Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jphotochem.2021.113659

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

DOI： 10.1021/acsomega.1c05816

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

DOI： 10.1038/s41467-021-24061-4

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Taylor & Francis  

DOI： 10.1080/02678292.2021.1991016

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

DOI： 10.3390/en14217011

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.3390/ma14195491

researchmap

Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acsaem.1c00258

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nature Publishing Group  

DOI： 10.1038/s41598-021-88535-7

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

DOI： 10.1039/D1AN00362C

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

DOI： 10.1016/j.jphotochem.2020.113107

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1080/15421406.2020.1856509

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

DOI： 10.1021/acs.jpcc.0c07609

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

DOI： 10.1063/5.0009312

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

DOI： 10.1039/C9SE01081E

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We prepared crosslinked azotolane liquid-crystalline polymer (LCP) films doped with a stilbene derivative (two-photon chromophore) utilizing an interpenetrating polymer network (IPN) structure. The IPN films bend toward the light source upon irradiation with femtosecond laser pulses at 600nm, which can excite the stilbene derivative by two-photon absorption. The bending speed of the IPN films increases with the square of the laser pulse intensity, which is compelling evidence for the two-photon processes.

DOI： 10.1080/15421406.2018.1466241

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Photo-responsive double emulsions made of liquid crystal (LC) were prepared by a microfluidic device, and the light-induced processes were studied. The phase transition was induced from the center of the topological defect for an emulsion made of (N-(4-methoxybenzylidene)- 4-butylaniline (MBBA), and strange texture change was observed for an emulsion made of 4-cyano-4'- pentylbiphenyl (5CB) doped with azobenzene. The results suggest that there are defect-involved processes in the phase change of LC double emulsions.

DOI： 10.3390/e19120669

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Quantum dots (QDs) provide an attractive alternative sensitizer to organic dyes. However, there have been few reports on QD-sensitized solar cells (QDSCs) that have photovoltaic conversion efficiencies exceeding those of dye-sensitized solar cells. This is because of the lack of fundamental studies of QDs on conventional nanocrystalline metal oxide electrodes which possess much amount of heterogeneity. An important first step is an investigation of the dependences of the optical absorption, the ground state energy level, and the interfacial electron transfer (IET) on the size of QDs deposited on well characterized single crystal oxides. The present study focuses on a system of CdSe QDs adsorbed on the (001), (110), and (111) surfaces of single crystal rutile-TiO2. The optical absorption spectra, characterized using photoacoustic spectroscopy, were found to be independent of the surface orientation concerning the optical absorption edge. The exponential optical absorption tail (Urbach tail) suggests that the disorder decreases with the increasing size of the QDs and is independent of the surface orientation. The ground state energy levels of the QDs were characterized using photoelectron yield spectroscopy. That on the (001) surface shifts upward, while that on the (110) surface shifts downward with increasing QD size. That on the (111) surface is independent of the QD size, indicating the difference of the influence of the surface orientation on adsorption of the QDs. The IET rate constant and the relaxation component were characterized. The JET rate constant was found to decrease as the size of the QDs increases and depends on the surface orientation, indicating the differences in the decrease of the free energy change and lower coupling between the excited state of CdSe QDs and the Ti 3d orbitals in rutile-TiO2. The relaxation component increases with increasing QD size and depends on the surface orientation, correlating with the density of states in the conduction band of rutile-TiO2.

DOI： 10.1021/acs.jpcc.7b09371

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Lead halide perovskites are attracting a great deal of interest for optoelectronic applications such as solar cells, LEDs, and lasers because of their unique properties. In solar cells, heat dissipation by hot carriers results in a major energy loss channel responsible for the Shockley-Queisser efficiency limit. Hot carrier solar cells offer the possibility to overcome this limit and achieve energy conversion efficiency as high as 66% by extracting hot carriers. Therefore, fundamental studies on hot carrier relaxation dynamics in lead halide perovskites are important. Here, we elucidated the hot carrier cooling dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy. We observe that the hot carrier cooling rate in CsPbI3 decreases as the fluence of the pump light increases and the cooling is as slow as a few 10 ps when the photoexcited carrier density is 7 x 10(18) cm(-3), which is attributed to phonon bottleneck for high photoexcited carrier densities. Our findings suggest that CsPbI3 has a potential for hot carrier solar cell applications. Published by AIP Publishing.

DOI： 10.1063/1.4991993

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

It has been believed that the TEMPO redox cannot be used for the dye-sensitized solar cells (DSCs) using a ruthenium dye as a sensitizer. However, we found that the photovoltaic performance of DSCs was gradually improved just by keeping them in dark, and it took more than 3 weeks until the performance was saturated. We identified the reason for it; 2,2,6,6-tetramethylpiperidine (TMP) molecule, which was generated during the aging, prevented the reverse charge transfer. This was caused by the molecular interaction of TMP either with the ruthenium dyes or TEMPO redox or both. We found that the freshly prepared DSCs with a ruthenium dye can give a photovoltaic performance just by adding the piperidine additives. Furthermore, we found that not only heterocyclic amine molecules but also alkylamine molecules which do not include the ring structure show the similar effect. This result will pave the way for a novel interfacial control for the charge transfer. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2017.06.015

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

The effects of various sample parameters for solid-state dye sensitized solar cells were studied with carrier dynamics measurements and electrochemical measurements. Although many parameters and processes have been decided based on the experience of researchers, the chemical and physical reasons for the selections have not been clarified. We studied the effect of the generally utilized materials and processing such as the blocking layer, titanium oxide thickness, surface treatment, and the selection of dyes and hole transfer materials. Based on our findings, we were able to rationally optimize the structure of the solid-state dye sensitized solar cells in terms of cell performance or the lifetime of charge carriers.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society  

Photoexcited carrier dynamics in a hematite film with and without amorphous NiFeOx on the surface was investigated using the heterodyne transient grating method. We found that two different electron/hole dynamics took place in the micro- and millisecond time regions and successfully assigned each component to the decay processes of electrons and holes trapped at surface states, respectively. It was also demonstrated that the amorphous NiFeOx coating plays a crucial role in increasing the survival of the holes at the surface trap states, which was caused by the decrease in the surface recombination rate.

DOI： 10.1021/acsomega.7b00021

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Many types of active matter, such as biological cells, have liquid-crystalline membranes, which are soft and flexible in their interactions with their surroundings and sometimes allow molecular-structural or -orientational changes to extend for long distances, owing to long-range molecular interactions. Despite the technological and fundamental importance of these long-range changes, there is no good physical property with which to express them for the liquid crystal. Here, we show direct measurements of the propagation of structural or orientational changes due to long-range molecular interactions in liquid crystals. We induced a patterned phase transition in a liquid crystal via illumination with a fringe pattern and observed the propagation of the phase-transition region. We determined that the propagation occurred in a ballistic manner with a velocity of 80-110 m/s and that two types of propagation-side-by-side and head-to-tail molecular interactions-were found.

DOI： 10.1038/srep44801

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Long-lived bleach responses with a lifetime of several milliseconds were found for the ruthenium and organic dyes in dye-sensitized solar cells. These responses were caused by the specific interaction between each dye and ionic species in the electrolyte. For the ruthenium and D131 dyes, iodide ions were necessary for the shift, while lithium cations induced it for D149, even though the molecular structure is quite similar for D131 and D149. The bleach peak was caused by the blue shift of the absorption peak even after the regeneration of the dye from the dye cation, which would be induced by the composition/concentration change of the ionic species on the electrolyte side due to the redox reactions or charge compensation. The result was confirmed by the dependence of the transient absorption spectra on the, order from microsecond to millisecond on various anion and cation conditions, dye structures, and redox species. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2016.11.004

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Phase transition dynamics of liquid crystal (LC) was measured by the heterodyne transient grating (HD-TG) method to clarify the difference between the photochemical and photothermal phase transitions. The phase transition was induced by the photo-excitation of different guest dyes doped in the host liquid crystals; azobenzene and solvent red were used as photochemical and photothermal dyes as guest dyes. The photochemical phase transition was partly induced even at much lower temperature than the nematic - isotropic phase transition temperature (T-NI) and the region was gradually increased as the temperature, while photothermal phase transition was induced in the whole area just when reaching T-NI. Furthermore, the anisotropic re-alignment of molecules was observed in the phase recovery process.

DOI： 10.1080/15421406.2016.1277327

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We fabricated the long-term air stable PbSe colloidal quantum dots (CQDs) based planar heterojunction solar cells (FTO/TiO2/PbSe/Au) with relatively larger active area (0.25 cm(2)) using tetrabutylammonium iodide (TBAI, I-) as ligand in solid state ligand-exchange process. For the first time, we have achieved the whole preparation process of the device in the ambient atmosphere from PbSe CQDs collection to PbSe colloidal quantum dot solar cells (CQDSCs) fabrication, then storage and in their following measurements. Especially, TBAI-treated PbSe CQDSCs exhibited a power conversion efficiency (PCE) of 3.53% under AM 1.5 G in air, and also a remarkable long-term stability (more than 90 days) of their storage in ambient atmosphere has been identified. By contrast, 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA) and cetyltrimethylammonium bromide (CTAB, Br-) treated PbSe CQDSCs were further studied. The ligand-dependent exciton dissociation, recombination, energy level shift, and air stability of PbSe CQDs treated with these different ligands were systematically investigated. It was noted that TBAI-treated PbSe CQDSCs exhibited suppressed recombination, faster charge transfer rate, and longer carrier lifetimes, which resulted in a higher PCE and long-term air stability.

DOI： 10.1021/acs.jpcc.6b10920

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Quantum dot sensitized solar cells (QDSSCs) have attracted much interest due to their theoretical efficiency, predicted to be as high as 44%. However, the energy conversion efficiency of QDSSCs is still a lot lower than the theoretical value, one reason for which is the number of surface defects on the QDs. In order to improve the conversion efficiency, surface passivation of the QDs has been applied to QDSSCs. Studying the mechanism of how the surface passivation influences the photoexcited carrier dynamics is very important. In this paper, we clarify the effects of CdS passivation on electron injection, trapping and recombination in CdS passivated PbS QDSSCs (called PbS/CdS double-layered QDSSCs). We found that electron trapping and recombination can be suppressed effectively, and that the electron injection efficiency can be increased significantly by surface passivation with CdS on PbS QDSSCs. Our findings provide a better understanding of the effects of surface passivation on QDSSCs, which will prove beneficial for making further improvements in the photovoltaic properties of QDSSCs. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemphys.2016.03.014

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Photocatalytic reactions include several different steps and routes for photoexcited carriers, and each dynamic is closely related to the reaction efficiency. Although commonly used time-resolved techniques can reveal the kinetics of photoexcited carriers, the reaction pathways are difficult to distinguish due to decay kinetics extending over many temporal orders and various contributions from the carriers and species involved. Herein, we report the distinction of the electron dynamics in the photocatalytic processes of titanium oxide through the combination of the transient grating method and maximum entropy analysis for the estimation of time constants. We were able to confirm three different carrier responses corresponding to an intrinsic recombination, an interfacial transfer or the decay of surface-trapped electrons, and the decay of polarons. Based on the responses, it appears that both gold and platinum work as good electron acceptors, but that only platinum shortened the lifetime of the polaron state due to the acceleration in the adsorption/desorption exchange of ions, which explains the shorter cycles of the photocatalytic reactions for platinum.

DOI： 10.1039/c6cp04016k

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Photocatalytic reactions, typically known as difficult to control due to secondary reactions and involvement of multiple radicals, were demonstrated to be. controlled well by optimizing the reaction time and the microchip design. The glass-milled microchip has a good resistivity for the organic solutions and withstands multiple usage more than 100 times. The oxidization and reduction reactions were demonstrated and the flow considerably improved the conversion and yield. Furthermore, an imine synthesis was demonstrated as a multi-step reaction by combination of photocatalytic oxidation and reduction reactions. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2016.02.020

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Semiconductor quantum dots (QDs) have many desirable characteristics for use as sensitizers, such as enabling tuning of the band gap on the basis of the quantum confinement effect, a higher extinction coefficient, and facilitating charge injection as a result of the large dipole moment. Despite these potential advantages, no major advance in the efficiency of quantum-dot-sensitized solar cells (QDSCs) has yet been reported. The poor efficiency can be attributed to electron-transfer (ET) reactions that compete with the ideal energy generation cycle in QDSCs. Despite the great technological significance, the interfacial ET between QDs and inorganic species remains poorly understood. In this paper, we describe the electronic structure and the interactions between multiple sized CdSe QDs and single crystal rutile TiO2 with (001), (110), and (111) orientations. Single crystal TiO2 is well characterized and is not only ideal for comparing the amount and the structure of the QDs but is also useful for studying ET reactions. The rate of adsorption of CdSe QDs depends on the crystal orientation, although the average increase in diameter of the QDs is independent of the crystal orientation. The highest occupied molecular orbital (HOMO) level is independent of the adsorption time. On the other hand, the value of the HOMO level depends on the crystal orientation of the R-TiO2 substrate. The ET rate constant increases as the change in free energy increases and depends on the crystal orientation. This suggests that the mixing of the wave functions between the conduction band in the R-TiO2 and the lowest unoccupied molecular orbital (LUMO) level in the CdSe QDs depends on the crystal orientation.

DOI： 10.1021/acs.jpcc.5b09528

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

It is crucial for the efficiency of photocatalytic reactions how to separate the photo-excited electrons and holes and how to utilize them at interfaces. There are two main difficulties to make these possible; variations of defects and co-catalysts. Most of the metal oxide photocatalysts have shallow and deep trap states, whose structure is always controversial. It is hard to tell which state helps reaction or not. Various co-catalysts have been applied, but also it is difficult to tell the real effect; charge separation or the surface passivation. Here, we will show the method to distinguish the defect type from the electron dynamics by using the transient grating (TG) method, which has a high sensitivity at the interface. We prepared a film sample by heating a TiO2 paste on a glass substrate. The film was contacted with a reactant solution sandwiched by another glass and a spacer. The TG method is one of the time-resolved techniques, which measures the refractive index change at the interface after shining a pulse excitation light. We could distinguish three different routes for photo-excited electrons; bulk trap (<100 ns), surface trap (1-5 us), Ti trap (0.5 - 10 s). Only the surface trap showed reactivity with reactants on the solution side. Ti trap had a longer lifetime, which was only observed when the photoexcited holes were scavenged. This trap seems to affect the cycle of the photocatalyst. This method offers simultaneous measurements of different trap states, and gives an insight of which defects have an actual reactivity.

DOI： 10.1117/12.2235996

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The molecular interaction sometimes propagates in a collective manner, reaching for a long distance on the order of millimeters. Such interactions have been well known in the field of strongly-correlated electron systems in a beautiful crystal interleaved by donor and acceptor layers, induced by photo-stimulus. The other examples can be found in liquid crystals (LCs), which could be found in many places in nature such as bio-membrane. Different from crystals, LCs features "softness", which enables it to be a curved structure such as a cell. In LCs, even a small molecular change would trigger the overall structural change by the propagation of the molecular interaction. Here we will show, for the first time, how long and how fast the molecular interaction propagates in LCs. The patterned phase transition was induced in a LC, causing the phase transition propagation in a controlled way and the propagation was measured with an time-resolved optical technique, called the transient grating. A LC sample doped with azobenzene was put into a thermally controlled LC cell. A grating pattern of a pulse light with 355 nm was impinged to the LC cell, and the light was absorbed by the dyes, releasing heat or photomechanical motion. We could observe the fringe spacing dependence on the phase transition response, which indicates that phase transition was delayed as the fringe spacing due to the delay by the phase transition propagation. This is the first direct evidence of the molecular interaction propagation of the LC molecules.

DOI： 10.1117/12.2235852

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In this work, the charge transfer and recombination mechanism is uncovered for the PbS/ZnS quantum dot sensitized solar cells (QDSSCs) based on nanoporous TiO2 electrodes. PbS quantum dots (QDs) were in-situ grown on TiO2 nanoparticles through the successive ionic absorption and reaction (SILAR) method, followed by the surface passivation of ZnS for the sensitized electrodes. It was observed that the ZnS coating cycles play a significant role in determining the photovoltaic parameters. The highest power conversion efficiency of 1.4% was achieved by coating 13 cycles of ZnS on TiO2/PbS electrode. It is essential to understand why and how ZnS passivation layers improve the photovoltaic performance of PbS QDSSCs. All obtained solar cells were characterized thoroughly by optical and electrical techniques. The open-circuit voltage decay technique and electrochemical impedance measurements indicated that the ZnS passivation layers significantly suppressed the charge recombination at the TiO2/electrolyte and TiO2/QD interfaces. The transient grating measurements suggested that the electron injection from PbS QDs to TiO2 was obviously enhanced by the ZnS coating layers. This could be attributed to the reduction of carrier trapping and recombination in PbS QDs after surface passivation. These beneficial effects of ZnS layers, therefore, resulted in the improved photovoltaic performances of PbS QDSSCs. This work provides better understanding on the passivation effect of ZnS layers in PbS QDSSCs, which would be beneficial for the further improvement of QDSSCs. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2015.08.035

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Multiple exciton generation (MEG) dynamics in colloidal PbS quantum dots (QDs) characterized with an improved transient grating (TG) technique will be reported. Only one peak soon after optical absorption and a fast decay within 1 ps can be observed in the TG kinetics when the photon energy of the pump light hv is smaller than 2.7E(g) (E-g: band gap between LUMO and HOMO in the QDs), which corresponds to hot carrier cooling. When hv is greater than 2.7E(g), however, after the initial peak, the TG signal decreases first and soon increases, and then a new peak appears at about 2 to 3 ps. The initial peak and the new peak correspond to hot carriers at the higher excited state and MEG at the lowest excited state, respectively. By proposing a theoretical model, we can calculate the hot carrier cooling time constant and MEG occurrence time constant quantitatively. When MEG does not happen for hv smaller than 2.7E(g), hot carrier cools with a time constant of 400 fs. When MEG occurs for by larger than 2.7E(g), hot carrier cools with a time constant as small as 200 fs, while MEG occurs with a time constant of 600 fs. The detailed hot carrier cooling and MEG occurrence dynamics characterized in this work would shed light on the further understanding of MEG mechanism of various type of semiconductor QDs. (C) 2015 Science Press and Dalian Institute of Chemical Physics. All rights reserved.

DOI： 10.1016/j.jechem.2015.11.002

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A blocking effect on the approach of electron acceptors into a dye/TiO2 electrode in a dye-sensitized solar cell was confirmed by the observation of charge dynamics at the interface when an alkyl-functionalized dye was used. It was found that the density of the adsorbed MK-2 on the TiO2 surface affected the ionic motion in an electrolyte at the interface, and that electron electrolyte recombination was suppressed with a high density of adsorbed MK-2 molecules, causing prevention of the approach of the redox ions.

DOI： 10.1246/bcsj.20150090

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

In this study, a photocatalytic plate bound to highly dispersible silica-doped titanium dioxide (SiT) on a trimethoxysilyl-propyldiethylenetriamine (dien)-coated glass plate (dien-plate) was newly synthesized, and was evaluated by a flow analytical (FA) system, which consists of a photocatalytic reactor and a spectrophotometer, to continuously monitor the absorbance of tested chemicals. The method was not required to collect any sample solution at a constant period. The SiT-dien-plate facilitated the photodecomposition of methylene blue (MB) and indigo carmine (InC) in aqueous solutions. Notably, MB was quantitatively photo-decomposed following 18 h of UV-light irradiation, related to the electrostatic adsorption of surface-bound particles. A water-treatment ability of visible-light-responsive vanadium-modified nitrogen/silica co-doped titanium dioxide fixed on the dien-plate was also evaluated by the FA system. It clarified to decompose MB and InC under visible-light irradiation. Finally, the decomposition of a humic substance dissolved from Middle West China peaty soils by the SiT-dien-plate under UV-irradiation was assessed as applying the FA system with a photocatalytic plate.

DOI： 10.2116/analsci.31.15

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

It has been a concern that the cobalt redox cannot give a good performance for the dye-sensitized solar cells when it is used with ruthenium dyes. The electron dynamics measurements clarified the electron loss processes, and clarified the cause. The result indicated the direct interaction between the ruthenium dyes with the cobalt redox, and it reduced the charge injection from the triplet state of the dyes to the titanium oxide, and also it increased the electron recombination process with the cobalt redox species. Both the problems of injection and recombination were solved by using the ruthenium dye with alkyl chains keeping a distance between the dye and the cobalt redox.

DOI： 10.1039/c4cp05981f

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We studied the photo-induced dynamics in a LC polymer film including azobenzene by using a time-resolved and a microscopic technique. The film was confined in a liquid crystal cell, while it is a photomobile film under a free standing condition, which is triggered by the photoisomerization of azobenezene. From the result of the time-resolved measurements, the change inside the film induced by UV irradiation was highly anisotropic polarization change. Microscopic observation revealed that the film was consisted of ordered and disordered region with a patched structure, and the UV induced change was travelled in the ordered region on the order of seconds.

DOI： 10.1117/12.2186414

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The interest in organometal trihalide perovskite (CH3NH3PbI3)-based solid-state hybrid solar cells has increased in recent years due to the high efficiencies achieved, with a record of over 20%, and the simple low temperature preparation method. Further improvements in the photovoltaic performance can be obtained by increasing the light harvesting in the NIR region up to 1000 nm. Recently, successful energy harvesting up to a wavelength of 1060 nm using Sn/Pb cocktail halide based perovskite materials has been achieved. However, the energy conversion efficiency of such solar cells (less than 10%) is much lower than that of CH3NH3PbI3 based solar cells, which is due to their lower open circuit voltage (V-oc) and fill factor (FF). In order to improve this, we need to have a good understanding of the key factors governing the photovoltaic performance of these solar cells, i.e., the optical absorption, the charge separation and the recombination dynamics. Therefore, for this study, we characterized the optical absorption properties, including the bandgap and the Urbach energy, clarified the photoexcited carrier recombination dynamics in Sn/Pb cocktail perovskite (CH3NH3Sn0.5Pb0.5I3) and the charge separation and recombination dynamics at each interface in TiO2/Sn/Pb perovskite/P3HT solar cells, and lastly investigated the relationships between these and the photovoltaic performance.

DOI： 10.1039/c5ta01246e

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Photocatalytic organic reactions were performed using automatic photocatalytic microreactor, where several open-end capillaries with photocatalytic materials coated inside were just soaked in a test tube including a reactant solution. Organic reactions of the alkyl radicals generated from carboxylic acids due to the photo-Kolbe reaction was studied, in analogy with the reactions using a photosensitizer. This methodology features the reusability of the reactor and an easy process for analysis due to easy separation of the reactant solution.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Two analytical methods for the evaluation of photocatalytic oxidation and reduction abilities were developed using a photocatalytic microreactor; one is product analysis and the other is reaction rate analysis. Two simple organic conversion reactions were selected for the oxidation and reduction. Since the reactions were one-to-one conversions from the reactant species to the product species, the product analysis was simply performed using gas chromatography, and the reactions were monitored in situ in the photocatalytic microreactor using the UV absorption spectra. The partial oxidation and reduction abilities for each functional group can be judged from the yield and selectivity, and the corresponding reaction rate, while the total oxidation ability can be judged from the conversion. We demonstrated the application of these methods for several kinds of visible light photocatalysts.

DOI： 10.1039/c3an02167j

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We studied the effect of the ratio between the monomer and cross-linker molecules in the azobenene included liquid crystal polymer films by using the heterodyne transient grating (HD-TG) technique, which is one of the time-resolved measurement techniques. Depending on the ratio, the magnitude of the refractive index change, its anisotropy, and the lifetime of the cis isomer of azobenzene, generated by a UV pulse irradiation. By increasing the cross-linker ratio, the refractive index change and its anisotropy was reduced, indicating less ability for the motion, while slower lifetime was observed by increasing the monomer ratio, indicating that the film is difficult to return the original shape by a visible-light irradiation. The obtained dynamics was consistent with the functionality of the films.

DOI： 10.1117/12.2059740

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

In recent years, organometal halide perovskite-based solid-state hybrid solar cells have attracted unexpected increasing interest because of their high efficiency (the record power conversion efficiency has been reported to be over 15%) and low fabrication cost. It has been accepted that the high efficiency was mainly attributed to the strong optical absorption (absorption coefficient: 15 000 cm(-1) at 550 nm) over a broader range (up to 800 nm) and the long lifetimes of photoexcited charge carriers (in the order of 10 ns - a few 100 ns) of the perovskite absorbers. However, much of the fundamental photophysical properties of perovskite relating to the high photovoltaic performance are remained to be investigated. The charge separation and recombination processes at the material interfaces are particularly important for solar cell performances. To better understand the high efficiency of perovskite solar cells, we systematically investigated the charge separation (electron and hole injection) and charge recombination dynamics of CH3NH3PbClI2 hybrid solar cells employing TiO2 nanostructures as the electron transfer material (ETM) and spiro-OMeTAD as the hole transfer material (HTM). The measurements were carried out using transient absorption (TA) techniques on a time scale from sub-picoseconds to milliseconds. We clarified the timescales of electron injection, hole injection, and recombination processes in TiO2/CH3NH3PbClI2/spiro-OMeTAD solar cells. Charge separation and collection efficiency of the perovskite-based solar cells were discussed. In addition, the effect of TiO2 size on the charge separation and recombination dynamics was also investigated. It was found that all TiO2-based perovskite solar cells possessed similar charge separation processes, but quite different recombination dynamics. Our results indicate that charge recombination was crucial to the performance of the perovskite solar cells, which could be effectively suppressed through optimising nanostructured TiO2 films and surface passivation, thus pushing these cells to even higher efficiency.

DOI： 10.1039/c4cp03073g

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The charge dynamics in the double-layered quantum dot sensitized solar cell (QDSSC) was studied to clarify the reason why the cell performance was much improved by a double-layer coating, by using the heterodyne transient grating (HD-TG) and transient absorption methods, based on a previous study for a conventional QDSSC (N. Maeda et al., Phys. Chem. Chem. Phys., 2013, 15, 11006.) In the double-layered QDSSC, the layer order of CdS and CdSe affected the cell performance. When CdS is in between TiO2 and CdSe, the conversion efficiency was enhanced by 70%, while it was lowered by 50% in the opposite order. From the information on charge dynamics, it was found that electrons were efficiently injected to TiO2 by appropriate band alignment of CdS and CdSe, while only a part of the electrons were transferred to the TiO2 when the layer order was opposite. Furthermore, the reverse electron transfer does not matter for the conversion efficiency, because the process increased even for the appropriate layer order.

DOI： 10.1039/c3cp55177f

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The performance of dye-sensitized solar cells (DSSCs) with an electrolyte including mixed cations was evaluated, and the relevant carrier dynamics were investigated by the heterodyne transient grating method. The performance of the DSSCs showed maximum conversion efficiency for an Li+ cation ratio of 75% with 25% other cations.

DOI： 10.1039/c4ra02309a

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

By using the depth selective imaging method, we studied the UV induced change in a photomobile liquid crystalline polymer film. With 1 mu m depth resolution, each slice inside the film was selectively observed. A network-like structure mixed with the ordered and disordered regions of molecules in the middle of the film, and a rubbed polymer layer at the bottom of the film were observed. In each slice of the film, the phase change induced by UV light was observed strongly dependent on the director direction, which indicates the ordering change of the liquid crystalline molecules in the director direction. It took several tens of seconds for the ordering change caused by the collaborative interaction between the molecules. Furthermore, it was suggested that the UV induced change travelled from the bottom layer to the middle layer on the micron order.

DOI： 10.1039/c4cp04602a

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The dynamic motion of ions in electrolyte solutions and its effect on recombination was investigated by the heterodyne transient grating method in addition to transient absorption and transient photocurrent methods in dye sensitized solar cells. Realignment of ionic species at the electrode/electrolyte interface was observed after the electron injection in TiO2 on the order of ms. The process was affected by the total quantity of ionic species as well as cation species in the electrolyte. The recombination processes of the electrons were also affected by the constituents; the probability of the electron-electrolyte recombination decreased with decrease in I-2 concentration; the dominant recombination process changed from the electron-electrolyte to the electron-dye recombination by decreasing I- concentration. It is concluded that sufficient I- is necessary for the suppression of the electron-dye recombination and that sufficient I-2 is necessary for an efficient redox cycle, while low concentration of I-3(-) ions at the electrolyte/TiO2 interface is preferable to suppress the electron-electrolyte recombination. The effect of the cation size in an electrolyte solution on the charge dynamics was also investigated, and it was revealed that the steric hindrance of cations changed the penetration of ionic species into the nanoporous dye/TiO2 electrode, causing a change in the electrostatic properties at the interface. The cation dependence indicated that the presence of large-sized cations suppressed the electron-electrolyte recombination by disturbing the approach of I-3(-) paired with the cations.

DOI： 10.1039/c3cp53964d

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Molecular dynamics of 4-methoxybenzylidene-4-n-butylaniline (MBBA) in a liquid crystal cell after the perturbation of a UV pulse was observed using the polarization dependent heterodyne transient grating (HD-TG) method. The response of a refractive index change showed different signs depending on the probe polarization, and each response was composed of 4 exponential components. These components were assigned to disordering, 2 types of ordering, and molecular diffusion, judged from the sign of the refractive index change and the dependence on the grating spacing and the pump intensity. The time constants for the disordering and the ordering processes drastically increased for the pump intensity above 0.10 mJ/pulse. To explain the threshold, we proposed that disordering/ordering of domains were observed for the higher pump intensities, while an individual molecule is subject to disordering/ordering for the lower pump intensity. (c) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2013.05.016

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The charge separation and charge recombination dynamics in P3HT-ZnO and P3HT-dye-ZnO bulk heterojunction organic-inorganic hybrid solar cells (OIHSCs) prepared by a one-pot method were studied using a transient absorption (TA) method, both for optical absorption of P3HT in the visible region and for optical absorption of SQ36 in the NIR region. In the case of P3HT-ZnO, the charge separation was very fast, occurring within 1 ps. On the other hand, high charge recombination between electrons in the surface states and/or the conduction band of ZnO and holes in P3HT was observed. In the case of P3HT-dye-ZnO, we found that the charge recombination could be greatly suppressed by locating the dye at the P3HT/ZnO interfaces while maintaining a fast charge separation rate (a few ps to 10 ps). Our findings provide one methodology for the design of OIHSCs for improving their conversion efficiency, which is to position the dye at the appropriate BHJ interfaces.

DOI： 10.1039/c3cp52093e

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The carrier dynamics in dye-sensitized solar cells was investigated by using the transient grating, in addition to the transient absorption method and transient photocurrent method on the order of microseconds to seconds. The signals for the same sample were obtained under a short-circuit condition to compare the carrier dynamics via refractive index change with the transient photocurrent measurement. Optically silent carrier dynamics by transient absorption have been successfully observed via a refractive index change. The corresponding signal components were originated from the charge dynamics at the solid/liquid interface, especially on the liquid side; rearrangement or diffusion motion of charged redox species occurred when the injected electrons were trapped at the TiO2 surface and when the electron-electrolyte recombination occurred at the interface. The assignments were confirmed from the dependence on the viscosity of the solvent and the presence of 4-tert-butyl pyridine. As the viscosity of the solvent increased, the rearrangement and the motion of the charged redox species were delayed. Since the rearrangement dynamics was changed by the presence of 4-tert-butyl pyridine, it affected not only the TiO2 surface but also the redox species close to the interface.

DOI： 10.1039/c3cp44597f

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Carrier dynamics in quantum-dot sensitized solar cells (QDSSCs) was clarified by combining the information obtained by the heterodyne transient grating (HD-TG), transient absorption (TA) and transient photocurrent (TP) measurements under the short circuit conditions in the time range from microseconds to seconds. The HD-TG signal is sensitive to the ionic species at the electrode/electrolyte interface, and the electrons in the titanium oxide layer injected from quantum dots (QDs) were monitored by the TA signal, and the photocurrent as a final output was monitored by the TP signal. By using the compensating information, the whole picture of the charge dynamics was obtained in the time region after the initial electron injection from QDs into the titanium oxide layer. In the former part of this paper, the assignment of the responses for each measurement was clarified based on the previous paper on dye sensitized solar cells (S. Kuwahara, et al. Phys. Chem. Chem. Phys., 2013, 15(16), 5975-5981). In the latter part, the effect of the device parameters for actual QDSSCs, such as electrolyte concentrations, and coating times of surface passivation of QDs were investigated.

DOI： 10.1039/c3cp51542g

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Ultrafast carrier dynamics in PbS quantum dots (QDs) is characterized using a transient grating technique. In addition to an initial peak, a new peak appears at about 3 ps when the excitation photon energy is greater than 2.7E(g) (E-g: band gap between LUMO and HOMO in the QDs). The first peak is considered to be related to hot carriers and the second one is believed to result from multiple exciton generation (MEG). We found that MEG began in as fast as 200 fs and complete around 3 ps. We succeeded in observing the dynamics of MEG occurrence in PbS QDs. (C) 2012 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.cplett.2012.05.076

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Diffusion of photoexcited carriers and the subsequent thermal diffusion by photoexcitation of a nanoparticulate TiO2 thin film were observed by the heterodyne transient grating (HD-TG) method. The observed HD-TG signal showed that the photoexcited carriers were generated inhomogeneously in the depth direction and they diffused both in the depth and parallel directions of the film. The diffusion processes were analyzed using a two-dimensional diffusion model. The thermal profile generated by the relaxation of the photoexcited carriers was treated by the same model. It was found that the effective diffusivities of the photoexcited carriers and heat decreased as the size of the nanoparticles in the film increased. It is suggested that the transport properties of the photoexcited carriers and heat are dominated by the inter-particulate resistance. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.042601

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Understanding the electron transfer dynamics at the interface between dye sensitizer and semiconductor nanoparticle is very important for both a fundamental study and development of dye-sensitized solar cells (DSCs), which are a potential candidate for next generation solar cells. In this study, we have characterized the ultrafast photoexcited electron dynamics in a newly produced linearly-linked two dye co-sensitized solar cell using both a transient absorption (TA) and an improved transient grating (TG) technique, in which tin(IV) 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (NcSn) and cis-diisothiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II) bis(tetrabutylammonium) (N719) are molecularly and linearly linked and are bonded to the surface of a nanocrystalline tin dioxide (SnO2) electrode by a metal-O-metal linkage (i.e. SnO2-NcSn-N719). By comparing the TA and TG kinetics of NcSn, N719, and hybrid NcSn-N719 molecules adsorbed onto both of the SnO2 and zirconium dioxide (ZrO2) nanocrystalline films, the forward and backward electron transfer dynamics in SnO2-NcSn-N719 were clarified. We found that there are two pathways for electron injection from the linearly-linked two dye molecules (NcSn-N719) to SnO2. The first is a stepwise electron injection, in which photoexcited electrons first transfer from N719 to NcSn with a transfer time of 0.95 ps and then transfer from NcSn to the conduction band (CB) of SnO2 with two timescales of 1.6 ps and 4.2 ps. The second is direct photoexcited electron transfer from N719 to the CB of SnO2 with a timescale of 20-30 ps. On the other hand, back electron transfer from SnO2 to NcSn is on a timescale of about 2 ns, which is about three orders of magnitude slower compared to the forward electron transfer from NcSn to SnO2. The back electron transfer from NcSn to N719 is on a timescale of about 40 ps, which is about one order slower compared to the forward electron transfer from N719 to NcSn. These results demonstrate that photoexcited electrons can be effectively injected into SnO2 from both of the N719 and NcSn dyes.

DOI： 10.1039/c2cp23522f

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The ultrafast photoexcited electron and hole dynamics of CdSe quantum dots (QDs) deposited onto nanostructured TiO2 films were studied using an improved transient grating (TG) technique. By comparing the TG responses measured in air and in a Na2S solution (holeacceptor), we succeeded in separating the dynamic characteristics of photoexcited electrons and holes in the CdSe QDs. We found that charge separation in the CdSe QDs occurred over a very fast time scale from a few hundreds of femtoseconds in the Na2S solution via hole transfer to S2- ions to a few picoseconds in air via hole trapping. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533374]

DOI： 10.1063/1.3533374

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We measured terahertz reflection responses utilizing a propagating phonon polariton wave, which was generated and detected by two different methods: the near-field heterodyne transient grating and the continuously variable spatial frequency transient grating method. The obtained results were compared for the purpose of clarifying which of both methods is better for measurements of terahertz reflection responses. The phonon polariton wave is propagated and reflected at a ferroelectric crystal edge. From the viewpoint of the separation between the excited and reflected phonon polariton waves, the latter method is better for measurements of reflection responses.

DOI： 10.1088/1742-6596/214/1/012123

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The dynamics of photoexcited electrons in a GaN wafer with an inhomogeneous dislocation density distribution in the depth direction was measured by the near-field heterodyne transient grating method. We investigated the dependence of the interfaces with different dislocation densities, the dependence on the pump wavelength for a sample with a decaying distribution of dislocation density, which gives information on the depth dependence on the carrier dynamics. In the latter experiment, the observed depth region was continuously changed by tuning the wavelength around the band gap of GaN. The responses of the electron dynamics can be fitted with the sum of two exponential decays for all the experiments and only the slower component decayed faster as the dislocation density increased. It was concluded that the faster component corresponded to the trap process of electrons by deep states due to inherent defects in the GaN wafer and the slower component corresponded to the recombination of the trapped electrons at the defect states by dislocation defects. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3197281]

DOI： 10.1063/1.3197281

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We developed a new technique for the measurement of terahertz reflection responses utilizing a propagating phonon polariton wave. Frequency tunable phonon polariton waves were generated by the recently developed continuously variable spatial frequency transient grating method [K. Katayama, H. Inoue, H. Sugiya, Q. Shen, T. Taro, and K. A. Nelson, Appl. Phys. Lett. 92, 031906 (2008)]. The phonon polariton wave traveled in a ferroelectric crystal in an in-plane direction with an inclined angle of 26 degrees, and the wave reflected at the crystal edge where a sample was positioned. The reflected polariton wave was detected by the same method as that used for the generation of the polariton waves. By comparing the reflection intensities in the presence and absence of the sample, reflectivity of the polariton wave was calculated, and the refractive index and absorption in the terahertz region were obtained.

DOI： 10.1063/1.3088884

Web of Science

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

A new type of dynamic light scattering method for the size measurement of nanoparticles was developed using a transmission grating. A sample cell was located behind the grating, and light was incident from the grating side. The scattered light by a solution with nanopariticles was mixed with diffracted light by the grating, and the mixed signal was detected; namely, the diffracted light was used as reference light for heterodyne detection. It was confirmed that the SIN ratio of the autocorrelation curve was 26-times improved by heterodyne detection. Furthermore, the SIN ratio was improved by setting the sample cell at the sample grating distance where the electromagnetic field is maximum due to the Talbot effect. Size measurements for several kinds of nanoparticles were demonstrated by this new method.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Active oxygen species generated by photoexcitation of TiO(2) sol solutions were directly observed by the single-shot near-field heterodyne transient grating method. Two kinds of dynamics due to chemical species were observed and their lifetimes and diffusion coefficients were determined. From the dependence of the quantity of dissolved oxygen, it was confirmed that one of the species was generated from dissolved oxygen, such as a superoxide anion. Furthermore, this species was found to have a very small diffusion coefficient compared with other molecules with similar molecular weight, thereby suggesting that it was adsorbed onto TiO(2) particles. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2008.03.020

Web of Science

researchmap

Language：English  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A Doppler velocimeter with a transmission grating was developed for flow rate measurements inside a microchannel. This velocimeter has the same optical setup as a recently developed flow velocimeter for transparent liquids, in which two beams (pump and probe) optically coupled to a fiber were used. Although the principle of the flow velocity measurement was quite different between the two methods, the optical setups used were almost similar; the differences are that only the probe beam is used and fast Fourier transform analysis is utilized for the signal processing in the new technique. This development offers hybrid flow velocimeter for both transparent and turbid liquids. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2839018

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Frequency tunable phonon polariton waves were generated and detected using an original optical configuration of the transient grating method. In this technique, the excitation beam was shone onto a transmission grating after being transmitted through a lens, and a lithium niobate wafer located at a defocus position of the lens was irradiated by an expanded or reduced image of the transmission grating, causing excitation of phonon polaritons. Because the magnification of the light intensity pattern can be controlled by the sample-grating distance, the wavelength of the phonon polaritons, which is equal to the optical fringe spacing, can be continuously varied. © 2008 American Institute of Physics.

DOI： 10.1063/1.2837617

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

CdSe quantum dots (QDs) are adsorbed onto nanostructured SnO2 and planar FTO electrodes by a chemical adsorption technique. Optical absorption and the incident-photon-to-current conversion efficiency (IPCE) are studied by using photoacoustic and photoelectrochemical methods. The growth rate of the CdSe QDs depends on the morphology of the substrate. Larger IPCE peak values and larger integrated area for the IPCE spectra are obtained for the nanostructured SnO2 electrodes. The ultrafast carrier dynamics of the CdSe QDs are studied using a transient grating technique. It is found that the electron relaxation of the CdSe QDs depends strongly on the morphology of the substrate. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.05.055

Web of Science

researchmap

Language：English  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

A new photothermal technique was developed for measuring the flow velocity and making solute concentration measurements in a microchip by using the same optical and instrumental setup. Collinear pump and probe light were irradiated onto a microchip surface on which a grating pattern was fabricated. The pump light induced a temperature change with the grating pattern in a microchannel, and a refractive index change due to a subsequent temperature rise was monitored by a heterodyned diffraction signal of the probe light. The flow velocity and concentration were obtained by monitoring the motion and intensity change of the thermally induced grating, respectively. The dynamic range of the flow velocity measurement was 0.17-670 mm/s, which is sufficient for covering most chemical applications of a microchip. The detection limit of the concentration measurement was 2 x 10(-6) M for a rhodamine B solution.

Web of Science

researchmap

Language：English  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Ultrafast dynamics was investigated for photo-excited electrons between a SERS-active gold substrate and several kinds of adsorbed dyes by using TRG spectroscopy. A charge transfer (CT) within 200 fs between them was observed for a SERS-active sample and the number of CT electrons had a strong correlation to both the relative adsorption energy states (AESs) of dyes and the enhancement factors of their SERS band. To increase the number of CT electrons, the AESs should be closer to the excited energy state of gold. A larger number of CT electrons are considered to make the enhancement of SERS band larger. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2006.11.036

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A highly concentrated aqueous solution of sodium borate with 5.24 mol/kg of boron was prepared at 20 degrees C by adjusting the Na/B ratio at 0.22 (pH 6.9). This is more than twice more concentrated than the most soluble known borate solution (Na2O center dot B2O3 center dot 8H(2)O, 2.49 mol/kg at 20 degrees C). Analysis using the Raman spectroscopy and the APCI/MS (atmospheric pressure chemical ionization/mass spectrometry) suggested the formation of polyborate ions such as B9O10(OH)(9)(2-), B10O12(OH)(8)(2-), B11O14(OH)(7)(2-), B12O16(OH)(6)(2-). (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.inoche.2006.08.019

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

A technique for the generation and detection of phonon polariton was developed based on the near-field heterodyne transient grating method. It features a compact and simple optical setup and easy wavelength tuning ability of the phonon polariton. The wavelength was tuned by changing the grating spacing of a transmission grating positioned in front of a sample, and this was performed by sliding a glass plate with transmission gratings with many different grating spacings along the glass plate surface. © 2007 American Institute of Physics.

DOI： 10.1063/1.2734388

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

The near-field heterodyne grating (NF-HDG) method was applied to flow rate measurements in a microtube. The NF-HDG method is a newly developed optical technique based on photothermal effects. In this technique, pump light is shone on a transmission grating in front of a fluid channel and the inside liquid is heated with a pattern of the grating due to the Talbot effect. Another probe light is similarly shone on the same place as the pump light, and the diffraction by the transmission grating (reference) and the diffraction by the temporally generated thermal grating inside the fluid channel (signal) are mixed and detected (heterodyne detection). Theoretical analysis reveals that the dependence of the heterodyne signal intensity on the flow rate originates from the change in the heterodyne phase difference between the signal and reference, and the experimentally obtained calibration curves can be fitted with the theoretically predicted function. Furthermore, the optical setup was optimized based on the theoretical analysis of the Talbot effect. Flow rates of the order of nl/min were quantitatively measured, and the detection limit of the flow rate was 17 nlmin. © 2007 American Institute of Physics.

DOI： 10.1063/1.2766826

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：JAPAN SOCIETY APPLIED PHYSICS  

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The dynamics of excited carriers in porous silicon were investigated using the near-field heterodyne transient grating method, and the fundamental processes related to light emission were determined. The processes include trapping to surface states and two-body recombination of excited carriers, with trapping being the dominant source of light emission. Since nonlinear processes, namely two-body recombination, are included, it is necessary to measure the pump intensity dependence of the transient responses and to analyze them with a nonlinear differential equation in order to obtain accurate decay times. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2006.06.041

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

TiO2 electrodes composed of nanotubes and nanowires are prepared from TiO2 gels using a surfactant-assisted self-assembly method reported earlier. CdSe quantum dots (QDs) are adsorbed onto the. TiO2 electrodes by chemical deposition (CD). Their average size increases from 4 to 6nm with increasing deposition time from 3 to 82h. The optical absorption and incident photon-to-current conversion efficiency (IPCE) of the electrodes are studied by photoacoustic (PA) and plIiotoelectrochemical (PEC) methods. The photosensitization of the TiO2 electrodes by CdSe QDs is demonstrated by both PA and IPCE spectra. The ultrafast carrier dynamics of the CdSe-sensitized TiO2 electrodes composed of nanotubes and nanowires is studied using a lens-free heterodyne detection transient grating (LF-HD-TG) technique.,Fast and slow decay processes with lifetimes of about 3 ps and 60-130 ps, respectively, are observed.

DOI： 10.1143/JJAP.45.5569

Web of Science

researchmap

Language：Japanese  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A single femtosecond laser pulse was irradiated at a water/silicon interface, and the processed surface was investigated. Rings surrounded by ripples were found within the irradiated spot. The diameter of the rings ranged from 500 nm to 10 mu m. It is proposed that acoustic waves, caused by the oscillating motion of bubbles near the water/silicon interface, deformed the melting silicon surface. In the present work, a pulse (pulse width: 150 fs) was tightly focused in water to induce optical breakdown, and a bubble was generated at an arbitrary spot. When the power density was below the ablation threshold and above the melting threshold at the silicon surface and set above the breakdown threshold at the focus in water, a pattern was generated at a specific place and with a specific size.

DOI： 10.1007/s00339-005-3269-2

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Ultrafast carrier dynamics of nanostructured TiO2 films with and without Use quantum dot (QD) deposition were studied using a lensfree heterodyne detection transient grating (LF-HD-TG) technique. The natiostructured TiO2 films were prepared with anatase TiO2 nanoparticles with an average diameter of 27 nm. Use quantum dots with an average size of 5 nm were adsorbed onto the TiO2 films by a chemical deposition (CD) technique. The relaxation processes of the photoexcited electrons and holes can be detected separately using the LF-HD-TG technique. For the TiO2 film without CdSe deposition, it was found that the photoexcited holes relaxed within 2 ps. For the Use QD deposited nanostructured TiO2 film, two decay processes with time constants of 2 ps (tau(1)) and 16 PS (tau(2)) were detected. The fast decay process was attributed to photoexcited hole relaxation due to trapping in Use QDs. The slow decay process mainly reflected photoexcited electron transfer from Use QDs to TiO2. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2004.11.238

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

Recently developed lens-free heterodyne transient grating technique was applied to samples with rough surfaces on the order of several microns and photo-induced transient responses were successfully obtained on the temporal order of picoseconds. It was shown that the limitation of the sample roughness considerably reduced, compared with other conventional ultrafast methods. Theoretically the sample roughness was allowed on the order of 100 microns under our experimental condition, while it is on the order of several hundreds nanometers using a transient grating method.

DOI： 10.1051/jp4:2005125082

Web of Science

researchmap

Language：English   Publisher：Elsevier Science  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

Ultrafast carrier dynamics of anatase and rutile TiO2 nanostructured electrodes deposited with CdSe quantum dots (QDs) are studied using lens-free heterodyne detection transient grating (LF-HD-TG) technique. We find that the relaxation time of the photoexcited holes is as long as a few hundreds ps for rutile TiO2, but is smaller than 2 ps for anatase TiO2. Two decay processes with time scales of 2 ps (τ1) and a few tens ps or hundreds ps (τ2) are observed for CdSe QDs. The fast decay process is considered as photoexcited hole relaxation owing to trapping by the surface states of CdSe QDs. While the slow decay process reflects photoexcited electron relaxation processes, and mainly electron transfer from CdSe QDs to TiO2. We find that relaxation time of electrons (τ2) depends greatly on the crystal structure of TiO2.

DOI： 10.1109/IQEC.2005.1561002

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

We investigate the effect of different size mixture of TiO2 nanoparticles (15 and 27 nm) in anatase-type electrodes sensitized with CdSe quantum dots on excited carrier dynamics. The decay time of excited electrons in CdSe quantum dots decreases with the increase of 27 nm nanoparticles mixture.

DOI： 10.1109/IQEC.2005.1560874

Scopus

researchmap

Language：Japanese  

researchmap

Language：Japanese   Publisher：日本表面科学会編  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The lens-free heterodyne transient grating method was shown to reveal the dynamics of photoexcited carriers and heat on the surface region of an ion-implanted silicon in the dose range of 10(11)-10(15) cm(-2). In addition to the fact that the detection limit of the dose was superior to that for conventional methods, several physical properties of the carrier and heat can be obtained by analyzing transient responses. Theoretical analysis provided the lifetime of carriers and thermal diffusion coefficients in the ion-implanted surface region. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1605255

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A recently developed lens-free heterodyne transient grating method was applied for the measurement of ultrafast photoexcited dynamics of several kinds of dye molecules in aqueous solutions. The principle of the lens-free heterodyne transient grating method was clarified in detail, especially for thick samples, such as liquid and semi-transparent solid samples. The ultrafast dynamics of malachite green and methyl orange molecules in aqueous solutions was successfully monitored, and the obtained time constants agreed with those in other reports. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0009-2614(03)01188-6

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

The formation of ring patterns by single-shot laser irradiation at the solid/liquid interface was investigated. The processed surface was found to have many ring patterns surrounded by sinusoidal patterns within the irradiated spot. The diameter of the rings were found to be from 500 nm to 10 μm.

DOI： 10.1063/1.1582372

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Ultrafast charge transfer (CT) between gold and crystal violet (CV) molecules in relation with the surface enhanced Raman scattering (SERS) activation was investigated using the transient reflecting grating (TRG) spectroscopic method. A charge transfer between gold and crystal violet was observed only for the SERS-active substrate and it occurred within 200 fs. Since the adsorbed dyes had electronic overlap with the metal substrate at the point of central carbon, considering the difference of the Raman spectra between adsorbed and free dyes, it was suggested that the charge transfer occurred through the central carbon of crystal violet. Furthermore, it was shown that the surface morphology of the substrates is in close correlation with the charge transfer process from its dependence on the preparation method of substrates. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1010-6030(03)00023-6

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated ultrafast photoexcited electrons dynamics in relation to the surface enhanced Raman scattering (SERS) effect, using the transient reflecting grating spectroscopy method. We observed that only SERS-active samples had transfer of photoexcited electrons from a metal surface to adsorbed molecules within 200 fs followed by return of these charge transferred electrons to the metal within several picoseconds. By analyzing charge transfer (CT) processes, we were able to identify the main influential factors of the adsorption state, stay time at adsorbed molecules, and quantity of CT carriers. That these obtained factors had correlations to each other may lead to clarification of the CT processes within several picoseconds with regard to the SERS enhancement mechanism. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1524007

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Ultrafast transient reflecting grating (TRG) spectroscopy was utilized for defect analysis in the surface region of ion-implanted silicon for the implantation range from 10(11) to 10(15) cm(-2). To deduce signals due to trapped carriers at defect states, the TRG spectra at the delay time of 30 ps were measured because ultrafast carrier dynamics such as many-body recombination had finished before the delay time. According to the dose quantity, the peak of the interband transition was affected and also defect-related transitions emerged. Using this technique, implantation damage can be detected for samples with their dose larger than 10(12) cm(-2). It was proposed that TRG spectroscopy can be used as a novel analytical method for characterizing defects in the surface region of semiconductors. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1517162

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Laser processing using light sources with ultrashort pulses was applied to solid/liquid interfaces. A single-shot 200-fs pulse light was simply focused and irradiated or two pulses were interfered and irradiated at a water or electrolyte solution/silicon interface. From the measured AFM images on the processed silicon surfaces, several features were revealed, which were characteristic of the laser processing at the solid/liquid interface. First, ring patterns surrounded by sinusoidal patterns like ripples were found within the irradiated spot. Secondly, the processed depth was reduced by coexisting electrolyte in water. Thirdly, there were less residual aggregates or debris.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The simultaneous detections of transient reflectivity (TR), transient reflecting first and second order diffraction signals, at a silicon surface revealed that each signal reflected different physical processes of carrier dynamics under a high pump power of 5 mJ/cm(2). It was shown that the second order diffraction could detect a refractive index change which was not linearly dependent on the excited carrier density, and it was suggested that the nonlinearity was caused by many-body interactions among carriers at the band-edge states. The dynamics observed with the second order diffraction corresponded to the recombination of the band-edge carriers. Analysis of the first and second order diffractions in combination with the recently developed spectroscopic detection provided selective information on the ultrafast carrier and heat dynamics for a silicon surface, that is, carrier-phonon scattering, recombination of carriers, heat generation, and diffusion. Additionally, it was shown the TR might allow observation of mixed physical processes detected by the first and second order diffractions and it was suggested that deducing exact physical processes only from the TR signal, especially under high pump power conditions, was difficult. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1510952

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Analytical Chemistry  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Ultrafast transient reflecting grating (TRG) spectroscopy was applied to investigate the influence of various defect states on ultrafast carrier dynamics of up to 3 ps duration in an ion-implanted silicon surface region. The TRG spectra revealed the energy-state distribution of two kinds of defect states, and it was observed that photoexcited carriers were trapped in each state depending on annealing time. It was proposed that TRG spectroscopy can be used as an analytical method for characterizing defects in the surface region of semicondcutors. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1492860

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Analytical Chemistry  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The recently developed spectroscopic transient reflecting grating technique with a time resolution of 200 fs was applied to a silicon surface under the pump intensity of more than 1 mJ/cm(2). This method provides information on excited free carrier dynamics and subsequent heat generation and diffusion selectively based on appropriate choice of probe wavelength. With regard to the thermal component, the temperature at the surface increased within several picoseconds and then decayed after about 300 ps. As the pump intensity was increased, the maximum temperature rise showed a nonlinear dependence on it, and also the temperature rise time became faster. The results led to the conclusion that the carrier dynamics causing a temperature rise at a silicon surface is dominated mainly by Auger recombination, not by the decay to a band edge under the high carrier density conditions. (C) 2002 American Institute of Physics.

Web of Science

researchmap

Language：English   Publisher：Elsevier Science  

researchmap

Language：English   Publisher：Elsevier Science  

researchmap

Language：English   Publisher：Elsevier Science  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Ultrafast charge transfer related to the surface enhanced Raman scattering (SERS) activation was found using the transient reflecting grating spectroscopic method. Two kinds of vapor-deposited gold films were prepared as SERS substrates. One of them induced the SERS effect (SERS active substrate), while the other did not (SERS inactive substrate). A charge transfer between gold and pyridine was observed only for the former and it occurred within 200 fs. Further, it was suggested that the surface roughness of the substrate not only induced electromagnetic enhancement, but also generated new adsorption sites that made a charge transfer occur easily. (C) 2001 Published by Elsevier Science B.V.

Web of Science

researchmap

Language：English   Publisher：Scientific Society of Measurement, Automation and Informatics  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Ultrafast dynamics of CdSxSe1-x (x=0.26) nanocrystals doped in glasses was studied using a femtosecond ultrafast transient lensing (UTL) technique. Three kinds of samples with different average diameters (5.3 nm, 6.5 nm and 9.4 nm, respectively) of CdSxSe1-x(x=0.26) nanocrystals were measured after photodarkened by irradiation of a pulsed laser light with a peak power density of 3 GW/cm(2) for 2 minutes. The UTL signals showed tri-exponential behaviors and three decay times were estimated to be about 1ps, 9 ps and > 300 ps. The three decay components were considered to be attributed to the direct recombination and trapping by some trapping states from the excited states, and subsequently radiative and nonradiative recombination processes through two kinds of trapping states at the nanocrystal-glass interfaces for the photo-excited carriers. It was found that as the averaged size of CdSxSe1-x (x=0.26) nanocrystals in the glasses decreased, the relative intensity of the 3rd component increased while that of the 2nd component decreased.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

We have developed an ultrafast carrier dynamics measurement method which provides both a transient reflecting grating signal and a transient reflectivity signal. The method was used to measure the carrier dynamics at a silicon surface in the carrier density range of 1.6-3.0 x 10(20) cm(-3), and the diffusion coefficient of non-equilibrium electrons was determined by a comparison between the transient reflecting grating and transient reflectivity signals. The diffusion coefficients increases as the carrier density becomes larger. This tendency is qualitatively in agreement with the theoretical prediction that increase of diffusion coefficients is caused by a temperature rise of the carriers and increase of their temperature gradient.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

We investigated photoexcited electron dynamics, which is considered to be related to the surface enhanced Raman scattering (SERS) effect, using the transient reflecting grating spectroscopic method. Two kinds of vapor-deposited gold films were prepared as SERS substrates. One of them induced the SERS effect (SERS active substrate), while the other did not (SERS inactive substrate). For the SERS active substrate, only the electrons excited at L in the gold band structure decreased faster when crystal violet (CV) molecules were adsorbed on the substrate, while no differences were observed between CV adsorbed and CV non-adsorbed substrates for the SERS inactive substrates. From these results, we concluded that excited electrons only around L in the band structure of gold have some relation to the SERS effect.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have observed two-step thermalization processes of photoexcited electrons in gold, by using a wavelength-selective transient reflecting grating method that provides information on carrier dynamics at each energy state selectively. We detected ultrafast processes around L and X points in the Brillouin zone. Within 1 ps, two relaxation components (40 +/- 10 and 280 +/- 40 fs) were observed only around L, and only the slower component was observed for every wavelength. We considered that the two relaxation processes occurred due to two kinds of electron-electron (e-e) scattering predicted from the Fermi-liquid theory, because their decay times are in good agreement with the times obtained from the theory. We concluded that faster and slower e-e scatterings physically correspond to the relaxations of the initially photoexcited electrons at the L point, and of nonthermalized electrons at various Brillouin-zone points, respectively.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

We optically generated and observed GHz ultrasonic waves on liquid surfaces and a liquid/liquid interface for the first time using the transient reflecting grating (TRG) method. Four kinds of samples were used for measurement of the surfaces
two types of black ink, an aqueous solution of crystal violet (CV aq solution) and ethanol aqueous solutions of CV. A cyclohexane/CV aq solution interface was used for measurement of the liquid/liquid interface. The 0.7 GHz and 0.6 GHz ultrasonic waves were generated on the liquid surfaces and the liquid/liquid interface, respectively. These ultrasonic waves resemble longitudinal acoustic waves partly localized at the surface, and they cause surface displacement. The amplitudes of TRG signals from surfaces of the CV mixed solvent solutions were found to be greatly affected by both the viscosity and surface tension. This result indicated the viscosity and interface tension must be considered as perturbations in the elastic theory. The strong dependence on interface tension showed the high selectivity of the TRG signals for the interface. © 1999 American Institute of Physics.

DOI： 10.1063/1.479852

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The energy transfer dynamics at gold/NaCl aq (0-0.5 M) interfaces was investigated using our recently developed surface plasmon resonance transient reflecting grating (SPR-TRG) method. We focused on two exponential decays in the SPR-TRG signals. The two decays correspond to the relaxation of hot electrons and interfacial heat transfer, respectively. The intensity of each decay changes systematically with increases in the concentration of NaCl, i.e., the former becomes smaller and the latter becomes larger. Considering the relation between the intensity and the dynamics, we concluded that there is some interaction between the hot electrons and the adsorbate on the interface and that the following temperature rise in gold after relaxation of the hot electrons becomes large: This conclusion shows that an ultrafast energy transfer processes by hot electrons exists, and that the process is hindered by the adsorbate. Finally, we discuss the ultrafast energy transfer in relation to the hot electrons and adsorbate on a molecular scale.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We generated and observed GHz ultrasonic waves on liquid surfaces for the first time using the transient reflecting grating (TRG) method. Three samples were used for measurement: two types of black inks and an aqueous solution of crystal violet (CV). We have investigated the pump power and the solute concentration dependencies of the intensities of the TRG signals from surfaces of the samples. As a result, it was found that these dependencies of the TRG signals are intrinsic to solute and dispersoid. These results presumably suggest that the TRG signals from the liquid surfaces reflect the dynamics of the energy transfer between solute and solvent molecules and of the adsorption and desorption on the liquid surfaces.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Mechanisms of unusual signal enhancement observed for transient reflecting grating (TRG) experiments are investigated under three types of surface plasmon resonance (SPR) conditions, where two pump beams only, a probe beam only, or two pump beams and a probe beam, excite surface plasmon. A gold thin film deposited on a glass prism is measured in the Kretschmann configuration with a temporal resolution of tens of picoseconds. The signal under each SPR condition exhibits different characteristic features in signal intensity and transient behavior unlike the usual non-SPR TRG experiments. Under SPR with pump beams, high conversion efficiency from Light to heat allows detection of a TRG signal 11 times larger in magnitude and much lower in background level than under a non-SPR with them. Under SPR with the probe beam, diffraction caused by heat-induced spatial modulation as described by complex reflection Fresnel coefficients is theoretically proved to enhance the TRG signal and to change transient behavior, which provides a way to get selective observation of heat diffusion near the surface. When both pump and probe beams excite surface plasmons, an additional signal is observed, almost at the same time as the optical pulse, having 100 times larger intensity than the other signals, which is due to electrons excited at the gold surface.

Web of Science

researchmap

Language：English   Publisher：The University of Tokyo  

researchmap

Language：Japanese   Publisher：日本化学会  

researchmap

Language：English  

DOI： 10.1103/PhysRevB.58.8428

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASJ proceeding  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：NANJING UNIVERSITY INSTITUTE ACOUSTICS  

Web of Science

researchmap

DOI： 10.1002/asia.201200591

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：English   Publisher：Steering committee of symposium on ultrasonic electronics  

CiNii Books

researchmap

Language：English   Publisher：Steering committee of symposium on ultrasonic electronics  

CiNii Books

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本化学会  

CiNii Books

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：工業調査会  

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本分析化学会  

CiNii Books

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：応用物理学会  

CiNii Books

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：日本化学会  

DOI： 10.20665/kakyoshi.47.6_390

CiNii Books

researchmap

J-GLOBAL

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：Japanese   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap