Development and preliminary results of the low-temperature gas evaporation method tounderstand nucleation conditions of water ice and related materials
Yuki Kimura, Tomoya Yamazaki, Yuga Yashima, Shoichi Mori,Fumiaki Saito, and Akira Kouchi
Institute of Low Temperature Science, Hokkaido University, Japan
In our previous studies, we have shown that the key factors governing nucleation from the gas
phase are the melting point depression of nanoparticles and sticking probability (dimerformation) [1,2]. In long years, nucleation theory has been known to be completely unable toexplain the results of experiments and molecular dynamics simulations. In contrast, we haveclarified that the latest nucleation theory can explain experimental results by using
appropriately determined sticking probabilities and surface free energies of nanoparticles asphysical parameters [1], and by including chemical potential differences that consider thenucleation pathway [2].
To understand the nucleation processes of ice, we developed a low-temperature gas
evaporation method to determine the sticking probability and surface free energy ofnanoparticles of ice. The gas evaporation method has been used to make nanoparticles ofrefractory materials through homogeneous nucleation during the cooling process of hightemperature vapor generated by heating and evaporating the starting material [3]. By
applying interferometry to this method, two physical quantities (surface free energy andsticking probability), which are essential for understanding the nucleation process, can beobtained. In addition, infrared spectral measurements can reveal the nucleation pathways.
The low-temperature nucleation chamber has a double-tube structure. The inner chamber,where ice nucleation takes place, is filled with neon gas to reduce the mean free path andcooled by liquid nitrogen. The evaporation source was also cooled with liquid nitrogen. The
space between the inner and outer chambers is evacuated to thermally insulate them andprevent condensation.
Water vapor generated by heating and sublimating ice in the low-temperature nucleationchamber is cooled by neon gas, and after becoming supersaturated, it undergoes homogeneous
nucleation to form nanoparticles. This process was observed in situ using a doublewavelength Mach-Zehnder laser interferometer and an infrared spectral system. Theinterferometer can quantitatively determine the temperature and concentration fields from
evaporation to nucleation. The infrared system can investigate the changes in the crystal
structure of water and ice particles during the nucleation process.
In the experiment, the interferometer succeeded in capturing the moment of nucleation, andthe infrared system also succeeded in capturing the temporal change in absorption intensity.
This means that the nucleation process of ice nanoparticles from water vapor was captured.
This achievement is expected to lead to the construction of a nucleation model that can predict
the state of ice dust formation that repeatedly sublimated and condensed in the primordial
solar nebula 4.6 billion years ago.
References
[1]
[2]
[3]

Y. Kimura, K. K. Tanaka et al., 2017, Science Advances 3, e1601992.
S. Ishizuka, Y. Kimura et al., 2018, Nature Communications 9, 3820.
C. Kaito, 1978, Japanese Journal of Applied Physics 17, 601.