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Ying Jiang's group discovered an unconventional ice structure, which completely breaks the ice rules.
《自然-通讯》:江颖等发现一种新奇的二维冰结构

       Water-solid interactions are of broad importance both in nature and technology. The hexagonal bilayer model based on the Bernal-Fowler-Pauling ice rules has been widely adopted to describe water structuring at interfaces. However, the validity of the hexagonal bilayer model on interfacial water is being challenged due to the subtle balance between the water-water and water-substrate interactions. Recently, the research team led by Prof. Ying Jiang of International Center of Quantum Materials (ICQM) of Peking University, in collaboration with Prof. Enge Wang and Prof. Xinzheng Li from the same center, discovered a highly defective tetramer-based ice structure on NaCl(001) surface, which goes well beyond the simple hexagonal bilayer model predicted by the ice rules. This work was published online in Nature Communications on May 30th, 2014 [Nat. Commun. DOI: 10.1038/ncomms5056].

During the past four years, Ying Jiang’s group has been working on the development of ultrahigh-resolution scanning tunneling microscope (STM) for single-molecule experiments. Recently, they made a breakthrough in achieving submolecular-resolution imaging of individual water molecules adsorbed on a Au-supported NaCl(001) film [Nat. Mater. 13, 184 (2014)]. Such a technique opens up the possibility of determining the detailed topology of H-bonded networks at water/solid interfaces with atomic precision.

As an important application of this technique, Ying Jiang and his collaborators stepped further to study the ice overlayer grown on the NaCl(001) film and discovered an unconventional bilayer ice structure built from cyclic water tetramers at 77 K. The water tetramers within the lower part of the bilayer act as the basic building blocks, which are interconnected via a novel bridging mechanism to form a regular array of Bjerrum D-type defects located in the upper layer. Ab initio theoretical calculations based on density functional theory rationalize the stabilization of such an unconventional bilayer ice and reveal a striking proton-disordered ice structure. Notably, the formation of the periodic Bjerrum defects with unusually high density is strongly against the Bernal-Fowler-Pauling ice rules and may play a crucial role in catalyzing heterogeneous chemical reactions on water-coated salt surfaces as well as in influencing various phenomena such as heterogeneous ice nucleation, salt dissolution and caking.

This work received supports from Ministry of Science and Technology of China, National Natural Science Foundation of China, Ministry of Education of China, and  National Program for Support of Eminent Professionals.

 

Paper link: http://www.nature.com/ncomms/2014/140530/ncomms5056/full/ncomms5056.html

 

(a) High-resolution STM image of a 2D ice nanocluster consisting of four tetramers and six bridging water molecules. Square lattices of the NaCl(001) surface arising from Cl are depicted by white grids. (b) and (c) Top and side views, respectively, of the calculated adsorption configurations of the ice nanocluster. H, Cl and Na are denoted by white, grey and dark-cyan spheres, respectively. For clarity, the O atoms of water molecules in lower and upper layers are represented by red and yellow spheres, respectively.

          固体表面冰的形成是自然界中最普遍最重要的问题之一。一直以来,传统的六角双层冰模型是人们描述固体表面冰结构的基本出发点,然而由于水与固体表面相互作用的复杂性,这种简单的模型受到越来越多的挑战。最近,北京大学量子材料中心、量子物质科学协同创新中心的江颖课题组和王恩哥课题组以及物理学院的李新征研究员合作,利用高分辨的扫描隧道显微镜首次在氯化钠表面发现了一种完全不同于体态冰的新型二维冰结构。相关研究成果于530在线发表在《自然-通讯》[Nature Communications DOI: 10.1038/ncomms5056]

江颖课题组在过去几年中一直致力于超高分辨扫描隧道显微镜系统的研制和开发,并在近期的工作中取得重大突破,实现了盐表面单个水分子内部自由度的成像 [Nature Materials 13,184 (2014)],使得人们首次可以在实空间中直接解析水的氢键网络构型。作为该技术的重要应用之一,江颖等进一步研究了氯化钠表面覆盖的二维冰层,通过高分辨成像并结合密度泛函理论模拟,发现这种二维冰的基本组成单元为水分子四元环团簇,这些四元环团簇之间通过一种奇特的“桥联”机制互相联结在一起,从而形成周期性的晶格。出乎意料的是,这种冰结构的表面存在着高密度周期性排列的缺陷与不饱和氢键,完全违背了人们普遍接受的“冰规则”(Bernal-Fowler-Pauling ice rules),修正了人们从前对固体表面冰结构的微观认识。盐颗粒作为大气中一种重要的气溶胶,是形成云滴和冰晶的凝结核,澄清盐表面冰层的结构对于理解大气中的异质催化反应和解决大气污染问题有着重要的意义。

该研究得到了科技部国家重点基础研究发展计划,国家自然科学基金委员会和中组部青年拔尖人才支持计划等项目的资助。江颖和李新征是文章的共同通讯作者,博士研究生陈基、郭静和孟祥志是文章的共同第一作者。

a:由四个四元环和六个“桥联”水分子形成的二维冰团簇的高分辨STM图像,图中的网格线为NaCl001)衬底的Cl-晶格。图b和图c:由第一性原理计算得到的冰团簇原子结构的顶视图和侧视图。位于冰团簇中间的两个“桥联”水分子形成一个Bjerrum D-type缺陷。在高覆盖度下,这种冰团簇可作为形核中心进一步生长为二维的冰层。