Mesoscale superlubric Brownian machine based on 2D graphitic interfaces

Abstract

Brownian motors utilize thermal activation and asymmetric physical interactions to generate directed motion of nanoscale elements in space. On the other hand, structural superlubricity refers to a macroscopic correlated state of nearly vanishing friction due to structural mismatch between sliding interfaces. In fact, the effective sliding barrier in these systems was shown to depend on temperature, manifested by the thermal lubrication phenomenon. Herein, the unique combination of a carefully designed tilted periodic potential landscape and virtually zero friction in 2D layered systems are used to demonstrate mesoscopic superlubric Brownian operation. We perform mechanical shearing of superlubric graphite contacts to examine the influence of velocity on friction and adhesion. Our results show that while friction is virtually independent of velocity below 2500 nm s⁻¹, the adhesion force increases by ∼10% with respect to the lowest measured velocity. This indicates that the system can intriguingly exhibit a counterclockwise hysteretic force loop in which a greater amount of energy can be generated once the retraction velocity is set above the protraction velocity, which is explained by utilizing the available thermal energy to reduce adhesion. The ability to realize mesoscopic mechanical systems that can conceptually extract useful mechanical energy by thermal fluctuations can potentially lead to disruptive technologies such as artificial surfaces, in which controlled motion of elements is manifested by manipulated Brownian motion and self-powered actuators with energy harvest capabilities.