Hexagonal Monolayer Ice without Shared Edges

X Zhang and JY Xu and YB Tu and K Sun and ML Tao and ZH Xiong and KH Wu and JZ Wang and QK Xue and S Meng, PHYSICAL REVIEW LETTERS, 121, 256001 (2018).

DOI: 10.1103/PhysRevLett.121.256001

When adsorbed on solids, water molecules are usually arranged into a honeycomb hydrogen-bond network. Here we report the discovery of a novel monolayer ice built exclusively from water hexamers but without shared edges, distinct from all conventional ice phases. Water grown on graphite crystalizes into a robust monolayer ice after annealing, attaining an exceedingly high density of 0.134 angstrom(-2). Unlike chemisorbed ice on metal surfaces, the ice monolayer can translate and rotate on graphite terraces and grow across steps, confirming its two- dimensional nature. First-principles calculations identify the monolayer ice structure as a robust self-assembly of closely packed water hexamers without edge sharing, whose stability is maintained by maximizing the number of intralayer hydrogen bonds on inert surfaces.

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