Water on anatase TiO$_{2}$(101): a scanning tunneling microscopy study

The discovery of photochemical water splitting on TiO$_{2}$ has motivated numerous studies of water on the surfaces of this important photocatalytic material. Previous temperature-programmed desorption and X-ray photoelectron spectroscopy studies of water on anatase TiO$_{2}$(101), the most stable surface of the photocatalytically efficient anatase form, have revealed that water adsorbs molecularly on the surface in accordance with theoretical predictions.$^{ }$In the present study, we have employed low-temperature scanning tunneling microscopy to study water adsorption on anatase TiO$_{2}$(101). We dose various amounts of water (0.2-1.8 Langmuir) at sample temperature T $\sim $ 130 K. Besides confirming that water favors molecular adsorption, atomically resolved STM images further reveal that water molecules adsorb at Ti$_{5c}$ sites forming preferentially one-dimensional chains with local doubling of the periodicity along the [010] direction. Near room temperature, the water molecules become mobile and hop between the Ti$_{5c}$ sites. Density Functional Theory calculations are under way to clarify the origin of the observed doubling of periodicity.