Observation of microscale superlubricity in graphite

• Published in: Physical review letters 2012-05, Vol.108 (20), p.205503-205503, Article 205503
• Main Authors: Liu, Ze, Yang, Jiarui, Grey, Francois, Liu, Jefferson Zhe, Liu, Yilun, Wang, Yibing, Yang, Yanlian, Cheng, Yao, Zheng, Quanshui
• Format: Article
• Language: English
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/physrevlett.108.205503

Upon shearing a microscale lithographically defined graphite mesa, the sheared section retracts spontaneously to minimize interface energy. Here, we demonstrate a sixfold symmetry of the self-retraction and provide a first experimental estimate of the frictional force involved, as direct evidence that the self-retraction is due to superlubricity, where ultralow friction occurs between incommensurate surfaces. The effect is remarkable because it occurs reproducibly under ambient conditions and over a contact area of up to 10×10  μm2, more than 7 orders of magnitude larger than previous scanning-probe-based studies of superlubricity in graphite. By analyzing the sheared interface, we show how the grain structure of highly oriented pyrolitic graphite determines the probability of self-retraction. Our results demonstrate that such self-retraction provides a novel probe of superlubricity, and the robustness of the phenomenon opens the way for practical applications of superlubricity in micromechanical systems.