Wang Yelingyi, Wang Jin, Wu Tielin, Chen Weipeng, Peng Deli, Wu Zhanghui, Ma Ming, Zheng Quanshui
Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China.
Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing 100084, China.
Natl Sci Rev. 2024 Jan 25;11(9):nwae019. doi: 10.1093/nsr/nwae019. eCollection 2024 Sep.
The current-carrying friction characteristics are crucial for the performance of a sliding electrical contact, which plays critical roles in numerous electrical machines and devices. However, these characteristics are influenced by multiple factors such as material surface quality, chemical reactions, and atmospheric environment, leading to a challenge for researchers to comprehensively consider these impacts. Structural superlubricity (SSL), a state of nearly zero friction and no wear between contact solid surfaces, provides an ideal experimental system for these studies. Here, with microscale graphite flakes on atomic-flattened Au surface under applied voltages, we observed two opposite friction phenomena, depending only on whether the edge of graphite flake was in contact with the Au substrate. When in contact the friction force would increase with an increasing voltage, otherwise, the friction force would decrease. Notably, when the voltage was turned off, the friction force quickly recovered to its original level, indicating the absence of wear. Through atmosphere control and molecular dynamics simulations, we revealed the mechanism to be the different roles played by the water molecules confined at the interface or adsorbed near the edges. Our experimental results demonstrate the remarkable tunable and robust frictional properties of SSL under an electrical field, providing an ideal system for the fundamental research of not only sliding electrical contacts, but also novel devices which demand tunable frictions.
载流摩擦特性对于滑动电接触的性能至关重要，而滑动电接触在众多电机和设备中起着关键作用。然而，这些特性受到材料表面质量、化学反应和大气环境等多种因素的影响，这给研究人员全面考虑这些影响带来了挑战。结构超润滑（SSL），即接触固体表面之间几乎零摩擦且无磨损的状态，为这些研究提供了理想的实验系统。在此，在施加电压的情况下，在原子级平整的金表面上有微米级石墨薄片，我们观察到了两种相反的摩擦现象，这仅取决于石墨薄片的边缘是否与金基底接触。当接触时，摩擦力会随着电压的增加而增大，否则，摩擦力会减小。值得注意的是，当关闭电压时，摩擦力会迅速恢复到其原始水平，这表明没有磨损。通过气氛控制和分子动力学模拟，我们揭示了其机制是界面处受限水分子或边缘附近吸附水分子所起的不同作用。我们的实验结果证明了SSL在电场作用下具有显著的可调谐且稳健的摩擦特性，不仅为滑动电接触的基础研究，也为需要可调谐摩擦的新型器件提供了理想的系统。
