Coulombic structural superlubricity at high sliding speeds under ambient conditions

Structural superlubricity is an intriguing physical phenomenon, whereby sliding at a structurally incommensurate, atomically flat interface yields vanishingly small friction forces. Despite its recent experimental validation under ambient conditions, critical questions remain regarding the physical limitations of the concept. In particular, it is not known whether the ultralow friction state would persist at high sliding speeds relevant for practical, small-scale mechanical systems. Here, we perform sliding experiments via atomic force microscopy on gold nanoislands on graphite at increasing speeds, extracting interfacial friction forces under ambient conditions. A heterodyne detection methodology enables the extraction of extremely weak friction signals buried deep in the noise, revealing that the structurally superlubric regime extends over 100 µm/s with minimal changes in friction force, spanning three orders of magnitude in sliding speed. It is proposed that molecular contaminants at the gold-graphite interface result in the observed insensitivity of friction forces on sliding speed, i.e., Coulombic behavior. Our results contribute significantly to the pursuit of functional, superlubric mechanical devices.