Structure and Dynamics of Water Confined at the SiO₂/WS₂ Interface

The WS₂/SiO₂ interface is of interest to a variety of research communities due to the electronic properties of WS₂ and the ubiquity of SiO₂ as a dielectric substrate. Due to the hydrophilic nature of silanol groups on the surface of SiO₂, water is difficult to remove at the surface, leading to confined water between WS₂ and SiO₂. Understanding the properties of confined water is important both fundamentally and for their effects on the interfacing materials. We investigated the structure and dynamics of confined water between WS₂ and SiO₂ using density functional theory and ab initio molecular dynamics, comparing it to adsorbed water on the surfaces of WS₂ and SiO₂. The results show that confined water becomes increasingly structured, with its orientation influenced by hydrogen bonding to the silanol groups as well as by the partial reorientation of water molecules to face WS₂ in an H-up configuration. The presence of silanol groups disrupts the hydrogen bonding network of water at monolayer coverage for both confined and unconfined water. For all interfaces explored, changes in both structural and dynamic properties are dependent on the number of water layers present.