Hydration Structures at Charged Surfaces

在这个项目中，我们的目标是研究应用电位对一系列金属和绝缘体表面的界面水化结构的影响。重点将放在阐明水偶极子在静电场中的排列和对表面的特定结合（例如通过氢键）之间的竞争。此外，当水形成一个扩展的氢键网络时，协同效应也将控制所产生的水化结构。此外，作为施加电位的函数，添加的离子可能会或可能不会集中在界面上。在经典的图像中，一个电双层形成，离子浓度可以根据连续介质理论计算。虽然离子的存在会影响水化结构，但对特定离子在分子尺度上的作用仍缺乏清晰的认识。在这里，我们将开发一种允许在电位控制下进行高分辨率水合层映射的设置。这一发展将建立在该小组现有的改良原子力显微镜的基础上，该显微镜已被证明可以进行三维水合层绘图。在这个项目中，我们将在现有的仪器上增加一个具有电位控制的电化学电池。作为测试新装置的第一个基准，我们将研究去离子水中的惰性金属表面，如金（111）和铂（111），以验证我们的结果与现有的理论计算和实验结果。下一步，我们将受益于原子力显微镜不局限于导电样品这一事实。因此，我们将研究经过充分研究的绝缘体表面，如氟化钙（111）、二氧化硅以及方解石（10.4）。这些研究将允许阐明水分子与表面的特定结合之间的相互作用，例如，通过氢键，以及静电势对分子电偶极子的影响。由于这些样品是透明的，它们是可访问的振动和频率产生光谱。这是非常有用的，因为它可以将水化层映射的空间分辨结构数据与来自和频率产生光谱的平均方向信息进行比较。最后，我们将研究在电位控制下加入离子对水化结构的影响。在这里，我们将系统地研究离子作为离子电荷和离子大小的函数对在外加电位存在下产生的水化结构的影响。因此，该项目将为控制带电界面水化结构形成的驱动力提供详细的见解。

In this project, we aim for investigating the influence of an applied potential on the interfacial hydration structure of a range of metal and insulator surfaces. An emphasis will be on elucidating the competition between the alignment of the water dipole in the electrostatic field and specific binding towards the surface, e.g., via hydrogen bonds. Furthermore, as water forms an extended hydrogen bonded network, also cooperative effects will govern the resulting hydration structure. Moreover, added ions might or might not concentrate at the interface as a function of the applied potential. In the classical picture, an electrical double layer forms, with ion concentrations that can be calculated based on continuum theory. While the presence of the ions will impact the hydration structure, a clear understanding of the effect of specific ions in a molecular-scale picture is still lacking. Here, we will develop a setup that allows for high-resolution hydration layer mapping under potential control. This development will build upon the existing modified atomic force microscopes in the group that have been proven to allow for three-dimensional hydration layer mapping. For this project, we will add an electrochemical cell with potential control to an existing instrument. As a first benchmark for testing the new setup, we will investigate inert metal surfaces such as gold (111) and platinum (111) in de-ionized water, to validate our results against existing theoretical calculations and experimental findings. In a next step, we will benefit from the fact that atomic force microscopy is not limited to electrical conducting samples. Therefore, we will investigate well-studied insulator surfaces such as calcium fluoride (111) and silica as well as calcite (10.4). These studies will allow for elucidating the interplay between specific binding of water molecules to the surface, e.g., via hydrogen bonds, and the impact of the electrostatic potential on the molecule’s electric dipole. Due to the fact that these samples are transparent, they are accessible to vibrational sum frequency generation spectroscopy. This is extremely helpful as it enables the comparison of the spatially resolved structural data from the hydration layer mapping with the averaged information on the orientation from the sum frequency generation spectroscopy. Finally, we will investigate the impact of added ions on the hydration structure under potential control. Here, we will systematically investigate the effect of ions as a function of both ionic charge and ion size on the resulting hydration structure in presence of an applied electric potential. The project will, therefore, provide detailed insights into the driving forces that govern the hydration structure formation at charged interfaces.