From slippery to superlubrication： the lubrication behavior of ice at the atomic scale

Why is ice so slippery? This question has puzzled scientists for over a century. In this study, we used high-resolution qPlus-based scanning probe microscopy to resolve the atomic-scale surface structure of hexagonal ice (ice Ih), the most common ice form in nature. We discovered, for the first time, a long-range periodic surface superstructure composed of alternating nanoscale Ih and Ic domains. Furthermore, we found that the defective domain boundaries significantly promote localized premelting, enabling the surface to exhibit lubricating behavior at temperatures as low as -153 ℃. By further“compressing”bulk ice Ih into its two-dimensional(2D) limit, we successfully fabricated 2D hexagonal ice on graphene and hexagonal boron nitride (h-BN) substrates. The 2D ice was found to be incommensurate with graphene, where it exhibited superlubricity with a friction coefficient below 0.01, while it remained commensurate with h-BN and displayed conventional friction——this is the first experimental evidence of structural superlubricity in confined water transport.