原子尺度上界面调控冰的结构和生长研究

The study of surface ice plays critical roles in an incredibly broad range of scientific disciplines and application fields, such as physical chemistry, atmospheric science, cryobiology, artificial rainmaking, anti-icing and storage of living organisms. Heterogeneous ice nucleation and growth could be inhibited or promoted by tuning the structure, charging and hydrophobic/hydrophilic property of the surface. However, the atomic/molecular level characterization and understanding of the hydrogen binding structure and growth process of surface ice is still a big challenge. In this project, we are going to develop non-invasive imaging technique with a qPlus-based noncontact atomic force microscopy (NC-AFM), which allows us to determine the detailed H-bonding structure including the position of the H atoms by probing the weak high-order electrostatic force between the charged tip and the polar water molecules of surface ice at large tip–sample distances. We then investigate the H-bonding structure of ice with different thickness on various hydrophobic/hydrophilic surfaces and explore how the water-solid surface interaction influence the detailed H-bonding network of ice and the growth processes. We will also focus on the characterization of the metastable or intermediate structures at the ice edges using the non-invasive AFM imaging method, so as to visualize the ice growth mechanism in atomic detail. This project will not only provide insight into how the surface mediates the structure and growth mechanism of ice, but may also open up a new avenue for studying the intrinsic structure and dynamics of weakly bonded systems with atomic precision.

界面冰的研究牵扯到物理化学、大气科学、低温生物学、人工降雨、表面防覆冰、低温细胞及功能器官保存等从基础到应用诸多领域。通过调控材料界面的晶格结构、表面电荷、亲疏水性，都可以选择性的促进或者抑制冰核的形成和生长。但是，如何从原子/分子尺度上认识和理解界面调控冰的氢键拓扑结构和微观生长过程一直是该领域的关键科学问题之一。本项目将发展基于qPlus的非接触式原子力显微术（NC-AFM）的非侵扰式成像，通过探测针尖-样品之间高阶静电相互作用力将冰表面上不同电性的氧原子和氢原子在实空间区分开来，实现氢原子的精确定位和氢键网络构型的识别。在原子尺度上研究不同亲疏水表面上单层冰到多层及体相绝缘冰的氢键网络结构演化和生长模式；通过对冰边界的zigzag、armchair及亚稳态氢键构型进行精确表征来解析冰的生长过程，从全新的角度理解界面调控冰形成的微观机制。

表界面上冰的结构和生长研究对于理解冰的成核生长、表面防覆冰以及低温生物学有着重要的意义，但是非常缺乏原子尺度的理解和认识。在本项目中，我们通过调控针尖尖端电荷状态，探测带电针尖与样品之间微弱的高阶静电相互作用，实现基于qPlus型原子力显微镜的非侵扰式成像，能够识别水氢键网络中氢的位置和OH取向。利用该技术，我们实现了低维冰的原子级成像，发现双层六角冰非常坚固，即使在非平整和非六角对称的Au衬底上依然可以稳定存在，是一种本征的二维冰。我们对该二维冰进行了高密度的氢离子掺杂，发现水合氢离子和水分子会自组装形成二维氢键网络；并且在多种金属表面（Au(111), Pt(111), Cu(111), Ru(0001)）都存在含有对称氢键构型（Zundel构型）的二维冰，这是一种由核量子效应催生和稳定的全新物态。本项目研究首次在实验上揭示了二维双层六角冰的结构鲁棒性，它与表面的相互作用极小，可以起到超润滑作用，将有助于理解受限环境中水分子的超快传输；通过界面以及离子掺杂调控二维冰表面悬挂键的密度，可以有效抑制或促进冰的成核生长，对于设计和研发防结冰材料具有潜在的应用价值。