Faculty Profiles - NAKAHARA Yoshio

Published Papers - NAKAHARA Yoshio

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Ester-free cross-linker molecules for ultraviolet-light-cured polysilsesquioxane gate dielectric layers of organic thin-film transistors

Shuichi Okada, Yoshio Nakahara, Kazuyuki Uno, Ichiro Tanaka

Japanese Journal of Applied Physics ( Japan Society of Applied Physics ) 57 ( 4 ) 2018.04 [Refereed]

Pentacene thin-film transistors (TFTs) were fabricated with ultraviolet-light (UV)-cured polysilsesquioxane (PSQ) gate dielectric layers using cross-linker molecules with or without ester groups. To polymerize PSQ without ester groups, thiol-ene reaction was adopted. The TFTs fabricated with PSQ layers comprising ester-free cross-linkers showed a higher carrier mobility than the TFTs with PSQ layers cross-linked with ester groups, which had large electric dipole moments that limited the carrier mobility. It was demonstrated that the thiol-ene reaction is more suitable than the conventional radical reaction for UV-cured PSQ with small dielectric constant.

Near-Infrared Dye Immobilized in Porous Silica Layer on Gold Nanorod and Its Fluorescence Enhancement by Strengthened Electromagnetic Field Based on Surface Plasmon Resonance

Yoshio Nakahara, Ryoko Takeda, Toshiyuki Tamai, Setsuko Yajima, Keiichi Kimura （Part： Lead author,　Corresponding author )

Plasmonics ( Springer New York LLC ) 13 ( 2 ) 645 - 652 2018.04 [Refereed]

We report immobilizing Nile Blue A, which is a cationic fluorescent dye emitting in the near-infrared region, in the porous silica layer on gold nanorod and its fluorescence enhancement by strengthened electromagnetic field based on surface plasmon resonance. The effect of the spacer corresponding to the silica layer on the metal-enhanced fluorescence effect is also discussed in detail. Hollow silica nanorod was in advance prepared, and then the silica layer was partly etched to increase the porosity for the improvement of the mass transfer. Subsequently, gold nanorod was fabricated in the restricted space of hollow silica nanorod. Finally, Nile Blue A was physically immobilized in the porous silica layer on gold nanorod through electrostatic interactions. The fluorescence enhancement of Nile Blue A based on surface plasmon resonance was semi-quantified by comparative experiments using hollow silica nanorod, which is exactly the same structure except for gold as silica-coated gold nanorod. Since our results demonstrated that the porosity degree of the silica layer significantly affected the fluorescence enhancement of Nile Blue A, it is hopeful that our design concept, distinct from the conventional one, can lay a foundation for further development of near-infrared fluorescence nanomaterials.

Effect of Protective Agents on Silver Nanoparticle Preparation by Vacuum Evaporation on Running Hydrocarbon Solution

Ienaga Takashi, Nakahara Yoshio, Yajima Setsuko, Kimura Keiichi （Part： Corresponding author )

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 18 ( 4 ) 2547 - 2554 2018.04 [Refereed]

Comparison of Physical Adsorption Strength of Protective Agents via Ligand Exchange of Silver Nanoparticles Prepared by Vacuum Evaporation on Running Oil Substrate (vol 90, pg 1251, 2017)

Ienaga Takashi, Okada Soichiro, Nakahara Yoshio, Watanabe Mitsuru, Tamai Toshiyuki, Yajima Setsuko, Kimura Keiichi

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 91 ( 3 ) 506 2018.03 [Refereed]

Comparison of Physical Adsorption Strength of Protective Agents via Ligand Exchange of Silver Nanoparticles Prepared by Vacuum Evaporation on Running Oil Substrate

Takashi Ienaga, Soichiro Okada, Yoshio Nakahara, Mitsuru Watanabe, Toshiyuki Tamai, Setsuko Yajima, Keiichi Kimura （Part： Corresponding author )

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN ( CHEMICAL SOC JAPAN ) 90 ( 11 ) 1251 - 1258 2017.11 [Refereed]

We compared adsorption strength of protective agents via ligand exchange of silver nanoparticles synthesized by the improved vacuum evaporation on running oil substrate (VEROS) method. This comparison concerns physical adsorption of protective agents on the surface of silver nanoparticles instead of chemisorption. Clean surfaces of silver nanoparticles synthesized by the improved VEROS method were suitable for this investigation. All the experiments in this study were designed so that as far as possible protective agents did not ionize. Thus, oleic acid capped silver nanoparticles were synthesized by the improved VEROS method. Next, octanoic acid, n-octylamine and oleic acid were used as additive protective agents in ligand exchanges. The ligand exchange is also closely related to physical adsorption strength of protective agents on the surface of metal nanoparticles. Oleic acid on the surface of silver nanoparticles was exchanged by octanoic acid and vice versa under the same experimental conditions. On the other hand, oleic acid on the silver surface was not exchanged by n-octylamine. These results were remarkably different from those reported in general chemical synthetic methods but they were well consistent with our previous study on performance of protective agents in the synthesis of silver nanoparticles with the improved VEROS method.

Improving the carrier mobility of pentacene thin film transistors by surface flattened polysilsesquioxane gate dielectric layers

Daisuke Michiura, Yoshio Nakahara, Kazuyuki Uno, Ichiro Tanaka

Zairyo/Journal of the Society of Materials Science, Japan ( Society of Materials Science Japan ) 66 ( 9 ) 644 - 647 2017.09 [Refereed]

The surface flatness of photo-curable polysilsesquioxane (PSQ) films for gate dielectric layers of pentacene thin film transistors (TFTs) was considerably improved by ultra-violet light (UV)/O3 treatment
the root-mean-squared (RMS) roughness was improved from 0.35 to 0.23 nm after 40-minute treatment. However, the PSQ surfaces became hydrophilic because hydroxyl groups, which degraded transistor performances, replaced the organic functional groups such as methyl groups by the UV/O3 treatment. Therefore, 1,1,1,3,3,3-hexamethyldisilazane (HMDS) treatment was successively performed after the UV/O3 treatment to replace the hydroxyl groups with hydrophobic silyl groups. It was found that four-hour HMDS treatment under dry nitrogen was enough to reduce off current of pentacene TFTs. As a result, the carrier mobility of the pentacene TFT fabricated with UV/O3 and HMDS-treated PSQ layers became 0.59 cm2V-1s-1, which was more than seven times higher than that of the pentacene TFTs with untreated PSQ layers.

Surface modification of PEN and PET substrates by plasma treatment and layer-by-layer assembly of polyelectrolyte multilayer thin films and their application in electroless deposition

T. Tamai, M. Watanabe, Y. Kobayashi, Y. Nakahara, S. Yajima

RSC ADVANCES ( ROYAL SOC CHEMISTRY ) 7 ( 53 ) 33155 - 33161 2017 [Refereed]

The surfaces of the polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) substrates were modified by plasma treatment and then layer-by-layer (LbL) assembly of polyelectrolyte multilayer thin films from two oppositely charged polyelectrolytes. Negatively or positively charged palladium complex ions bound to oppositely charged multilayer surfaces and were reduced to form palladium nanoparticles and then a nickel film was electrolessly deposited on the substrate surfaces. The multilayers on PEN and PET substrate surfaces are suitable for supporting palladium nanoparticle catalysts and their properties can be controlled by the conditions of LbL assembly.

Improving the carrier mobility of pentacene thin film transistors by surface treatment of polysilsesquioxane gate dielectric layers

Daisuke Michiura, Yoshio Nakahara, Kazuyuki Uno, Ichiro Tanaka

Zairyo/Journal of the Society of Materials Science, Japan ( Society of Materials Science Japan ) 65 ( 9 ) 652 - 655 2016.09 [Refereed]

We improved the carrier mobility of the pentacene thin film transistors (TFT), which were fabricated with polysilsesquioxane (PSQ) gate dielectric layers, from 0.082 to 0.31 cm2V-1s-1 by treating the PSQ surface with ultra-violet irradiation (UV)/O3 and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). It was found that the PSQ layers were flattened by the UV/O3 treatment, and the PSQ surface became hydrophilic at the same time because the organic functional groups on the PSQ surface were changed to hydroxyl groups. The grains of the pentacene films deposited on the UV/O3-treated PSQ surfaces were found to be as large as a few microns. However, the carrier mobility of the pentacene TFTs was not so much improved as expected from the largely grown pentacene grains probably because the hydroxyl groups scattered the charged carriers. In addition, the off-current of the pentacene TFTs increased by 4 orders of magnitude. It is thus considered that the hydroxyl groups also worked as hopping sites for the increased off-current which flew without the gate voltage. On the other hand, the carrier mobility of the pentacene TFTs fabricated with the PSQ dielectric layers of which surfaces were treated with UV/O3 and HMDS became ∼4 times larger than that without any surface treatment of the PSQ layers, and also the off-current decreased by 3 orders of magnitude because the hydroxyl groups were changed with silyl groups by the HMDS treatment.

Investigation of Ultraviolet Light Curable Polysilsesquioxane Gate Dielectric Layers for Pentacene Thin Film Transistors

Hideto Shibao, Yoshio Nakahara, Kazuyuki Uno, Ichiro Tanaka

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY ( AMER SCIENTIFIC PUBLISHERS ) 16 ( 4 ) 3327 - 3331 2016.04 [Refereed]

Polysilsesquioxane (PSQ) comprising 3-methacryloxypropyl groups was investigated as an ultraviolet (UV)-light curable gate dielectric material for pentacene thin film transistors (TFTs). The surface of UV-light cured PSQ films was smoother than that of thermally cured ones, and the pentacene layers deposited on the UV-light cured PSQ films consisted of larger grains. However, carrier mobility of the TFTs using the UV-light cured PSQ films was lower than that of the TFTs using the thermally cured ones. It was shown that the cross-linker molecules, which were only added to the UV-light cured PSQ films, worked as a major mobility-limiting factor for the TFTs.

High-Mobility 6,13-Bis(triisopropylsilylethynyl) Pentacene Transistors Using Solution-Processed Polysilsesquioxane Gate Dielectric Layers

Yu Matsuda, Yoshio Nakahara, Daisuke Michiura, Kazuyuki Uno, Ichiro Tanaka

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY ( AMER SCIENTIFIC PUBLISHERS ) 16 ( 4 ) 3273 - 3276 2016.04 [Refereed]

Polysilsesquioxane (PSQ) is a low-temperature curable polymer that is compatible with low-cost plastic substrates. We cured PSQ gate dielectric layers by irradiation with ultraviolet light at similar to 60 degrees C, and used them for 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) thin film transistors (TFTs). The fabricated TFTs have shown the maximum and average hole mobility of 1.3 and 0.78 +/- 0.3 cm(2)V(-1)s(-1), which are comparable to those of the previously reported transistors using single-crystalline TIPS-pentacene micro-ribbons for their active layers and thermally oxidized SiO2 for their gate dielectric layers. It is therefore demonstrated that PSQ is a promising polymer gate dielectric material for low-cost organic TFTs.

Evaluation of Stretching Properties of [7]Thiaheterohelicene Framework Called "Molecular Spring" Using AFM Force Measurements and Electrostatic State Calculations

Yoshio Nakahara, Minako Higashi, Ryoto Funayama, Yasuo Horii, Hideji Osuga, Hidefumi Sakamoto, Masato Oda, Shinpei Kado, Keiichi Kimura （Part： Lead author )

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN ( CHEMICAL SOC JAPAN ) 88 ( 4 ) 544 - 550 2015.04 [Refereed]

The stretching properties of a [7]thiaheterohelicene framework, what we call molecular spring, have not been investigated so far, despite a variety of [7]thiaheterohelicene derivatives having very interesting characteristics due to both the rigidity arising from fused benzene rings and the flexibility like a spring originating from helical structure. In this study, a novel [7]thiaheterohelicene derivative, which has a disulfide moiety for bonding to a gold-coated substrate and a carboxy group for reacting with an amino-modified probe tip at each of its end groups, was synthesized in order to elucidate the elasticity of the [7]thiaheterohelicene framework by atomic force microscopy (AFM). The AFM force measurements were carried out using two carboxy-terminated disulfide derivatives with or without a [7]thiaheterohelicene moiety, and the deviation between two kinds of force-extension curves was related to the stretching originating from the [7]thiaheterohelicene framework here. Furthermore, its elasticity was compared to that of biphenyl, which is generally known as a rigid framework, using electrostatic state calculations.

Synthesis of Spherical SiO2@TiO2 Core-Shell Nanoparticles with Anatase-Type Crystallinity and High Aqueous Dispersibility and Their Photocatalytic Properties

Yoshio Nakahara, Masahiro Hayashizaki, Mitsuru Watanabe, Toshiyuki Tamai, Keiichi Kimura （Part： Lead author )

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN ( CHEMICAL SOC JAPAN ) 88 ( 1 ) 133 - 138 2015.01 [Refereed]

Up to date, the development of TiO2 nanoparticles with well-defined morphology, crystallinity, and high solvent dispersibility has been still a big challenge. In this study, monodisperse and spherical SiO2@TiO2 core shell nanoparticles, whose diameter was 20.7 +/- 2.7 nm, with anatase-type crystallinity and high aqueous dispersibility were fabricated by a simple and facile method combing a sol gel reaction using tetrabutyl orthotitanate as a precursor in the presence of colloidal SiO2 nanoparticles and a very mild crystallization process of the TiO2 layer. Transmission electron microscope measurements showed that the size and shape of the obtained core shell nanoparticles were considerably uniform. The anatase crystallinity of the TiO2 layer on the particle surface was endowed by heating at 100 degrees C in the acidic aqueous solution under atmospheric pressure. Also, they maintained high aqueous dispersibility even after the crystallization process. Most importantly, their photocatalytic ability towards methylene blue was comparable to that of commercially available pure TiO2 nanoparticles. The SiO2@TiO2 core shell nanoparticles developed in this study are highly expected to be membranous materials for very thin TiO2 films due to their high aqueous dispersibility and shape homogeneity.

Fluorescent silica nanoparticles modified chemically with terbium complexes as potential bioimaging probes: their fluorescence and colloidal properties in water

Yoshio Nakahara, Yoichi Tatsumi, Ikuko Akimoto, Shusuke Osaki, Motomichi Doi, Keiichi Kimura （Part： Lead author )

NEW JOURNAL OF CHEMISTRY ( ROYAL SOC CHEMISTRY ) 39 ( 2 ) 1452 - 1458 2015 [Refereed]

It generally requires a complicated reaction protocol for the synthesis of silylated fluorescent lanthanide complexes. In this study, a silylated terbium complex was prepared by a very simple procedure through formation of a Schiff base between a terbium complex bearing a formyl group and 3-aminopropyltriethoxysilane. Using the silylated terbium complex, highly fluorescent silica nanoparticles modified chemically with terbium complexes (Tb-SNPs) were efficiently synthesized by a reverse micelle method with Triton X-100 as a surfactant in cyclohexane. The fluorescence properties of Tb-SNPs were remarkably improved by photostability, pH dependence and fluorescence lifetime, compared to free terbium complexes. Also, Tb-SNPs hardly aggregated under aqueous conditions with different salt concentrations and pHs. From these results, it was found that Tb-SNPs are applicable under physiological aqueous conditions. Furthermore, as an application model, Tb-SNPs were used as the fluorescent label for the imaging of African green monkey kidney cells.

Synthesis and Characterization of Silver Nanoparticles by Vacuum Evaporation on Running Hydrocarbon Solution Containing Nonionic Surfactant in Cylindrical Glass Chamber

Takashi Ienaga, Yoshio Nakahara, Keiichi Kimura

CHEMISTRY LETTERS ( CHEMICAL SOC JAPAN ) 43 ( 12 ) 1893 - 1895 2014.12 [Refereed]

A single-molecule force-spectroscopic study on stabilization of G-quadruplex DNA by a telomerase inhibitor

Ryoto Funayama, Yoshio Nakahara, Shinpei Kado, Mutsuo Tanaka, Keiichi Kimura

ANALYST ( ROYAL SOC CHEMISTRY ) 139 ( 16 ) 4037 - 4043 2014.08 [Refereed]

Single-molecule force spectroscopy was carried out using AFM force measurements for the purpose of direct observation of the stabilization of G-quadruplex DNA by a telomerase inhibitor, which is 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin tetrakis(p-toluenesulfonate) (TMPyP). In AFM force measurements, we used an AFM tip and an Au substrate modified chemically with terminal-biotinylated telomere DNA and streptavidin, respectively. The telomere DNA was fully stretched by the AFM tip based on the bridge formation between the AFM tip and the Au substrate through the streptavidin-biotin interaction. The force-extension curves, which reflected the stretching of a single DNA molecule, were distinguished from all of the curves, judging from the rupture force and the contour length. The selected curves were analyzed using a worm-like chain model, and one of the fitting parameters, persistence length (l(p)), was used as an index for the stabilization of the G-quadruplex structure. Consequently, the l(p) value was significantly increased by the addition of TMPyP under the experimental conditions where the G-quadruplex structure could be formed. On the other hand, the value was hardly changed by the addition of TMPyP under the conditions except the above. Furthermore, the methodology developed and demonstrated in this work was applied to evaluate the stabilization of G-quadruplex DNA by other telomerase inhibitors such as ethidium bromide and p-xylene-bis(N-pyridinium bromide).

Single-molecule force spectroscopic study on chiral recognition of cysteine derivatives immobilized on a gold substrate by using AFM tips chemically modified with optically active crown ethers

Yoshio Nakahara, Hitoshi Mitani, Shinpei Kado, Keiichi Kimura （Part： Lead author )

RSC ADVANCES ( ROYAL SOC CHEMISTRY ) 4 ( 101 ) 57850 - 57854 2014 [Refereed]

The chiral recognition of cysteine derivatives immobilized on a gold substrate using atomic force microscopy (AFM) tips chemically modified with optically active crown ethers was quantitatively investigated with single-molecule force spectroscopy (SMFS). Interestingly, the chiral recognition ability of the optically active crown ether-modified tip was entirely opposite to that of its optical isomermodified tip. The difference of rupture forces for the chiral recognition was determined to be about 40 pN under our experimental conditions.

原子間力顕微鏡を用いるカチオン性ポルフィリンによるグアニン四重鎖構造の安定化効果の定量評価

舩山遼斗, 中原佳夫, 門晋平, 田中睦生, 木村恵一

日本分析化学会講演要旨集 ( (公社)日本分析化学会 ) 62年会 65 - 65 2013.08

Synthesis of Silicon Quantum Dots Functionalized Chemically with Monosaccharides and Their Use in Biological Fluorescence Imaging

Yoshio Nakahara, Kazuki Machiya, Toshiyuld Sato, Ni Tar Nwe, Tetsuya Furaike, Hiroshi Tamura, Keiichi Kimura （Part： Lead author )

CHEMISTRY LETTERS ( CHEMICAL SOC JAPAN ) 42 ( 5 ) 498 - 500 2013.05 [Refereed]

Novel water-dispersible, pH-stable, and biocompatible quantum dots were synthesized through the surface modification of silicon quantum dots (SiQDs) with monosaccharides. The presence of the monosaccharide on the surface of the SiQDs was recognized by fluorescence measurements using its complementary lectin (concanavalin A). The fluorescence cell imaging was carried out by using SiQDs functionalized chemically with D-glucosamine, and it was shown that the SiQDs developed in this study are applicable as blue chromophores for biological fluorescence imaging.

Highly selective sensing of hydrophilic anions based on structural-color change of inverse opal hydrogel functionalized with a thiourea group

Shinpei Kado, Haruka Otani, Yoshio Nakahara, Keiichi Kimura

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY ( AMER CHEMICAL SOC ) 245 2013.04 [Refereed]

Highly selective recognition of acetate and bicarbonate by thiourea-functionalised inverse opal hydrogel in aqueous solution

Shinpei Kado, Haruka Otani, Yoshio Nakahara, Keiichi Kimura

CHEMICAL COMMUNICATIONS ( ROYAL SOC CHEMISTRY ) 49 ( 9 ) 886 - 888 2013 [Refereed]

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