Thermal Gradients on Graphene to Drive Nanoflake Motion.

Thermophoresis has been emerging as a novel technique for manipulating nanoscale particles. Materials with good thermal conductivity and low surface friction, such as graphene, are best suited to serve as a platform for solid-solid transportations or manipulations. Here we employ nonequilibrium molecular dynamics simulations to explore the feasibility of utilizing a thermal gradient on a large graphene substrate to control the motion of a small graphene nanoflake on it. Attempts to systematically investigate the mechanism of graphene-graphene transportation have centered on the fundamental driving mechanism of the motion and the quantitative effect of significant parameters such as temperature gradient and geometry of graphene on the motion of the nanoflake. Simulation results have demonstrated that temperature gradient plays the pivotal role in the evolution of the motion of the nanoflake on the graphene surface. Also, the geometry of nanoflakes has presented an intriguing signature on the motion of the nanoflake, which shows the nanoflakes with a circular shape move slower but rotate faster than other shapes with the identical area. It reveals that edge effects can stabilize the angular motion of thermophoretically driven particles. An interesting relation between the effective initial driving force and temperature gradient has been quantitatively captured by employing the steered molecular dynamics. These findings will provide fundamental insights into the motion of nanodevices on a solid surface due to thermophoresis, and will offer the novel view for manipulating nanoscale particles on a solid surface in techniques such as cell separation, water purification, and chemical extraction.