On the formation of OH ordered layers by dissociation of H2O on an oxygen covered Ag(1 1 0) surface: An STM investigation

We present results of an STM investigation of water interaction with an oxygen covered Ag(1 1 0) on the example of the O(4 × 1) reconstructed surface. In agreement with numerous previous experimental works, using diffraction techniques, we found that a structure of OH(1 × 2) type, displaying rows in the [1 −1 0] direction, is formed. The new features revealed by this local probe study, is the presence of quasi rectangular islands evenly distributed across the terraces, with a density of 0.22 ± 0.03 and a mean area of 90 ± 15 nm2 at 220 K. They are imaged at an apparent height of 0.14 nm. It is remarkable that the same OH row structure is present on the whole terrace “on top” and “in between” the islands. These features are attributed to silver islands of mono-atomic height, formed by clustering of silver ad-atoms released during reaction of the O atoms with the water molecules. These findings point to a more complex behaviour of the reaction dynamics than previously described. They emphasise the key role of the silver ad-atoms, present in the added rows of the initial Ag(1 1 0)-O(4 × 1) surface, in the formation of the nanostructures. In turn it is concluded that the rows evidenced by this STM and previous diffraction studies, are formed by OH chains.