ice is the solid form of water in nature, and it also exists widely in nature. The study of ice structure and formation mechanism is very important to cloud physics and low temperature storage physics, so scientists have a long history of ice research. When it comes to the existence of ice on a smaller scale, we are most likely to think of snowflakes. As shown in the figure below, snowflakes have obvious six-fold symmetry, because ice mostly exists in the hexagonal phase (Ice Ih) in nature.

Fig.1 Photos of Snowflakes (Pictures from the Internet)

If we look up the literature, we will find that scientists mostly use diffraction technology that can provide spatial average information to characterize the structure of ice, transmission electron microscope (TEM), as a high-end instrument with the capability of atomic scale characterization, is rarely used in the study of ice structure. There are two main obstacles: first, it is quite difficult to prepare stable transmission electron microscope samples of ice in a low-pressure state; second, the damage effect of the electron beam provides a huge obstacle to the transmission electron microscopy characterization of ice. Recently, the team of Bai Xuedong, a researcher at the Institute of Physics of the Chinese Academy of Sciences, cleverly used cryo-electron microscopy technology to deposit the residual water vapor in the transmission electron microscope column on a low-temperature (102K) copper grid, and used spherical aberration correction low-dose transmission electron microscopy imaging technology to characterize the crystal structure, defect characteristics, and structural dynamics evolution of ice on different substrates in detail and systematically, it is found that the preferential nucleation of cubic ice (Ice Ic) at the low temperature interface increases gradually with the increase of time.

Relevant results were published in Nature magazine under the title of "Tracking cubic ice at molecular resolution". Associate researcher Wang Lifen of Institute of Physics of Chinese Academy of Sciences was the co-first author (2/3) and corresponding author of the article. Doctoral student Huang Xudan (1/3) of Institute of Physics of Chinese Academy of Sciences and doctoral student Liu Keyang of Peking University were both the first authors (3/3), researcher Chen Ji of Peking University, Academician Wang Enge and Researcher Bai Xuedong of Institute of Physics of Chinese Academy of Sciences are the co-authors of the article. The co-authors include Professor Jiang Ying of Institute of Physics of Peking University, Researcher Liu Lei of Institute of Materials, Researcher Xu Zhi of Songshan Lake Materials Laboratory, Special Researcher Tian Xuezeng of Institute of Physics of Chinese Academy of Sciences and Researcher Wang Wenlong.

Original Link: https://doi.org/10.1038/s41586-023-05864-5

Fig.2 Structural Characterization of Single Crystal Cubic Ice (Ice Ic) Grown on Different Substrates. The images of each row of a hydrophobic carbon film, B hydrophilic carbon film, c graphene, d monolayer h-BN

are respectively truncated polyhedron, local HRTEM image, corresponding FFT image, crystal structure diagram and corresponding high-resolution analog image of cubic ice (Ice Ic). The researchers analyzed that heterogeneous nucleation played an important role in the preferential nucleation of cubic ice.

Figure. 3 Electron microscopy characterization of defects in cubic ice (ice Ic)

relies on direct high-resolution imaging techniques. They have fine-grained characterization of microscopic defects in cubic ice (ice Ic) at the molecular level. According to whether or not stacking disordered crystal domains are introduced into cubic phase ice (ice Ic), they divide defects into two categories: the first type is that the surface defect features are limited to close-packed {111} crystal planes, including twins and stacking faults and their interaction. Type two is a domain disorder caused by defects in a region, including misfit dislocations or hexagonal close-packed sequences at the twin interface.

Fig.4 Dynamic Evolution of Stacking Disorder in Cubic Ice (Ice Ic) In-situ Observation

Fig.4a Shows the Initial Morphology of Ice Crystals, Including a Perfect Defect-free Cubic Ice (ice Ic) Crystal Domain (I) and a Stacking Disorder Crystal Domain (II). With the increase of the electron beam dose, the excitation effect of the electron beam makes the local energy of the ice increase, and the sublimation process shows the gradual peeling of the crystal surface layer (Fig. 4b-d). Domain II was initially a stripe-like lattice, and with the increase of irradiation time, the stripe distribution gradually changed, indicating that the defect structure was unstable. The researchers further evaluated the stacking-disorder evolution path and the corresponding potential energy diagram using molecular dynamics simulation methods. It is important to note that the cubic phase ice can exist stably during the growth process or under electron beam irradiation, and the solid phase transition from cubic phase ice (Ic) to hexagonal phase ice (Ih)Ih will not occur.

This work enables direct, real-world spatial imaging of ice formation and its dynamic behavior at the molecular scale, provides a basis for the study of ice using transmission electron microscopy, provides a reference for electron microscopy studies of other hydrogen-bonded crystals, and provides new insights into the evolution of the crystal structure of ice as it grows.

Fig.5 Screenshot of Experimental Method in this article

Anhui Zyou Technology Co., Ltd. is a pioneer in the domestic in-situ electron microscope industry. The newly released cryo-TEM sample rod PicoFemto JN02 provides technical support for this work.

Fig. 6 PicoFemto of Zeyu Technology (ZEPTOOLS) used in this study®Series In-situ Cryogenic Sample Rod