Water Chain Formation on TiO2(110).

The adsorption of water on a reduced rutile TiO2(110)-(1×1) surface has been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM measurements show that at a temperature of 50 K, an isolated water monomer adsorbs on top of a Ti(5f) atom on the Ti row in agreement with earlier studies. As the coverage increases, water molecules start to form one-dimensional chain structures along the Ti row direction. Supporting DFT calculations show that the formation of an H-bonded one-dimensional water chain is energetically favorable compared to monomer adsorption. In the chain, there are H-bonds between adjacent water molecules, and the water molecules also form H-bonds to neighboring bridging oxygens of TiO2(110). Thermal annealing at T = 190 K leads to the formation of longer chains facilitated by the diffusion of water on the surface. The results provide insight into the nature of the hydrogen bonding in the initial stage of wetting of TiO2.