低温真空条件下通过氖基质升华形成的结晶水冰的结构
Structure of crystalline water ice formed through neon matrix sublimation under cryogenic and vacuum conditions
AI总结：
本研究利用低温RHEED技术，发现13 K下氖基质升华可形成堆叠无序度极低的立方冰Ic，揭示了其形成过程，为低温低压下立方冰的形成提供了新途径。
摘要：
冰I根据其层的堆叠排列方式分为三种形式：六方冰Ih、立方冰Ic和堆叠无序冰Isd。在约60 K以下，非晶态水处于亚稳态，通常默认不会形成任何形式的冰I。利用最新开发的低温反射高能电子衍射（RHEED）技术，我们发现，在13 K的温度下，固态H2O/Ne（比例1:1000）基质中的氖升华后，形成了具有立方堆叠序列的结晶冰（即冰Ic）。通过氖基质升华形成的冰中，堆叠无序（立方与六方堆叠序列无序）的程度低于在143 K下制备的气相沉积冰Isd，且低于低温RHEED的检测限。所得冰结构对H2O/Ne基质厚度的依赖关系表明，在氖升华的早期阶段首先形成非晶态水，随后形成立方堆叠序列。由于此处形成的立方冰Ic的温度（13 K）远低于此前观测到的温度（通常高于78 K），氖基质升华为低温低压条件下立方冰Ic的形成提供了一条新途径。
英文摘要：
Ice I has three forms depending on the stacking arrangements of its layers: hexagonal ice Ih, cubic ice Ic, and stacking disordered ice Isd. Below ~60 K, amorphous water becomes metastable, and the formation of any form of ice I is often implicitly precluded. Using a newly developed low-temperature reflection high-energy electron diffraction (RHEED) technique, we show that crystalline ice with cubic stacking sequences (i.e., ice Ic) formed through Ne sublimation from a solid H2O/Ne (1:1000 ratio) matrix at 13 K. The extent of staking disorder (disordered cubic and hexagonal stacking sequences) in the ice formed by Ne matrix sublimation is smaller than that in vapor-deposited ice Isd prepared at 143 K and below the limit of detection of low-temperature RHEED. Dependence of the resulting ice structures on the thickness of the H2O/Ne matrix shows that amorphous water first forms in the early stages of Ne sublimation and the cubic stacking sequence subsequently takes place. As the cubic ice Ic formed here at a much lower temperature (13 K) than previously observed (typically above 78 K), Ne matrix sublimation represents a novel route to the formation of cubic ice Ic under low-temperature and low-pressure conditions.
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