Salmeron M, Bluhm H, Tatarkhanov M, Ketteler G, Shimizu T K, Mugarza A, Deng Xingyi, Herranz T, Yamamoto S, Nilsson A
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Faraday Discuss. 2009;141:221-9; discussion 309-46. doi: 10.1039/b806516k.
We discuss the role of the presence of dangling H-bonds from water or from surface hydroxyl species on the wetting behavior of surfaces. Using scanning tunneling and atomic force microscopies and photoelectron spectroscopy, we have examined a variety of surfaces, including mica, oxides and pure metals. We find that in all cases, the availability of free, dangling H-bonds at the surface is crucial for the subsequent growth of wetting water films. In the case of mica, electrostatic forces and H-bonding to surface O atoms determine the water orientation in the first layer and also in subsequent layers with a strong influence in its wetting characteristics. In the case of oxides like TiO2, Cu2O, SiO2 and Al2O3, surface hydroxyls form readily on defects upon exposure to water vapor and help nucleate the subsequent growth of molecular water films. On pure metals, such as Pt, Pd and Ru, the structure of the first water layer and whether or not it exhibits dangling H-bonds is again crucial. Dangling H-bonds are provided by molecules with their plane oriented vertically, or by OH groups formed by the partial dissociation of water. By tying the two H atoms of the water molecules into strong H-bonds with pre-adsorbed O on Ru can also quench the wettability of the surface.
我们讨论了来自水或表面羟基物种的悬垂氢键的存在对表面润湿行为的作用。利用扫描隧道显微镜、原子力显微镜和光电子能谱，我们研究了多种表面，包括云母、氧化物和纯金属。我们发现，在所有情况下，表面自由悬垂氢键的可用性对于随后润湿水膜的生长至关重要。对于云母，静电力以及与表面O原子的氢键作用决定了第一层以及后续层中的水取向，对其润湿特性有很大影响。对于像TiO2、Cu2O、SiO2和Al2O3这样的氧化物，暴露于水蒸气时，表面羟基会在缺陷处迅速形成，并有助于引发分子水膜的后续生长。对于纯金属，如Pt、Pd和Ru，第一层水的结构以及它是否表现出悬垂氢键再次至关重要。悬垂氢键由平面垂直取向的分子提供，或者由水的部分解离形成的OH基团提供。通过将水分子的两个H原子与Ru上预先吸附的O形成强氢键，也可以降低表面的润湿性。
