Ta2O5 templated growth of droplet-like platinum particles by potentiodynamic polarization of tantalum in aqueous solution of hexachloroplatinic acid

By potentiodynamic polarization of mechanically polished tantalum in a diluted aqueous solution of hexachloroplatinic acid, droplet-like platinum microparticles were electrodeposited, embedded into the simultaneously formed Ta₂O₅ film. The roughness factor of platinum of 31 was achieved. Within the potential region of both hydrogen and oxygen underpotential deposition, in both acidic and alkaline solutions, the composite Pt/Ta₂O₅ electrode displayed an excellent electrochemical response characteristic of smooth polycrystalline platinum. The preparation method applied in this work presents an easy way to obtain an electrode surface combining the behaviour of smooth polycrystalline platinum with the behaviour of microdisc arrays. Its electrocatalytic effectiveness was demonstrated for an oxygen reduction reaction in alkaline solutions.     

The photovoltaic effect of the p–n heterojunction organic photovoltaic device using a nano template method

Characteristics of ITO/polypyrrole (PPy) nano fibers/poly(3-hexylthiophene)/Al photovoltaic devices prepared by nano template method were studied. PPy nano fibers on ITO glass were formed through nano pores of polymer membrane template using home made special sample holder by electrochemical polymerization in an electrolyte solution of pyrrole and lithium perchlorate as a dopant in acetonitrile. Ordered structure with enhanced interfacial area formed by nano template method enable to fabricate polymeric photovoltaic device with improved photo-conversion efficiency. This nano fiber structures film possesses increased interfacial area, large charge separation area (photoactive zone) and secured charge transportation route. The effect of altering energy levels of PPy by changing doped state was also studied. Device made with nano fiber structure showed enhanced photovoltaic effect than that of overlayed film device.     

High magnetic field researches in Tohoku University

Using hybrid magnets for fields up to 31 T, superconducting magnets up to 20 T and cryogen-free magnets up to 15 T, characterization of superconductors, materials synthesis and condensed matter physics are being done in the High Field Laboratory for Superconducting Materials. We have developed thin strong superconducting wire, which enable us to construct compact magnet, cryogen-free magnet and cryogen-free hybrid magnet for the first time. We have found that polymer materials, high T_c superconductors and protein single crystals synthesized in high magnetic fields show different characters from those synthesized in normal condition. Magnetic levitation is performed to make a microgravity condition for materials processing similar to the space.     

A new dithiolene complex magnet: [Ni(Cp*Rubdt)2][CF3SO3]

The unique salt [Ni(Cp*Rubdt)₂][CF₃SO₃], containing the features of both a metal dithiolene complex and a metallocene, has been studied by d.c. and a.c. magnetic susceptibility measurements. This indicated ferromagnetism with T_c=3.5 K as evidenced by splitting of the field-cooled and zero-field-cooled d.c. susceptibility, remnant magnetisation, a non-zero imaginary component and a peak in the real component of the a.c. susceptibility and magnetic hysteresis. Studies of magnetisation against field indicated superparamagnetic behaviour above the ordering temperature up to around 10–20 K, suggesting correlated behaviour of the spins in one or two dimensions before the onset of 3D order. In contrast to many mixed dithiolene complex—metallocene salts, the structure of the title compound ensures that no segregation of the dithiolene and metallocene components into separate stacks can occur, a structural feature that has previously led to interesting magnetic materials.     

High-quality GaMnAs films grown with arsenic dimers

We demonstrate that GaMnAs films grown with As₂ have excellent structural, electrical and magnetic properties comparable or better than similar films grown with As₄. Using As₂, a Curie temperature of 112 K has been achieved, which is slightly higher than the best reported to date. However, more significantly films showing metallic conduction have been obtained over a much wider range of Mn concentrations from 1.5% to 8% than has previously been reported for films grown with As₄. The improved properties of the films grown with As₂ are related to the lower concentration of antisite defects at the low growth temperatures employed.     

Non-contact spectral analysis of cytochrome c on carbon electrodes with optical waveguide spectroscopy

To realize the spectral analysis of molecules on the opaque substrate, we proposed non-contact optical waveguide (NOW) spectroscopy. The cyt.c was adsorbed on the carbon substrate by dipping method. This was fixed above the optical waveguide. The gap between the carbon substrate and the waveguide was controlled by latex beads with a diameter of 120 nm as a spacer. A clear NOW spectrum based on the adsorbed cyt.c on the carbon substrate was observed. The cyt.c was easily adsorbed on the carbon surface with an oxidized form by the dipping method. The electrochemical cell system constructed on the waveguide enabled the dynamic analysis on the redox reaction of the adsorbed cyt.c on the carbon electrode. The adsorbed cyt.c showed stable redox reaction without the dislocation or re-dissolution in an aqueous solution.     

An investigation of time-dependent domain wall pinning effects in Tb/Fe multilayer thin films

Reverse domain nucleation time measurements have been performed on two Tb/Fe multilayer magneto-optic films exhibiting different degrees of domain wall pinning. A linear relationship between ln (reverse domain nucleation time) and the applied field has been predicted and observed for a sample exhibiting weak domain wall pinning. This is in agreement with theoretical work presented which addresses time dependence in systems possessing weak domain wall pinning. A non-linear relationship applicable over a restricted field range has been derived for a sample exhibiting strong domain wall pinning. Experimental results have indicated that this relationship is also valid.     

Relative stability of multiple bonds between germanium and arsenic. A theoretical study

Substituent effects on the potential energy surface of XGeAs (X=H, Li, Na, BeH, MgH, BH₂, AlH₂, CH₃, SiH₃, NH₂, PH₂, OH, SH, F, and Cl) were investigated by using B3LYP and CCSD(T) methods. The isomers include structures with formal double (GeAsX) and triple (XGeAs) bonds to germanium–arsenic, so a direct comparison of these types of species is possible. Our model calculations indicate that electropositively substituted GeAsX species are thermodynamically and kinetically more stable than their isomeric XGeAs molecules. Moreover, the theoretical findings suggest that F, OH, NH₂, and CH₃ substitution prefer to shift the double bond (GeAsX) by forming a triple bond (XGeAs).     

Positronium study of porous structure of sol–gel prepared SiO2: influence of pH

Positron annihilation lifetime and Doppler broadening of annihilation line techniques have been used to obtain information about the small-pore structure of SiO₂ prepared by the alkoxide method in different experimental conditions. Samples prepared in strong acidic environment (pH = 2) contain only small pores with mean radius R∼5 Å, while those prepared at pH = 6 and pH = 9 contain pores of two sizes, R∼5 and R∼17–26 Å. The influence of pH, water/alkoxide molar ratio and temperature of heat-treatment of the samples on their pore structure has been studied.