Radiation induced synthesis of Au-Pd nanoparticles of random alloy structure supported on carbon particles using the high energy electron beam

Au-Pd bimetallic nanoparticles supported on carbon particles were synthesized by reduction of precursor ions in an aqueous solution irradiated with a high energy electron beam. The composition of the samples was analyzed by the inductively coupled plasma atomic emission spectrometry (ICP-AES), and the morphology of the samples was observed by the transmission electron microscope (TEM). TEM micrographs indicated that Au-Pd particles of ca. 5-nm were well dispersed on the surface of carbon particles of ca. 30-nm without any serious agglomeration. Addition of citric acid to the initial solution and high pH were found to be effective for formation of random alloy structure in the resultant bimetallic nanoparticles. The change in the bimetallic structure from core-shell to random alloy was identified by techniques of the X-ray diffraction (XRD) and the extended X-ray absorption fine structure (EXAFS).     

950 keV, 3.95 MeV and 6 MeV X-band linacs for nondestructive evaluation and medicine

We are developing compact X-band linac X-ray sources for nondestructive evaluation and medicine. First, we develop a portable X-ray system by a 950 keV 9.4 GHz X-band linac to realize on-site inspection. We use a low power (250 kW) magnetron as an RF source for compactness of the whole system. Since the RF power source is quite small and the stored energy in the structure is also small, we faced the problem of beam loading and current/RF-power oscillation. We are analyzing the problem by the circuit model. We plan to use this system for erosion inspection of metal pipes of petrochemical complex. By adopting a side-coupling cavity design to avoid the oscillation, we have developed 6 MeV X-band (9.3 GHz) linac for pinpoint dynamic tracking cancer therapy. Furthermore, we are manufacturing 3.95 MeV X-band (9.3 GHz) linac X-ray source with flexible waveguides for on-site bridge inspection. Updated results and situations are presented.     

Strain-mediated phase control and electrolyte-gating of electron-doped manganites

A prototype Mott transistor, the electric double layer transistor with a strained CaMnO(3) thin film, is fabricated. As predicted by the strain phase diagram of electron-doped manganite films, the device with the compressively strained CaMnO(3) exhibits an immense conductivity modulation upon applying a tiny gate voltage of 2 V.     

Enhancement of optical absorption for below 5 μm thin-film poly-Si solar cell on glass substrate

Optical confinement effect of thin-film polycrystalline-Si (poly-Si) solar cell on glass substrate fabricated at low-temperature has been investigated as a function of cell thickness of less than 5 μm. We found that it is possible to fabricate the textured Si thin film in situ on a glass substrate and that the reflectance at long-wavelength light is reduced by surface texturing. Thin-film poly-Si solar cell and a-Si:H/(0.45 μm)/poly-Si (5 μm) tandem solar cell exhibit the efficiency of 8.6% and 12.8%, respectively. The numerical study in terms of the light trapping explains the excellent high short-circuit current density (_sc above 27 mA/cm² at the 4.7 μm thin-film poly-Si solar cell.     

Benzobisthiazole as Weak Donor for Improved Photovoltaic Performance: Microwave Conductivity Technique Assisted Molecular Engineering

New donor–acceptor‐type copolymers comprised of benzobisthiazole (BBTz) as a weak donor rather than acceptor are proposed. This approach can simultaneously lead to deepening the HOMO and LUMO of the polymers with moderate energy offset against fullerene derivatives in bulk heterojunction organic photovoltaics. As a proof‐of‐concept, BBTz‐based random copolymers conjugated with typical electron acceptors: thienopyrroledione (TPD) and benzothiadiazole (BT) based on density functional theory calculations are synthesized. Laser‐flash and Xe‐flash time‐resolved microwave conductivity (TRMC) evaluations of polymer:[6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) blends are conducted to screen the feasibility of the copolymers, leading to optimization of processing conditions for photovoltaic device application. According to the TMRC results, alternating BBTz‐BT copolymers are designed, exhibiting extended photoabsorption up to ca. 750 nm, deep HOMO (–5.5 to –5.7 eV), good miscibility with PCBM, and inherent crystalline nature. Moreover, the maximized PCE of 3.8%, the top‐class among BBTz‐based polymers reported so far, is realized in an inverted cell using TiO_x and MoO_x as the buffer layers. This study opens up opportunities to create low‐bandgap polymers with deep HOMO, and shows how the device‐less TRMC evaluation is of help for decision‐making on judicious molecular design.     

Analysis of atmospheric electric field variation signals using digital natural observation method

As the atmospheric electric field always fluctuates, its observed waveforms are very complicated. It is important to detect the characteristic variation from the observed signals and determine its cause. The natural observation method is adequate for analyzing such nonperiodic signals as the atmospheric electric field signals. In this method the aspectum is proposed as the quantity to estimate the instantaneous power. In this study signal processing by the aspectum was applied to signals of atmospheric electric field variation. It was clarified that a strong correlation exists between the instantaneous fluctuations of atmospheric electric field and the wind speed in the convenient meteorological environment. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(1): 27–34, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20302     

De-t-butylation of t-butylphenols over dealuminated zeolites in liquid-solid system

Liquid-solid phase de-t-butylation of p-t-butylphenols was carried out over original and dealuminated zeolites to determine the effect of catalyst pore size and acidity on the reaction rate and catalyst fouling rate. The de-t-butylation rate over the original zeolites was mainly dependent upon their micro pore sizes. Although the dealumination by acid leaching decreased strong acid sites, the de-t-butylation rate over dealuminated HY zeolite was higher than that on the original zeolite. The present dealumination is a useful method to prepare an acid catalyst for de-t-butylation in a liquid-solid system.     

Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO.

Since the successful demonstration of a blue light-emitting diode (LED), potential materials for making short-wavelength LEDs and diode lasers have been attracting increasing interest as the demands for display, illumination and information storage grow. Zinc oxide has substantial advantages including large exciton binding energy, as demonstrated by efficient excitonic lasing on optical excitation. Several groups have postulated the use of p-type ZnO doped with nitrogen, arsenic or phosphorus, and even p-n junctions. However, the choice of dopant and growth technique remains controversial and the reliability of p-type ZnO is still under debate. If ZnO is ever to produce long-lasting and robust devices, the quality of epitaxial layers has to be improved as has been the protocol in other compound semiconductors. Here we report high-quality undoped films with electron mobility exceeding that in the bulk. We have used a new technique to fabricate p-type ZnO reproducibly. Violet electroluminescence from homostructural p-i-n junctions is demonstrated at room-temperature.     

A new generation of modems for power efficient radio systems

A new class of generalized intersymbol-interference and jitter-free (GIJF) modulated signals is introduced. Computer simulation and hardware experimental research results demonstrate that our proposed new generation of signals and modulators leads to significant performance improvements in non-linearly amplified broadband radio systems. For increased power efficiency, non-linear amplification is required in most commercial satellite and terrestrial microwave systems. In particular, we demonstrate that the 3 dB envelope fluctuation of currently used offset raised-cosine overlapped QPSK systems is reduced to 0-5 dB, and that the BER performance is improved by approximately 1 dB. These significant technical performance advantages are expected to lead to more economical implementations of digital transmission systems.     

Ti-Containing Silsesquioxane Gels with Tunable Porosity: Preparation and Catalytic Activity for the Epoxidation of Cyclooctene by Aqueous Hydrogen Peroxide

Novel Ti-containing silsesquioxane gel catalysts were prepared by the hydrosilylative condensation of Ti-containing silsesquioxanes together with cubic silsesquioxanes and spherosilicates. The porosity of gels was controlled by changing the composition and the mixing order of the starting materials. Both porous and nonporous gels were found to act as excellent heterogeneous catalysts towards the selective epoxidation of cyclooctene by the use of aqueous hydrogen peroxide as an oxidant.