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35 results on '"Toyooka, Takehiro"'

13. Photoinduced circular anisotropy in a photochromicW-shaped-molecule-doped polymeric liquid crystal film

Author

Choi, Suk-Won, primary, Ha, N. Y., additional, Shiromo, Kazuaki, additional, Rao, Nandiraju V. S., additional, Paul, Manoj Kr., additional, Toyooka, Takehiro, additional, Nishimura, Suzushi, additional, Wu, J. W., additional, Park, Byoungchoo, additional, Takanishi, Yoichi, additional, Ishikawa, Ken, additional, and Takezoe, Hideo, additional

Published
2006
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18. Lasing characteristics of a dye-doped nematic liquid crystal layer sandwiched by two polymeric cholesteric liquid crystals

Author

Song, Myoung Hoon, primary, Park, Byoungchoo, additional, Shin, Ki-Chul, additional, Ohta, Takashi, additional, Tsunoda, Yuko, additional, Hoshi, Hajime, additional, Takanishi, Yoichi, additional, Ishikawa, Ken, additional, Watanabe, Junji, additional, Nishimura, Suzushi, additional, Toyooka, Takehiro, additional, Zhu, Zhengguo, additional, Swager, Timothy M., additional, and Takezoe, Hideo, additional

Published
2004
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24. Structural and Electrochemical Characterizations on Li2MnO3-LiCoO2-LiCrO2 System as Positive Electrode Materials for Rechargeable Lithium Batteries.

Author

Yabuuchi, Naoaki, Yamamoto, Kazuyo, Yoshii, Kazuhiro, Nakai, Izumi, Nishizawa, Takeshi, Omaru, Atsuo, Toyooka, Takehiro, and Komaba, Shinichi

Subjects
MANGANESE oxides, CRYSTAL structure, ELECTRIC discharges, CHROMIUM ions, OXYGEN
Abstract

Cobalt and chromium substituted lithium-excess manganese oxides, Li[Li0.2CoxCr0.4.xMn0.4]O2 (x = 0, 0.2, and 0.4), are synthesized by a simple combustion method. Crystal structures of the samples are examined by an X-ray diffraction (XRD) method. The samples crystallize into a rhombohedral layered phase with in-plane cation ordering between lithium and transition metal ions. Li[Li0.2Co0.2Cr0.2Mn0.4]O2 can deliver more than 200 mAh g-1 of discharge capacity above 3.0 V vs. Li at a rate of 10 mA g-l. Discharge capacity further increases to 300 mAh g-1 when the Li cell is discharged to t.5 V with appearance of a voltage plateau at 1.7 V. A combined study of synchrotron XRD and X-ray absorption spectroscopy (XAS) reveals that originally trivalent chromium ions are oxidized to hexavalent state, resulting in the migration of chromium ions into face-shared tetrahedral sites in lithium layers. Although a part of hexavalent chromium ions are immobilized at the tetrahedral sites, the reduction process to 1.5 V allows the chromium ions to migrate to octahedral sites associated with the reduction process to trivalent state. The chromium substitution bas a beneficial effect on stabilization of oxide ion framework structures of the lithium-excess manganese system by suppressing oxygen loss upon charge to a high voltage region, leading to good cyclability as electrode materials. [ABSTRACT FROM AUTHOR]

Published
2013
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25. Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles.

Author

Won Hoe Koo, Soon Moon Jeong, Araoka, Fumito, Ishikawa, Ken, Nishimura, Suzushi, Toyooka, Takehiro, and Takezoe, Hideo

Subjects
LIGHT emitting diodes, REFRACTIVE index, TIN compounds, INDIUM compounds, WAVELENGTHS
Abstract

Most of the light in conventional organic light-emitting diodes is confined to high-refractive-index layers (such as an organic medium, indium tin oxide and glass substrate) resulting in a low light extraction efficiency of ∼20% (refs 1,2). Many studies have used wavelength-scale periodic gratings to increase the external efficiency of organic light-emitting diodes. However, the efficiency is only enhanced at particular wavelengths satisfying the Bragg condition. Here, we demonstrate that a quasi-periodic buckling structure with broad distribution and directional randomness can enhance the light extraction efficiency without introducing spectral changes and directionality. Organic light-emitting diodes corrugated by buckles showed improved current and power efficiencies and an electroluminescence spectrum enhanced by at least a factor of two across the entire visible wavelength regime. These buckling patterns are formed spontaneously on elastic materials with a thin metallic film. The buckled organic light-emitting diode devices are practical and attractive for use in fabricating full colour and white organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

Published
2010
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27. Structural and Electrochemical Characterizations on Li2MnO3-LiCoO2-LiCrO2 System as Positive Electrode Materials for Rechargeable Lithium Batteries

Author

Yabuuchi, Naoaki, Yamamoto, Kazuyo, Yoshii, Kazuhiro, Nakai, Izumi, Nishizawa, Takeshi, Omaru, Atsuo, Toyooka, Takehiro, and Komaba, Shinichi

Abstract

Cobalt and chromium substituted lithium-excess manganese oxides, Li[Li0.2CoxCr0.4-xMn0.4]O2 (x = 0, 0.2, and 0.4), are synthesized by a simple combustion method. Crystal structures of the samples are examined by an X-ray diffraction (XRD) method. The samples crystallize into a rhombohedral layered phase with in-plane cation ordering between lithium and transition metal ions. Li[Li0.2Co0.2Cr0.2Mn0.4]O2 can deliver more than 200 mAh g[?]1 of discharge capacity above 3.0 V vs. Li at a rate of 10 mA g[?]1. Discharge capacity further increases to 300 mAh g[?]1 when the Li cell is discharged to 1.5 V with appearance of a voltage plateau at 1.7 V. A combined study of synchrotron XRD and X-ray absorption spectroscopy (XAS) reveals that originally trivalent chromium ions are oxidized to hexavalent state, resulting in the migration of chromium ions into face-shared tetrahedral sites in lithium layers. Although a part of hexavalent chromium ions are immobilized at the tetrahedral sites, the reduction process to 1.5 V allows the chromium ions to migrate to octahedral sites associated with the reduction process to trivalent state. The chromium substitution has a beneficial effect on stabilization of oxide ion framework structures of the lithium-excess manganese system by suppressing oxygen loss upon charge to a high voltage region, leading to good cyclability as electrode materials.

Published
2013

31. Structural and Electrochemical Characterizations on Li2MnO3-LiCoO2-LiCrO2System as Positive Electrode Materials for Rechargeable Lithium Batteries

Author

Yabuuchi, Naoaki, Yamamoto, Kazuyo, Yoshii, Kazuhiro, Nakai, Izumi, Nishizawa, Takeshi, Omaru, Atsuo, Toyooka, Takehiro, and Komaba, Shinichi

Abstract

Cobalt and chromium substituted lithium-excess manganese oxides, Li[Li0.2CoxCr0.4-xMn0.4]O2(x= 0, 0.2, and 0.4), are synthesized by a simple combustion method. Crystal structures of the samples are examined by an X-ray diffraction (XRD) method. The samples crystallize into a rhombohedral layered phase with in-plane cation ordering between lithium and transition metal ions. Li[Li0.2Co0.2Cr0.2Mn0.4]O2can deliver more than 200 mAh g−1of discharge capacity above 3.0 V vs. Li at a rate of 10 mA g−1. Discharge capacity further increases to 300 mAh g−1when the Li cell is discharged to 1.5 V with appearance of a voltage plateau at 1.7 V. A combined study of synchrotron XRD and X-ray absorption spectroscopy (XAS) reveals that originally trivalent chromium ions are oxidized to hexavalent state, resulting in the migration of chromium ions into face-shared tetrahedral sites in lithium layers. Although a part of hexavalent chromium ions are immobilized at the tetrahedral sites, the reduction process to 1.5 V allows the chromium ions to migrate to octahedral sites associated with the reduction process to trivalent state. The chromium substitution has a beneficial effect on stabilization of oxide ion framework structures of the lithium-excess manganese system by suppressing oxygen loss upon charge to a high voltage region, leading to good cyclability as electrode materials.

Published
2013
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32. Determination of Twist Elastic Constant K22in 5CB by Four Independent Light-Scattering Techniques

Author

Toyooka, Takehiro, Chen, Guo-ping, Takezoe, Hideo, and Fukuda, Atsuo

Abstract

The twist elastic constant K22in 5CB was determined as a function of temperature by the following four independent methods; (1) electric field static light scattering, (2) electric field dynamic light scattering, (3) angular dependence of the scattered light intensity combined with a K11or K33measurement, and (4) Frederiks transition detected by forced Rayleigh scattering. The first one is a measurement of relative scattered light intensity as a function of the applied voltage in a proper optical geometry, and was used to determine K22for the first time. Each measurement gave a K22value within an accuracy of ±4%. The collected values that were determined by the four methods were located within ±7% from each other. It was also confirmed that they agree with other recent measurements.

Published
1987
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33. Determination of Twist Elastic Constant K22by Forced Rayleigh Scattering

Author

Takezoe, Hideo, Toyooka, Takehiro, Hirakata, Jun-ichi, and Fukuda, Atsuo

Abstract

A novel method for determining the twist elastic constant K22is proposed. A critical magnetic field strength due to a Frederiks transition was detected by utilizing the anisotropy of diffusion constants of a dye by means of forced Rayleigh scattering technique. Measurements were made for 5CB and were compared with those made by other methods. It was found that the obtained values are comparable with those from other recent measurements.

Published
1987
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34. Accurate Determination of K1/?splay, K2/?twistand K3/?bendin Nematic Liquid Crystalsby Using Photon Correlation Spectroscopy

Author

Hirakata, Jun-ichi, Chen, Guo-ping, Toyooka, Takehiro, Kawamoto, Shunji, Takezoe, Hideo, and Fukuda, Atsuo

Abstract

A system based on photon correlation spectroscopy has been constructed using a microcomputer to measure the spectral width of Rayleigh light scattered from nematic liquid crystals. Maps in the (?, ?, ?=0° ) space have been devised to find the most suitable scatterinu geometries for the determination of K1/?splay, K2/?twistand K3/?bend, where ?, ? and ? specify the scattering angle and the director direction. The ratios have been obtained as a function of TNI-Tfor 4'-alkyl-4-cyanobiphenyls (n=5?8).

Published
1986
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35. Photoinduced circular anisotropy in a photochromic W-shaped-molecule-doped polymeric liquid crystal film.

Author

Choi SW, Ha NY, Shiromo K, Rao NV, Paul MK, Toyooka T, Nishimura S, Wu JW, Park B, Takanishi Y, Ishikawa K, and Takezoe H

Abstract

Photoinduced circular anisotropy has been demonstrated in thin films of a main-chain polymeric liquid crystal (PLC) system doped with photochromic W-shaped molecules containing two azobenzene groups by irradiating with circularly polarized light (CPL). Reversible photoinduced circular dichroism (CD) was observed with sign relevant to the handedness of the CPL. The experimentally observed CD spectra were analyzed using the DeVoe polarizability model associated with the coupled oscillator method. We also propose a mechanism for the photoinduced circular anisotropy in our system; nucleating the W-shaped molecules with preferential twisted conformation by CPL irradiation, and triggering the local formation of a chiral structure in the W-shaped-molecule-doped main-chain PLC medium.

Published
2006
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