TARO TOYODA
| Emeritus Professor etc. | Emeritus Professor |
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Paper
- Characterization of Photoexcited Carriers and Thermal Properties of Nanoparticulate TiO2 Film Using Heterodyne Transient Grating Method
Hiroaki Hata; Kenji Katayama; Qing Shen; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 51, 4, 042601, Apr. 2012, Peer-reviwed, 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
Scientific journal, English - Multiple electron injection dynamics in linearly-linked two dye co-sensitized nanocrystalline metal oxide electrodes for dye-sensitized solar cells
Qing Shen; Yuhei Ogomi; Byung-wook Park; Takafumi Inoue; Shyam S. Pandey; Akari Miyamoto; Shinsuke Fujita; Kenji Katayama; Taro Toyoda; Shuzi Hayase
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 14, 13, 4605-4613, 2012, Peer-reviwed, 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.
Scientific journal, English - Dependences of the optical absorption and photovoltaic properties of CdS quantum dot-sensitized solar cells on the CdS quantum dot adsorption time
Sojiro Hachiya; Yohei Onishi; Qing Shen; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 110, 5, 054319, Sep. 2011, Peer-reviwed, We have studied the optical absorption properties of CdS quantum dots (QDs) adsorbed on TiO(2) electrodes and the photovoltaic properties of CdS quantum dot-sensitized solar cells (QDSSCs). CdS QDs were grown directly on a nanostructured TiO(2) surface by a chemical bath deposition method for different adsorption times from 30 min to 8 h. The growing size of CdS QDs on the TiO(2) electrodes with increasing adsorption time was confirmed by a redshift in the optical spectra, measured using photoacoustic (PA) spectroscopy. The steepness factor, which reflects the amount of disorder and the number of defects, was also estimated from the PA spectrum. The steepness factor decreased sharply at 1 h adsorption time when the CdS QDs commenced aggregating. Subsequently, the steepness factor increased for longer adsorption times, indicating that the density of surface states of the CdS QDs had decreased due to a decrease in the ratio of surface area to volume with the growth in average size. The photovoltaic properties of sandwich structure solar cells were studied under an illumination of air mass (AM) 1.5 using Cu(2)S on brass as a counter electrode and a polysulfide (S/S(2-)) redox system as the electrolyte. The maximum photovoltaic conversion efficiency obtained was 1.22%, which was for the device that had 2 h CdS adsorption. The variations in series resistance and shunt resistance were estimated from the slopes of photocurrent density-photovoltage curves near the short circuit and open circuit conditions, respectively. With increasing adsorption time, both resistances decreased until 2 h adsorption when the maximum photoconversion efficiency was observed. These results indicate that the CdS adsorption time is closely correlated with the photovoltaic properties of CdS QDSSCs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3626061]
Scientific journal, English - Highly efficient CdS/CdSe-sensitized solar cells controlled by the structural properties of compact porous TiO2 photoelectrodes
Quanxin Zhang; Xiaozhi Guo; Xiaoming Huang; Shuqing Huang; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 13, 10, 4659-4667, 2011, Peer-reviwed, At present, the photovoltaic performance of quantum dot-sensitized solar cells (QDSCs) is still much lower than conventional DSCs. Appropriate porous TiO2 photoanodes for QDSCs need to be further investigated, and optimization of the nanoparticle-based photoanodes is highly desirable as well. In this article, the influence of the structural properties of various TiO2 photoanodes on CdS/CdSe-sensitized solar cells have been systematically studied. Quantitative analyses of light-harvesting efficiency (LHE) and electron-transfer yield (Phi(ET)) for the QDSCs are investigated for the first time. It is revealed that the LHE increases in the long wavelength region with the addition of large size TiO2 particles to the transparent film. In the meantime, the balance between the light scattering and surface area also needs to be controlled, which can significantly restrain the dark current of the device. A double-layer photoanodic structure can give 4.92% of light-to-electricity conversion efficiency with a photoactive area of 0.15 cm(2)
Scientific journal, English - Uncovering the role of the ZnS treatment in the performance of quantum dot sensitized solar cells
Nestor Guijarro; Jose M. Campina; Qing Shen; Taro Toyoda; Teresa Lana-Villarreal; Roberto Gomez
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ROYAL SOC CHEMISTRY, 13, 25, 12024-12032, 2011, Peer-reviwed, Among the third-generation photovoltaic devices, much attention is being paid to the so-called Quantum Dot sensitized Solar Cells (QDSCs). The currently poor performance of QDSCs seems to be efficiently patched by the ZnS treatment, increasing the output parameters of the devices, albeit its function remains rather unclear. Here new insights into the role of the ZnS layer on the QDSC performance are provided, revealing simultaneously the most active recombination pathways. Optical and AFM characterization confirms that the ZnS deposit covers, at least partially, both the TiO(2) nanoparticles and the QDs (CdSe). Photoanodes submitted to the ZnS treatment before and/or after the introduction of colloidal CdSe QDs were studied by electrochemical impedance spectroscopy, cyclic voltammetry and photocurrent experiments. The corresponding results prove that the passivation of the CdSe QDs rather than the blockage of the TiO(2) surface is the main factor leading to the efficiency improvement. In addition, a study of the ultrafast carrier dynamics by means of the Lens-Free Heterodyne Detection Transient Grating technique indicates that the ZnS shell also increases the rate of electron transfer. The dual role of the ZnS layer should be kept in mind in the quest for new modifiers for enhancing the performance of QDSCs.
Scientific journal, English - Highly efficient quasi-solid-state quantum-dot-sensitized solar cell based on hydrogel electrolytes
Zhexun Yu; Quanxin Zhang; Da Qin; Yanhong Luo; Dongmei Li; Qing Shen; Taro Toyoda; Qingbo Meng
ELECTROCHEMISTRY COMMUNICATIONS, ELSEVIER SCIENCE INC, 12, 12, 1776-1779, Dec. 2010, Peer-reviwed, Chemically crosslinked polyacrylamide-based hydrogel has been first used as the polymer matrix to prepare quasi-solid-state polysulfide electrolyte for CdS/CdSe co-sensitized solar cells (QDSCs). The room temperature ionic conductivity of the gel electrolyte reaches 0.093 S.cm(-1). QDSCs based on this quasi-solid-state electrolyte can present up to 4.0% of light-to-electricity conversion efficiency. Meanwhile, the interfacial recombination at TiO(2)/electrolyte interface of the cell is also investigated by Electrochemical Impedance Spectroscopy (EIS). (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English - Photoacoustic and photoelectrochemical current spectra of combined CdS/CdSe quantum dots adsorbed on nanostructured TiO2 electrodes, together with photovoltaic characteristics
Taro Toyoda; Keita Oshikane; Dongmei Li; Yanhong Luo; Qingbo Meng; Qing Shen
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 108, 11, 114304, Dec. 2010, Peer-reviwed, We describe the performance of quantum dot (QD)-sensitized solar cells based on CdSe QD sensitizer on a preadsorbed layer of CdS QDs (combined CdS/CdSe QDs) together with the basic studies of optical absorption and photoeletrochemical current characteristics. It can be observed from optical absorption measurements using photoacoustic spectroscopy that the CdSe QDs on the nanostructured TiO2 electrodes preadsorbed with CdS QDs grow more rapidly during the initial adsorption process than those without preadsorption. The maximum incident photon-to-current conversion efficiency (IPCE) value of the CdSe QDs on the nanostructured TiO2 electrodes preadsorbed with CdS QDs is higher than that without preadsorption, indicating the possibilities of decreases in recombination centers, interface states, and inverse transfer rate. Short-circuit current (J(sc)) in combined CdS/CdSe QD-sensitized solar cells shows maximum with the increase in CdSe QDs adsorption times between 2 and 24 h. The other parameters, open-circuit voltage (V-oc) and fill factor, is independent of adsorption time. Therefore, the photovoltaic conversion efficiency (eta) of combined CdS/CdSe QD-sensitized solar cell shows a maximum value of 3.5%. (c) 2010 American Institute of Physics. [doi:10.1063/1.3517066]
Scientific journal, English - Sensitization of Titanium Dioxide Photoanodes with Cadmium Selenide Quantum Dots Prepared by SILAR: Photoelectrochemical and Carrier Dynamics Studies
Nestor Guijarro; Teresa Lana-Villarreal; Qing Shen; Taro Toyoda; Roberto Gomez
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 114, 50, 21928-21937, Dec. 2010, Peer-reviwed, Quantum dot sensitized solar cells have the potentiality to emerge as viable third-generation photovoltaic devices. In these cells, the photoanode is constituted by a nanostructured oxide layer sensitized to the visible by suitable quantum dots (QDs). Here, we report on some aspects of the sensitization of titanium dioxide nanoparticulate electrodes with CdSe QDs deposited by the so-called successive ionic layer adsorption and reaction (SILAR) method. Parallel SILAR experiments with nanoparticulate and rutile single crystal electrodes indicate that an almost full coverage of the titanium dioxide surface is achieved from the initial stages of the process. However, photoelectrochemical experiments done with both SILAR and colloidal CdSe QD sensitized electrodes indicate a faster recombination in the former case. Furthermore, a study of the ultrafast carrier dynamics of CdSe QDs by means of the near-field heterodyne detection transient grating method reveals that the rate of the photogenerated electron injection from the QD to the oxide significantly decreases with the number of deposition cycles. This parallels the performance of the photoanode as well as the overall behavior of the photovoltaic cell, which tends to saturate as the number of SILAR cycles increases. The intrinsic limitations of the photoanodes prepared by SILAR are attributed to both the existence of a high concentration of QD/QD interfaces and the absence of effective passivation of the TiO(2) and CdSe surfaces.
Scientific journal, English - Direct Correlation between Ultrafast Injection and Photoanode Performance in Quantum Dot Sensitized Solar Cells
Nestor Guijarro; Qing Shen; Sixto Gimenez; Ivan Mora-Sero; Juan Bisquert; Teresa Lana-Villarreal; Taro Toyoda; Roberto Gomez
JOURNAL OF PHYSICAL CHEMISTRY C, AMER CHEMICAL SOC, 114, 50, 22352-22360, Dec. 2010, Peer-reviwed, The performance of quantum dot (QD) sensitized solar cells depends mainly on both electron injection from the QDs to the oxide matrix and recombination rates. Here we show a direct correlation between ultrafast carrier dynamics and photoanode (and complete solar cell) performance. TiO(2) nanoparticulate electrodes sensitized with colloidal CdSe QDs are prepared by either direct or linker-assisted adsorption (using cysteine, p-mercaptobenzoic acid, and mercaptopropionic acid). These electrodes are examined by ultrafast carrier dynamics, photopotential, and incident photon-to-current efficiency measurements to unravel factors controlling the efficiency in a closed solar cell. Subpicosecond time-resolved measurements are carried out by means of a lens-free heterodyne transient grating technique. In general, faster electron injection is observed for QDs directly adsorbed on TiO(2), which correlates with a better cell performance. Otherwise, increasingly faster electron injection is obtained as QD size decreases, regardless the mode of attachment. Photopotential measurements are performed in either sulfite or polysulfide solutions, in order to isolate different recombination pathways. The slowest recombination is reported for direct adsorption, whereas cysteine-mediated adsorption shows faster recombination. This study stresses the utility of ultrafast kinetic characterization in the development of efficient photoconverter devices.
Scientific journal, English - Separation of ultrafast photoexcited electron and hole dynamics in CdSe quantum dots adsorbed onto nanostructured TiO2 films
Qing Shen; Yasumasa Ayuzawa; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 97, 26, 263113, Dec. 2010, Peer-reviwed, 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]
Scientific journal, English - Screen-printed Cu2S-based Counter Electrode for Quantum-dot-sensitized Solar Cell
Minghui Deng; Shuqing Huang; Quanxin Zhang; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
CHEMISTRY LETTERS, CHEMICAL SOC JAPAN, 39, 11, 1168-1170, Nov. 2010, Peer-reviwed, Cu2S-based counter electrodes screen-printed on different substrates for CdS/CdSe quantum-dot-sensitized solar cells are reported The photovoltaic conversion efficiency of 3 71% was obtained with Cu2S counter electrode deposited on conductive substrate due to low charge-transfer resistance By addition of conductive carbon material, a cell with Cu2S/C composite counter electrode screen-printed on insulated glass substrate displayed an efficiency of 3 37% These results showed the potential application of such Cu2S-based counter electrode for large-scale quantum-dot-sensitized solar cells in the future
Scientific journal, English - CdSe quantum dot-sensitized solar cell employing TiO2 nanotube working-electrode and Cu2S counter-electrode
Qing Shen; Akari Yamada; Satoru Tamura; Taro Toyoda
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 97, 12, 123107, Sep. 2010, Peer-reviwed, We proposed a CdSe quantum dot (QD)-sensitized solar cell (QDSSC), which is constructed with a CdSe QD adsorbed TiO2 nanotube working electrode on a Ti substrate, a ring shaped Cu2S counter electrode, prepared on a brass substrate having a glass window, and polysulfide electrolyte. The light was incident from the counter electrode. An incident photon to current conversion efficiency as high as 65% and a photovoltaic conversion efficiency as high as 1.8% under one sun have been achieved. We have demonstrated less costly QDSSC, without the requirement for both a transparent conductive electrode or a platinum film. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3491245]
Scientific journal, English - Fibrous CdS/CdSe quantum dot co-sensitized solar cells based on ordered TiO2 nanotube arrays
Shuqing Huang; Quanxin Zhang; Xiaoming Huang; Xiaozhi Guo; Minghui Deng; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
NANOTECHNOLOGY, IOP PUBLISHING LTD, 21, 37, 375201, Sep. 2010, Peer-reviwed, A new kind of fibrous quantum dot sensitized solar cell has been designed and fabricated by using CdS and CdSe co-sensitized TiO2 nanotubes on Ti wire as the photoanode and highly active Cu2S as the counter electrode. By optimizing the CdSe deposition time and the length of the nanotube, a power conversion efficiency of 3.18% has been obtained under AM 1.5 illumination (100 mW cm(-2)). The potential application of this kind of solar cell has also been discussed in this paper.
Scientific journal, English - Low-Cost Flexible Nano-Sulfide/Carbon Composite Counter Electrode for Quantum-Dot-Sensitized Solar Cell
Minghui Deng; Quanxin Zhang; Shuqing Huang; Dongmei Li; Yanhong Luo; Qing Shen; Taro Toyoda; Qingbo Meng
NANOSCALE RESEARCH LETTERS, SPRINGER, 5, 6, 986-990, Jun. 2010, Peer-reviwed, Cu(2)S nanocrystal particles were in situ deposited on graphite paper to prepare nano-sulfide/carbon composite counter electrode for CdS/CdSe quantum-dot-sensitized solar cell (QDSC). By optimization of deposition time, photovoltaic conversion efficiency up to 3.08% was obtained. In the meantime, this composite counter electrode was superior to the commonly used Pt, Au and carbon counter electrodes. Electrochemical impedance spectra further confirmed that low charge transfer resistance at counter electrode/electrolyte interface was responsible for this, implied the potential application of this composite counter electrode in high-efficiency QDSC.
Scientific journal, English - Studies of Defects and Thermal Conductivity of Mixed Polytype in 6H-SiC Single Crystal by Polarized Optical Microscopy, Light Scattering Tomography, and Thermal Microscopy
Passapong Wutimakun; Jun Morimoto; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 49, 9, 095502, 2010, Peer-reviwed, This study was performed to investigate the defects and thermal conductivity of a mixed polytype of 6H-SiC single crystal using polarized optical microscopy (POM), light scattering tomography (LST), and thermal microscopy. First, we used Raman scattering spectroscopy to identify the mixed polytype, and we observed 15R-SiC mixed in a 6H-SiC single crystal. Next, as POM enables color distinction, we could clearly examine the defects in the mixed polytype area and border of 6H-SiC and 15R-SiC. Furthermore, we successfully presented defects that existed in the mixed polytype area and border in three-dimensional (3D) display by 3D light scattering tomography (3D-LST). Finally, we confirmed that there is a difference between the thermal conductivities of mixed polytypes of a 6H-SiC single crystal by thermal microscopy. The thermal conductivities of 6H-SiC, 15R-SiC, and their mixture were 475, 427, and 396 W m(-1) K(-1), respectively. These differences in thermal conductivity are caused by the existence of defects and the difference in carrier mobility between all polytypes. (C) 2010 The Japan Society of Applied Physics
Scientific journal, English - Recombination in Quantum Dot Sensitized Solar Cells
Ivan Mora-Sero; Sixto Gimenez; Francisco Fabregat-Santiago; Roberto Gomez; Qing Shen; Taro Toyoda; Juan Bisquert
ACCOUNTS OF CHEMICAL RESEARCH, AMER CHEMICAL SOC, 42, 11, 1848-1857, Nov. 2009, Peer-reviwed, Quantum dot sensitized solar cells (QDSCs) have attracted significant attention as promising third-generation photovoltaic devices. In the form of quantum dots (QDs), the semiconductor sensitizers have very useful and often tunable properties; moreover, their theoretical thermodynamic efficiency might be as high as 44%, better than the original 31% calculated ceiling. Unfortunately, the practical performance of these devices still lags behind that of dye-sensitized solar cells. In this Account, we summarize the strategies for depositing CdSe quantum dots on nanostructured mesoporous TiO2 electrodes and discuss the methods that facilitate improvement in the performance and stability of QDSCs.
One particularly significant factor for solar cells that use polysulfide electrolyte as the redox couple, which provides the best performance among QDSCs, is the passivation of the photoanode surface with a ZnS coating, which leads to a dramatic increase of photocurrents and efficiencies. However, these solar cells usually show a poor current-potential characteristic, so a general investigation of the recombination mechanisms is required for improvements. A physical model based on recombination through a monoenergetic TiO2 surface state that takes into account the effect of the surface coverage has been developed to better understand the recombination mechanisms of QDSCs. The three main methods of QD adsorption on TiO2 are (i) in situ growth of QDs by chemical bath deposition (CBD), (ii) deposition of presynthesized colloidal QDs by direct adsorption (DA), and (iii) deposition of presynthesized colloidal QDs by linker-assisted adsorption (LA).
A systematic investigation by impedance spectroscopy of QDSCs prepared by these methods showed a decrease in the charge-transfer resistance and increased electron lifetimes for CBD samples; the same result was found after ZnS coating because of the covering of the TiO2 surface. The increase of the lifetime with the ZnS treatment has also been checked independently by open-circuit potential (V-OC) decay measurements. Despite the lower recombination rates by electron transfer to electrolyte as well as the higher light absorption of CBD samples, only a moderate increase of photocurrent compared with colloidal QD samples is obtained, indicating the presence of an additional, internal recombination pathway in the closely packed QD layer.
Scientific journal, English - Electron dynamics in GaN wafers with an inhomogeneous distribution of defects in the depth direction
Yuji Ohashi; Kenji Katayama; Qing Shen; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 106, 6, 063515, Sep. 2009, Peer-reviwed, 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]
Scientific journal, English - Improving the performance of colloidal quantum-dot-sensitized solar cells
S.Gimenez; I.Mora-Sero; L.Macor; N.Guijarro; T.Lala-Villarreal; R.Gomez; L.J.Diguna; Q.Shen,T.Toyoda; J.Bisquert
Nanotechnology, 20, 295204, May 2009, Peer-reviwed
Scientific journal, English - Terahertz reflection response measurement using a phonon polariton wave
Hayato Inoue; Kenji Katayama; Qing Shen; Taro Toyoda; Keith A. Nelson
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 105, 5, 054902, Mar. 2009, Peer-reviwed, 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.
Scientific journal, English - Electric Characteristics of Li2O-Doped TiO2 Nanocrystalline Film and Its Application to Dye-Sensitized Solar Cells
Masahiro Nada; Tomohiro Gonda; Qing Shen; Hiroshi Shimada; Taro Toyoda; Naoki Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS, JAPAN SOC APPLIED PHYSICS, 48, 2, 025505, Feb. 2009, Peer-reviwed, The effects of Li2O doping on TiO2 nanocrystalline film are investigated to improve the conversion efficiency of dye-sensitized solar cells (DSC), while considering the mechanism of electric conduction in the TiO2 nanocrystalline film. The temperature dependence of carrier concentration and electric conductivity of Li2O-doped TiO2 nanocrystalline film are determined by Hall effect and high-impedance conductivity measurements. At the doping condition of 4.5 x 10(-5) molar ratio of Li2O to TiO2, the electric conductivity at room temperature is maximum, which is almost two orders of magnitude higher than that of the undoped sample. The conduction type and carrier concentration at 500 K are n-type and 1.75 x 10(13) cm(-3), respectively. From the temperature dependence of the electron concentration, the donor depth is estimated as 1.0 eV. By applying Li2O doping to DSC, the conversion efficiency and open-circuit voltage are maximum at the highest conductivity of the Li2O-doped TiO2 layer. (C) 2009 The Japan Society of Applied Physics
Scientific journal, English - Photoacoustic spectra of Au quantum dots adsorbed on nanostructured TiO2 electrodes together with the photoelectrochemical current characteristics
Taro Toyoda; Sae Tsugawa; Qing Shen
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 105, 3, 034314, Feb. 2009, Peer-reviwed, The optical absorption of Au quantum dots (QDs) was studied by applying the photoacoustic (PA) spectroscopic technique, which is useful for optically opaque samples. The characteristic bands of Au QDs were observed at around 2.4 eV for electrodes consisting of 15 nm TiO2 nanoparticles and at around 2.3 eV for those consisting of 37 nm ones, which correspond to the characteristic surface plasmon resonance bands in the visible region. The electrode thickness dependence of the PA signal intensity around the characteristic band showed a tendency toward saturation in both cases. There was a great difference in the saturation characteristics of the PA signal intensity between the electrodes made with different sized TiO2 nanoparticles, even though the preparation conditions for the Au QDs were the same. The saturation time for electrodes made with 37 nm TiO2 nanoparticles was shorter than those made with 15 nm particles, indicating that the penetration of the QDs into the electrodes made with 37 nm nanoparticles was less than those made with 15 nm nanoparticles, although the porous area observed was high. Also, the PA signal intensity around the peak of electrodes with 15 nm nanoparticles is larger than that with 37 nm ones, indicating a higher adsorption rate for the smaller nanoparticles due to the lower surface activation energy of larger nanoparticles. There was no photoelectrochemical current response although the characteristic optical absorption bands of the Au QDs were observed by surface plasmon resonance.
Scientific journal, English - Room-Temperature Absorption Edge of InGaN/GaN Quantum Wells Characterized by Photoacoustic Measurement
Yosuke Takeda; Daigo Takagi; Tatsuji Sano; Shin Tabata; Naoki Kobayashi; Qing Shen; Taro Toyoda; Jun Yamamoto; Yuzaburo Ban; Kou Matsumoto
JAPANESE JOURNAL OF APPLIED PHYSICS, IOP PUBLISHING LTD, 47, 12, 8805-8807, Dec. 2008, Peer-reviwed, The absorption edges of five periods of InxGa1-xN (3nm)/GaN (15mn) (x = 0.07-0.23) quantum wells (QWs) are characterized by photoacoustic (PA) measurement at room temperature. The absorption edge is determined by differentiating the PA signal Curve to obtain the inflection point on the assumption that the signal curve consists of Urbach tail in the low-energy region and Elliott's equation in the high-energy region. The constant absorption edge of GaN is observed at 3.4 eV and an absorption edge redshift with increasing In composition is observed for InGaN QWs. As a result, the Stokes shift increases with In composition and the highest shift of 435 meV is observed at x = 0.23. From the energy calculation of optical transition in the InGaN/GaN QWs under an internal polarization field, the transition between the ground states confined in the well with it triangular potential causes a low-energy shift in the photoluminescence peak from the bulk band-gap energy, and the excited bound states whose wave functions are confined by the step-linear potential extending over the GaN barrier lead to the high-energy shift in the, absorption edge. [DOI: 10.1143/JJAP.47.8805]
Scientific journal, English - Characterization of electron transfer from CdSe quantum dots to nanostructured TiO2 electrode using a near-field heterodyne transient grating technique
Qing Shen; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 516, 17, 5927-5930, Jul. 2008, Peer-reviwed, The ultrafast carrier dynamics of the CdSe QDs adsorbed on a nanostructured TiO2 electrode and on a glass substrate were studied using a near-field heterodyne detection transient grating (NF-HD-TG) method. Two decay processes were observed in the TG responses. The fast decay time constants tau(1) were the same (2.3 ps) for these two kinds of substrates, corresponding to the photoexcited hole relaxation in the CdSe QDs. However, the slow decay time constants tau(2) were very different for these two kinds of substrates, reflecting the photoexcited electron relaxation (i.e., trapping and/or transfer). Since no electron transfer from the CdSe QDs to the glass substrate could occur, we could estimate the electron transfer rate from the CdSe QDs into the nanostructured TiO2 electrode to be approximately 5.4 x 10(9) s(-1) using the values of tau(2) detected for these two kinds of substrates. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English - Effect of ZnS coating on the photovoltaic properties of CdSe quantum dot-sensitized solar cells
Qing Shen; Junya Kobayashi; Lina J. Diguna; Taro Toyoda
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 103, 8, 084304, Apr. 2008, Peer-reviwed, CdSe quantum dots (QDs) were adsorbed onto nanostructured TiO(2) films for different times by using a chemical bath deposition method in order to produce QD-sensitized solar cells (QDSSCs). Surface modification was done by coating ZnS onto the CdSe QDs. The optical absorption and current-voltage characteristics of these devices were studied. The size of the CdSe QDs increased with increasing adsorption time, and there was an optimum CdSe adsorption time for achieving the best photovoltaic conversion efficiency. The photovoltaic properties of short-circuit current density, open-circuit voltage, and photovoltaic conversion efficiency were significantly improved after modifying the surface with ZnS. Under a solar illumination of 100 mW/cm(2), an efficiency as high as 2.02% was achieved for the CdSe QDSSCs that were made by using this method. (C) 2008 American Institute of Physics.
Scientific journal, English - Correlation between crystal growth and photo sensitization of nanostructured TiO2 electrodes using supporting Ti substrates by self-assembled CdSe quantum dots
Taro Toyoda; Junya Kobayashi; Qing Shen
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 516, 9, 2426-2431, Mar. 2008, Peer-reviwed, Crystal growth of semiconductor quantum dots (QDs) adsorbed on nanostructured TiO2 electrodes is important not only for crystallographic studies but also for improving the photovoltaic efficiency of semiconductor-sensitized solar cells. In this study, nanostructured TiO2 electrodes using supporting Ti substrates were prepared. These electrodes are then adsorbed with self-assembled Use QDs as photosensitizers to investigate the crystal growth and photoelectrochemical current properties. Average diameters of the Use QDs can be estimated from optical absorption spectra by using photoacoustic (PA) technique. PA technique is a powerful tool for evaluating the optical absorption of opaque and scattered samples because of the detection by photothermal phenomenon. When the adsorption time increases, the CdSe QDs diameter increases and then shows saturation for all the cases. Normal solution growth plus suppression (negative growth) contributions can be derived by PA spectroscopic analysis. Both of them depend on adsorption temperatures for CdSe QDs formation. Photosensitization of the nanostructured TiO2 electrodes in the visible region resulting from Use QDs deposition can be clearly observed. Incident photon to current conversion efficiency (IPCE) of Use QDs adsorbed at high temperature formation is smaller than that adsorbed at low temperature one, indicating the increase of recombination centers with increasing adsorption temperature. This implies that negative growth, or dissolving effect, produces much more recombination centers inside of Use QDs and/or interface between the QDs and TiO2. (C) 2007 Elsevier B.V. All rights reserved.
Scientific journal, English - Generation and detection of tunable phonon polaritons using a single transmission grating
Kenji Katayama; Hayato Inoue; Hisashi Sugiya; Qing Shen; Taro Toyoda; Keith A. Nelson
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 92, 3, 031906, Jan. 2008, Peer-reviwed, 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.
Scientific journal, English - Photoacoustic spectra on Mn-doped zinc silicate powders by evacuated sealed silica tube method
Yoshihiro Inoue; Taro Toyoda; Jun Morimoto
JOURNAL OF MATERIALS SCIENCE, SPRINGER, 43, 1, 378-383, Jan. 2008, Peer-reviwed, The non-radiative transition processes on nondoped Zn(2)SiO(4) and Zn(2)SiO(4): Mn powders with various Mn concentrations were studied by photoacoustic (PA) spectroscopy. Zn(2)SiO(4): Mnx powders were prepared by dry reaction within an evacuated silica glass tube. As the result of photoluminescence (PL) measurement, the increase of PL intensity for green emission on samples doped with Mn between 1% and 6% and the concentration quenching for luminescence on samples doped with Mn between 7% and 12% were confirmed. For the green luminescence on zinc silicate doped with Mn phosphor, the PL decay behavior is assumed to be due to tunneling directly from excited states of electron traps to the excited states of Mn-ion. The Mncontent dependence of PL intensity for green emission is well interpreted by tunneling theory and the results of PA spectra, that is, the green emission is assisted by tunneling from non-radiative levels of Mn-ion to luminescencet level as (4)T(1)((4)G).
Scientific journal, English - Optical absorption and ultrafast carrier dynamics characterization of CdSe quantum dots deposited on different morphologies of nanostructured TiO2 films
Lina J. Diguna; Qing Shen; Akira Sato; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, ELSEVIER SCIENCE BV, 27, 5-8, 1514-1520, Sep. 2007, Peer-reviwed, in this study, CdSe QDs were chemically adsorbed onto the inverse opal TiO2 film as well as the common nanocrystalline TiO2 film. The optical absorption studied by using photoacoustic (PA) spectroscopy implies the growing and larger amount of CdSe QDs onto inverse opal TiO2 by increasing deposition time. For the same deposition time, the growth of CdSe QD size are independent on TiO2 matrixes, but largely deposited on the common nanocrystalline TiO2 film than the inverse opal TiO2. Ultrafast carrier dynamics shows a fast (hole) decay process and a slow (electron) decay process with lifetimes of a few ps and a few tens to hundreds ps, respectively. With increasing deposition time, regarding larger size and amount of CdSe QDs, the time constant of these two processes become longer for CdSe deposited inverse opal TiO2 samples. However, for the same deposition time, CdSc deposited inverse opal TiO2 have the shorter lifetime of both hole and electron decay processes compared to one on nanocrystalline TiO2, showing that the amount of CdSe QDs, the interfaces between CdSe QDs, play important role in carrier relaxation. (C) 2006 Elsevier B.V All rights reserved.
Scientific journal, English - Effect of Fe doping on photoluminescence of yttria-stabilized zirconia
H. Nakajima; H. Ishihara; Q. Shen; T. Toyoda; K. Itoh; H. Kaneko; Y. Tamaura
JOURNAL OF ALLOYS AND COMPOUNDS, ELSEVIER SCIENCE SA, 441, 1-2, 255-258, Aug. 2007, Peer-reviwed, Photoluminescence (PL) spectra of yttria-stabilized zirconia (YSZ) samples with different Fe mole fractions were measured to study the influence of Fe doping on their spectra. The PL spectra of all the samples can be decomposed into two Gaussian bands centered around 440 and 510 nm, and the two bands can be attributed to oxygen vacancy states in the bulk and the surface of the samples. We found that the intensity ratio of the PL band around 440 nm to that around 510 nm increases as the Fe mole fraction increases. This can be explained by considering the distribution of Fe-associated defects (bulk or surface) and the PL quenching by the defects. These results show that PL spectroscopy can be used to study properties of Fe dopant in YSZ. Moreover, photoacoustic spectra of the samples were measured to characterize defects in the samples. (C) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English - Crystal growth. of CdSe quantum dots adsorbed on nanoparticle, inverse opal, and nanotube TiO2 photoelectrodes characterized by photoacoustic spectroscopy
Taro Toyoda; Terumasa Uehata; Rihito Suganuma; Satoru Tamura; Akira Sato; Kana Yamamoto; Qing Shen; Naoki Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 46, 7B, 4616-4621, Jul. 2007, Peer-reviwed, The crystal growth of semiconductor quantum dots (QDs) adsorbed on nanostructured TiO2 photoelectrodes is important not only for crystallographic studies but also for improving the photovoltaic efficiency of semiconductor-sensitized solar cells. In this study, nanoparticle, inverse opal, and nanotube TiO2 electrodes are prepared. These electrodes are then adsorbed with CdSe QDs as photosensitizers to investigate crystal growth. The average diameters of the CdSe QDs can be estimated from the photoacoustic (PA) spectra. When the adsorption time increases, the CdSe QD diameter increases and then shows saturation. Normal solution growth plus suppression (negative growth) can be obtained by PA analysis. Both of them depend on the morphology of TiO2 electrodes and the final solution concentration for the CdSe QD preparation.
Scientific journal, English - High efficiency of CdSe quantum-dot-sensitized TiO2 inverse opal solar cells
Lina J. Diguna; Qing Shen; Junya Kobayashi; Taro Toyoda
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 91, 2, 023116, Jul. 2007, Peer-reviwed, The authors have demonstrated an approach to sensitized-type solar cells, based on TiO2 inverse opal and the use of CdSe quantum dots (QDs) as sensitizers. CdSe QDs were grown in situ on TiO2 inverse opal electrodes, utilizing a chemical bath deposition method. All of the photovoltaic performances, including short circuit photocurrent density, open circuit voltage, fill factor, and efficiency, were significantly improved by surface modification with ZnS and fluoride ions. A power conversion efficiency of about 2.7% has been attained, under solar illumination of 100 mW/cm(2). This value is relatively high for metal oxide solar cells, sensitized with semiconductor QDs. (C) 2007 American Institute of Physics.
Scientific journal, English - Optical absorption, photosensitization, and ultrafast carrier dynamic investigations of CdSe quantum dots grafted onto nanostructured SnO2 electrode and fluorine-doped tin oxide (FTO) glass
Qing Shen; Makoto Yanai; Kenji Katayama; Tsuguo Sawada; Taro Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 442, 1-3, 89-96, Jul. 2007, Peer-reviwed, 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.
Scientific journal, English - Phonon polariton generation and detection using near-field heterodyne transient grating method
Kenji Katayama; Qing Shen; Taro Toyoda; Keith A. Nelson
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 90, 17, 171117, Apr. 2007, Peer-reviwed, 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. (c) 2007 American Institute of Physics.
Scientific journal, English - Carrier dynamics in porous silicon studied with a near-field heterodyne transient grating method
Masahiro Yamaguchi; Kenji Katayama; Qing Shen; Taro Toyoda; Tsuguo Sawada
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 427, 1-3, 192-196, Aug. 2006, Peer-reviwed, 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.
Scientific journal, English - Photoacoustic and photoelectrochemical characterization of inverse opal TiO2 sensitized with CdSe quantum dots
Lina J. Diguna; Motonobu Murakami; Akira Sato; Yuki Kumagai; Taishi Ishihara; Naoki Kobayashi; Qing Shen; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 45, 6B, 5563-5568, Jun. 2006, Peer-reviwed, Inverse opal TiO2 may offer a novel and promising solution for enhancing the light harvesting efficiency of dye-sensitized solar cells (DSSCs). Its large interconnected pores enable a better penetration of the dye sensitizers via the matrix pores, making this material surpasses the efficiency of conventional TiO2 electrodes. Moreover, it also exhibits a photonic band gap that may enable a significant change in its dye absorbance by the adjustment of the photon localization near the red edge of the photonic band gap to the position of dye absorption. In this study, we report a simple method of fabrication of inverse opal TiO2, wherein the voids in artificial opal latex are filled with nanosized TiO2 particles by adding a drop of TiCl4 into the latex matrix, hydrolyzing, and heating. In this process, we investigate the effect of different heat treatment times on the properties of inverse opal TiO2. Photoacoustic (PA) characterization shows that longer heat treatment times could produce more defect sites. The presence of defects causes the inhibition of electron transfer and results in a decrease in incident photon-to-current conversion efficiency (IPCE). CdSe quantum dots were adsorbed onto inverse opal TiO2 by chemical deposition. The blue shift of PA spectra relative to the bulk CdSe and the gain in IPCE were clearly observed. This result indicates the quantum confinement effect and photosensitization of CdSe quantum dots.
Scientific journal, English - Optical absorption, photoelectrochemical, and ultrafast carrier dynamic investigations of TiO2 electrodes composed of nanotubes and nanowires sensitized with CdSe quantum dots
Qing Shen; Kenji Katayama; Tsuguo Sawada; Masahiro Yamaguchi; Taro Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 45, 6B, 5569-5574, Jun. 2006, Peer-reviwed, 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.
Scientific journal, English - Evaluation of Co- and Pr-doped zinc silicate powders by photoacoustic spectroscopy
Y Inoue; T Toyoda; J Morimoto
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 45, 5B, 4604-4608, May 2006, Peer-reviwed, Photoacoustic (PA) spectroscopy was applied to evaluate the roles of Co and Pr in Zn2SiO4:Co and Zn2SiO4:Pr powders in relation to non-radiative transitions. These samples were prepared by dry reaction within an evacuated silica glass tube, where the sintering temperature was 800, 900, or 1000 degrees C. The Co and Pr concentrations were adjusted to a stoichiometry of Zn1.82SiO4:M(Co or Pr)(0.18). From the results of X-ray diffraction (XRD) analysis, all samples indicated a rhombohedral structure (R (3) over bar) of Zn2SiO4; however, the formation of Zn2SiO4 was not enhanced below a sintering temperature of 900 degrees C. PA spectra in the visible range of all samples reflected the coloration of samples and the XRD results. The Co-ion and Pr-ion in Zn2SiO4:Co and Zn2SiO4:Pr were assumed to behave as non-radiative centers in the visible range. Furthermore, for Zn2SiO4:Co sintered at 1000 degrees C, PA spectroscopy could extract new information about the location of unknown non-radiative levels between 390 and 470nm.
Scientific journal, English - The effect of ultraviolet irradiation on the photothermal, photo luminescence and photo luminescence excitation spectra of Mn-doped ZnS nanoparticles
AB Cruz; Q Shen; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 499, 1-2, 104-109, Mar. 2006, Peer-reviwed, Research involving Mn doped nanocrystalline ZnS (ZnS:Mn) has grown in recent years, partly due to the high quantum luminescence efficiencies that have been reported. We measured the photoacoustic (PA), the photoluminescence (PL) and the photoluminescence excitation (PLE) spectra of surface-passivated and unpassivated ZnS:Mn. The effects of UV irradiation on the PL and PLE spectra were also studied. A decrease in the PA intensity after UV exposure was observed for the ZnS:Mn, indicating a decrease in the nonradiative relaxation probability. The observed increase in PL intensity indicates a corresponding increase in the radiative transition probability. For the PLE spectra, possible aggregation of the primary particles could have resulted in the lower measured energy of the PLE peak compared to the value predicted by the effective mass approximation theory. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - The influence of chemical post-etching and UV irradiation on the optical absorption and thermal diffusivity of porous silicon studied by photoacoustic technique
Q Shen; M Inoguchi; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 499, 1-2, 161-167, Mar. 2006, Peer-reviwed, We applied a photoacoustic (PA) technique to study the optical absorption and thermal diffusivity of porous silicon (Psi) samples. The Psi layers were formed on p-type Si wafers in an HF electrolyte. Three kinds of Psi samples that had undergone chemical post-etching were studied before and after UV irradiation for 2 h. We observed that a strong confinement effect occurred in all of the Psi samples from the blue shift of the band gap energy compared with that of crystalline Si, while the effective thermal diffusivities were almost two orders of the magnitude smaller than that of conventional Si crystals. The band gap shifted to higher energy and the effective thermal diffusivity decreased as the post-etching time increased. In the case of a Psi sample that was not chemically post-etched, the optical absorption and effective thermal diffusivity before and after UV irradiation were almost unchanged. However, for the Psi samples that were chemically post-etched, the optical absorption decreased and the effective thermal diffusivity increased after UV irradiation. This indicates that Psi samples that are post-etched are more readily affected by UV irradiation, i.e., oxidized by replacing Si-H, bonds by Si-O-x, than those that do not undergo post-etching. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - Photoacoustic and photo electrochemical characterization of CdSe-sensitized TiO2 electrodes composed of nanotubes and nanowires
Q Shen; T Sato; M Hashimoto; CC Chen; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 499, 1-2, 299-305, Mar. 2006, Peer-reviwed, Morphology of titanium dioxide (TiO2) electrodes and the choice of the sensitizers have been important factors for the improvement of dye-sensitized solar cell (DSSC) efficiency. TiO2 electrodes, having a higher degree of order than random fractal-like assemblies of nanoparticles, are desirable for the improvement of the electron transport characteristics. In recent years, semiconductor quantum dots (QDs) have attracted much attention as sensitizers, replacing organic dyes in DSSCs. In this study, TiO2 electrodes, composed of nanotubes and nanowires, were prepared from TiO2 gels using a surfactant-assisted self-assembling method reported recently. Since use of semiconductor QDs as sensitizers has some advantages in solar cell applications, CdSe QDs were adsorbed onto the TiO2 electrodes as a sensitizer. The photoacoustic (PA) and the incident photon-to-current conversion efficiency (IPCE) spectra were measured for the TiO2 electrodes, both with and without CdSe QD deposition to evaluate their optical absorption property and photon-to-electron conversion efficiencies. Dependencies of the optical absorption and the IPCE on the TiO2 electrode thickness (0.7 mu m-2.8 mu m) were studied. It was found that the IPCE peak value and the integrated area of the IPCE spectra for the TiO2 electrodes with CdSe deposition increased as the electrode thickness increased. The highest IPCE value of about 45% was obtained from an electrode with a thickness of 2.8 mu m. This value is as high as those obtained from CdSe QD-sensitized TiO2 electrodes made from nanoparticles, of which the thicknesses were 10 mu m. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - Photoexcited hole dynamics in TiO2 nanocrystalline films characterized using a lens-free heterodyne detection transient grating technique
Q Shen; K Katayama; T Sawada; M Yamaguchi; Y Kumagai; T Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 419, 4-6, 464-468, Feb. 2006, Peer-reviwed, A lens-free heterodyne detection transient grating (LF-HD-TG) technique has been applied to study the ultrafast carrier dynamics of anatase and rutile TiO2 films made from TiO2 nanoparticles. The decay of photoexcited hole concentrations in TiO2 films can be directly detected using the technique, since the effective mass of holes in TiO2 is much smaller than that of electrons. We find that the relaxation of holes in anatase occurs via first-order kinetics as fast as 1 ps, which is attributed to a hole trapping process. However, the lifetimes of holes in rutile are found to be longer than hundreds of ps. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - Studies on the effect of UV irradiation on Mn-doped ZnS nanoparticles
AB Cruz; Q Shen; T Toyoda
MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, ELSEVIER SCIENCE BV, 25, 5-8, 761-765, Dec. 2005, Peer-reviwed, With the advent of the increased attraction in compound semiconductors, attention has been focused on the research involving nanocrystalline Mn2+ doped ZnS (ZnS: Mn). In this paper, nano-scaled ZnS: Mn (both unpassivated and pasivated samples) was synthesized and we report the photoacoustic (PA) as well as photo luminescence (PL) properties upon exposure to ultraviolet (UV) light. It was found that passivation with acrylic acid (AA) yielded higher photoluminescence intensity. UV exposure caused a decrease in the PA intensity observed owing to a decrease in the nonradiative processes during exposure. A corresponding increase in the radiative processes was verified with the increase in the PL intensity during UV exposure. These experimental results suggest the possibility of UV curing for the passivating AA monomer and photochemical reactions around the nanocrystals, indicating the increase of the fluorescence quantum efficiency. Luminescent time decay measurements for the sample without AA showed a lengthening in the time decay constant after UV exposure. On the other hand, for the sample with AA, no change in the time decay constants was observed. This further strengthens the theory that during UV exposure, different luminescent decay mechanisms exist for the unpassivated and passivated samples. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - Effect of rutile-type content on nanostructured anatase-type TiO2 electrode sensitized with CdSe quantum dots characterized with photoacoustic and photoelectrochemical current spectroscopies
T Toyoda; Tsuboya, I; Q Shen
MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, ELSEVIER SCIENCE BV, 25, 5-8, 853-857, Dec. 2005, Peer-reviwed, Two types of nanostructured. TiO2 electrodes were prepared without rutile-type (100% anatase-type) and with rutile-type (12%) content. CdSe quantum dots (QDs) were adsorbed onto each of the two types of TiO2 electrodes using a chemical deposition (CD) technique. Optical absorption and photoelectrochemical properties were characterized with photoacoustic (PA) and photoelectrochemical current (PEC) methods. The redshift of the PA and PEC spectra with increasing CdSe sizes were clearly observed, indicating quantum confinement effects and photosensitization. It was found that the PA and PEC spectra in the visible region were different for the two types of TiO2 electrodes for the same deposition time. The PA and PEC intensities of TiO2 electrodes with rutile-type content were larger than those without rutile-type content, indicating that adsorbed CdSe QDs in the TiO2 electrodes with rutile-type content might be higher than those without rutile-type content. Moreover, the transport properties in the TiO2 electrodes with rutile-type content might be improved. These results suggest that the rutile-type content is advantageous to increase the photoelectrochemical properties of TiO2 electrodes. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - Magnetic and photoconductive properties of the CoxPt1-x-Pt-TiO2 nanocomposite films prepared by reactive sputter-deposition
CC Chen; T Sato; Y Azuma; J Shi; Y Nakamura; T Toyoda; M Hashimoto
VACUUM, PERGAMON-ELSEVIER SCIENCE LTD, 80, 4, 265-271, Oct. 2005, Peer-reviwed, Co-Pt-Ti-O films were prepared on SiO2 glass substrate by sputtering of a Co-Pt-Ti composite target in Ar + O-2 atmosphere with the total pressure of 4Pa and then in situ annealed at an elevated temperature T,,, to form the CoxPt1-x-TiO2 films. It is found that the ferromagnetic films grow in the form of fiber-like columnar grain about 10 nm in diameter when sputtered in the pressure ratio of O-2/Ar = 1/133 followed by in situ annealing at T-a>= 600 degrees C. The films contain Pt and amorphous anatase-type TiO2 phases besides the ferromagnetic fcc-CoxPt1-x phase. Thus, such nanocomposite films show photoconductive properties due to the anatase-type TiO2 phase as well as ferromagnetic properties due to the CoxPt1-x phase. (c) 2005 Elsevier Ltd. All rights reserved.
Scientific journal, English - Study of ultrafast carrier dynamics of nanostructured TiO2 films with and without CdSe quantum dot deposition using lens-free heterodyne detection transient grating technique
Q Shen; K Katayama; M Yamaguchi; T Sawada; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 486, 1-2, 15-19, Aug. 2005, Peer-reviwed, 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.
Scientific journal, English - Photoluminescence study of mixtures of anatase and rutile TiO2 nanoparticles: Influence of charge transfer between the nanoparticles on their photo luminescence excitation bands
H Nakajima; T Mori; Q Shen; T Toyoda
CHEMICAL PHYSICS LETTERS, ELSEVIER SCIENCE BV, 409, 1-3, 81-84, Jun. 2005, Peer-reviwed, We have measured photoluminescence (PL) excitation spectra of TiO2 powders with various rutile phase contents, and have found a correlation between the energy level of the PL excitation band (E-PLE) and the rutile phase content. The EPLE of the mixture and its band-gap energy were redshifted compared to those expected from its rutile phase content. We can explain this correlation by considering the charge transfer between the anatase and rutile TiO2 nanoparticles of the mixture. These results suggest that the extent of charge transfer can be estimated by PL spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.
Scientific journal, English - Photoacoustic and photoluminescence characterization of passivated and unpassivated Mn-doped ZnS nanoparticles
AB Cruz; Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 44, 6B, 4354-4357, Jun. 2005, Peer-reviwed, In this study, passivated and unpassivated nanocrystalline ZnS with varying Mn(2+) concentrations (ZnS:Mn) were synthesized and their photoacoustic (PA) and photoluminescence (PL) characteristics were studied. The PA intensity peak for the nanocrystalline ZnS was found to be blue-shifted compared with that for the bulk material due to quantum confinement effects. The difference of the PA signals of doped ZnS and undoped ZnS yielded the Mn(2+) optical absorption spectra. The intensity of the PA peak increased linearly with Mn concentration. The PL spectra showed a peak position at 2.08eV corresponding to the d-d transition of Mn(2+). For the unpassivated sample, a decrease in the PL intensities for higher Mn concentrations was observed. This could be attributed to concentration quenching. Addition of acrylic acid as a passivator led to an increase in PL intensity for all Mn concentrations and prevented the decrease in the PL intensity for higher Mn concentrations. These could be attributed to the surface passivation, which reduces the nonradiative recombination probabilities, thus increasing PL intensities.
Scientific journal, English - Photoacoustic and photoelectrochemical characterization of CdSe quantum dots grafted onto fluorine-doped tin oxide (FTO) substrate
T Toyoda; D Arae; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 44, 6B, 4465-4468, Jun. 2005, Peer-reviwed, We report on the optical absorption properties, measured by the photoacoustic (PA) method, and photoelectrocheinical current (PEC) characteristics (including transient measurements) of CdSe quantum dots (Q-dots) grafted onto a planar fluorine-doped SnO2 (FTO) substrate. CdSe Q-dots were fabricated by the chemical solution deposition (CD) technique. With increasing deposition time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots can be demonstrated. The average diameters of the CdSe Q-dots for each deposition time can be estimated using an effective mass approximation producing diameters of 5.1 not to 5.6 nm for deposition times of 5 h to 25 It, respectively. Thus, PA spectroscopy is useful in obtaining the Q-dots sizes even though there is no use of a high-resolution scanning electron microscope (SEM). An increase in PEC and the clear shift of the spectra to the lower energy region are observed with increasing deposition time, indicating the photosensitization of the FTO electrodes in the visible region resulting from CdSe Q-dots. It can be seen that the maximum value of incident photon to current conversion efficiency (IPCE) is similar to 10%, which is higher than that previously reported (similar to 6%). Transient PEC measurements show that electron recombination in a smaller amount of CdSe Q-dots is lower than that in a higher amount of Q-dots.
Scientific journal, English - Lens-free heterodyne transient grating technique
K Katayama; Q Shen; T Toyoda; M Yamaguchi; T Sawada
JOURNAL DE PHYSIQUE IV, EDP SCIENCES S A, 125, 349-353, Jun. 2005, Peer-reviwed, 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.
Scientific journal, English - Effect of ligand carboxylation on adsorption and photosensitization in Ru(II)-complex dye-sensitized nanocrystalline TiO(2) solar cell
T Ishihara; J Tokue; T Sano; Q Shen; T Toyoda; N Kobayashi
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, JAPAN SOC APPLIED PHYSICS, 44, 4B, 2780-2782, Apr. 2005, Peer-reviwed, The kinetics of dye adsorption onto a mesoporous TiO(2) film is compared between Ru(II) complex dyes with and without carboxy groups in the bipyridyl ligand, by diffuse reflectance spectroscopy at room temperature. Both dyes show adsorption saturation, and the dye without carboxy groups simply obeys the Langmuir isotherm equation. The dye with carboxy groups exhibits the same kinetics as the dye without carboxy groups in the period up to 20 min. However, in contrast to the latter, it increases its adsorption rate after this time, suggesting a change of the adsorption mode from physisorption to chemisorption. The carboxy group in the dye-sensitized solar cell is assumed to play a role in the chemical modification of the TiO(2) surface via a two-step adsorption from physisorption to chemisorption.
Scientific journal, English - Photosensitization of nanostructured TiO2 with CdSe quantum dots: effects of microstructure and electron transport in TiO2 substrates
Q Shen; D Arae; T Toyoda
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, ELSEVIER SCIENCE SA, 164, 1-3, 75-80, Jun. 2004, Peer-reviwed, Four sample types of nanostructured titanium dioxide (TiO2) electrodes were studied, variously prepared with TiO2 nanocrystalline particles of different sizes (15 and 27 nm in diameter) and with the addition of polyethylene glycol (PEG) binders having two different molecular weights (MW) (20,000 and 500,000). CdSe nanoparticles (CdSe quantum dots: CdSe QDs) were adsorbed on to each of the four types of TiO2 electrode using a chemical deposition technique. Photoacoustic (PA) and photoelectrochemical (PEC) current spectra were measured, together with the incident photon to current conversion efficiency (IPCE). The photosensitization by the CdSe QDs was confirmed. It was found that the PEC current and IPCE are strongly dependent on the TiO2 nanoparticle size and the MW of PEG in the TiO2/water paste. The correlation of the PEC and IPCE with the microstructure and the electron diffusion coefficient for each of TiO2 nanostructured electrode type are discussed, providing information which could lead to the optimization of dye-sensitized solar cells (DSSC). (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English - Characterization of nanostructured TiO2 electrodes sensitized with CdSe quantum dots using photoacoustic and photoelectrochemical current methods
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 43, 5B, 2946-2951, May 2004, Peer-reviwed, Two types of nanostructured titanium dioxide (TiO2) electrodes were prepared with anatase TiO2 nanoparticles of different sizes (average diameters of 15 and 27 nm). CdSe quantum dots were adsorbed onto each of the two types of TiO2 electrodes, by a chemical deposition (CD) technique, the average sizes of which increased to 7 nm on increasing the deposition time. Optical absorption and photoelectrochemical properties were characterized by using photoacoustic (PA) and photoelectrochemical (PEC) current methods. Redshift of the PA and PEC current spectra with increasing CdSe sizes was clearly observed, which indicates quantum confinement effects and photosensitization by the CdSe quantum dots. It was found that the PEC current spectra in the visible region were quite different for the two types of TiO2 electrodes for the same deposition time, although the PA spectra were very similar to each other. The correlation of the PEC current spectra with the microstructures of the two types of TiO2 electrodes was discussed, which provided information that could lead to the optimization of dye-sensitized solar cells (DSSC).
Scientific journal, English - Irradiation time dependence of Mn-doped ZnS nanocrystals with carboxylic acid on radiative and non-radiative transitions
T Toyoda; AB Cruz
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 438, 132-136, Aug. 2003, Peer-reviwed, ZnS nanocrystals doped with Mn2+ ions (ZnS:Mn) have attracted much attention in the past few years due to the changes in their optical properties in accordance with quantum confinement effects. ZnS:Mn nanocrystal systems form a new class of luminescent materials with some kind of applications because of the high fluorescence quantum efficiency. The addition of surface passivators and ultraviolet (UV) irradiation caused an increase of photoluminescence (PL) signal intensity. In this article, we report the UV irradiation time dependence of the optical absorption and PL signal intensities of ZnS:Mn nanocrystals with and without acrylic acid (AA). It is noted that the PL signal intensities of ZnS:Mn nanocrystals with and without AA undergo significant increases. On the contrary, the optical absorption intensities and/or non-radiative transition of ZnS:Mn nanocrystals with and without AA measured by photoacoustic (PA) technique decrease with the increase of UV irradiation. These experimental results suggest that there are possibilities of UV curing of the passivating AA polymer and photochemical reactions around the nanocrystals, which increase the fluorescence quantum efficiency. (C) 2003 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Irradiation time dependence of Mn-doped ZnS nanocrystals with carboxylic acid on radiative and non-radiative transitions
T Toyoda; AB Cruz
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 438, 132-136, Aug. 2003, Peer-reviwed, ZnS nanocrystals doped with Mn2+ ions (ZnS:Mn) have attracted much attention in the past few years due to the changes in their optical properties in accordance with quantum confinement effects. ZnS:Mn nanocrystal systems form a new class of luminescent materials with some kind of applications because of the high fluorescence quantum efficiency. The addition of surface passivators and ultraviolet (UV) irradiation caused an increase of photoluminescence (PL) signal intensity. In this article, we report the UV irradiation time dependence of the optical absorption and PL signal intensities of ZnS:Mn nanocrystals with and without acrylic acid (AA). It is noted that the PL signal intensities of ZnS:Mn nanocrystals with and without AA undergo significant increases. On the contrary, the optical absorption intensities and/or non-radiative transition of ZnS:Mn nanocrystals with and without AA measured by photoacoustic (PA) technique decrease with the increase of UV irradiation. These experimental results suggest that there are possibilities of UV curing of the passivating AA polymer and photochemical reactions around the nanocrystals, which increase the fluorescence quantum efficiency. (C) 2003 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Degradation effect of porous silicon on photoacoustic and photoluminescence signal intensities with photoexcitation
T Toyoda; R Torai
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 438, 137-141, Aug. 2003, Peer-reviwed, The discovery of efficient photoluminescence (PL) from electrochemically anodized porous silicon (PS) initiated a strong effort to characterize and understand PS properties. It was noted that quite soon after the discovery, PL undergoes significant degradation (long term instability) under normal photoexcitation conditions. Determining the source of the degradation is not only important with regard to assessing the optoelectronic potential of luminescent PS, but also might provide further insight into the origin of the luminescence and factors that control efficiency. In this article, we report the time-dependence of the photoacoustic (PA) signal intensities of PS with different anodization and etching times together with that of PL signal intensities. PA method is a photothermal (PT) technique, which is useful to obtain optical absorption characteristics for strongly scattering PS and existence of a silicon substrate. The experimental results suggest that the changes of the optical absorption centered by light exposure is different from that of luminescent center in anodizing and etching conditions, indicating the difference of photoenhanced oxidization processes (photochemical, photothermal, photoelectric and photostructure) in these conditions. (C) 2003 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Studies of optical absorption and electron transport in nanocrystalline TiO2 electrodes
Q Shen; T Toyoda
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 438, 167-170, Aug. 2003, Peer-reviwed, Four kinds of nanostructured titanium dioxide (TiO2) electrodes were prepared by changing the sizes of the TiO2 nanocrystalline particles (15 urn and 27 nm in diameter) and the molecular weight (MW) of the polyethylene glycol (PEG) (MW: 20 000 and 500 000) in TiO2/water paste, which was used for sample preparation. The effects of the sizes of the TiO2 particles and MW of the PEG on the microstructure, optical absorption, photoelectrochemical current (PEC) and electron transport properties of the resultant electrodes were studied. When the size of the TiO2 nanocrystalline particles used in the paste is larger, the porosity and the sizes of the TiO2 nanocrystals produced in the resultant electrodes increases. The TiO2/water paste with different MW of the PEG has different viscosity resulting to different microstructure and electron transport property of the TiO2 electrodes. It was found that the largest PEC current intensity and best electron transport property was obtained when the TiO2 electrode was prepared with the smaller TiO2 nanocrystals (15 nm) and the PEG with MW of 500 000. (C) 2003 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Effect of sensitization by quantum-sized CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes
T Toyoda; J Sato; Q Shen
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 297-299, Jan. 2003, Peer-reviwed, We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes, on which CdS nanocrystal particles are adsorbed, measured by the photoacoustic (PA) method together with the photoelectrochemical (PEC) current characteristics. The PA spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase in the number of CdS coating layers to 20 and becomes almost constant at more than 20 layers, indicating the possibility of the growth of CdS coated layers. The increase in PEC current intensity and a clear shift of spectra to the lower photon energy region are observed with the increased number of CdS coated layers, indicating the possibility of the transfer of photoexcited electrons of the CdS nanocrystals to the TiO2 conduction band. The PEC current spectrum shifts to the lower photon energy region and the intensity below the band-gap energy of TiO2 increases rapidly with an increase of in the number of CdS coating layers to 20 and decreases with a further increase in the number of layers coated to 40. Thus, nanocrystals of low-band-gap semiconductors are suitable for the sensitization of TiO2 PEC solar cells as well as dye sensitization. (C) 2003 American Institute of Physics.
Scientific journal, English - Effect of voltage treatment applied on photoacoustic and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes
T Toyoda; M Hayashi
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 337-339, Jan. 2003, Peer-reviwed, We report the effect of different voltages in a concentrated KCl electrolyte applied to highly porous, polycrystalline TiO2 films during their final preparation processes on photoacoustic (PA) and photoelectrochemical (PEC) current spectra. Below the band-gap energy region, the PA signal intensities of the TiO2 films with different voltage treatment applied are higher than those without treatment and they increase with an increase of applied voltage. These experimental results suggest an innerband transition from an increase in carrier concentration due to the formation of donor levels by partially reduced Ti ions (Ti4+-->Ti3+) by the voltage treatment. The PEC current spectra for applied voltage treatment over -1.5 V show two peaks above the band-gap energy region whose intensities increase rapidly above applied voltage of -1.5 V (eight times larger for voltage of -3.5 V than those without treatment), which is similar to that of the PA intensity at a photon energy of 2.0 eV. The modulation frequency dependence of the PEC current intensity at the peak position shows different characteristics depending on the voltage treatment applied, indicating the difference in PEC current response due to the formation of donor levels by the treatment. (C) 2003 American Institute of Physics.
Scientific journal, English - Apparent band-gap energies of mixed TiO2 nanocrystals with anatase and rutile structures characterized with photoacoustic spectroscopy
T Toyoda; Tsuboya, I
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 782-784, Jan. 2003, Peer-reviwed, Extreme small-sized titanium dioxide (TiO2) particles (nanocrystals) have been extensively used in the field of heterogeneous photo-oxidation catalysis for environmental cleanup. We have measured the optical absorption of mixed TiO2 nanocrystals with rutile and anatase structures (10-40 nm diameter) by photoacoustic (PA) spectroscopy. The values of apparent band-gap energies E-g of the TiO2 nanocrystals with different rutile contents were determined by the theory of interband transition. The value of E-g of a mixed TiO2 nanocrystal with rutile and anatase structures decreases continuously with the increase of rutile content. This indicates that E-g can be controlled by mixing the nanometer-sized TiO2 powders with rutile and anatase structures, hence, we can obtain TiO2 materials with an arbitrary apparent E-g between rutile and anatase structures. The PA spectrum of anatase-type TiO2 nanocrystals with a diameter of 15 nm shows a maximum around a photon energy of 3.9 eV, suggesting a quantum confinement effect with decreasing particle size. Applying the effective mass approximation to the PA spectrum, we can deduce the value of the hole effective mass in anatase-type TiO2 as 0.01 m(0) (where m(0) is electron rest mass). (C) 2003 American Institute of Physics.
Scientific journal, English - Photoacoustic spectroscopy of CdTe nanocrystals doped in a GeO2 glass matrix.
I.Tsuboya; D.Arae; Q.Shen; T.Toyoda
Review of Scientific Instruments, 74, 792, Jan. 2003, Peer-reviwed
Scientific journal, English - Mn ion concentration dependence of the photoacoustic and photoluminescence spectra of ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Review of Scientific Instruments, 74, 793, Jan. 2003, Peer-reviwed
Scientific journal, English - Exposure time dependence of the photoacoustic and photoluminescence intensities of porous silicon with different wavelengths of excitation light
T Toyoda; T Yamazaki; Q Shen
REVIEW OF SCIENTIFIC INSTRUMENTS, AMER INST PHYSICS, 74, 1, 869-871, Jan. 2003, Peer-reviwed, We report the exposure time dependence of the photoacoustic (PA) intensities of porous silicon (PS) with different excitation wavelengths together with that of the photoluminescence (PL). Although the PA intensity decreases somewhat slowly with exposure time, the PL intensity undergoes significant degradation at a first stage until 50 min. The exposure time dependencies of PA and PL show the combinations of two exponential decays. Fast decay time in the PA intensity decreases with the increase of the excitation wavelength. On the other hand, that in the PL intensity increases with the increase of the excitation wavelength. In the shorter wavelength excitation, the degradation at first stage in PL is faster than that in PA. However, in the larger wavelength excitation, the degradation at first stage in PL is slower than that in PA. Slow decay times in PA and PL increase with the increase of the excitation wavelength. These experimental results suggest that the change of the optical absorption center is different from that of luminescent center. The former is related to the formation of oxides inside PS layers although the latter relates to the surface of PS. (C) 2003 American Institute of Physics.
Scientific journal, English - Photoacoustic and photoelectrochemical current spectra of nanocrystalline TiO2 electrodes.
M.Hayashi; T.Toyoda
Proceedings of the International Workshop on Modern Science and Technology, 74-78, Sep. 2002
International conference proceedings, English - Porosity dependence of thermal conductivity for porous silicon characterized by photoaccoustic technique.
Q.Shen; T.Toyoda
Proceedings of the International Workshop on Modern Science and Technology, 79-82, Sep. 2002
International conference proceedings, English - Pressure dependence of Brillouin scattering spectra in semiconductors CdSxSe1-x doped glasses
Yasunari Takagi; Naoko Sato; Qing Shen; Taro Toyoda
Journal of Non-Crystalline Solids, 307-310, 785-789, Sep. 2002, Peer-reviwed, In the glasses doped with semiconductors CdSxSe1-x (low-pass sharp-cut filters), the semiconductors in the glass matrix are developed by thermal treatments with various annealing times (ta) and temperatures (Ta). No size effects were previously obtained for Brillouin shifts of these samples. Therefore, Brillouin scattering of the samples with various ta and Ta = 700 °C have been investigated under pressure. Any heat treatments made samples slightly soft and the internal strain inside the samples almost vanished. The slopes, d log ω/dP, were plotted as a function of ta 1/3, respectively. It was possible that the slopes indicated a linear increase. This result revealed that the semiconductor micro-crystals in the glasses contributed to the stiffening of the glasses. There seems to be some kind of size effect. © 2002 Elsevier Science B.V. All rights reserved.
International conference proceedings, English - Photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 films fabricated with different applied voltage treatments
T Toyoda; M Hayashi; J Sato; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3367-3370, May 2002, Peer-reviwed, We report the effect of voltage in a concentrated KCl electrolyte applied to highly porous, polycrystalline TiO2 films during their final preparation processes on photoacoustic (PA) and photoelectrochemical (PEC) current spectra. The PA signal intensities of the TiO2 films with different applied voltage treatments are higher than those without the treatments below the band-gap region, suggesting an inner-band transition due to an increase in carrier concentration by the voltage treatments. The PA intensity below the band-gap region increases with the increase of the applied voltage, indicating the increase in the carrier concentration due to the formation of donor levels by partially reduced Ti ions (Ti4+ --> Ti3+). The PEC spectra for the applied voltage treatments with -1.5 V and without the treatments show broad bands at approximately 3.31 eV. The PEC spectra for the applied voltage treatments over -1.5 V show two peaks at approximately 3.31 eV and 3.88 eV. The PEC intensities at each peak position increase rapidly above the applied voltage of -1.5 V (eight times larger for the voltage of -3.5 V than those without the treatments), which is similar to that of the PA intensity at a photon energy of 2.0 eV. The increase of the PEC intensity with different applied voltage treatments implies an increase in carrier concentration due to the formation of donor levels by the treatments. These results suggest that TiO2 electrodes suitable for the sensitization by dyes or quantum-sized semiconductors can be obtained by applying the voltage treatments.
Scientific journal, English - Piezoelectric photothermal spectra of Co doped ZnO semiconductor
K Sakai; A Fukuyama; T Toyoda; T Ikari
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3371-3373, May 2002, Peer-reviwed, Piezoelectric photothermal spectroscopy (PPTS) is a powerful tool for investigating optical properties of semiconductors. Temperature dependence of the PPT signal intensity of the Co-doped ZnO semiconductor was measured from 4.2 to 300 K. The Co concentration dependence of the PPT signal intensity was also studied to clarify the effect of doping with transition metals. In the case of doping at a low level, Co atoms form deep impurity levels in the ZnO matrices in the spectral region from 1.2 to 1.7 eV. However, for samples doped at higher levels, many crystal field split-off levels from localized Co2+ ions appeared at approximately 0.7-1.2 and 1.7-2.4 eV and these two bands became dominant in the spectra. The doping effect was investigated from the point of view of nonradiative transition for the first time.
Scientific journal, English - Photoacoustic and photoluminescence spectra of ZnS : Mn nanocrystals
T Toyoda; J Matsuzawa; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 41, 5B, 3383-3386, May 2002, Peer-reviwed, The optical absorption spectra of ZnS:Mn nanocrystals can be obtained by applying photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of highly scattered materials. The peak position in PA difference spectra increases linearly within experimental accuracy with the decrease of Mn2+ ion concentration. These results correspond to the following possibilities, (1) the increase of the higher excited energy states relative to the ground state of (6)A(1), (2) the increase of state density for the higher excited states and (3) the increase of transition probability from the (6)A(1) state to the higher excited states. These possibilities suggest the hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn2+ ion impurity. The peak position of the PL spectrum (the transition from T-4(1) to (6)A(1) states) is similar to2.08 eV with a half width of 0.24 eV, similar to that of the bulk ZnS:Mn, and it is independent of the Mn2+ ion concentration. This result might be attributed to the fact that the Mn2+ emission is due to phonon assisted transition. Hence, there might be a slight shift of the peak position with increase of Mn2+ ion concentration due to hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn2+ ion impurity. The peak intensity of the PL spectrum shows a maximum at a certain value of Mn2+ ion concentration and it decreases with the increase of concentration of Mn2+ ion impurities (concentration quenching).
Scientific journal, English - Modification of photoacoustic and photoluminescence spectra of Manganese-doped nanocrystals of ZnS due to carboxylic acids.
T.Toyoda; M.Unno; N.Nakajima
Physica B, 316-317, 472-475, May 2002, Peer-reviwed
Scientific journal, English - Effect of size confinement on CdSe nanocrystals in a GeO2 glass matrix characterized by photoacoustic spectroscopy.
T.Toyoda; D.Arae; Q.Shen
Physica B, 316-317, 476-478, May 2002, Peer-reviwed
Scientific journal, English - 量子コロイド化した半導体超微結晶の無輻射遷移過程と化学計測・分析への応用
豊田太郎
平成9年度ー平成12年度科学研究費補助金基盤研究(c)(2)研究成果報告書, 1-128, Feb. 2002
Scientific journal, Japanese - Photothermal characterization of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
T Toyoda; M Hayashi; J Sato; Q Shen
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, KLUWER ACADEMIC PUBL, 69, 3, 1037-1044, 2002, Peer-reviwed, We report the optical absorption characteristics of highly porous, polycrystalline TiO2 electrodes and the influence of hydrolysis period for the preparation processes by photoacoustic (PA) spectroscopy together with photoelectrochemical (PEC) current ones. The PA spectra show peaks which are attributed to the lowest transition energy due to the quantum confinement effect. The peak intensity decreases with the increase of hydrolysis periods, indicating the possibilities of the changes in the thermal properties and the densities due to hydrolysis processes. The PEC spectra indicate that the photocurrent intensity also show peak and that of the longer hydrolysis periods is somewhat smaller than others, indicating the increase of interface states due to the formation of grain boundaries with the increase of hydrolysis processes.
Scientific journal, English - Characterization of thermal properties of porous silicon film/silicon using photoacoustic technique
Q Shen; T Toyoda
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, SPRINGER, 69, 3, 1067-1073, 2002, Peer-reviwed, We have applied photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching. Four PS samples with close thicknesses but greatly different porosities (from 20 to 60%) were examined. From the dependences of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration (TDC), effective thermal diffusivities for the two-layered PS/Si samples were determined and found to decrease greatly from 0.095 to 0.020 cm(2) s(-1) as the porosity increased from 20 to 60%.
Scientific journal, English - Photoacoustic spectra of CdSe nanocrystals in a GeO2 glass matrix.
Dai Arae; Qing Shen; Taro Toyoda
Analytical Sciences, 17, Supplement, i1149-i1152, 2002, Peer-reviwed
Scientific journal, English - Effect of voltage treatment on the photoacoustic and photoelectrochemical current spectra of highly poros, polycrystalline TiO2 electrodes.
Jun Sato; Masashi Hayashi; Qing Shen; Taro Toyoda
Analytical Sciences, 17, Supplement, i1153-i1155, 2002, Peer-reviwed
Scientific journal, English - Effect of voltage treatment on modulation frequency dependence of the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 electrodes
T Toyoda; J Sato; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 40, 5B, 3583-3586, May 2001, Peer-reviwed, We report the effect of voltage on a concentrated KCl electrolyte applied to a highly porous TiO2 electrode during its final preparation process on the photoelectrochemical current (PEC) spectra. Optical absorption measurements were monitored by a photoacoustic (PA) method. The PA spectrum of the TiO2 electrode with the voltage treatment is similar to that without the treatment above the band-gap region. Below the band-gap region, the intensities of the PA spectrum of the TiO2 electrode with the voltage treatment are higher than those without the treatment, suggesting an increase of carrier concentration by the voltage treatment. The PEC spectra without the voltage treatment show a monotonic increase with the photon energy above the band-gap region. The PEC intensity with the voltage treatment increases rapidly immediately above the band-gap region and shows saturated values. The PEC intensity of the TiO2 electrode with the voltage treatment is approximately twice that without the treatment above the band-gap region. The increase of the PEC intensity implies an increase of carrier concentration due to partially reduced Ti ions. The modulation frequency dependence of the PEC intensity of TiO2 electrodes with and without the voltage treatment shows two types of exponential decay. The decay rate in the TiO2 electrode with the voltage treatment is slower than that without the treatment below the modulation frequency of 100 Hz. The decay rate with the voltage treatment agrees with that without the treatment above the modulation frequency of 100 Hz.
Scientific journal, English - Effect of voltage treatment on modulation frequency dependence of the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 electrodes
T Toyoda; J Sato; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, INST PURE APPLIED PHYSICS, 40, 5B, 3583-3586, May 2001, Peer-reviwed, We report the effect of voltage on a concentrated KCl electrolyte applied to a highly porous TiO2 electrode during its final preparation process on the photoelectrochemical current (PEC) spectra. Optical absorption measurements were monitored by a photoacoustic (PA) method. The PA spectrum of the TiO2 electrode with the voltage treatment is similar to that without the treatment above the band-gap region. Below the band-gap region, the intensities of the PA spectrum of the TiO2 electrode with the voltage treatment are higher than those without the treatment, suggesting an increase of carrier concentration by the voltage treatment. The PEC spectra without the voltage treatment show a monotonic increase with the photon energy above the band-gap region. The PEC intensity with the voltage treatment increases rapidly immediately above the band-gap region and shows saturated values. The PEC intensity of the TiO2 electrode with the voltage treatment is approximately twice that without the treatment above the band-gap region. The increase of the PEC intensity implies an increase of carrier concentration due to partially reduced Ti ions. The modulation frequency dependence of the PEC intensity of TiO2 electrodes with and without the voltage treatment shows two types of exponential decay. The decay rate in the TiO2 electrode with the voltage treatment is slower than that without the treatment below the modulation frequency of 100 Hz. The decay rate with the voltage treatment agrees with that without the treatment above the modulation frequency of 100 Hz.
Scientific journal, English - ZnOセラミックス中のCo不純物の光音響スペクトル
豊田太郎; 海野 誠; 沈 青
電子情報通信学会技術研究報告, The Institute of Electronics, Information and Communication Engineers, 100, 640, 17-22, 2001, Photoacoustic(PA) spectroscopy is applied to study the optical absorption of ZnO ceramics doped with 0-2.0 mol% CoO impurities sintered at 1200℃. PA spectroscopy is useful for scattering materials such as ceramics to get the optical absorption characteristics. Both of PA intensity and phase spectra showed the optical absorption peaks by Co impurities which were interpreted in terms of the inner transition of the(3d)^7 electrons in Co^<2+>(crystal field splitting). These signal intensities increase linearly with the increase of Co impurities at the low concentration region. At higher concentration region, they showed the constant values. These nonlinearlity of the PA intensities suggest the increase of magnetic interaction between Co impurities, and, hence, the PA intensities are saturated with the increase of Co impurities.
Japanese - Effect of size confinement on CdSe nanocrystals in a GeO_2_ glass matrix characterized by photoacoustic spectroscopy
T. Toyoda; D. Arae; T. Iio; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 238-239, 2001
English - Optical absorption characteristics and modulation frequency dependence of the photoelectrochemical current spectra of highly porous,polycrystalline TiO_2_ electrodes
T. Toyoda; J. Sato; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 240-241, 2001
English - Influence of anodization period on the photoacoustic spectra of poros silicon
T. Toyoda; R. Torai; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 242-243, 2001
English - Photoacoustic spectra of mixed TiO_2_ ultrfine powders with rutile and anatase types
T. Toyoda; R. Taira; Q. Shen
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 244-245, 2001
English - Photoacoustic spectra of manganese-doped nanocrystals of ZnS with and without modification by methcrylic acid
T. Toyoda; M. Unno; N. Nakajima
Extended Abstracts of the 4th NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 268-269, 2001
English - ポーラスSiの光音響スペクトルの陽極化成電流時間依存性
虎井礼司; 沈 青; 豊田太郎
第48回応用物理学関係連合講演会講演予稿集, 812, 2001
Japanese - 光音響分光法によるGeO_2_ガラス中に分散したCdSeナノクリスタル野評価
新江 大; 沈 青; 豊田太郎
第48回応用物理学関係連合講演会講演予稿集, 1419, 2001
Japanese - フラクタル状ポーラスTiO_2_電極の光吸収と光電流スペクトルの変調周波数依存性
佐藤 淳; 沈 青; 豊田太郎
第48回応用物理学関係連合講演会講演予稿集, 1420, 2001
Japanese - ルチル型とアナターゼ型のTiO_2_混合微粒子系の光音響法による評価
豊田太郎; 平 梨恵; 沈 青
第48回応用物理学関係連合講演会講演予稿集, 1420, 2001
Japanese - 透過型光音響分光法による半導体の熱物性と電子物性の評価
沈 青; 豊田太郎
熱物性, 15, 15-22, 2001
Japanese - Photoacoustic spectra of mixed ceramics of Al2O3 and Cr2O3
T. Toyoda; H. Yamamoto; M. Togashi; Q. Shen
Analytical Sciences, 17, s43-s46, 2001
English - Photoacoustic spectra of low-dimensional magnet of VOMoO4
T. Toyoda; Q. Shen; I. Shiozaki
Analytical Sciences, 17, s47-s49, 2001
English - Ultrafast dynamics of CdSxSe1-x nanocrystals doped in glasses studied by ultrafast transient lensing effect
Q. Shen; T. Toyoda; Y. Hirose; K. Katayame; H. Yui; M. Fujinami; T. Sawada; A. Harata
Analytical Sciences, 17, s241-s244, 2001
English - Effect of size confinement on photoacoustic spectra and photothermal response of CdSxSe1-x nano-crystals in a glass matrix
T. Toyoda; Q. Shen
Analytical Sciences, 17, s259-s261, 2001
English - Characterization of optical and thermal properties of porous silicon using photo-acoustic technique
Q. Shen; T. Takahashi; T. Toyoda
Analytical Sciences, 17, s281-s283, 2001
English - Effect of voltage treatment on modulation frequency dependence of the photoacoustic and photoelectrochemical current spectra of highly porous
T. Toyoda; J. Sato; Q. Shen
Japanese Journal of Applied Physics, 40, 3853-3856, 2001, Peer-reviwed
Scientific journal, English - Photoacoustic spectra of mixed TiO2 ultra-fine powders with rutile and anatase structures
T. Toyoda; R. Taira; Q. Shen; M. Ohmori
Jpn. J. Appl. Phys., 40, 3857-3590, 2001
English - ポーラスSiの光音響スペクトルと蛍光スペクトルに及ぼす化学エッチング効果
豊田太郎; 高橋徹治; 沈 青
日本分光学会平成13年度春季講演会講演要旨集, 60, 2001
Japanese - ポーラスSiの光音響スペクトルと蛍光スペクトルの陽極化成時間依存性
豊田太郎
日本分光学会平成13年度春季講演会講演要旨集, 61, 2001
Japanese - ZnS:Mnナノ粒子系の光音響および蛍光スペクトル
豊田太郎
日本分光学会平成13年度春季講演会講演要旨集, 62, 2001
Japanese - Photo-acoustic spectra of CdSe nanocrystals in a GeO2 glass matrix
T. Toyoda; D. Arae; Q. Shen
Abstracts of the International Congress on Analytical Sciences 2001, 277, 2001
English - Effect of voltage treatments on the photoacoustic and photoelectrochemical current spectra highly porous, polycrystalline TiO2 electrodes
T. Toyoda; J. Sato; Q. Shen
Abstracts of the International Congress on Analytical Sciences 2001, 277, 2001
Scientific journal, English - Photoacoustic and photoluminescence spectra of Manganese-doped nanocrystals of ZnS with and without modification by carboxylic acids
T. Toyoda; M. Unnno; N. Nakajima
Abstracts of the International Congress on Analytical Sciences 2001, 278, 2001
Scientific journal, English - Photo- acoustic and photoluminescence spectra of porous silicon with different anodization period
T. Toyoda; R. Torai; Q. Shen
Abstracts of the International Congress on Analytical Science 2001, 278, 2001
English - Influence of anodization period on the photoacoustic spectra of porous silicon
T. Toyoda; R. Torai; Q. Shen
Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter, 216, 2001
English - Photoacoustic and photoluminescence spectra of ZnS with and without modification by carboxylic acids
T. Toyoda; M. Unnno; N. Nakajima
Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter, 217, 2001
English - Effect of size confinement on CdSe nanocrystals in a GeO2 glass matrix characterized by photoacoustic spectroscopy
T. Toyoda; D. Arae; Q. Shen
Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter, 218, 2001
Scientific journal, English - ポーラスSiの光吸収と発光の時間依存性
虎井礼司; 沈 青; 豊田太郎
第62回応用物理学会学術講演会講演予稿集, 1076, 2001
Japanese - フラクタル状TiO2膜の光音響スペクトル
佐藤 淳; 林 雅; 沈 青; 豊田太郎
第62回応用物理学会学術講演会講演予稿集, 1082, 2001
Japanese - ZnS:Mnナノ粒子系の光音響スペクトルと蛍光特性
豊田太郎; 海野 誠; 中島伸夫
第62回応用物理学会学術講演会講演予稿集, 1107, 2001
Scientific journal, Japanese - Photoacoustic spectra of mixed ceramics of Al2O3 and Cr2O3.
Taro Toyoda; Hidenori Yamamoto; Masami Togashi; Qing Shen
Analytical Sciences, 17, pp. s43-s46, 2001, Peer-reviwed
Scientific journal, English - Photoacoustic spectra of low-dimensional magnet of VOMoO4.
Taro Toyoda; Qing Shen; Ikuyo Shiozaki
Analytical Sciences, 17, s47-s49, 2001, Peer-reviwed
Scientific journal, English - Photoacoustic spectra of mixed ceramics of Al2O3 and Cr2O3.
Taro Toyoda; Hideyuki Yamamoto; Masami Togashi; Qing Shen
Analytical Sciences, 17, s43-s46, 2001, Peer-reviwed
Scientific journal, English - Ultrafast dynamics of CdSxSe1-x nanocrystals doped in GeO2 glasses studied by ultrafast lensing effect.
Qing Shen; Taro Toyoda; Y. Hirose; Kenji Katayama; H. Yui; M. Fujinami; Tsuguo Sawada; Akira Harata
Analytical Sciences, 17, s241-s243, 2001, Peer-reviwed
Scientific journal, English - Effect of size cionfinement on photoacosutic spectra and photothermal respense of CdSxSe1-x nanocrystals in a glass matrix.
Taro Toyoda; Qing Shen
Analytical Sciences, 17, s259-s261, 2001, Peer-reviwed
Scientific journal, English - Characterization of optical and thermal properties of porous silicon using photoacoustic technique.
Qing Shen; Tetsuharu Takahashi; T. Toyoda
Analytical Sciences, 17, s281-s283, 2001, Peer-reviwed
Scientific journal, English - Proceeding of the 25th International Conference on the Physics of Semiconductors
Ikuyo Shiozaki; S. Tanaka; Shinji Wada; Taro Toyoda
220-221, 2001, Peer-reviwed
International conference proceedings, English - Photoacoustic spectra of mixed TiO2 ultrafine powders with rutile and anatase struct5ure.
Taro Toyoda; Rie Taira; Qind Shen; Masahiro Ohmori
Japanese Journal of Applied Physics, 40, 3587-3590, 2001, Peer-reviwed
Scientific journal, English - Evaluation of ZnO varistors by photoacoustic spectroscopy
Y. Ohbuchi; A. Kimura; T. Kawahara; Jun Morimoto; Taro Toyoda
Japanese Journal of Applied Physics, 40, 3605-3609, 2001, Peer-reviwed
Scientific journal, English - Photoacoustic, photoelectrochemical current, and photoluminescence characterization of highly porous, polycrystalline TiO2 electrodes.
Taro Toyoda; T. Hayakawa; Qing shen
Progress of Natural Sciences, 11, s199-s204, 2001, Peer-reviwed
Scientific journal, English - Photoacoustic investigation of CdInGaS4.
Qing Shen; Taro Toyoda
256-261, 2001, Peer-reviwed
Scientific journal, English - Photoacoustic, photoelectrochemical current, and photoluminescence spectra of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
T Toyoda; T Hayakawa; Q Shen
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, ELSEVIER SCIENCE SA, 78, 2-3, 84-89, Dec. 2000, We report the effect of the application of a voltage in a concentrated KCI electrolyte on photoacoustic (PA), photoelectrochemical current (PEC), and photoluminescence (PL) spectra for the preparation of highly porous, polycrystalline TiO2 electrodes. The intensities of the PA spectra of the TiO2 electrode with the voltage treatments are larger than those without the treatments below the bandgap region, suggesting a decrease of scattering and/or an increase of the carrier concentration by the voltage treatments. The modulation frequency dependence of the PA intensity above the bandgap of the former is different from the Latter in the low-frequency region, indicating a good contact (namely, the reduction of interface states) between the TiO2 film and the substrate (Ti metal). Also, the modulation frequency dependence of the PA phase above the bandgap region of the former is different from the latter, suggesting larger thermal conductivity of the TiO2 electrode with the voltage treatments than that without treatments. The intensity of the PEC spectrum of the TiO2 electrode with the voltage treatments is threefold that without the treatments above the bandgap region, also suggesting good contact (namely, the reduction of interface states). Although the peak positions in the PL spectra are in agreement with each other, the PL intensity of the TiO2 electrode with the voltage treatments is higher, suggesting the increase of the radiative recombination center owing to the increase of donor levels formed by partially reduced Ti ions. (C) 2000 Elsevier Science S.A. All rights reserved.
Scientific journal, English - Photoacoustic and photoluminescence studies of porous silicon etched by low-concentration hydrofluoric acid
T Toyoda; T Takahashi; Q Shen
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 88, 11, 6444-6450, Dec. 2000, We applied photoacoustic (PA), photoluminescence (PL), photoluminescence excitation (PLE), and atomic force microscopy (AFM) techniques on porous silicon (PS) layers to study the influence of chemical etching by low-concentration hydrofluoric acid. The chemical etching reveals the formation of PS layers of small dimensions by AFM observations, indicating the possibility of a strong quantum confinement effect. PA spectroscopy is useful to obtain the optical absorption characteristic for strongly scattering media such as PS and it helps to confirm the above speculation by indicating the blueshift of the fundamental absorption edge for the PS layer with chemical etching. PL spectroscopy also confirms the possibility of a quantum confinement effect by revealing the strong intensity and blueshift for the PS layer with chemical etching. PLE measurements suggest that the site for the radiative processes is different from that for the recombination of carriers and the PL of PS layers were dominated only by small crystallites in various size distributions. (C) 2000 American Institute of Physics. [S0021-8979(00)02919-4].
Scientific journal, English - Photoacoustic and photoluminescence characterization of highly porous, polycrystalline TiO2 electrodes made by chemical synthesis
T Toyoda; T Hayakawa; K Abe; T Shigenari; Q Shen
JOURNAL OF LUMINESCENCE, ELSEVIER SCIENCE BV, 87-9, 1237-1239, May 2000, We report the effect of the application of a voltage in a concentrated electrolyte on photoacoustic (PA) and photoluminescence (PL) spectra for the preparation of porous TiO2 electrodes. The intensities of the PA spectrum of the TiO2 electrode with the treatments are larger than those without the treatments below the band-gap region, indicating the formation of defect states at the surface. The modulation frequency dependence of the PA intensity of the former is different from the latter in the low-frequency region, indicating good contact and/or the reduction of the interface states between TiO2 film and substrate. The PL spectrum of the former shows more intense signal intensities than the latter, indicating the increase of recombination processes by the defect states at the surface. These states might aid in the formation of a good Schottky barrier. (C) 2000 Elsevier Science B.V. All rights reserved.
Scientific journal, English - Photoacoustic characterization of thermal and electronic transport properties of CdInGaS4 in a transmission detection configuration
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 39, 5B, 3164-3168, May 2000, Photoacoustic (PA) measurement under a transmission detection configuration (TDC) was applied to study the thermal and electronic transport properties of CdIaGaS(4). It was shown that the PA signal in the TDC originated from both electronic transport process and heat transport process in the semiconductor sample, and these could be separated by changing the modulation frequency of the elicited light. By fitting the theoretically calculated PA signal amplitudes as a function of the modulation frequence to the experimental ones for a variety of thicknesses, the values of the excess-carrier lifetime, carrier diffusivity, surface recombination velocity, and thermal diffusivity of the CdInGaS4 were determined. The contributions of three heat sources to the PA signals were investigated. We found that the PA signals of CdInGaS4 mainly resulted from nonradiative surface recombination under our experimental conditions.
Scientific journal, English - Dependence of the photoacoustic signal intensity on modulation frequency for CdInGaS4 crystals under a transmission detection configuration
Q Shen; T Toyoda
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 39, 2A, 511-512, Feb. 2000, Peer-reviwed, Dependence of the photoacoustic (PA) signals on the modulation frequency was measured for CdInGaS4 crystals in the reflection and transmission detection configurations (RDC and TDC). The PA signals originate from both the thermal diffusion and photo-excited carrier diffusion processes under TDC. The two processes can be separated by changing the modulation frequency of the excited light. The experimental results show the possibility of characterizing the thermal and electronic properties of CdInCaS4 crystals by the PA technique in TDC.
Scientific journal, English - Dependence of the Photoacoustic Signal Intensity on Modulation Frequency for CdInGaS4 Crystals under a Transmission Detection Configuration.
Q. Shen; T. Toyoda
Japaneese Journal of Applied Physics, 39, 511-512, 2000
Scientific journal, English - Electrical Resistivity and Band Structure in VOMoO_4_
I. Shiozaki; T. Toyoda
Abstract of the 18th General Conference of the Condensed Matter Division of the European Physical Society, 153, 2000
English - Photoacoustic, Electrochemical Photocurrent, and Photoluminescence Spectra of Highly Porous, Polycrystalline TiO_2_ electrodes Fabricated by Chemical Synthesis
T. Toyoda; T. Hayakawa; Q. Shen
Extended Abstracts of the 3rd NIMC International Symposium on Photoreaction Control and Phtofunctional Materials, 256-257, 2000
English - Characterization of Electronic States for TiO_2_Powders by Photoacoustic Spectroscopy
T. Toyoda; H. Kawano; Q. Shen; A. Kotera; M. Ohmori
Extended Abstracts of the 3rd NIMC International Symposium on Photoreaction Control and Photofunctional Materials, 258-259, 2000
English - CdSeをドープしたGeO_2_ガラスの作製と光音響分光法による評価
沈 青; 飯尾能将; 豊田太郎
第47回応用物理学関係連合講演会講演予稿集, 1366, 2000
Japanese - Al_2_O_3_とCr_2_O_3_との結晶セラミックスの光音響スペクトル
豊田太郎; 山本洋秀; 富樫昌美; 沈 青
第47回応用物理学関係連合講演会講演予稿集, 1366, 2000
Japanese - TiO_2_膜の光音響ならびにフォトルミネッセンススペクトルに及ぼす電圧印加処理効果
豊田太郎; 早川智也; 沈 青
第47回応用物理学関係連合講演会講演予稿集, 1366, 2000
Japanese - TiO_2_膜の光音響ならびに光電流スペクトルに及ぼす電圧印加処理効果
豊田太郎; 早川智也; 沈 青
第47回応用物理学関係連合講演会講演予稿集, 1367, 2000
Scientific journal, Japanese - Photoluminescence and photoacoustic investigations of the photodarkening effect in CdS_x_Se_1-x_ nanocrystal-doped glasses
Q. Shen; K. Abe; T. Shigenari; T. Toyoda
J. Lumin, 87-89, 444-446, 2000
English - Characterization of electronic states of TiO2 powders by photoacoustic spectroscopy
T. Toyoda; H. Kawano; Q. Shen; A. Kotera; M. Ohmori
Jpn. J. Appl. Phys., 39, 3160-3163, 2000
English - Modulation frequency dependence of the photoacoustic intensities for multinary compound CdInGaS4 with a dc electric field
T. Toyoda; M. Yamamuro; Q. Shen
Jpn. Appl. Phys., 39,Suppl.39-1, 457-458, 2000
English - Modulation frequency dependences of photoacoustic signal intensities and phase for CdInGaS
Q. Shen; T. Toyoda
Jpn. Appl. Phys., 39,Suppl.39-1, 459-460, 2000
English - Brillouin scattering of glasses doped with semiconductors CdS_x_Se_1-x_
Y. Takagi; N. Sato; Q. Shen; T. Toyoda
Trans. Mater. Res. Sco. Jpn., 25, 951-954, 2000
English - Effect of size confinement on photoacoustic spectra and photothermal response of CdS_x_Se_1-x_（0≦x≦1）nanocrystals in a glass matrix
T. Toyoda; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena,（invited）, A-26-p1, 2000
English - Effect of chemical etching on photoacoustic and photocurrent spectra of highly porous, polycrystalline TiO_2_ electrodes
T. Toyoda; T. Hayakawa; H. Kawano; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, A-26-p4, 2000
English - Photoacoustic spectra of mixed ceramics of Al_2_O_3_ and Cr_2_O_3_
T. Toyoda; H. Yamamoto; M. Togashi; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-01-11, 2000
English - Photoacoustic spectra of low-demensional magnet of VOMoO_4_
T. Toyoda; Q. Shen; I. Shiozaki
Abstracts of the 11th International Conference on Photoacoustic and Photohermal Phenomena, P-01-12, 2000
English - Photoacoustic studies of thermal and electronic properties of CdInGaS_4_
Q. Shen; T. Toyoda
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-03-25, 2000
English - Ultrafast dynamics of CdSxSe1-x nanocrystals doped in glasses studied by ultrafast lensing effect
Q. Shen; T. Toyoda; Y. Hirose; K. Katayama; M. Fujinami; T. Sawada; A. Harata
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-05-06, 2000
English - Photoacoustic and photolmminescence studies of porous silicon etched by low-concentration HF
T. Toyoda; T. Takahashi; M. Yammamuro; Q. Shen
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-06-12, 2000
English - Characterization of electronic states of TiO2 powders by photoacoustic spectroscopy
T. Toyoda; H. Kawano; Q. Shen; A. Kotera; M. Ohmori
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-06-13, 2000
English - Chracterization of thermal and electronic properties of porous silicon using photoacoustic technique
Q. Shen; T. Takahashi; T. Toyoda
Abstracts of the 11th International Conference on Photoacoustic and Photothermal Phenomena, P-06-14, 2000
English - ポーラス化TiO_2_電極の，光音響ならびに光電流スペクトルに及ぼす電圧印加処理効果
豊田太郎; 早川智也; 河野 寛; 沈 青
第8回「高効率太陽電池および太陽光発電システム」ワークショップ予稿集, 155-158, 2000
Japanese - Chracterization of thermal and electronic properties of CdInGaS_4_ by photoacoustic technique
Q. Shen; T. Toyoda
Abstracts Book of the 1st Asian Conference on Crystal Growth and Crystal Technology, 427, 2000
English - Photoacoustic spectra of CdSe nenocrystals grown in a GeO_2_ glass mitrix
T. Toyoda; Q. Shen
Abstracts Book of the 1st Asian Conference on Crystal Growth and Crystal Technology, 428, 2000
English - Optical absorption characterization of low-dimensional magnet of VOMoO_4_ by photoacoustic spectroscopy
T. Toyoda; Q. Shen; I. Shiozaki
Abstracts Book of the 1st Asian Conference on Crystal Growth and Crystal Technology, 497, 2000
English - Low-dimensional magnetism in polymorphic compounds, VOMoO_4_ and (V_0.56_, Mo_0.44_)_2_O_5_
I. Shiozaki; T. Tanaka; S. Wada; T. Toyoda
Abstracts of the 25th International Conference on the Physics of Semiconductors, 55, 2000
Scientific journal, English - Effect of size confinement on ultrafast relaxation dynamics of CdS_x_Se_1-x_（x=0.26）nanocrystals in a glass matrix investigated by ultrafast lensing effect
T. Toyoda; Q. Shen; Y. Hirose; K. Katayama; M. Fujinami; T. Sawada; A. Harata
Abstracts of the 25th International Conference on the Physics of Semiconductors, 535, 2000
English - 光音響法によるルチル型成分含有率の異なるTiO_2_微粒子の評価
豊田太郎; 平 梨恵; 河野 寛; 沈 青; 大森将弘
第21回日本熱物性シンポジウム講演論文集, 138-140, 2000
Japanese - 光音響法によるポーラスシリコンの熱物性評価
沈 青; 高橋徹治; 豊田太郎
第21回日本熱物性シンポジウム講演論文集, 157-159, 2000
Japanese - Photoacoustic, photoelectrochemical current, and photoluminescence spectra of highly porous, polycrystalline TiO_2_ electrodes fabricated by chemical synthesis
T. Toyoda; T. Hayakawa; Q. Shen
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 77, 2000
English - Dependence of the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO_2_ electrodes on mudulation frequency
J. Sato; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 86, 2000
English - Photoacoustic spectra of mixed TiO_2_ powders with rutile and anatase types
R. Taira; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 87, 2000
English - Photoacoustic spectra of CdS nanocrystals in a GeO_2_ glass matrix
D. Arae; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 88, 2000
English - Photoacoustic spectra of ternarhy and multinary semiconducting compound CdIn_2_S_4_ with different stoichiometric ratio
N. Nakajima; T. Takizawa; Q. Shen; T. Toyoda
Conference Digest of the 8th International Workshop on Modern Acoustics-NDE, 89, 2000
English - フラクタル状ポーラス化TiO_2_膜の光音響・光電流スペクトル変調周波数依存性
佐藤 淳; 沈 青; 豊田太郎
第21回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 109-110, 2000
Japanese - ルチル型とアナターゼ型のTiO_2_混合微粒子系の光音響スペクトル
豊田太郎; 平 梨恵; 沈 青
第21回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 111-112, 2000
Japanese - Dependence of the photoacoustic signal intensity on modulation frequency for CdInGaS4 crystals imder a transmission detection configuration
Q.Shen; T.Toyoda
Japanese Journal of Applied Physics, 39, 511-512, 2000, Peer-reviwed
Scientific journal, English - Brilouin Scattering of Glasses Doped with Semiconducters CdS_x_Se_1-x_
Yasunari Takagi; Naoko Sato; Qing Shen; Taro Toyoda
第11回日本MRS学術シンポジウム予稿集，（KSP 神戸サイエンスパーク）, 221, Dec. 1999
English - 半導体（CdS_x_Se_1-x_）ドープガラスの顕微ブリルアン散乱
佐藤真子; 高木康成; 沈 青; 豊田太郎
日本物理学会講演概要集４，（岩手大）, 620, Sep. 1999
Japanese - Photoacoustic and photoluminescence characterization of highly porous polycrystalline TiO_2_ electrodes made by chemical synthesis
T. Toyoda; T. Hayakawa; K. Abe; T. Shigenari; Q. Shen
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 176, Aug. 1999
English - Photoluminescence and photoacoustic investigations of the photodarkening effect in CdS_x_Se_1-x_ nanocrystal-doped glasses
Q. Shen; K. Abe; T. Shigenari; T. Toyoda
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 122, Aug. 1999
English - Influence of chemical etching for porous silicon of photoacoustic, photoluminescence, and photoluminescence excitation spectra
T. Toyoda; T. Takahasi; M. Yamamuro; K. Abe; T. Shigenari; Q. Shen
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 224, Aug. 1999
English - Photoacoustic and photocurrent studies of highly porous TiO2 electrodes sensitized by quantum-sized CdS
T Toyoda; K Saikusa; Q Shen
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 38, 5B, 3185-3186, May 1999, Photoacoustic (PA) and photocurrent (PC) spectra of highly porous TiO2 have been measured. The PA spectrum shifts to the lower energy region and the PA intensity below the fundamental absorption edge of TiO2 increases rapidly with an increase in the number of CdS coating layers to seven and becomes almost constant at more than seven layers. The increase in PC intensity and a clear shift of spectra to the lower energy region are observed with increasing number of CdS layers coated, indicating the possibility of the transfer of photoexcited electrons of CdS nanocrystals to the conduction band of TiO2.
Scientific journal, English - Siの光音響スペクトルの電界依存性
高橋徹治; 豊田太郎
電子情報通信学会技術研究報告（超音波）, US98-1, 17-22, Apr. 1999
Japanese - CdS_x_Se_1-x_（x＝0.26）ドープガラスの光音響スペクトル
豊田太郎; 沈 青
電子情報通信学会技術研究報告（超音波）, US98-1～9, 23-28, Apr. 1999
Japanese - Photoacoustic spectroscopy of annealed CdS_x_Se_1-x_ （x＝0.26）nanocrystal doped glasses
Q. Shen; T. Toyoda
AIP Proceedings（463）of the Photoacoustic and Photothermal Phenomena, 498-496, Mar. 1999
English - Photoacoustic spectra and corrent-voltage characteristics of ceramic ZnO doped with Bi_2_O_3_ impurities
S. Shimamoto; T. Toyoda
AIP Proceedings（463）of the Photoacoustic and Photothermal Phenomena, 548-550, Mar. 1999
English - 光音響を用いた，ポーラス化TiO_2_に吸着したCdSナノクリスタルの評価
豊田太郎; 七種耕治; 沈 青
日本音響学会1999年春季研究発表講演論文集, 819-820, Mar. 1999
English - 光音響を用いた，Bi_2_O_3_を不純物として含むZnOセラミックスの評価
豊田太郎; 島本 聡
日本音響学会1999年春季研究発表講演論文集, 1017-1018, Mar. 1999
Japanese - P型Siの光音響スペクトルの電界依存正
石田征幸; 高橋徹治; 豊田太郎
487, Mar. 1999
Japanese - Al_2-_xCr_x_O_3_（0≦x≦1）セラミックスの光音響スペクトルと無輻射遷移
富樫昌美; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 488, Mar. 1999
Japanese - 光音響分光法によるCdInGaS_4_の電子輸送と熱物性の評価
沈 青; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 1342, Mar. 1999
Japanese - 光音響分光法によるphotodarkeningしたCdS_x_Se_1-x_ドープガラスの評価
沈 青; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 1342, Mar. 1999
Japanese - フラクタル化多結晶TiO_2_の光音響ならびに光電流スペクトル
早川智也; 沈 青; 豊田太郎
第46回応用物理学会連合講演会講演予稿集, 1343, Mar. 1999
Japanese - Photoacoustic spectra of CdInGaS4 with a dc electric field
T Toyoda; M Yamamuro; Q Shen
PHOTOACOUSTIC AND PHOTOTHERMAL PHENOMENA, AMER INST PHYSICS, 463, 274-276, 1999, Photoacoustic (PA) spectroscopy is used to study the heat generated by nonradiative processes of CdInGaS4, with an external de electric field transverse to the light path in order to stud! the correlation between carrier diffusion effects and nonradiative processes. Maxima are observed in PA spectra at 2.7 and 2.3 eV, the amplitude of which values are proportional to the square of the applied voltage. The peak at 2.7 eV shifted toward higher energy when the modulation frequency increased. That at 2.3 eV did not shift. The PA signal intensity at 2.7 eV changes from f(-1.0) to f(-1.5) with the increase of de electric field. On the contrary, that at 2.3 eV changes suddenly from f(-1.0) to f(-2.0) with the increase of de electric field.
International conference proceedings, English - Photoacoustic spectra of ceramic CdS films doped with CdCl2
M Yamamuro; T Toyoda
PHOTOACOUSTIC AND PHOTOTHERMAL PHENOMENA, AMER INST PHYSICS, 463, 557-559, 1999, We have studied the effect of the content of CdCl2 in the sintering ceramic CdS films on the optical absorption measured by photoacoustic (PA) method PA spectra depend on CdCl2 content at the region below the fundamental absorption edge. The steepness factor sigma (slope of exponential optical absorption) increases with increasing content of CdCl2. Also, average grain size increases with increasing content of CdCl2 by scanning electron microscopy observations. The increase of sigma can be explained by the results of the grain size growing effect and/or the decrease of vacancies due to the cadmium and sulfur during sintering processes.
International conference proceedings, English - Photoacoustic Studies of Annealed CdSxSei-x(x=0.26)Nanocrystals in a Glass Matrix.
Q. Shen; T. Toyoda
Japanese Journal of Applied Physics, The Japan Society of Applied Physics, 38, 5, 3163-3167, 1999, Photoacoustic (PA) spectroscopy is applied to study an optical absorption of CdSxSe1-x (x=0.26) nanocrystals in a glass matrix annealed at 700°C for different time durations. As the annealing time increases, a shift of the absorption peak (due to the quantum confinement effect) to lower energy is observed in the PA spectra at room temperatures. The observed absorption peak shifts are used to evaluate the average size of CdSxSe1-x nanocrystals in terms of a simple model. The average radius increases from 2.3 to 4.7 nm as the annealing time increases from 0 to 120 min. The PA signal intensities plotted in the semilogarithmic scale vary linearly below the fundamental absorption edges in accordance with the Urbach rule for the optical absorption coefficient. The steepness factor (slope of exponential optical absorption) of the PA spectra increases with increasing annealing time. The change of the electronic states by annealing is explained by considering that the contribution of the surface states decreases with the increase of the nanocrystal size.
Scientific journal, English - Photoacoustic and Electrical Properties of Ceramic ZnO Doped with Bi_2_O_3_ Impurities
S. Shimamoto; T. Toyoda
Key Engineering Materials, 169-170, 97-100, 1999
English - Photoacoustic Spectra of Ceramic CdS Films
M. Yamamura; T. Toyoda
Key, Enjineering Material, 169-170, 183-186, 1999
English - ポーラスSiの光音響スペクトルと発光特性
高橋 徹治; 山室正倫; 沈 青; 豊田太郎
電子情報通信学会技術研究報告（超音波）, The Institute of Electronics, Information and Communication Engineers, 99, 32, 7-12, 1999, Porous silicon,which can be prepared by electrochemical method on the Si surface, shows photoluminesoence in visible region at room temperature. So it has attracted much attention for application to optical devices. Although the optical absorption properties are very important for basic and applied studies,these properties can not be measured using the conventional method because of the light scattering and the opaque substrate. It is well known that photoacoustic (PA) method is useful for studying the optical absorption on those samples. In this work, the chemical etching effects of porous silicon are studied using photoacoustic, photoluminescence (PL) and photoluminescence excitation (PLE) methods. The PA signal intensity above the fundamental absorption edge of porous silicon with chemical etching is smaller than that without etching, indicating the larger fluorescence quantum efficiency in porous silicon with chemical etching than that without etching.
Japanese - 光音響法による四元化合物半導体CdInGaS_4_の電子物性と熱物性の評価
沈 青; 豊田太郎
電子情報通信学会技術研究報告（超音波）, The Institute of Electronics, Information and Communication Engineers, 99, 132, 9-14, 1999, CdInGaS_4 has received interest because of attractive properties as photoconducting and plnotoluminescence material and potential for applicatios in light-emitting and optoelectronic devices. The studies on the optical, electronic and thermal properties are much important for applications. Photoacoustic (PA) technique is one of the photothermal detection and it has proved to be useful for investigating optical, electronic and thernml properties of various materials. In this work, we applied the PA method to investigate the electronic and thermtal propertis of CdInGaS_4. For semiconductor materials such as CdInGaS_4, the PA signals obtained in the transmission configuration were attributed to both the thermal diffusion and carrier transport processes. By fitting theoretical results of PA signal dependence on the modulation frequency to the experimental ones, we could determine the values of the thermal diffusivity (〜0.005 cm^2/s), the excess-carrier lifetime (〜1 ms), carrier diffusivity (〜0.27 cm^2/s) and the surface recombination velocity (〜150 cm/s) of the CdInGaS_4 samples.
Japanese - 光音響法によるポーラス化フラクタル状TiO_2_の電圧印加処理の評価
豊田太郎; 早川智也; 沈 青
電子情報通信学会技術研究報告（超音波）, The Institute of Electronics, Information and Communication Engineers, 99, 132, 15-20, 1999, TiO_2 is one of the candidates for photoanode materials that split water in solar energy conversion cells because of its high chemical and photoelectrochemical durability. In order to increase solar energy conversion efficiency, the preparation of highly porous, polycrystalline TiO_2 to increase surface area by chemical synthesis has been proposed. In the present paper, we report the optical absorption spectra by photoacousric (PA) method of the materials to show the effect of applying voltage in electrolyte for final preparation processes. Although the PA spectrum of TiO_2 with applying voltage treatments is similar to that wihout the treatments above the band gap, the former below the band gap shows larger singal intensities than the latter, indicating the possibility of the formation of defect states by applying voltage treatments.
Japanese - Photoacoustic and Photoluminescence Excitation Studies of Ceramic Al_2-x_Cr_x_O_3_（0.002＜x＜0.05）
T. Toyoda; T. Obikawa
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 80, 1999
English - Nonradiative Character of Ceramic Al_2-x_Cr_x_O_3_（0.002＜■.―.x＜■.―.1.0）by Means of Photoacoustic Measurements
T. Toyoda; M. Togashi; Q. Shen
Collected Abstracts of the International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 248, 1999
English - Photothermal Investigation of Ceramic Al_2-x_Cr_x_O_3_（0＜x＜1）
T. Toyoda; M. Togashi
Abstracts of the 15th European Conference on Thermophysical Properties, 125, 1999
English - Photothermal Investigation of CdS_x_Se_1-x_（x＝0.26）Nanocrystals in a Glass Matrix（Annealing and Temperature Effect）
T. Toyoda; Q. Shen
Abstracts of the 15th European Conference on Thermophysical Properties, 324, 1999
English - Photothermal Investigation of Highly Porous, Polycrystalline TiO_2_ electrodes
T. Toyoda; T. Hayakawa; Q. Shen
Abstracts of the 15th European Conference on Thermophysical Properties, 325, 1999
English - Photothermal Investigation of P-Type Si with an Apllied DC-Electric Field
T. Toyoda; M. Ishida; T. Takahashi; Q. Shen
Abstracts of the 15th European Conference on Thermophysical Properties, 326, 1999
English - 化学エッチングしたポーラスシリコンの発光と光音響スペクトル
高橋徹治; 沈 青; 豊田太郎
第60回応用物理学会学術講演会講演予稿集, 658, 1999
Japanese - 光音響分光法によるCdInGaS_4_の電子物性と熱物性の評価（Ⅱ）
沈 青; 豊田太郎
第60回応用物理学会学術講演会講演予稿集, 658, 1999
Japanese - 光音響法によるTiO_2_微粒子の評価
豊田太郎; 河野 寛; 沈 青; 小寺昭彦; 大森将弘
第20回日本熱物性シンポジウム講演論文集, 70-73, 1999
Japanese - 光音響法によるポーラス化TiO_2_とその表面に吸着したCdSナノクリスタルの評価
豊田太郎; 七種耕治; 早川智也; 沈 青
第20回日本熱物性シンポジウム講演論文集, 74-77, 1999
Japanese - 光音響分光法によるCdInGaS_4_の熱物性と電子物性の評価
沈 青; 豊田太郎
第20回日本熱物性シンポジウム講演論文集, 94-97, 1999
Japanese - CdSSe系ドープガラスの光音響スペクトル（アニール温度依存性）
沈 青; 飯尾能将; 豊田太郎
第20回日本熱物性シンポジウム講演論文集, 98-101, 1999
Japanese - ポーラスシリコンの光音響スペクトル
高橋徹治; 沈 青; 豊田太郎
第20回日本熱物性シンポジウム講演論文集, 106-109, 1999
Japanese - Al_2_O_3_とCr_2_O_3_との結晶セラミックスの光音響スペクトル
豊田太郎; 山本洋秀; 富樫昌美; 沈 青
第20回日本熱物性シンポジウム講演論文集, 110-113, 1999
Japanese - Al_2_O_3_とCr_2_O_3_との結晶セラミックスの光音響スペクトルと発光特性
豊田太郎; 山本洋秀; 高橋徹治; 沈 青
第19回電子材料研究討論会講演論文集, 62, 1999
Japanese - ポーラス化TiO_2_膜の光音響法による電子状態評価
豊田太郎; 早川智也; 河野 寛; 沈 青
第19回電子材料研究討論会講演論文集, 63, 1999
Japanese - TiO_2_微粒子の光音響スペクトル
豊田太郎; 河野 寛; 沈 青; 小寺昭彦; 大森将弘
第20回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 91-91, 1999
Japanese - 透過型光音響法による CdInGaS_4_の熱物性と電子物性の評価
沈 青; 豊田太郎
第20回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 93-94, 1999
Japanese - ガラス中のCdS_x_Se_1-x_（x＝0.26）マイクロクラスター粒径変化が光音響スペクトルに及ぼす効果
沈 青; 豊田太郎
第19回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 59-60, Nov. 1998
Japanese - 溶液成長によるCdS薄膜と，ポーラス化TiO_2_に吸着したCdSナノクリスタルの光音響スペクトル
豊田太郎; 七種耕治; 山室正倫; 沈 青
第19回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集, 141-142, Nov. 1998
Japanese - CdS膜の光音響スペクトル
山室正倫; 豊田太郎
第18回電子材料研究討論会講演予稿集, 23-24, Oct. 1998
Japanese - Bi_2_O_3_を不純物として含むZnoセラミックスの光音響スペクトル
島本 聡; 豊田太郎
第18回電子材料研究討論会講演予稿集, 65-66, Oct. 1998
Japanese - Al_2-x_Cr_x_O_3_（0.002≦x≦0.05）セラミックスの光音響スペクトル
豊田太郎; 帯川 崇; 富樫昌美
第18回電子材料研究討論会講演予稿集, 67-68, Oct. 1998
Japanese - CdS微粒子を吸着したポーラス化TiO_2_の光音響ならびに光電流スペクトル
豊田太郎; 七種耕治; 沈 青
第18回電子材料研究討論会講演予稿集, 69-70, Oct. 1998
Japanese - CdSSe系ドープガラスの光音響スペクトル
沈 青; 豊田太郎
第18回電子材料研究討論会講演予稿集, 71-72, Oct. 1998
Japanese - 光音響分光法を用いたZnOセラミックスの評価
島本 聡; 豊田太郎
第59回応用物理学会学術講演会講演予稿集, 1140, Sep. 1998
Japanese - CdS膜の光音響スペクトル
山室正倫; 豊田太郎
第59回応用物理学会学術講演会講演予稿集, 1140, Sep. 1998
Japanese - CdS微粒子を吸着したポーラス化TiO_2_の光音響ならびに光電流スペクトル
豊田太郎; 七種耕治; 沈 青
第59回応用物理学会学術講演会講演予稿集, 1141, Sep. 1998
Japanese - Photoacoustic spectra of CdS_x_Se_1-x_（x＝0.26）nanocrystals in a glas matrix
T. Toyoda; Q. Shen
Abstracts of the Oji International Seminar on Photothermal Phenomena and Their Applications(invited), 26-33, Aug. 1998
English - Photoacoustic and photoluminescence excitation spectra for ceramic Al_2-x_Cr_x_O_3_（0.002≦x≦0.05）
T. Toyoda; T. Obikawa
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 203-204, Aug. 1998
English - Photoacoustic spectra of CdInGaS_4_ with a dc electric field
T. Toyoda; M. Yamamuro; Q. Shen
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 205-206, Aug. 1998
English - Photoacoustic studies annealed GdS_x_Se_1-x_（x＝0.26）nanocrystals in a glass matrix
Q. Shen; T. Toyoda
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 391-392, Aug. 1998
English - Photoacoustic spectra and current-voltage characteristics of ceramic ZnO doped with Bi_2_O_3_ impurities
S. Shimamoto; T. Toyoda
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 445-446, Aug. 1998
English - Dependence of the photoacoustic spectra on sintering temperature for ceramic CdS and CdS_0.5_Se_0.5_
T. Toyoda; H. Fujimoto; T. Konaka; K. Shinoyama
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 453-454, Aug. 1998
English - Photoacoustic spectra of ceramic CdS folms deped with CdCl_2_
M. Yamamuro; T. Toyoda
Abstracts of the 10th International Conference on Photoacoustic and Photothermal Phenomena, 455-456, Aug. 1998
English - Photoacoustic spectroscopy of ceramic ZnO doped with Bi_2_O_3_
T. Toyoda; S. Shimamoto
Mat. Sci. Eng B, 54, 29-32, Jun. 1998
English - Photoluminescence spectroscopy of Cr^3+^ in ceramic Al_2_O_3_
T. Toyoda; T. Obikawa; T. Shigenari
Mat. Sci. Eng B, 54, 33-37, Jun. 1998
English - Effects of Bi233 Impurities in Ceramic ZnO on Photoacoustic Spectra and Current-Voltage Characteristics.
T. Toyoda; S. Shimamoto
Japanese Journal of Applied Physics, 37, 5B, 2827-2831, May 1998
Scientific journal, English - Dependence of the Photoacoustic Signal Intensity Spectra on Sintering Temperature for Ceramic CdS and CdS0.5Se0.5.
Japanese Journal of Applied Physics, 36, 3292, 1997
Scientific journal, English - Photoacoustic and Photoluminescence Studies of CdSxSe1-x Doped Glasses
Japanese Journal of Applied Physics, 36, 3297, 1997
Scientific journal, English - Photoacoustic Spectroscopy of Cu Impurities in Ceramic ZnS.
Japanese Journal of Applied Physics, 36, 3300, 1997
Scientific journal, English - Photoluminescence Excitation and Photoacoustic Spectra for Ceramic Al2-χ Crχ O3(0.002≦χ≦0.05)
Japanese Journal of Applied Physics, 36, 7A, 4339, 1997
Scientific journal, English - Influence of Bi2O3 Impurities in Ceramic ZnO on Photoacoustic Spectra.
Japanese Journal of Applied Physics, 36, 12A, 7257, 1997
Scientific journal, English - Photoacoustic Spectroscopy of Cr3+ in Ceramic Al2O3.
Materials Science & Engineering B, 41, 72, 1996
Scientific journal, English - Hydrostatic Pressure Dependence of the Fundamental Absorption Edges of CdIn GaS4 and ZnIn2S4
Japanese Journal of Applied Physics, 1993
Scientific journal, English - X-Ray Photoacoustic Spectroscopy of ZnO Thin Film
Japanese Journal of Applied Physics, 32, 2550, 1993
Scientific journal, English - Dependence of the X-Ray Photoacoustic Signal Intensity of Pure Copper and Brass on Sample Thickness
Japanese Journal of Applied Physics, 32, 2554, 1993
Scientific journal, English - Photothermal Effect in Compound Semiconductors CdInGaS4 and CdIn2S4
Japanese Journal of Applied Physics, 1993
Scientific journal, English - Optical Properties of ZnxCd1-X InGaS4 System
Japanese Journal of Applied Physics, 1993
Scientific journal, English - Green Emission in CdS Films Deposited on CdInGaS4 by Evaporation Method
Japanese Journal of Applied Physics, 1993
Scientific journal, English - Dependence of the X-Ray Photoacoustic Signal Intensity of Brass on Sample Thickness and Modulation Frequency.
Japanese Journal of Applied Physics, 31, 8, 1992
Scientific journal, English - Hard X-ray Absorption Spectroscopy of CuO and Cu2O with a photoacoustic Detector.
Applied Physics Letters, 59, 27, 1991
Scientific journal, English - X-ray Photoacoustic Spectroscopy of Brass.
Japanese Journal of Applied Physics, 29, 1990
Scientific journal, English - Photoacoustic Response to X-ray Absorption in Copper and Brass.
Japanese Journal of Applied Physics, 29, 1990
Scientific journal, English - The Dependence of Optical Absorption in Bi12SiO20 on Temperature and Hydrostatic Pressure.
Journal of Crystal Growth, 99, 1990
Scientific journal, English - X-ray Photoacoustic Absorption Spectra of CuInSe2.
Journal of Crystal Growth, 99, 1990
Scientific journal, English - Refractive indices and the exponential optical absorption for Hg 1-xCdxTe (0.2<x<0.3)
Taro Toyoda
Journal of Applied Physics, 63, 1, 228-230, 1988, For Hg1-xCdxTe, in the range of x≅0.2-0.3, the optical dispersion parameters (single-oscillator energy E0, dispersion energy Ed, and lattice-oscillator energy E1) and the fitting parameter of the exponential optical absorption (steepness factor σ) were analyzed using the data by Finkman and co-workers [J. Appl. Phys. 50, 4356 (1979)
J. Appl. Phys. 56, 2896 (1984)]. For Hg1-xCdxTe the values of E0, E d, and σ in this composition range are smaller than those for CdTe, and E1 is larger than that for CdTe. The results suggest that the chemical bonding of Hg1-xCdxTe in the range of x≅0.2-0.3 is smaller than that of CdTe.
Scientific journal, English - Hydrostatic Pressure Dependence of the Optical Absorption Edge in Bi12SiO20.
Journal of Applied Physics, 61, 1987
Scientific journal, English - The Fitting Parameters of Exponential Optical Absorption in Bi12SiO20.
Journal of Physics C : Solid State Physics, 19, 1986
Scientific journal, English - The Electronic Structure of Dilute (Cu(Pd), Cu(Pt) and Cu(Rh) Alloys.
Journal of Physics F : Metal Physics, 11, 1981
Scientific journal, English
Books and other publications
- Solar Cells- New Aspects and Solutions
Q. Shen; T. Toyoda
English, Joint work, Chapter 13, InTec, 2011 - Solar Cells - New Aspects and Solutions
T. Toyoda; Q. Shen
English, Joint work, InTec, 2011 - 電子材料ハンドブック
木村忠正; 八百隆文; 奥村次徳; 豊田太郎
Japanese, Editor, 朝倉書店, Nov. 2006 - 半導体の科学とその応用
豊田 太郎
Japanese, Editor, 裳華房, 2001 - Photothewmal Spectroscopy of Ceramic and Nanocrystal (]G0002[)-(]G0006[) Compound Semiconductors, together with Ternary and Multinary Compounds.
T. Toyoda
English, Joint work, Progress in Photothermal and Photoacoustic Science and Technology (ed.A.Mandelies and P.Hess) (Semiconductors and Electronic Materials), 2000
Lectures, oral presentations, etc.
- 半導体量子ドットの分光増感機能と太陽電池への応用
豊田太郎; 沈 青
Invited oral presentation, Japanese, 平成22年度第1回研究会, 近畿化学協会エレクトロニクス部会, 大阪, International conference
May 2010 - 半導体量子ドットの分光増感機能と太陽電池への応用
豊田太郎; 沈 青
Invited oral presentation, Japanese, 平成22年度第1回研究会, 近畿化学協会エレクトロニクス部会
May 2010 - 半導体量子ドットの太陽電池への応用
豊田太郎
Invited oral presentation, Japanese, 「量子ドット太陽電池」セミナー, R&D支援センター
Apr. 2010 - 半導体量子ドットの分光増感機能と太陽電池への応用
豊田太郎
Invited oral presentation, Japanese, 第48回研究会「高効率太陽電池の研究開発最前線」, 日本学術振興会
Apr. 2010 - Combined CdS/CdSe quantum dot-sensitized solar cells with nanocrystalline TiO2 electrodes
T.Toyoda; Q.Shen
Invited oral presentation, English, 第4回次世代太陽電池センターセミナー, （独）物質・材料研究機構、次世代太陽電池センター
Mar. 2010 - Semiconductor quantum dot-sensitized soalr cells and photoexcited carrier dynamics
T.Toyoda; Q.Shen
Invited oral presentation, English, International Workshop on Semicinductor Sensitized Solar Cells, Society of hybrid and organic photovoltaics, Jerusalem, Israel, International conference
Feb. 2010 - 量子ドットの基礎とその応用ー量子ドットの太陽電池への応用
豊田太郎; 沈 青
Invited oral presentation, Japanese, Electronic Journal 第48回Technical Seminar「量子ドット応用技術の最前線」, （株）電子ジャーナル
Feb. 2010 - Photovoltaic properties and ultrafast carrier dynamics of semiconductor quantum dot-sensitized solar cells
T.Toyoda; Q.Shen
Invited oral presentation, English, Materials Research Society Fall Meeting 2009, Materials Research Society, Boston, USA, International conference
Dec. 2009 - 半導体量子ドットの分光増感と太陽電池への応用
豊田太郎
Invited oral presentation, Japanese, 情報機構セミナー「量子ドット太陽電池の可能性を探る」, （株）情報機構
Dec. 2009 - 量子ドット増感太陽電池の開発と将来展望
豊田太郎
Invited oral presentation, Japanese, 第24回高分子エレクトロニクス研究会講座, 高分子学会 高分子エレクトロニクス研究会
Nov. 2009 - Semiconductor quantum dot-sensitized solar cells using nanostructured TiO2 electrodes with different morphologies
T.Toyoda; Y.Yoshida; Y.Ayuzawa; Q.Shen
Invited oral presentation, English, The 14th international Conference on TiO2 Photocatalysis: Fundamentals and Applications, Redox Technologies, Inc, Niagara Falls, USA, International conference
Oct. 2009 - Photovoltaic and ultrafast carrier dynamic properties of CdSe quantum dot-sensitized solar cells
T.Toyoda; L.J.Diguna; Q.Shen
Invited oral presentation, English, Conference on Hybrid and Organic Photovoltaics 2009, Organizing Comittee of the Conference on Hybrid and Organic Photovoltaics, Benidorm, Spain, International conference
May 2009 - 量子ドット分光増感と光電変換特性
豊田太郎; 沈 青
Invited oral presentation, Japanese, 日本化学会第89回春季年会, 日本化学会
Mar. 2009 - Photovoltaic and ultrafast carrier dynamic properties of CdSe quantum dot-sensitized solar cells using inverse opal TiO2 electrodes
T.Toyoda
Keynote oral presentation, English, 24th Regional Conference on Solid State Science and Technology 2008, Malaysian Solid State Science and Technology Society, Port Dickson, Malaysia, International conference
Dec. 2008 - 半導体量子ドットの光励起キャリアと光電変換特性
豊田太郎; L.J.Diguna; 沈
Invited oral presentation, Japanese, 第57回高分子討論会, 高分子学会
Sep. 2008 - 半導体量子ドットの光励起キャリアダイナミクスと光電変換特性
豊田 太郎; 沈 青
Invited oral presentation, Japanese, 日本化学会関東支部講演会, 日本化学会関東支部
Jun. 2008 - ナノ構造TiO2に吸着した半導体量子ドットの分光増感特性
豊田太郎; 沈 青
Invited oral presentation, Japanese, 日本化学会第88回春季年会(2008), 日本化学会
Mar. 2008 - Characterization of carrier dynamics in semiconductor nanomaterials using near-field heterodyne transient grating method
Q.Shen; K. Katayama; T.Sawada; T.Toyoda
Invited oral presentation, English, 20th International Microprocesses and Nanotechnology Conference, The Japan Soceity of Applied Physics, Kyoto, Japan, International conference
Nov. 2007 - 各種表面形態の異なるナノ構造TiO2電極に吸着したCdSe量子ドットの分光増感特性と過渡応答評価
豊田太郎; 沈 青
Invited oral presentation, Japanese, 第56回高分子討論会, 高分子学会
Sep. 2007 - 光熱変換法の現状と課題
沈 青; 豊田太郎
Invited oral presentation, Japanese, 研究会「薄膜・極表面・ナノスケール領域の熱物性評価」, 独立行政法人 物質・材料研究機構
Jul. 2007 - Photovoltaic and ultrafast carrier dynamic properties of CdSe quantum dots sensitized solar cells using inverse opal TiO2 electrodes
L.J.Diguna; Q.Shen; K.Katayama; T.Sawada; T.Toyoda
Invited oral presentation, English, Japan-China Bilateral Workshop on Science & Technology for Clean Energy, Japan Science and Technology Agency (JST), Tokyo, Japan, International conference
Jun. 2007 - 半導体量子ドットの分光増感特性と光電変換特性
豊田太郎; 沈 青
Invited oral presentation, Japanese, 日本化学会第1回関東支部大会(2007), 日本化学会関東支部
Jun. 2007 - ナノ構造TiO2と複合化した化合物半導体量子ドットの分光増感特性と過渡応答評価
豊田太郎; 沈 青
Invited oral presentation, Japanese, 第54回応用物理学関係連合講演会, 応用物理学会
Mar. 2007 - 各種表面形態の異なるナノ構造TiO2光電極に吸着した半導体量子ドットの分光増感特性と過渡応答評価
豊田太郎; 沈 青
Invited oral presentation, Japanese, 日本化学会第87春季年会(2007), 日本化学会
Mar. 2007 - 表面形態の異なるナノ構造TiO2電極の光音響評価と光電気化学特性
豊田太郎
Invited oral presentation, Japanese, 第２６回超音波エレクトロニクスの基礎と応用に関するシンポジウム, 超音波シンポジウム運営委員会
Nov. 2005 - Photo-acoustic and photo-electrochemical characterization of nanostructured TiO2 electrodes
T.Toyoda
Invited oral presentation, English, 2003 Canadian Association of Physicists Annual Congress, Canadian Association of Physicists, Charlottetown, Canada, International conference
Jun. 2003 - 光音響法と光化学電流法によるナノ構造TiO2膜電極の評価
沈 青; 豊田太郎
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003 - メゾポーラス化TiO2膜に固定化したCdSeナノ粒子の光音響・光化学電流スペクトル
豊田太郎; 山本浩之; 林 雅; 新江 大; 沈 青
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003 - ナノ構造を有するTiO2膜電極の光音響・光電流応答特性
豊田太郎; 林 雅; 沈 青
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003 - Mnを不純物として含むZnSナノ粒子の光音響・発光強度の紫外線照射効果
豊田太郎; A.B.Cruz; 沈 青
Oral presentation, Japanese, 第50回応用物理学関係連合講演会講演予稿集
Mar. 2003 - Irradiation time depndence of Mn-doped ZnS nanocrystals with carboxylic acids on radiative and nonradiative transitions.
T.Toyoda; A.B.Cruz
Oral presentation, English, Abstracts of the 5th International Conference on Nano-Molecular Electronics
Dec. 2002 - Degradation effect of porous silicon on photoacoustic and photoluminescence intensities with photoexcitation.
T.Toyoda; R.Torai
Oral presentation, English, Abstracts of the 5th International Conference on Nano-Molecular electronics
Dec. 2002 - Study of optical absorption and electron transport in nanoporous nanocrystalline TiO2 films.
Q.Shen; T.Toyoda
Oral presentation, English, Abstracs of the 5th International Conference on Nano-Molecular Electronics
Dec. 2002 - Mnを不純物として含むZnSナノ粒子系の光音響信号と発光強度の紫外線 照射時間依存性
豊田太郎; A.B.Cruz
Oral presentation, Japanese, 第23回超音波エレクトロニクスも基礎と応用に関するシンポジウム講演予稿集
Nov. 2002 - ナノ構造を有するTiO2電極の光音響・光電流応答特性
豊田太郎; 林 雅; 沈 青
Oral presentation, Japanese, 第23回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集
Nov. 2002 - CdSナノ粒子を吸着したTiO2光電極の光音響スペクトルと光電変換
豊田太郎; 佐藤 淳; 林 雅; 沈 青
Oral presentation, Japanese, 第21回固体・表面光化学討論会講演要旨集
Nov. 2002 - Mnを不純物として含むZnSナノ粒子の光誘起蛍光増加と光熱変換現象
A.B.Cruz; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002 - 光熱変換現象によるITOおよびメゾポーラス酸化チタンに固定化したCdSeナノ粒子の評価
新江 大; 沈 青; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002 - ナノ粒子を用いたTiO2光電極の光音響スペクトル
林 雅; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002 - CdSナノ粒子を吸着したTiO2光電極の光音響スペクトルと光電変換
豊田太郎; 佐藤 淳; 沈 青
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002 - 光音響法によるTiO2ナノ粒子系の光吸収評価
坪谷育実; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002 - 光音響法によるポーラスシリコンの熱伝導率の評価
沈 青; 豊田太郎
Oral presentation, Japanese, 第23回日本熱物性シンポジウム講演論文集
Nov. 2002 - 光音響法によるTiO2ナノ粒子系の光吸収評価
豊田太郎; 坪谷育実
Oral presentation, Japanese, 第40回粉体に関する討論会講演論文集
Nov. 2002 - ナノ構造を有するTiO2電極の光音響ならびに光電流スペクトル
沈 青; 豊田太郎
Oral presentation, Japanese, 第40回粉体に関する討論会講演論文集
Nov. 2002 - 光音響法によるITOおよびメゾポーラスTiO2に固定化したCdSeナノ粒子の光吸収評価
新江 大; 豊田太郎
Oral presentation, Japanese, 第40回粉体に関する討論会講演論文集
Nov. 2002 - Mn ion concentration dependence of the photothermal and photoluminescence spectra for ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002 - Exposure time dependence of the photothermal and photoluminescence intensities for porous silicon with different wavelengths of excitation light
T.Toyoda; T.Yamazaki; R.torai; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermaphysical Properties
Sep. 2002 - Efffect of applied voltage treatments on photothermal and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Theermophysical Properties
Sep. 2002 - Effect of applied voltage treatments on photothermal and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrods.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002 - Effect of sensitization by quantum-sized CdS on photothermal and photoelectrochemical current spectra of porous TiO2 electrodes.
T.Toyoda; J.Sato; Q.shen
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002 - Characterization of optical and thermal properties of porous silicon films on silicon substrate using photothermal technique.
Q.Shen; T.Toyoda
Oral presentation, English, Abstracts of the 16th European Conference on Thermophysical Properties
Sep. 2002 - Photoacoustic and photoelectrochemical current spectra of nanocrystalline TiO2 electrodes.
M.Hayashi; T.Toyoda
Invited oral presentation, English, Proceedings of the International Workshop on Modern Science and Technology, International conference
Sep. 2002 - Porosity dependence of thermal conductivity for porous silicon characterized by photoaccoustic technique.
Q.Shen; T.Toyoda
Invited oral presentation, English, Proceedings of the International Workshop on Modern Science and Technology, International conference
Sep. 2002 - 光音響法によるTiO2ナノ粒子系の評価
坪谷育実; 豊田太郎
Oral presentation, Japanese, 第63回応用物理学会学術講演会講演予稿集
Sep. 2002 - ナノ構造を有するTiO2光電極の光音響スペクトルと光電変換ー電圧印加処理効果ー
林 雅; 豊田太郎
Oral presentation, Japanese, 第63回応用物理学会学術講演会講演予稿集
Sep. 2002 - Apparent band-gap energies of mixed TiO2 nanoparticles with anatase and rutile structures characterized with photoacoustic intensity and phase spectra.
T.Toyoda; R.Taira; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002 - Photoabsorption and photoluminescence properties of photocatalysis-TiO2 and K2Ga2Sn616.
H.Nakajima; T. Mori; S.Awatsu; T.Toyoda; M.Watanabe
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002 - Effect of applied voltage treatments on photoacoustic and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002 - Mn ion concentration dependence of the photoacoustic and photoluminescence spectra for ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002 - Effect of sensitization by quantum-sized CdS on Photoacoustic and photoelectrochemical current spectra of porous TiO2.
T.Toyoda; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 14th International Conference on Photochemical Conversion and Storage of Solar Energy
Aug. 2002 - Efffect of applied voltage treatments on photoacoustic and photoelectrochemical current spectra in final preparation processes of porous TiO2 electrodes.
T.Toyoda; M.Hayashi; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacosutic and Photothermal Phenomena
Jun. 2002 - Effect of sensitization by quantum-sied CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes.
T.Toyoda; J.Sato; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002 - Dependence of the thermal conductivity of porous silicon on its porosity characterized by photoacoustic technique.
Q.Shen; T.Toyoda
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002 - Apparent band-gap energies of mixed TiO2 nanoparticles with anatase and rutile structures characterized with photoacoustic intensity and phase spectra.
T.Toyoda; R.Taira; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena.
Jun. 2002 - Mn ion concentration dependence and photoluminescence spectra of ZnS:Mn nanocrystals.
T.Toyoda; J.Matsuzawa; A.B.Cruz; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002 - Photoacoustic spectroscopy of CdTe nanocrystals doped in a GeO2 glass matrix.
I.Tsuboya; D.Arae; Q.Shen; T.Toyoda
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002 - Exposure time dependence of the photoacoustic and photoluminescence intensities of porous silicon with different wavelengths of excitation light.
T.Toyoda; T.Yamazaki; R.Torai; Q.Shen
Oral presentation, English, Abstracts of the 12th International Conference on Photoacoustic and Photothermal Phenomena
Jun. 2002 - TiO2電極における電圧印加処理が光音響スペクトルに及ぼす効果
林 雅; 沈 青; 豊田太郎
Oral presentation, Japanese, 電子情報通信学会技術研究報告
May 2002 - Characterization of optical and thermal properties of porous silicon films on silicon substrates using photoacoustic technique.
Qing Shen; Taro Toyoda
Oral presentation, English, Extended Abstracts of the 5th AIST International Symposium on Photoreaction Control and Photofunctional Materials
Mar. 2002 - Mn ion concentration dependence of the photoacoustic and photoluminescence spectra for ZnS:Mn nanocrystals.
Taro Toyoda; Junnichiro Matsuzawa; Almira B. Vruz; Qing Shen
Oral presentation, English, Extended Abstracts of the 5th AIST International Symposium on Photoreaction Control and Photofunctional Materials
Mar. 2002 - Exposure time dependence of the photoacoustic and photoluminescence intensities for porous silicon with different wavelengths of excitation light.
Taro Toyoda; Takahumi Yamazaki; Reiji Torai; Qing Shen
Oral presentation, English, Extended Abstracts of the 5th AIST International Symposium on Photoreaction Control and Photofunctional Materials
Mar. 2002 - Effect of applied voltage treatments on photoacoustic and photoelectrochemical current spectra in final preparation processews of porous TiO2 electrodes.
Taro Toyoda; Masashi Hayashi; Jun Sato; Qing Shen
Oral presentation, English, Extended Abstracts of the 5th AIST International Symposium on Photoreaction Control and Photofunctional Materials
Mar. 2002 - Effect of sensitization by quantum-sized CdS on photoacoustic and photoelectrochemical current spectra of porous TiO2 electrodes.
Taro Toyoda; Jun Sato; Qing Shen
Oral presentation, English, Extended Abstracts of the 5th AIST International Symposium on photoreaction Control and Photofunctional Materials.
Mar. 2002 - CdSナノ粒子を吸着したポーラス状TiO2電極の光音響・光電流スペクトル
佐藤 淳; 沈 青; 豊田太郎
Oral presentation, Japanese, 第49回応用物理学関係連合講演会講演予稿集
Mar. 2002 - フラクタル状ポーラス化多結晶TiO2膜の電圧印加処理効果と光音響・光電流スペクトル
林 雅; 佐藤 淳; 沈 青; 豊田太郎
Oral presentation, Japanese, 第49回応用物理学関係連合講演会講演予稿集
Mar. 2002 - ZnS:Mnナノ粒子系のMn濃度と光音響・フォトルミネッセンススペクトル
豊田太郎; 松澤寿一郎; Almira B. Cruz; 沈 青
Oral presentation, Japanese, 第49回応用物理学関係連合講演会講演予稿集
Mar. 2002 - ポーラスシリコンの光音響強度とフォトルミネッセンス強度の経時変化
豊田太郎; 山崎崇弘; 虎井礼司; 沈 青
Oral presentation, Japanese, 第49回応用物理学関係連合講演会講演予稿集
Mar. 2002 - 透過型光音響法によるSi基板上のポーラスシリコン膜の熱物性評価
沈 青; 豊田太郎
Oral presentation, Japanese, 第49回応用物理学関係連合講演会講演予稿集
Mar. 2002 - 光熱分光法による多孔質TiO2膜の評価
豊田太郎; 佐藤 淳; 林 雅; 沈 青
Oral presentation, Japanese, 研究構想公開シンポジウム「光機能界面の学理と技術」要旨集
Jan. 2002 - 光熱変換分光法によるポーラスシリコンの評価
沈 青; 豊田太郎
Oral presentation, Japanese, 研究公開シンポジウム「光機能界面の学理と技術」要旨集
Jan. 2002 - ポーラスSiの光音響スペクトルと蛍光スペクトルに及ぼすエッチング効果
豊田太郎; 高橋徹治; 沈 青
Oral presentation, Japanese, 日本分光学会平成13年度春講演要旨集
2001 - 日本分光学会平成13年度春講演要旨集
豊田太郎; 虎井礼司
Oral presentation, Japanese, 日本分光学会
2001 - ZnS:Mnナノ粒子系の光音響および蛍光スペクトル
豊田太郎; 海野 誠; 中島伸夫
Oral presentation, Japanese, 日本分光学会
2001 - Influence of anodization period on the photoacoustic spectra ｏｆporous silicon.
Taro Toyoda; Reiji Torai; Qing Shen
Oral presentation, English, Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter
2001 - Photoacoustic and photoluminescence spectra of manganese-doped nanocrystals of ZnS with and without modification by carboxylic acids.
Taro Toyoda; Makoto Unno; Nobuo Nakajima
Oral presentation, English, Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter.
2001 - Effect of size confinement on CdSe nanocrystals in a GeO2 glass matrix characterized by photoacoustic spectroscopy.
Taro Toyoda; Dai Arae; Qing Shen
Oral presentation, English, Abstracts of the 10th International Conference on Phonon Scattering in Condensed Matter.
2001 - Photoacoustic spectra of CdSe nanocrystals in ａ GeO2 glass matrix.
Taro Toyoda; Dai Arae; Qing Shen
Oral presentation, English, Abstracts of the International Congress on Analytical Sciences 2001
2001 - Effect of voltage treatments on the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 electrodes.
Taro Toyoda; Jun Sato; Qing Shen
Oral presentation, English, Abstracts of the International Congress on Analytical Sciences 2001
2001 - Photoacoustic and photoluminescence spectra of manganese-doped nanocrystals of ZnS with and without modification by carboxylic acids.
Taro Toyoda; Makoto Unno; Nobuo Nakajima
Oral presentation, English, Abstracts of the International Congress of Analytical Sciences 2001
2001 - Photoacoustic and photoluminescence spectra of porous silicon with different anodization period.
Taro Toyoda; Reiji Torai; Qing Shen
Oral presentation, English, Abstracts of the International Congress on Analytical Sciences 2001
2001 - ポーラスSiの光吸収と発光の時間依存性
虎井礼司; 沈 青; 豊田太郎
Oral presentation, Japanese, 第62回応用物理学会学術講演会講演予稿集
2001 - フラクタル状TiO2膜の光音響スペクトル
佐藤 淳; 林 雅; 沈 青; 豊田太郎
Oral presentation, Japanese, 第62回応用物理学会学術講演会講演予稿集
2001 - ZnS:Mnナノ粒子系の光音響スペクトルと蛍光測定
豊田太郎; 海野 誠; 中島伸夫
Oral presentation, Japanese, 第62回応用物理学会学術講演会講演予稿集
2001 - ポーラス化多結晶TiO2膜の光音響・光電流スペクトル
林 雅; 佐藤 淳; 沈 青; 豊田太郎
Oral presentation, Japanese, 第22回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集
2001 - ZnS:Mnナノ粒子系の光音響スペクトル
松澤寿一郎; 沈 青; 豊田太郎
Oral presentation, Japanese, 第22回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集
2001 - ZnS:Mn2+ナノ粒子系の光熱変換評価
豊田太郎; 松澤寿一郎; 沈 青
Oral presentation, Japanese, 第22回日本熱物性シンポジウム講演論文集
2001 - ポーラスSiの光吸収と発光の時間依存性
豊田太郎; 山崎崇弘; 虎井礼司; 沈 青
Oral presentation, Japanese, 第22回日本熱物性シンポジウム講演論文集
2001 - 光音響分光法による多孔質二酸化チタン膜の評価
佐藤 淳; 林 雅; 沈 青; 豊田太郎
Oral presentation, Japanese, 第22回日本熱物性シンポジウム講演論文集
2001 - 光音響分光法によるGeO2ガラス中に分散したCdSeナノクリスタルの評価
新江 大; 林 雅; 沈 青; 豊田太郎
Oral presentation, Japanese, 第22回日本熱物性シンポジウム講演論文集
2001 - Characterization of thermal properties of porous silicon film/silicon using photoacoustic technique.
Qing Shen; Taro Toyoda
Oral presentation, English, Abstracts of the 2nd International Symposium on the New Frontiers of Thermal Studies of Materials
2001 - Photothermal characterization of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis
Taro Toyoda; Masashi Hayashi; J. Sato; Qing Shen
Oral presentation, English, Abstracts of the 2nd International Symposium on the New Frontiers of Thermal Studies of Materials.
2001 - CoをドープしたZnOの圧電素子光熱分光スペクトル
境健太郎; 福山敦彦; 碇 哲雄; 豊田太郎
Oral presentation, Japanese, 第22回超音波エレクトロニクスの基礎と応用に関するシンポジウム講演予稿集
2001 - Photoacoustic studies of CdxSe1-x (X=0.26) nanocrystals in a glass matrix
T.Toyoda; Q. Shen
Invited oral presentation, English, Oji International Seminar on Photothermal Phenomena and their Applications, The Fujihara Foundation of Science, Japan Society for tyhe Promotion of Science, Tomakomai, Japan, International conference
Aug. 1998