Publications (24)52.8 Total impact
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Article: Grain size dependence of surface plasmon enhanced photoluminescence.
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ABSTRACT: Photoluminescence (PL) in the InGaN quantum well based light-emitting diodes (LED) is greatly mediated through the coupling with the Surface Plasmons (SPs) at the interface of the sputtered Ag film. SPs coupled PL is independently tuned through controlling the grain size of the sputtered Ag films. The grain size of ~50 nm exhibits the maximum light extraction efficiency (LEE) at the wavelength of 460 nm. This grain size agrees with the periodic lattice constant of the grating structure in the calculation, where the momentum mismatch between the SPs and the radiative light can be compensated.Optics Express 02/2013; 21(3):3145-3151. · 3.59 Impact Factor -
Article: Drug screening for ALS using patient-specific induced pluripotent stem cells.
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ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a late-onset, fatal disorder in which the motor neurons degenerate. The discovery of new drugs for treating ALS has been hampered by a lack of access to motor neurons from ALS patients and appropriate disease models. We generate motor neurons from induced pluripotent stem cells (iPSCs) from familial ALS patients, who carry mutations in Tar DNA binding protein-43 (TDP-43). ALS patient-specific iPSC-derived motor neurons formed cytosolic aggregates similar to those seen in postmortem tissue from ALS patients and exhibited shorter neurites as seen in a zebrafish model of ALS. The ALS motor neurons were characterized by increased mutant TDP-43 protein in a detergent-insoluble form bound to a spliceosomal factor SNRPB2. Expression array analyses detected small increases in the expression of genes involved in RNA metabolism and decreases in the expression of genes encoding cytoskeletal proteins. We examined four chemical compounds and found that a histone acetyltransferase inhibitor called anacardic acid rescued the abnormal ALS motor neuron phenotype. These findings suggest that motor neurons generated from ALS patient-derived iPSCs may provide a useful tool for elucidating ALS disease pathogenesis and for screening drug candidates.Science translational medicine 08/2012; 4(145):145ra104. · 7.80 Impact Factor -
Article: Diffusion of gold ions and gold particles during photoreduction processes probed by the transient grating method.
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ABSTRACT: The translational diffusion of Au (gold) ions and Au particles during the photoreduction process from AuCl4(-) to metallic Au particles in aqueous ethanol solutions containing poly(N-vinyl-2-pyrrolidone) was investigated by using UV-vis absorption and the laser-induced transient grating (TG) methods. The TG signal of AuCl4(-) solution before photoirradiation was composed of three contributions; the thermal grating, the species grating due to the creation of AuCl2(-), and that due to the depletion of AuCl4(-). Upon photoirradiation, the species grating signal due to AuCl4(-) diminished rapidly and the TG signal due to Au particles appeared within a few minutes and became stronger at a very short time. The subsequent reduction of AuCl2(-) was concomitant with the formation of Au metal particles. The rapid growth of Au(0) atoms into Au particles took place in the short-duration photoirradiation. With the increase of the photoirradiation time, the TG signal was composed of two kinds of Au particle fragments possessing different diffusion coefficients. This is probably due to the pulse-laser induced fragmentation of the larger Au particles. Effects of the polymer on the particle formation were investigated by the concentration dependence of the polymer in the solution. The formation of Au particles by the photoreduction was also compared with that of Pt particles.Journal of Colloid and Interface Science 01/2009; 332(2):373-81. · 3.07 Impact Factor -
Article: Surface plasmon enhanced light emission from semiconductor materials
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ABSTRACT: Surface plasmon (SP) coupling technique was used to enhance light emissions from semiconductor nanocrystals with evaporated metal layers. We found that the SP coupling can increase the internal quantum efficiencies (IQE) of emission from CdSe-based nanocrystals regardless of the initial efficiencies. This suggests that this technique should be much effective for various materials that suffer from low quantum efficiencies. We also obtained 70-fold enhancement of emission from silicon nanocrystals in silicon dioxide. Obtained IQE value is 38physica status solidi (c). 01/2008; 5:2822--2824. -
Article: Diffusion of platinum ions and platinum nanoparticles during photoreduction processes using the transient grating method.
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ABSTRACT: The photoreduction process of PtCl(6)2- to Pt nanoparticles in poly(N-vinyl-2-pyrrolidone) solutions upon UV light irradiation was investigated by monitoring the change in the diffusion coefficient (D). The D values of chemical species during UV irradiation was measured by the laser-induced transient grating (TG) method. The TG signal of the PtCl(6)2- solution before UV irradiation was composed of three kinds of contributions, the thermal grating, the species grating due to the creation of PtCl4(2-), and the species grating due to the depletions of PtCl6(2-). Upon UV irradiation of the solution, the species grating signal due to PtCl6(2-) diminished and then the TG signal of Pt nanoparticles gradually appeared. This result indicates that the gradual clustering of Pt0 atoms into Pt nanoparticles occurs after all PtCl(6)2- ions are photochemically reduced to PtCl(4)2- and subsequently transformed to Pt0 atoms with a short delay. With increasing time of the UV irradiation, the TG signal intensity increased, while D of the Pt nanoparticles did not change. This suggests that the number of Pt nanoparticles increases, but the size of the Pt nanoparticles with the polymer layer is unchanged, in the course of the UV irradiation.Langmuir 11/2006; 22(22):9142-9. · 4.19 Impact Factor -
Article: Surface plasmon enhanced super bright InGaN light emitter
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ABSTRACT: We use surface plasmons to increase the light emission efficiency from InGaN/GaN quantum wells by covering these with thin metallic films. Large luminescence enhancements were measured when silver or aluminum layers are deposited 10 nm above an InGaN light emitting layer, whereas no such enhancements are obtained from gold coated samples. The internal quantum efficiencies of quantum wells before and after metallization were determined from the temperature dependence of the photoluminescence intensity. Our results indicate that the use of surface plasmons will lead to a new class of very bright light emitting diodes, and highly efficient solid-state light sources. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)physica status solidi (c) 04/2005; 2(7):2841 - 2844. -
Article: Surface-plasmon-enhanced light emitters based on InGaN quantum wells.
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ABSTRACT: Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP-QW coupling. Large enhancements of the internal quantum efficiencies (eta(int)) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.Nature Material 10/2004; 3(9):601-5. · 32.84 Impact Factor -
Article: Sub‐microscopic transient lens spectroscopy of InGaN/GaN quantum wells
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ABSTRACT: Transient lens (TL) spectroscopy was developed with sub-micrometer spatial resolution to observe the temporal and special behavior of the nonradiative processes of carrier dynamics in InGaN/GaN quantum wells (QW). We have observed the carrier density dynamics and the thermal dynamics in the TL signals with a nanosecond pulsed laser. We have also observed TL and photoluminescence (PL) signals by using near-field scanning optical microscopy (NSOM), and find that both PL and TL images are correlated and exhibit submicron scale spatial inhomogeneity. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)physica status solidi (b) 10/2003; 240(2):368 - 371. · 1.32 Impact Factor -
Article: Transient radical diffusion in photoinduced hydrogen abstraction reactions of benzophenone probed by the transient grating method
04/2002; -
Article: Diffusion process of methyl red in organic solvents studied by the transient grating method
04/2002; -
Article: Microscopic Patterning on the Polysilane Films by the Laser Induced Grating Technique
Molecular Crystals and Liquid Crystals. 10/2001; 370(1):379-382. -
Article: Translational Diffusion of Ion Radicals Created by Electron Transfer in Charged Micellar Solutions Probed by the Transient Grating Method and the Taylor Dispersion Method
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ABSTRACT: Diffusion processes of intermediate ion radicals created by the photoexcited electron-transfer reaction of benzoquinone (BQ) and aniline (AN) in sodium dodecyl sulfate (SDS; anionic micelle) and cetyltrimethylammonium bromide (CTAB; cationic micelle) solutions were studied by using the transient grating (TG) and Taylar dispersion (TD) methods. The diffusion coefficients (D) of the anion radical of BQ (BQ•-) in SDS and the cation radical of AN (AN•+) in CTAB are similar to D of those radicals in neat water, while D of AN•+ in SDS and D of BQ•- in CTAB are smaller than D in neat water and more close to D of the self-diffusion of the micelles of SDS and CTAB. This fact suggests that most of the ion radicals exist in the bulk phase by the electric repulsion when the ion radicals have the same charge as the micellar surface. On the other hand, when the ion radicals have an opposite charge to that of the micellar surface, they are trapped on the surface and diffuse with the micelles. In any case, the parent molecules (BQ and AN) predominantly exist in the micelles. A diffusion model, which takes into account of the equilibrium between the micellar surface and bulk phase, can reproduce the observed micellar concentration dependence of D and the equilibrium constants of the transient radicals are determined.06/2001; -
Article: Time-resolved fluorescence spectroscopy of dopamine in single cells
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ABSTRACT: Dopamine hydrochloric acid salt in aqueous solution was excited at 266 nm Al 2 O 3 :Ti laser and the sufficient fluorescence emission peaking at 330 nm was detected with a streak camera. The fluorescence decay curve was fitted by 1-exponentional functions, with the lifetime of approximately 0.80 ns. The influence of deep-UV laser excitation on cells is also discussed for the direct observation of dopamine in the living cells. In addition, it is needed to detect the dopamine fluorescence in the living cell sensitively, and separately from emission of other fluorescent species. When instrumental arrangement and time-resolved spectral analysis can make it possible to solve such problems, direct visualization of the secretion process of individual cells will be achieved by the laser-induced native fluorescence imaging microscopy, without using any additional fluorescent probes. This quantitative imaging technique will provide a useful noninvasive approach for the study of dynamic cellular changes and the understanding of the molecular mechanisms of information transporting processes.01/2001; -
Article: Comments on “Diffusion of Free Radicals in Solution. TEMPO, Diphenylpicrylhydrazyl, and Nitrosodisulfonate”
07/1997; -
Article: Diffusion Process of the Benzyl Radical Created by Photodissociation Probed by the Transient Grating Method
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ABSTRACT: Translational diffusion processes of the benzyl radical (BR) created by the photodissociation from dibenzyl ketone (DBK) were studied by using the transient grating (TG) method in organic solvents (hexane, cyclohexane, ethanol, and 2-propanol). The values of the diffusion constants (D) of BR, DBK, and carbon monoxide (CO) and the rates for the self-termination reaction of BR in these solvents are accurately determined from the TG signals. The ratios of D of BR to that of DBK are independent of the solvent, and they are close to 1.25, which is expected from the ratio of the molecular volume of BR to that of DBK. This result is contrary to those of radicals created by the photoinduced hydrogen abstraction reaction, which show anomalously slow diffusions. A possible origin of this difference is discussed by comparison of the spin densities, dipole moments, and polarizabilities of BR and the radicals produced by hydrogen abstraction.07/1997; -
Article: High-Efficiency InGaN/GaN Light Emitters Based on Nanophotonics and Plasmonics
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ABSTRACT: We report novel methods to enhance light emission efficiencies from InGaN/GaN quantum wells (QWs) based on nanophotonics and plasmonics. First, the nanoscopic optical properties were observed and characterized based on the carrier localization and the quantum confinement Stark effect depending on the In composition of InGaN. Based on the results, we proposed that the emission efficiencies should be improved by making nanostructures, and showed actual enhancement of photoluminescence (PL) intensities by using fabricated random nanodisk and arrayed nanopillar structures. Moreover, surface plasmon (SP) coupling technique was used to enhance blue and green light emissions from InGaN/GaN QWs. We obtained a 14-fold increase in the PL intensity along with a 7-fold increase in the internal quantum efficiency (IQE) of light emission from InGaN/GaN when nanostructured Ag layers were deposited 10 nm above the QWs. The possible enhancement mechanism was discussed and reproduced by using the 3-D finite-difference time-domain simulations. Electron-hole pairs in InGaN QWs couple to electron oscillations at the metal surface and produce SPs instead of photons or phonons. This new path increases the spontaneous emission rate and the IQEs. The SP-emitter coupling technique would lead to superbright and high-speed solid-state light-emitting devices that offer realistic alternatives to conventional fluorescent light sources. -
Article: Direct observation of the nonradiative recombination processes in InGaN-based LEDs probed by the third-order nonlinear spectroscopy
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ABSTRACT: Nonradiative dynamics of the carriers and/or excitons created by the photoexcitation in InGaN-based light emitting diodes (LEDs) with blue (460nm, 470nm), green (510nm, 540nm), and amber (600nm) emissions were observed by using the transient grating (TG) method which is one of the third-order nonlinear spectroscopy. The dynamics of carries and/or exciton diffusion and dynamics of heat energy released by the nonradiative recombination were observed by the time profile of the TG signals in picosecond and nanosecond time region, respectively. The diffusion coefficients and the temperature change by the heat generation were detected for several LEDs and potted against the peak wavelengths of emission (In composition in active layers). Those results were compared with the results of the time-resolved photoluminescence (PL) spectroscopy. Dependence of In composition on the radiative and nonradiative recombination lifetimes, the luminescence intensities, the internal quantum efficiencies, the heat generation and conduction processes, and the diffusion coefficients of excitons and/or careers were interpreted by the model in terms of the fluctuation and phase separation of In composition. -
Article: Surface plasmon enhanced InGaN light emitter
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ABSTRACT: We report a dramatic increase in the photoluminescence (PL) emitted from InGaN/GaN quantum wells (QW), obtained by covering these sample surface with thin metallic films. Remarkable enhancements of PL peak intensities were obtained from In 0.3 Ga 0.7 N QWs with 50 nm thick silver and aluminum coating with 10 nm GaN spacer. These PL enhancements can be attributed to strong interaction between QWs and surface plasmons (SPs). No such enhancements were obtained from samples coated with gold, as its well-known plasmon resonance occurs only at longer wavelengths. We also showed that QW-SP coupling increase the internal quantum efficiencies by measuring the temperature dependence of PL intensities. QW-SP coupling is a very promising method for developing the super bright light emitting diodes (LEDs). Moreover, we found that the metal nano-structure is very important facto to decide the light extraction. A possible mechanism of QW-SP coupling and emission enhancement has been developed, and high-speed and efficient light emission is predicted for optically as well as electrically pumped light emitters. -
Article: Surface plasmon enhanced bright light emission from InGaN/GaN
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Article: Molecular Dynamics in Solution Probed by the Transient Grating Method With a Nanosecond Pulsed Laser
Top co-authors
Top Journals
Institutions
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2006–2009
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Nara Women's University
- Faculty of Human Life and Environment
Nara-shi, Nara, Japan
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2003–2005
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California Institute of Technology
- Department of Electrical Engineering
Pasadena, CA, USA
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2001
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Kyoto University
- Department of Electronic Science and Engineering
Kyoto, Kyoto-fu, Japan
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