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Abstract Growth of ice crystals is ubiquitous around us, but we still do not know what is occurring at the forefront of crystallization. In general, the interfacial structure is inseparably involved in the microscopic ordering during crystal growth. However, despite its importance in nature and technology, the intrinsic role of the interfacial structure in the melt growth of ice remains to be elucidated. Here, using extensive molecular dynamics simulations, we comprehensively explore how supercooled water molecules are incorporated into the ice basal face. Structural and dynamic characterizations of the ice-water interface demonstrate that the ice basal face is sharp at the molecular level and its growth proceeds layer-by-layer through two-dimensional nucleation without any intermediate structures. We further quantify the crossover from layerwise to adhesive growth, called kinetic roughening, with the height difference correlation and the normal growth rate analysis. Moreover, we identify the presence of an ultra-low density water layer in contact with the structural interface, which assists two-dimensional nucleation at a small amount of supercooling without involving any triggers, such as dislocations.

We review our recent study on step-bunching instability (SBI) of ice melt growth, one of the interfacial instabilities driven by self-organization of elementary step flow associated with crystal growth dynamics. With the aid of an advanced optical microscope and its combination with a two-beam interferometer, we realized quantitative in situ observations of the spatiotemporal dynamics of the SBI. This enables us to examine the origin of the SBI at the level of the step-step interaction. Our finding offers a significant clue to understanding the general mechanism of melt growth beyond ice-crystal growth, inseparably involving several broad research fields, including cryobiological, geophysical, and material branches. [ABSTRACT FROM AUTHOR]