DataSheet1_Confined Monolayer Ice Between CaF2 (111) and Graphene: Structure and Stability.docx

Water monolayer can form in layered confined systems. Here, CaF2 (111) and graphene are chosen as modeling systems to explore the structure and stability of confined monolayer water. First, water molecules tend to intercalate into a confined space between graphene and CaF2, rather than on a bare surface of graphene. Water molecules can move fast in the confined space due to a low diffusion barrier. These water molecules are likely to aggregate together, forming monolayer ice. Four ice phases including ice II, ice III, ice IV, and ice Ih are compared in this confined system. Intriguingly, all the ice phases undergo very small deformation, indicating the 2D monolayer ice can be stable in the CaF2–graphene–confined system. Beyond, projected band structures are also plotted to understand the electronic behavior of these confined ice phases. Nearly all the bands originated from confined ices are flat and locate about 2–3 eV below the Fermi level. Binding energy calculations suggest that the stability sequence in this confined system as follows: Ih-up ≈ Ih-down ≈ II < IV < III. Our results bring new insights into the formation of water monolayer production in such a confined condition.

在层状受限体系中，水单分子层能够形成。本研究选取CaF2（111）和石墨烯作为建模系统，旨在探究受限单分子水层的结构和稳定性。首先，水分子倾向于嵌入到石墨烯与CaF2之间的受限空间，而非直接附着在石墨烯的裸露表面上。由于扩散势垒较低，水分子在该受限空间内能够迅速移动。这些水分子倾向于聚集，形成单分子层冰。在本研究中，对包括冰II、冰III、冰IV和冰Ih在内的四种冰相进行了比较。令人惊奇的是，所有冰相均经历了极小的形变，表明二维单分子层冰能够在CaF2-石墨烯-受限体系中保持稳定。此外，还绘制了投影能带结构，以理解这些受限冰相的电子行为。几乎所有源自受限冰的能带均呈现平坦状态，并位于费米能级下方约2-3电子伏特处。结合能计算表明，在该受限体系中，稳定性序列如下：Ih-up ≈ Ih-down ≈ II < IV < III。本研究结果为受限条件下水单分子层形成的机制提供了新的洞见。