Frictional Behavior of van der Waals Heterojunctions Driven by Elastic Pinning at Edges and Corners.

Due to the significant friction and wear in micro- and nano-electromechanical systems (M/NEMS), achieving reliable sliding in M/NEMS remains a critical challenge. Structural superlubricity with ultralow friction and wear in van der Waals (vdW) heterojunctions is a promising route to realize long-lifetime sliding in M/NEMS for practical applications. However, the fundamental origin of friction in vdW heterojunctions remains elusive. In this paper, through detailed experimental measurements by adopting various slider geometries and cracked substrates, we demonstrate that friction is dominated by edge and corner effects, driven by the pinning effects associated with moiré superlattices at these boundaries. Specifically, friction enhancement correlates inversely with the radius of curvature at the corners. Furthermore, edges oriented perpendicular to the sliding direction induce more pronounced frictional enhancement than those aligned parallel. These results elucidate a fundamental frictional mechanism in vdW heterojunctions, providing critical insights for the design of future M/NEMS.