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Journal Articles

Restoration of oxygen vacancies on an anatase TiO $_{2}$ (001) surface with supersonic seeded oxygen molecular beam

Katsube, Daiki*; Ono, Shinya*; Inami, Eiichi*; Yoshigoe, Akitaka; Abe, Masayuki*

Vacuum and Surface Science, 65(11), p.526 - 530, 2022/11

https://doi.org/10.1380/vss.65.526

The oxidation of oxygen vacancies at the surface of anatase TiO $_{2}$ (001) was investigated by synchrotron radiation photoelectron spectroscopy and supersonic O $_{2}$ beam (SSMB). The oxygen vacancies at the top surface and subsurface could be eliminated by the supply of hyperthermal oxygen molecules. Oxygen vacancies are present on the surface of anatase TiO $_{2}$ (001) when it is untreated before transfer to a vacuum chamber. These vacancies, which are stable in the ambient condition, could also be effectively eliminated by using oxygen SSMB. This result is promising as a surface processing for various functional oxides.

Journal Articles

Oxidation of anatase TiO $_{2}$ (001) surface using supersonic seeded oxygen molecular beam

Katsube, Daiki*; Ono, Shinya*; Takayanagi, Shuhei*; Ojima, Shoki*; Maeda, Motoyasu*; Origuchi, Naoki*; Ogawa, Arata*; Ikeda, Natsuki*; Aoyagi, Yoshihide*; Kabutoya, Yuito*; et al.

Langmuir, 37(42), p.12313 - 12317, 2021/10

https://doi.org/10.1021/acs.langmuir.1c01752

Times Cited Count：1 Percentile：6.77(Chemistry, Multidisciplinary)

We investigated the oxidation of oxygen vacancies at the surface of anatase TiO $_{2}$ (001) using supersonic seeded molecular beam (SSMB) of oxygen. The oxygen vacancies at the top-surface and sub-surface could be eliminated by the supply of oxygen using an SSMB. These results indicate that the interstitial vacancies can be mostly assigned to oxygen vacancies, which can be effectively eliminated by using an oxygen SSMB. Oxygen vacancies are present on the surface of anatase TiO $_{2}$ (001) when it is untreated before transfer to a vacuum chamber. These vacancies, which are stable in the as-grown condition, could also be effectively eliminated using the oxygen SSMB.

Journal Articles

Fabrication and characterization of C-doped anatase TiO $_{2}$ photocatalysts

Choi, Y.; Umebayashi, Tsutomu; Yoshikawa, Masahito

Journal of Materials Science, 39(5), p.1837 - 1839, 2004/03

https://doi.org/10.1023/B:JMSC.0000016198.73153.31

Times Cited Count：227 Percentile：97.87(Materials Science, Multidisciplinary)

Carbon (C)-doped anatase TiO $_{2}$ photocatalysts have been prepared by the oxidative annealing of TiC powders at 623 K for 50-100 hrs. From XRD and XPS analysis, it is clear that C is incorporated into O site of the TiO $_{2}$ lattice. Diffuse reflectance spectroscopy (DRS) showed that the optical absorption edge of the C-doped anatase TiO $_{2}$ shifted to lower energy compared with that of pure anatase TiO $_{2}$ . The decomposition of methylene blue (MB) adsorbed on the C-doped sample was observed under a visible light range of 420-500 nm. We conclude that substitution of C for O in the TiO $_{2}$ leads to a photocatalytic decomposition of MB under visible light irradiation.

Journal Articles

Nanoparticle formation by pulsed laser ablation of TiO $_{2}$

Yamaki, Tetsuya; Ito, Hisayoshi; Matsubara, Masakazu*; Abe, Hiroaki*; Asai, Keisuke*

Transactions of the Materials Research Society of Japan, 28(3), p.879 - 882, 2003/10

Titanium oxide nanoparticles were formed by pulsed laser ablation of a TiO $_{2}$ rutile pellet with a KrF excimer laser ( = 248 nm). The ablation was performed in atmospheres of Ar and O $_{2}$ at total pressures ranging from 0.2 and 10 Torr. At a higher pressure than 1 Torr, Ti in the nanoparticles had an oxidation state of 4+ to form TiO $_{2}$ . According to the X-ray diffraction analyses, the nanopartiles were found to contain both the anatase and rutile phases, which crystallized through extremely energetic, non-equilibrium reactions in an ablation plume. In contrast, at pressures of 0.2 and 0.5 Torr, the nanoparticles were composed of dominant TiO $_{2}$ with a small amount of a less oxidized phase such as Ti $_{2}$ O $_{3}$ . The important result is that the XRD patterns of the samples prepared at 1 and 5 Torr showed the different anatase-to-rutile ratio of the peak intensities. This indicates that the weight fraction of the rutile/anatase crystalline phases can be controlled by the ambient gas pressure.

Journal Articles

In-situ observation of oxidation of Ti(0001) surface by real-time photoelectron spectroscopy using synchrotron radiation

Takakuwa, Yuji*; Ishizuka, Shinji*; Yoshigoe, Akitaka; Teraoka, Yuden; Mizuno, Yoshiyuki*; Tonda, Hideki*; Homma, Teiichi*

Hyomen Kagaku, 24(8), p.500 - 508, 2003/08

https://doi.org/10.1380/jsssj.24.500

Temperature dependence of the initial oxidation kinetics of Ti(0001) surface was investigated by low energy electron diffraction (LEED) and real-time photoelectron spectroscopy. The LEED observation revealed that the oxide layers grew epitaxially. From the oxygen uptake curve, it was clarified that oxigen diffusion was significantly enhanced by surface temperature and the oxide layers thickness reached to 7 nm at 400 $^{circ}$ C. From Ti-2p photoelectron spectroscopy, TiO $_{2}$ was predominant at the subsurface while TiO and Ti $_{2}$ O $_{3}$ components were also observed at the interface.

Journal Articles

Preparation of TiO $_{2}$ nanoparticles by pulsed laser ablation; Ambient pressure dependence of crystallization

Matsubara, Masakazu*; Yamaki, Tetsuya; Ito, Hisayoshi; Abe, Hiroaki*; Asai, Keisuke*

Japanese Journal of Applied Physics, Part 2, 42(5A), p.L479 - L481, 2003/05

Pulsed laser ablation with a KrF excimer laser was used to prepare fine particles of titanium dioxide (TiO $_{2}$ ). The ablation in an atmosphere of Ar and O $_{2}$ (5:5) at total pressures of 1 Torr led to the formation of TiO $_{2}$ nanoparticles composed of anatase and rutile structures without any suboxides. The weight fraction of the rutile/anatase crystalline phases was controlled by the pressure of the Ar/O $_{2}$ gas. The TiO $_{2}$ nanoparticles had a spherical shape and their size, ranging from 10 and 14 nm, also appeared to be dependent on the ambient pressure.

Journal Articles

Fluorine-doping in titanium dioxide by ion implantation technique

Yamaki, Tetsuya; Umebayashi, Tsutomu; Sumita, Taishi*; Yamamoto, Shunya; Maekawa, Masaki; Kawasuso, Atsuo; Ito, Hisayoshi

Nuclear Instruments and Methods in Physics Research B, 206(1-4), p.254 - 258, 2003/05

https://doi.org/10.1016/S0168-583X(03)00735-3

Times Cited Count：136 Percentile：98.91(Instruments & Instrumentation)

Single crystalline titanium dioxide (TiO $_{2}$ ) rutile were implanted with 200keV F $^{+}$ at a nominal fluence of 110 $^{16}$ to 110 $^{17}$ ions cm $^{-2}$ and then thermally annealed in air up to 1200 $^{circ}C$ for 5h. The radiation damage and its recovery during the subsequent annealing were analyzed by Rutherford backscattering spectrometry in channeling geometry and variable-energy positron annihilation spectroscopy. The lattice disorder was completely annealed at 1200 $^{circ}C$ by the diffusion of point defects to the surface acting as a sink. According to the secondary ion mass spectrometry, the F depth profile was shifted to a shallower region along with the damage recovery, finally producing an F-doped layer where the impurity concentration increased steadily towards the surface. The F doping proved to provide a small modification to the conduction-band edge of TiO $_{2}$ , as assessed by theoretical band calculations.

Journal Articles

Visible light-induced degradation of methylene blue on S-doped TiO $_{2}$

Umebayashi, Tsutomu; Yamaki, Tetsuya; Tanaka, Shigeru; Asai, Keisuke*

Chemistry Letters, 32(4), p.330 - 331, 2003/04

https://doi.org/10.1246/cl.2003.330

Times Cited Count：501 Percentile：99.17(Chemistry, Multidisciplinary)

A sulfur (S)-doped titanium dioxide (TiO $_{2}$ ) photocatalyst was synthesized by oxidative annealing of titanium disulfide (TiS $_{2}$ ). TiS $_{2}$ turned into anatase TiO $_{2}$ when annealed in air. The residual S atoms occupied O-atom sites in the TiO $_{2}$ to form Ti-S bonds. The S doping caused the absorption edge of TiO $_{2}$ to be shifted into the lower energy region. Consequently, methylene blue adsorbed on the S-doped TiO $_{2}$ was photocatalytic decomposed by visible light irradiation.

Journal Articles

High-quality epitaxial TiO $_{2}$ thin films grown on -Al $_{2}$ O $_{3}$ substrates by pulsed laser deposition

Shinohara, Ryuji*; Yamaki, Tetsuya; Yamamoto, Shunya; Ito, Hisayoshi; Asai, Keisuke*

Journal of Materials Science Letters, 21(12), p.967 - 969, 2002/06

https://doi.org/10.1023/A:1016090110315

Times Cited Count：9 Percentile：36.89(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Characterization of TiO $_{2}$ -doped Li $_{2}$ TiO $_{3}$

Tsuchiya, Kunihiko; Kawamura, Hiroshi

Fusion Technology, 39(2-Part2), p.624 - 627, 2001/03

no abstracts in English

Journal Articles

Formation of TiO $_{2-x}$ F $_{x}$ compounds in fluorine-implanted TiO $_{2}$

Yamaki, Tetsuya; Sumita, Taishi; Yamamoto, Shunya

Journal of Materials Science Letters, 21(1), p.33 - 35, 2001/01

https://doi.org/10.1023/A:1014282225859

Times Cited Count：89 Percentile：91.01(Materials Science, Multidisciplinary)

We showed the effects of 200 keV F $^{+}$ implantation in TiO $_{2}$ rutile single crystals followed by the thermal annealing. The isochronal annealing at 573 and 873 K for 5 h for each step led to the formation of an F-doped TiO $_{2}$ phase, along with the recovery of the radiation damage and the simultaneous impurity diffusion. This phase was identified to be a TiO $_{2-x}$ F $_{x}$ compound with x = 0.0039 in the outmost region as determined by X-ray photoelectron spectroscopy (probably the first few atomic layers). The fluorination of TiO $_{2}$ leads to interesting characteristics and opens avenues towards photoelectronic films with various applications. In addition, our method enabled dopants to be introduced in a controlled manner at specific locations to realize impurity concentration gradients in TiO $_{2}$ .

Journal Articles