How Cubic Can Ice Be?
How Cubic Can Ice Be?
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DOI：
10.1021/acs.jpclett.7b01142
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发表时间：
2017-07-20
影响因子：
5.7
通讯作者：
Wyslouzil, Barbara E.
中科院分区：
文献类型：
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作者：
Amaya, Andrew J.;Pathak, Harshad;Wyslouzil, Barbara E.
利用x射线激光，研究了深度过冷水纳米滴（r约为10 nm）中均匀冰核形成的冰的晶体结构。纳米滴是由蒸汽在超音速喷嘴中凝结形成的，在Linac相干光源自由电子x射线激光的飞秒广角x射线散射下，在冻结100 μ s内探测了冰。x射线衍射谱表明，这种冰具有亚稳的、以立方结构为主的结构；第一个冰衍射峰的形状表明是堆积无序的冰，立方度值chi在0.78 +/- 0.05范围内。这里确定的立方度值高于在微米大小的液滴实验中确定的值，但与分子动力学模拟中发现的值相当。高立方度很可能是由于极低的冻结温度和快速冻结造成的，这在单个纳米液滴中发生的时间尺度类似于1 μ s。
Using an X-ray laser, we investigated the crystal structure of ice formed by homogeneous ice nucleation in deeply supercooled water nanodrops (r approximate to 10 nm) at similar to 225 K The nanodrops were formed by condensation of vapor in a supersonic nozzle, and the ice was probed within 100 mu s of freezing using femtosecond wide-angle X-ray scattering at the Linac Coherent Light Source free-electron X-ray laser. The X-ray diffraction spectra indicate that this ice has a metastable, predominantly cubic structure; the shape of the first ice diffraction peak suggests stacking-disordered ice with a cubicity value, chi, in the range of 0.78 +/- 0.05. The cubicity value determined here is higher than those determined in experiments with micron-sized drops but comparable to those found in molecular dynamics simulations. The high cubicity is most likely caused by the extremely low freezing temperatures and by the rapid freezing, which occurs on a similar to 1 mu s time scale in single nanodroplets.