A Quantitative Structural Investigation of the 0.1 wt % Nb-SrTiO₃(001)/H₂O Interface

Surface X-ray diffraction has been employed to elucidate the structure of the interface between a well-characterized (001) surface of 0.1 wt % Nb-SrTiO₃ and liquid H₂O. Results are reported for the clean surface, the surface in contact with a drop of liquid water, and the surface after the water droplet has been removed with a flow of nitrogen. The investigation revealed that the clean surface, prepared via annealing in 1 × 10^-2 mbar O₂ partial pressure, is unreconstructed and rough on a short length scale. The surface is covered with large terraces, the topmost layer of which is either TiO₂ or SrO with an area ratio of about 7/3. For the surface in contact with water, our results reveal that associative H₂O adsorption is favored for the TiO₂-terminated terrace whereas adsorption is dissociative for the SrO-terminated terrace, which validates recent first-principles calculations. After removal of the water droplet, the surface largely resembles the water-covered surface but now with a disordered overlayer of water present on the surface.