Ice II-like Monolayer Ice Grown on Graphite Surface

Water on solid surfaces is essential for a wide range of scientific and technological processes. Previous studies reveal that water molecules on metal surfaces usually form layered structures with a honeycomb hydrogen-bond network, similar to the basal plane of hexagonal ice I-h. Here we report a new type of monolayer ice grown on graphite surface at low temperature with subsequent annealing. High-resolution STM images reveal that the monolayer ice is composed of cyclic water hexamers without sharing edges. Moreover, the monolayer ice exhibits multiple orientations relative to the graphite lattices, resulting in various moire patterns. First-principles calculations reveal that the moire superstructures contain both tilted and planar water hexamers, corresponding to the horseshoe-like and flat water rings observed in the STM images. All water molecules within the monolayer are saturated by four hydrogen bonds, and the strong intralayer bonding gives rise to a high stability of the monolayer ice.