Atomic scale identification of the terminating structure of compound materials by CAICISS (coaxial impact collision ion scattering spectroscopy)

Photoinduced Surface Reactions on TiO2 and SrTiO3 Films: Photocatalytic Oxidation and Photoinduced Hydrophilicity

“…[21][22][23] It is also reported that the SrTiO 3 surface is composed of Ti-O, and no Sr 2+ ions are exposed. 24,25 However, it should be noted that the crystal structure of SrTiO 3 is neither rutile nor anatase, but is perovskite which contains only corner-sharing TiO 6 octahedra, not edge-shared octahedra.Both TiO 2 and SrTiO 3 polycrystalline films were prepared on SiO 2 -coated glass plates, by a spin-coating method and using commercial alkoxide solutions [NDH-510C (Nihon Soda, Ltd.) for TiO 2 and DSRT150 (GELEST, Inc.) for SrTiO 3 , respectively], followed by a calcination at 500 °C for 30 min in air. Such coating steps were repeated twice, yielding thin films of ∼350 nm.…”

“…[21][22][23] It is also reported that the SrTiO 3 surface is composed of Ti-O, and no Sr 2+ ions are exposed. 24,25 However, it should be noted that the crystal structure of SrTiO 3 is neither rutile nor anatase, but is perovskite which contains only corner-sharing TiO 6 octahedra, not edge-shared octahedra.…”

“…On SrTiO 3 surfaces, the topmost atomic layer is mostly composed of Ti-O, and no Sr 2+ ions are exposed after annealing in air 24 or etching in HF solution. 25 It is reported that oxygen vacancies on SrTiO 3 surfaces can be created by Ar + ion sputtering [34][35][36] when the material is heated under ultrahigh vacuum. 36 However, our recent results on X-ray photoelectron spectroscopy for Ti 2p after Ar + bombardment suggest that defect sites on TiO 2 are created much more easily than SrTiO 3 .…”

“…From the discovery of photoinduced water splitting on titanium dioxide (TiO 2 ) electrodes in 1972, TiO 2 has attracted many researchers due to its potential usage in industry. , The strong oxidation power of the photogenerated holes, the chemical inertness, and nontoxicity of TiO 2 have made it a superior photocatalyst and thus it has been extensively studied first in powder form and then in film form. − In recent years, environmental cleanup has become one of the most active topics in photocatalysis. − Conversely, we have found that the UV illumination of TiO 2 produces a highly hydrophilic surface, exhibiting a water contact angle of zero degree. , On the basis of investigations with friction force microscopy (FFM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), we have suggested that these hydrophilic surfaces are caused by a surface structural change on TiO 2 , the production of surface oxygen vacancies, leading to preferential adsorption of water. − Here we compare photoinduced processes proceeding on TiO 2 and strontium titanate (SrTiO 3 ) films. Like TiO 2 , SrTiO 3 is known as an efficient photocatalyst for the production of gaseous hydrogen from water and for the decomposition of various organic compounds. − Moreover the electronic structure of SrTiO 3 resembles that of TiO 2 , i.e., the valence and conduction bands of these metal oxides consist mainly of O-2p-like orbitals and Ti-3d-like orbitals, respectively, with band gaps of about 3 eV. − It is also reported that the SrTiO 3 surface is composed of Ti−O, and no Sr 2+ ions are exposed. , However, it should be noted that the crystal structure of SrTiO 3 is neither rutile nor anatase, but is perovskite which contains only corner-sharing TiO 6 octahedra, not edge-shared octahedra.…”

“…On SrTiO 3 surfaces, the topmost atomic layer is mostly composed of Ti−O, and no Sr 2+ ions are exposed after annealing in air 24 or etching in HF solution . It is reported that oxygen vacancies on SrTiO 3 surfaces can be created by Ar + ion sputtering 34-36 when the material is heated under ultrahigh vacuum .…”