Preparation of Alkoxy-Derived Tantalum Vanadate

Compound formation in the system Ta₂O₅–V₂O₅ has been studied using amorphous materials prepared by the simultaneous hydrolysis of tantalum and vanadyl alkoxides. Three compounds exist in this system: 9Ta₂O₅· V₂O₅, 9Ta₂O₅·2V₂O₅, and Ta₂O₅·V₂O₅ (TaVO₅). Solid solutions of δ-Ta₂O₅ are formed at low temperatures up to 10 mol% V₂O₅. They transform to β-Ta₂O₅ solid solutions at higher temperatures; the transformation temperature falls with increasing V₂O₅ A new compound, 9Ta₂O₅·V₂O₅, 670° to 755°. It has an orthorhombic unit cell with a = 0.7859 nm, b = 1.733 nm, and c = 1.766 nm. Orthorhombic TaVO₅ crystallized at 535° to 560° decomposes into 9Ta₂O₅°V₂O₅ at 1010°.     

Electrical properties of La-doped SrTiO3 (La: 0.1 to 2.0 at %) single crystals grown by xenon-arc image floating zone method

Lanthanum-doped semiconducting strontium titanate single crystals having various lanthanum contents were grown in an air atmosphere by the xenon-arc image floating zone method. The crystals were characterized by X-ray powder diffraction, EPMA analysis and chemical analysis. Each lanthanum was accompanied by a trivalent titanium ion in the grown crystal. The electrical conductivity of these crystals was measured at 20 to 1150° C, and it was found to increase linearly with increasing lanthanum content. The mobility of the charge carrier was estimated from the concentration of trivalent titanium and the conductivities of the crystals. The mobility in the low temperature region agreed with previous studies. However, a significant difference was found at high temperatures. An error in the temperature dependence in the previous study is responsible for this difference. It is stressed that care is necessary in applying the results of single crystalline studies when discussing high-temperature bulk defect chemistry.     

Numerical study on an equivalent source model for inhomogeneous magnetic field dosimetry in the low-frequency range

A new equivalent numerical source model is proposed for efficient dosimetric investigations in the low-frequency range. This approach allows the reproduction of complicated inhomogeneous magnetic field distributions around electronic appliances with full generality (i.e., supports three-dimensional vector fields). This paper investigates the accuracy of the equivalent source model using the geometry-based numerical reference model of a current loop to simulate the magnetic field distribution of a real electronic appliance. Good agreement between the equivalent source model and the reference is obtained with regard to the magnetic field distribution and the induced electric current density in a homogeneous human body model, respectively.     

Effects of two-phase reactions on composition and potential response of zirconium(IV)-tetraphenylporphyrin complexes as carrier for citrate-selective electrode

The reactions between zirconium(IV)-tetraphenylporphyrin(tpp)-hydroxide complexes ([ZrIV2(OH)4(tpp)2] and [ZrIV(OH)2(tpp)]) in chlorobenzene and various acids (HX: HClO4, HCl, HNO3, CH3COOH) in water were studied. Three species [ZrIV2(OH)3(tpp)2],X, [ZrIV(OH)X(tpp)], and [ZrIVX2(tpp)] were identified, and their stability constants were determined. The extent of formation of each species depends on the coordination ability and lipophilicity of X-. The performance of these complexes was evaluated as a carrier of an anion-selective electrode. The cationic complex [ZrIV2(OH)3(tpp)2],X exhibited selectivity following the Hofmeister series to weakly coordinating anions, while showing a super-Nernstian response to strongly coordinating citrates. The latter suggests the cleavage of the dimeric structure. The dichloro complex [ZrIVCl2(tpp)] was prone to hydrolyze in contact with an aqueous solution and gave drifting potentials. The monochloro complex [ZrIV(OH)Cl(tpp)] was more stable and strongly responded to acetates, which may be ascribed to substitution of a weakly bound chloride. A slow hydrolysis giving [ZrIV(OH)2(tpp)], however, caused gradual deterioration of this strong response to acetates. Conditioning of the membrane in 1 M HCl regenerated the once-deteriorated carrier [ZrIV(OH)Cl(tpp)], while continuous conditioning extended its operating life. This carrier was effectively used to continuously monitor the acetate in a flow system. The dihydroxo complex [ZrIV(OH)2(tpp)] showed lower responses to common anions due to strong Zr-OH bonding and was thus successfully used for selective potentiometry of citrates.     

a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical filters

We examined the optical properties of a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical bandpass filters (BPFs). Because of the high refractive-index contrast between a-Si:H and SiO2, the total number of layers of an a-Si:H/SiO2 multilayer can be relatively small. We obtained an a-Si:H refractive index of 3.6 at lambda = 1550 nm and its extinction coefficient k < 1 x 10(-4) and confirmed by Fourier-transform infrared spectroscopy that such small k is influenced by the Si-H bonding in the film. We fabricated a-Si:H/SiO2 BPFs by using in situ optical monitoring. Thermal tuning of a-Si:H/SiO2 BPF upon a silica substrate was also performed, and a thermal tunability coefficient of 0.07 nm/degree C was obtained.     

Ultra-stable nanoparticles of CdSe revealed from mass spectrometry

Nanoparticles under a few nanometres in size have structures and material functions that differ from the bulk because of their distinct geometrical shapes and strong quantum confinement. These qualities could lead to unique device applications. Our mass spectral analysis of CdSe nanoparticles reveals that (CdSe)(33) and (CdSe)(34) are extremely stable: with a simple solution method, they grow in preference to any other chemical compositions to produce macroscopic quantities. First-principles calculations predict that these are puckered (CdSe)(28)-cages, with four- and six-membered rings based on the highly symmetric octahedral analogues of fullerenes, accommodating either (CdSe)(5) or (CdSe)(6) inside to form a three-dimensional network with essentially heteropolar sp(3)-bonding. This is in accordance with our X-ray and optical analyses. We have found similar mass spectra and atomic structures in CdS, CdTe, ZnS and ZnSe, demonstrating that mass-specified and macroscopically produced nanoparticles, which have been practically limited so far to elemental carbon, can now be extended to a vast variety of compound systems.     

A practical method for the remote control of the scanning electron microscope

We have developed a remote control system for the scanning electron microscope (SEM). It is called Web-SEM and can be accessed by anyone through the Web browser. It is not necessary to install special software to control the SEM. Because the operating performance changes with the amount of traffic on the Internet, we have connected the Web-SEM to a LAN/Internet in order to overcome this. We have checked the performance of the remote control operation and we were able to perform focus adjustment, stage movement, etc. over the Internet by improving the method of operation and image transfer.     

Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth

The synthesis of large single crystals of GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue-light-emitting diodes and lasers. Although high-quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N(2) at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melting of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred at about 2,220 degrees C, and decreasing the temperature allowed the GaN melt to crystallize to the original structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.     

Development of a Geant4 solid for stereo mini-jet cells in a cylindrical drift chamber

Stereo mini-jet cells will be indispensable components of a future e⁺e⁻ linear collider central tracker such as JLC-CDC. There is, however, no official Geant4 solid available at present to describe such geometrical objects, which had been a major obstacle for us to develop a full Geant4-based simulator with stereo cells built in. We have thus extended Geant4 to include a new solid (TwistedTubs), which consists of three kinds of surfaces: two end planes, inner and outer hyperboloidal surfaces, and two so-called twisted surfaces that make slant and twisted φ-boundaries. Design philosophy and its realization in the Geant4 framework are described together with algorithmic details. We have implemented stereo cells with the new solid, and tested them using geantinos and Pythia events (e⁺e⁻→ZH at  GeV). The performance was found reasonable: the stereo cells consumed only 25% more CPU time than ordinary axial cells.     

Effect of the thickness of Bi–Te compound and Cu electrode on the resultant Seebeck coefficient in touching Cu/Bi–Te/Cu composites

The resultant Seebeck coefficient α of the touching p- and n-type Cu/Bi–Te/Cu composites with different thicknesses of t _Bi–Te and t _Cu was measured as a function of t, where t _Bi–Te was varied from 0.1 to 2.0 mm, t _Cu from 0.3 to 4.0 mm and t is the lapse time after imposing the voltage. The temperature difference ΔT is produced by imposing a constant voltage of 1.70 V on two Peltier modules connected in series. The resultant α of composites was calculated from the relation α = ΔV/ΔT, where ΔV and ΔT were measured with two probes placed on both end coppers. ΔV decreases abruptly with an increase of t below t = 5 min, while above t = 7 min, it tends to saturate to a constant value. The resultant α and saturated ΔV vary significantly with changes in t _Cu and t _Bi–Te. When a composite has a combination of t _Cu = 1.0 mm and t _Bi–Te=0.1 mm, the generating powers ΔW (=(ΔV)²/4R) estimated using the saturated ΔV and calculated electrical resistance R for the p- and n-type composites have great local maximum values which are 4–5 times as large as those obtained for the conventional combination of t _Bi-Te = 2.0 mm and t _Cu = 0.3 mm. It is surprising that the generating power ΔW is enhanced significantly by sandwiching a very thin Bi–Te material between two thick coppers, unlike the conventional composition of thermoelectric modules. On the other hand, when a composite has a combination of t _Bi–Te = 0.1 mm and t _Cu = 0.3 mm, the resultant α of the p- and n-type composites exhibited great values of 711 and −755 μV/K, respectively, so that the maximum resultant ZT of the p- and n-type composites reached extremely large values of 8.81 and 5.99 at 298 K. However, the resultant ZT decreases rapidly with an increase of t _Cu or t _Bi–Te. The resultant ZT is thus found to be enhanced significantly not only in superlattice systems but also in macroscopic composites. The present enhancement in ZT is attributed to the large barrier thermo-emf generated in the Bi–Te region shallower than 50 μm from the boundary.