Abstract
The rutile TiO2(011) surface exhibits a (2 × 1) reconstruction when prepared by standard techniques in ultrahigh vacuum (UHV). Here we report that a restructuring occurs upon exposing the surface to liquid water at room temperature. The experiment was performed in a dedicated UHV system, equipped for direct and clean transfer of samples between UHV and liquid environment. After exposure to liquid water, an overlayer with a (2 × 1) symmetry was observed containing two dissociated water molecules per unit cell. The two OH groups yield an apparent “c(2 × 1)” symmetry in scanning tunneling microscopy (STM) images. On the basis of STM analysis and density functional theory (DFT) calculations, this overlayer is attributed to dissociated water on top of the unreconstructed (1 × 1) surface. Investigation of possible adsorption structures and analysis of the domain boundaries in this structure provide strong evidence that the original (2 × 1) reconstruction is lifted. Unlike the (2 × 1) reconstruction, the (1 × 1) surface has an appropriate density and symmetry of adsorption sites. The possibility of contaminant-induced restructuring was excluded based on X-ray photoelectron spectroscopy (XPS) and low-energy He+ ion scattering (LEIS) measurements.
Highlights
Many technologically important processes take place at the interface between solid and aqueous solutions
We report on the interfacial structure between the less-investigated (011) surface of TiO2 rutile and liquid water
The experiments were performed in a ultrahigh vacuum (UHV) chamber with a base pressure of 1 × 10−10 mbar equipped with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), low-energy He+ ion scattering (LEIS), low-energy electron diffraction (LEED), and a separately pumped load lock
Summary
Many technologically important processes take place at the interface between solid and aqueous solutions. The interaction of liquid water with TiO2(110), the predominant rutile surface, has been studied by exposing the surface to humid environment and subsequently characterizing it in ultrahigh vacuum (UHV)[10−12] or directly by STM in liquid.[13,14] Here we report on the interfacial structure between the less-investigated (011) surface of TiO2 rutile and liquid water This surface is the second-lowest energy termination of TiO2 rutile and constitutes a sizable fraction of equilibrium-shape nanoparticles.[15] In addition, a difference in photocatalytic activity of the (011) surface with respect to the (110) has been reported.[16]
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