表/界面水的扫描探针技术研究进展

表面和界面水在自然界、人们的日常生活以及现代科技中无处不在.它在物理、化学、环境学、材料学、生物学、地质学等诸多基础学科和应用领域起到至关重要的作用.因此,表面和界面水的功能与特性的研究,是水基础科学的一项核心任务.然而,由于水分子之间氢键相互作用的复杂性,及其与水-固界面相互作用的竞争,使得表(界)面水对于局域环境的影响非常敏感,往往需要深入到分子层次研究其微观结构和动力学过程.近年来,新型扫描探针技术的发展使得人们可以在单分子甚至亚分子尺度上对表(界)面水展开细致的实空间研究.本文着重介绍几种代表性的扫描探针技术及其在表(界)面水体系中的应用,包括:超高真空扫描隧道显微术、单分子振动谱技术、电化学扫描隧道显微术和非接触式原子力显微术.此外,本文还将对表(界)面水扫描探针技术研究面临的挑战和未来发展方向进行了展望.

Recent advances in probing surface/interfacial water by scanning probe microscopy

Surface and interfacial water is ubiquitous in nature and modern technology.It plays vital roles in an extremely wide range of basic and applied fields including physics,chemistry,environmental science,material science,biology,geology, etc.Therefore,the studies of surface/interfacial water lies at the heart of water science.When water molecules are brought into contact with various materials,a variety of phenomena can show up,such as wetting,corrosion,lubrication, nanofluidics,ice nucleation,to name just a few.Due to the complexity of hydrogen-bonding interactions between water molecules and the competition between water-water interaction and water-solid interaction,surface/interfacial water is very sensitive to local environment,which makes it necessary to study the structure and dynamics of water at the molecular level.In recent years,the development of new scanning probe techniques allows detailed real-space research on surface/interfacial water at single-molecule or even submolecular scale.In Section 2,several representative scanning probe techniques and their applications in surface/interfacial water are reviewed.The first one is ultra-high vacuum scanning tunneling microscopy,which allows molecular imaging of single water molecules,water clusters,wetting layers,and even water multilayers on metal surfaces as well as ultrathin insulating films.Based on scanning tunneling microscopy,the single-molecule vibrational spectroscopy can be further developed to probe the vibration and movement of individual water molecules,which assist us in understanding water diffusion,dissociation and quantum nature of hydrogen bonds.As a versatile tool at liquid/solid interfaces,electrochemical scanning tunneling microscopy opens up the unique possibility of probing the double electric layer and identifying water dynamics during electrochemical reactions. Moreover,non-contact atomic force microscopy yields higher resolution than scanning tunneling microscopy,such that the topology of hydrogen-bonding skeleton of surface/interfacial water and even the degree of freedom of hydrogen atoms can be discerned.To conclude this review,the challenges and future directions of this field are discussed in Section 3, focusing on non-invasive imaging under ambient conditions,ultrafast molecular dynamics,and novel structures under high pressures.