Abstract: Water and ice are ubiquitous in nature. The structure and growth of ice play critical roles in an incredibly broad spectrum of materials science, tribology, biology, atmospheric science, and planetary science. Addressing those issues requires the atomicscale
understanding of the interaction between water molecules and substrate as well as that between water molecules. Limited by
the theoretical methods and experimental techniques, the microscopic picture of ice nucleation and growth still remains under debate despite of enormous scientific efforts in the past decades. Thus, the precise description of ice nucleation and growth at atomic scale is of crucial importance. Using a combined system of low-temperature scanning tunneling microscope (STM) and non-contact atomic force microscope (NC-AFM), we succeed in achieving atomic resolution of a 2D ice on Au(111) and confirming its interlocked flat bilayer structure in real space with a CO-decorated qPlus-tip, which further allows us to deduce the growth process of the 2D
ice. Through weakly perturbative AFM imaging of the 2D ice edges, we observed the intermediate and metastable states during the growing process of the 2D ice for the first time. Combined with the first principle calculations and molecular dynamics simulations, we proposed two different growth mechanisms for zigzag and armchair edges. This work provides techniques and methods applicable to investigate the growth mechanism of a large family of 2D materials other than 2D ices, thus opening up a new avenue of visualizing the structure and dynamics of low-dimensional matter at the cutting edges.