Papers by Author: Masayuki Nogami

Abstract: A family of TeO₂-based glasses is known to have high third-order nonlinear properties and expected as nonlinear optical devices. In the present study, we fabricated Ag₂O-TeO₂ and Ag₂O-Nb₂O₅-TeO₂ glasses, and estimated their structures and linear/nonlinear optical properties. The main results showed that the absorption-edge of the glasses was shifted to longer wavelength side with increasing Ag₂O content. By Raman spectroscopy, it was found that an increase in Ag₂O content promoted to change TeO₄ to TeO₃/TeO₃₊₁ units. X-ray photoelectron spectroscopy (XPS) revealed the presence of an electronic state of Ag²⁺ ions, which was supposed to have a large influence on the absorption-edge wavelength. In Ag₂O-Nb₂O₅-TeO₂ glass system, the third-order nonlinear susceptibility χ⁽³⁾ increased with increasing Ag₂O content at the expense of Nb₂O₅ content.

Abstract: Solid-state potentiometric thin film hydrogen gas sensors were successfully fabricated using a sol-gel-derived high proton-conducting P2O5-SiO2 glass films. Manganese oxide thin film coated on an indium tin oxide (ITO)-coated glass substrate was used for reference electrode. The sensor exhibited high speed responsibility within 10 s and 120 s at 30 oC and -30oC, respectively, for 1 vol.% hydrogen gas. A linear relationship between the electromotive force (EMF) and the logarithmic hydrogen concentration of 0.1~1 vol.% was obtained in the temperature ranging from -30 to 30 oC. The sensing mechanism was also discussed to improve the sensitivity and sensing speed against low H2 concentration at low temperatures.

Abstract: As an alternative to a solid-state electrolyte for proton exchange membrane fuel cells (PEMFCs), ordered mesoporous membranes (OMMs) were prepared using a sol-gel technique, followed by a deep-UV irradiation. Structure and impedance spectroscopy analyses revealed that the porous architecture and proton conductivity of OMMs were influenced by the nature of the substrates. Compared with hydrophilic substrate, hydrophobic substrate was beneficial to an accessible porous architecture in the interface layer and an increase of proton conductivity of the whole membrane. The proton conductivity of the OMMs was up to 10-3 S cm-1.

Abstract: Surface-enhanced Raman scattering (SERS) integrates high levels of sensitivity with spectroscopic precision and thus has tremendous potential for chemical and biomolecular sensing. The key to the wider application of Raman spectroscopy using roughened metallic surfaces is the development of highly enhancing substrates for analytical purposes, i.e., for better detection sensitivity of tracing contaminants and pollutants. Controlled methods for preparing nano-structured metals may provide more useful correlations between surface structure and signal enhancement. Here, we self-assembled silver nanorods on glass substrates for sensitive SERS substrates. The enhanced surface Raman scattering signals were observed and mainly attributed to the local field enhancement.

Abstract: A new type of porous composite with a porous framework was prepared using a mixture of hydroxyapatite whiskers (W-HA) and poly(L-lactic acid) short fibers (F-PLLA) by a particle-leaching technique. The material, composed of a porous framework with interconnecting pore of >1 µm, has large-sized pores of about 200 µm. The large-sized pores were formed by leaching sucrose granules. The porosity can be controlled in the range from 60 to 85 % by the sucrose content. The small-sized pores in the framework formed due to the poor densification of the W-HAs / F-PLLAs mixture. The pore distribution in the framework can be controlled by the compressing pressure without change in the distribution of large-sized pores.

Abstract: Silicon is one of the essential ions with a stimulating effect on bone formation. β- tricalcium phosphate ceramic (β-TCP) with a modified surface containing silica was prepared in order to accelerate the bone formation. Sintered β-TCP pellets were spin-coated with a prehydrolyzed silica sol, and subsequently laser-irradiated using CO2 laser at the power of 6.5W. Scanning electron microscopy attached with X-ray energy dispersive spectrometry (SEM-EDS) showed that the silica was doped into the β-TCP surface. The silicon ion was released into a trisbuffer solution at pH 7.4 at 37 oC during one week of soaking.

Abstract: When fine-sized 45ZnO·55P2O5 glass powders were mixed with water, hydration immediately occurred, resulting in the formation of a viscous hydrogel. 31P MAS-NMR spectra showed that the hydrogel contains orthophosphates and long polyphosphates. 45ZnO·55P2O5 glass-derived hydrogel (45ZP gel) showed high conductivities of 9.9 mS/cm at 30 °C. The conductivities were related to the proton amount in the hydrogel. The electric double-layer capacitor (EDC) cell for the 45ZP gel showed no oxidation-reduction processes in the range of 0~1 V and the specific capacities of 2.40 F/g. The possibility as an EDC electrolyte may be related to the conductivities of the hydrogels.

Abstract: Gold nanoparticles were prepared by NaBH4 reduction method, and homogeneous SiO2 were coated on gold nanoparticles and assembled into densely-packed 3-dimensional arrays by the layer-by-layer self-assembly (LBL) technique. Every layer of films exhibited densely packed 2-dimensional arrays of Au@SiO2 composite nanoparticles and the film thickness was controllable through the number of deposition cycles. These multilayer films exhibited high volume fraction of gold nanoparticles (0.047). The imaginary part of the third-order nonlinear optical susceptibility (Imχ(3)) with different deposition layer have been investigated by femtosecond pump and probe spectroscopy. The Imχ(3) value is about (-8.7±3.3)×10-11 esu and almost not dependent with the layer numbers which indicates every layer of our films has the same structural and optical properties.

Abstract: By overcoming less excitation efficiency of rare-earth ions due to small oscillator strength (∼10-6) of f-f transition, Eu3+ ions were intentionally introduced to nano-sized semiconductor of tin oxide (SnO2) in silica (SiO2)
matrix via a sol-gel route. As a consequence, the excitation energy was significantly absorbed by the nano-sized SnO2 with controlled band-gap energy owing to quantum size effect (QSE) and subsequently transferred from nano-sized SnO2 to the Eu3+ ions doped, resulting in the enhancement of Eu3+ red emission (external quantum efficiency : 75.6 %).

Abstract: Recently, the increase in production, consumption causes the shortage of the natural resources and the increase in waste disposal. In order to build up a sustainable society, the input and the output of the natural system should be reduced by the recirculation of materials and energy. We have tried to develop high performance building materials by solidification technology at low temperature. The starting materials were the inorganic wastes or soil. These solidified inorganic waste and solidifying soil have good mechanical strength for paving tile. Solidifying soil called as Tataki works has good performance of mitigating urban heat islands. Numerical simulation method based on heat transfer model was studied to estimate performance of mitigating urban heat islands of solidifying soil. Numerical model was calculated by the surface temperature changes in the outside with air temperature changes. Simulation result was compared with experimental measurement.