Water        growth on metals and oxides: binding, dissociation and role of hydroxyl groups

M. Salmeron; H. Bluhm; M. Tatarkhanov; G. Ketteler; T. K. Shimizu; A. Mugarza; Xingyi Deng; T. Herranz; S. Yamamoto; A. Nilsson

doi:10.1039/B806516K

Water growth on metals and oxides: binding, dissociation and role of hydroxyl groups

M. Salmeron,^ab H. Bluhm,^a M. Tatarkhanov,^ac G. Ketteler,^a T. K. Shimizu,†^a A. Mugarza,‡*^a Xingyi Deng,^a T. Herranz,^a S. Yamamoto^d and A. Nilsson^d

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* Corresponding authors

^a Lawrence Berkeley National Laboratory, Berkeley, CA, USA

^b Materials Science and Engineering Department, University of California, Berkeley, CA, USA

^c Physics Department, University of California, Berkeley, CA, USA

^d Stanford Synchrotron Radiation Laboratory, SLAC, 2575 Sand Hill Road, Menlo Park, CA, USA

Abstract

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.

This article is part of the themed collection: Water - From Interfaces to the Bulk

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Water growth on metals and oxides: binding, dissociation and role of hydroxyl groups

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