The interaction mechanism of cesium with water on the SrTiO3(100) surface at room temperature

Abstract

The interaction of water with cesium on the strontium titanate surface SrTiO3(100), was studied, mainly by means of work function measurements and thermal desorption spectroscopy. The catalytic role of cesium with respect to the dissociation of water on surface was investigated, by applying two different adsorption processes at room temperature (RT): (1) The adsorption of water on the cesium covered surface (sequential adsorption), and (2) the co-adsorption process (simultaneous adsorption) on surface. Based on the results and by adopting the Lewis acid–base model, we conclude that during the sequential adsorption the water molecules are mostly adsorbs non-dissociatively on surface, without oxidizing the alkaline overlayer. This seems to be due, first to the strong interaction between the alkaline adatoms and the substrate, and secondly to the limited maximum pre-deposited amount of cesium (≤ 0.45 ML). Instead, water dissociation appears to merely occur on defective sites of the substrate in accordance with previous studies. For a full cesium layer covered surface, the adsorbed water retracts the metallicity of cesium due to electrostatic interactions. In contrast to the sequential adsorption, during the co-adsorption process the oxidation of cesium takes place above a critical coverage of cesium (≥ 0.45 ML). It appears that the co-adsorbed cesium with water modifies the surface potential providing an effective template for cesium oxide, Cs2O development. Based on that, we suggest a catalytic reaction of water dissociation according to the Langmuir–Hinshelwood mechanism. Finally, we propose atomistic adsorption models for both processes of cesium with water adsorption.