The phenomenon that the surface of ice is covered with a thin film of water (pseudo-liquid layer) even at 0 ° C or lower is known as surface melting, and was first taken up by Michael Faraday, the founder of electromagnetism, in the 1850s.After that, research was repeated, but the mechanism of water film formation remained unclear.

　This time, we observed using an optical microscope that can visualize the difference in atomic and molecular height developed in collaboration with Olympus Corporation.As a result, when approaching the state of equilibrium vapor pressure, the pseudo-liquid layer spontaneously repels water (ice repels the pseudo-liquid layer), and the ice cannot be completely wetted as a thin film, resulting in condensation. It became a state (drop form).After that, it was found that the pseudo-liquid layer evaporates in order to eliminate the unstable state in which the ice, air, and water layers exist at the same time, and finally a dry bare ice surface appears.On the other hand, it was also found that a pseudo-liquid layer is formed only when the ice surface satisfies certain ice growth conditions or sublimation conditions.This result indicates that the pseudo-liquid layer is an intermediate state that is transiently created in the process of phase change from water vapor to ice (or vice versa).

　Surface melting itself is said to be a universal phenomenon that occurs not only on ice but also on the crystal surface of various other substances including metals and semiconductors.Therefore, the results of this research are expected to have a great impact on a wide range of research fields such as condensed matter physics, materials science, and global environmental science.