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Brownian motors are nanoscale machines that utilize asymmetric physical interactions to generate directed motion in space. The operation mechanism relies on the random motion of nanoscale elements generated by thermal activation. On the other hand, structural superlubricity (SSL) refers to a state of nearly vanishing friction due to structural mismatch between sliding interfaces. Van-der-Waals layered materials, such as graphene are of particular interest in this regard as they exhibit atomically flat surfaces and weak interlayer interaction. In particular, the sliding barrier in these systems turned out to be extremely sensitive to temperature, leading to the observation of thermal lubrication at elevated temperatures. Herein, the unique combination of a carefully designed tilted periodic potential landscape and virtually zero friction in incommensurate 2D layered systems are used to realize a mesoscopic superlubric Brownian machine. In particular, 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*sec-1, the conservative adhesion force increases by ~ 10 % with respect to the lowest measured velocity. Intriguingly, a greater amount of energy can be collected by the system once the retraction velocity is set above the protraction velocity. Our numerical calculations based on force field modelling indicate that a slow adiabatic sliding allows to utilize the available thermal energy to reduce the adhesion in agreement with our experimental observations. As a result, we demonstrate a mesoscale Brownian motor that can harvest thermal energy by adjusting the forward and backward sliding velocities and can pave the way for macroscale directed motion and energy harvesting. |
