballistic and diffusion friction is most pronounced at low temperatures, since the mobility of nanoparticles in the ballistic regime of motion decreases with increasing temperature, while in the diffusion regime it monotonously increases. It is shown that the presence of a normal force pressing the nanoparticle to the substrate leads to an increases in its friction with the substrate.