Katsuyoshi Hoshino

New Avenues in Dinitrogen Fixation Research

The present article focuses on a recent finding concerning dinitrogen fixation by using titanium oxide/conducting polymer composite systems and its comparison with an earlier fixation method (Schrauzer process) that makes use of a powdered titanium oxide. Both processes work under the stimulus of light at room temperature and pressure, but dinitrogen is fixed to a solid ammonium salt crystal in the former and to a gaseous ammonia molecule in the latter process. Differences in the physicochemical concepts between the two processes are discussed.

Bismuth Electrochromic Device with High Paper-Like Quality and High Performances

An electrochromic-type electronic paper was prepared using nanocomposites that consisted of silica nanoparticles (silica 60 wt %) and polyamide pulp. Its light scattering, ion transport, and aqueous electrolyte retention characteristics were examined. As a result, the shape of the nanocomposites was completely self-standing, though it could be impregnated with about nine times as much water on a weight basis. Moreover, its light scattering property was extremely similar to paper. Because of the impregnation of a large amount of water, the ion transport property of the nanocomposites was the same as that of the electrolyte solution without the nanocomposites. The nanocomposites was impregnated using an aqueous solution in which bismuthyl perchlorate (redox species), copper perchlorate, perchloric acid, sodium perchlorate, hydroquinone (electron mediator) and 2-buthyne-1,4-diol (leveling agent) were dissolved. The electronic paper was then prepared by sandwiching the nanocomposites between an indium-tin-oxide transparent electrode and a copper sheet. This electronic paper utilizes the reversible codeposition reaction of black Bi-Cu from bismuthyl perchlorate and copper(II) ions. The characteristics of this electronic paper were examined, and excellent characteristics with a white reflectivity of 65%, black reflectivity of 6.4%, contrast ratio of 10:1, operating life of over 1 x 10(6) cycles and open-circuit memory of at least 1 month were obtained. In addition, its driving voltage was 1.2 V, and the write time was 500 ms.

Electric Conductivity-Tunable Transparent Flexible Nanowire-Filled Polymer Composites: Orientation Control of Nanowires in a Magnetic Field

Cobalt compound nanowires were dispersed in a transparent nonconductive polymer film by merely stirring, and the films transparency and electrical conductivity were examined. This composite film is a unique system in which the average length of the nanowires exceeds the films thickness. Even in such a system, a percolation threshold existed for the electric conductivity in the direction of the film thickness, and the value was 0.18 vol%. The electric conductivity value changed from ∼1 × 10(-12) S/cm to ∼1 × 10(-3) S/cm when the volume fraction exceeded the threshold. The electric conductivity apparently followed the percolation model until the volume fraction of the nanowires was about 0.45 vol %. The visible light transmission and electric conductivity of the composite film of about 1 vol % nanowires were 92% and 5 × 10(-3) S/cm, respectively. Moreover, the electric conductivity in the direction parallel to the film surface did not depend on the amount of the dispersed nanowires, and its value was about 1 × 10(-14) S/cm. Even in a weak magnetic field of about 100 mT, the nanowires were aligned in a vertical and parallel direction to the film surface, and the electric conductivity of each aligned composite film was 2.0 × 10(-2) S/cm and 2.1 × 10(-12) S/cm. The relation between the average wire length and the electric conductivity was examined, and the effect of the magnetic alignment on that relation was also examined.

Enhancement in Chemical Interaction at Conducting Polymers/n‐Si Interfaces by Their Electroreduction

Studies of chemical and electronic interaction at organic/inorganic interfaces are described. Electrochemical deposition of conducting polymers [poly(3-methylthiophene), polythiophene, poly(3-methylpyrrole), polypyrrole, poly(3-methylthiophene-co-pyrrole)] on an n-Si wafer does not give rise to high-quality p-n heterojunctions, but it is found that their junction properties are greatly improved by their electrochemical reduction (cathodic treatment). For example, the cathodic treatment of an as-grown poly(3-methylthiophene)/n-Si junction cell with rectifying ratio, γ, of 1.4 x 10 1 and diode factor, n, of 2.6 gives a high quality junction with γ = = 1.7 x 10 4 and n = 1.2. The treatment involves not only the development of polymer films but the improvement in junction interface, since the treatment can contribute to the improvement only when conducted in the presence of polymer films. In order to understand this modification at the interface, the effects of cathodic treatment conditions (treatment potential and time) and the presence of an interfacial oxide layer on the junction properties are investigated. As a result, it is revealed that the improvement is explained by a junction formation model described as the evolution of covalent bond formation at the interface. Further electrochemical studies reveal that such bondings are disrupted by hydrolysis and/or oxidation, and the bond disruption model is used to describe the degradation of the junctions in the air.

Reversible formation and disruption of micelles by control of the redox state of the surfactant tail group

Reversible disruption and re-formation of micelles is observed by following the redox reaction of the redox-active micelles formed by the bromide salt of (11-ferrocenyl)undecyltrimethylammonium having a ferrocene moiety instead of the terminal methyl proton.

Electrochromic properties of ITO nanoparticles/viologen composite film electrodes

Nanostructured composite electrodes were prepared by dip-coating a mixed dispersion of ITO nanoparticles and 1,1′-didodecyl-4,4′-bipyridinium (DDV2+) dibromide on an ITO-coated glass plate, and their electrochromic properties were investigated in a 0.1 M Li2SO4 aqueous solution. The electrodes showed a color change from pale white to violet as they were oxidized and reduced, respectively, and good electrochromic performances; i.e., switching times of coloration (500 ms) and decoloration (380 ms), coloration efficiency of 140 cm2 C−1, long-term stability (>500 test cycles), and a memory life time greater than at least 24 h.

Polycarbazole Nanocomposites with Conducting Metal Oxides for Transparent Electrode Applications

The preparation and characterization of conducting polycarbazole (PCz) hybrid films with a colorless transparency are described. They were prepared by the vacuum evaporation of tin, aluminum, or gallium onto anion-doped green-colored PCz films, or by applying gallium to the films, followed by their exposure to ambient air. The resultant hybrid films consisting of an undoped PCz backbone and metal compounds exhibited good transparencies (90-95% at a wavelength of 550 nm). The hybrid films have a specific cross-sectional structure in which the small regions of the metal compounds are dispersed in the PCz backbone. The hybridization reaction was mechanistically explained on the basis of the combination of a metal corrosion reaction and polymer dedoping reaction, which was successfully supported by the chemical analyses of the hybrid films. The electric conductivities of the hybrid films, measured by a four-point-probe method, ranged from 2.2 x 10(-4) to 6.0 x 10(-3) S cm(-1), which are considered to be the lowest limit because the use of the hybrid films as an electrochemical electrode reveals that a network of conductive paths is preferentially formed in the film thickness direction rather than in the in-plane direction.

Properties of Heterojunction of Si/Poly(3-methylthiophene) as a Function of Polymerization Condition

A detailed analysis of poly(3-methylthiophene) (P3MeT) films deposited on a n-Si substrate is presented. In order to perform junction analysis, potentiometric measurements during the growth of the film, current-voltage measurements, degradation of electrical properties, FT-IR (Fourier transform infrared) measurements, and SEM (scanning electron microscope) observations are studied. New insights into the junction are obtained. The rectifying behavior is greatly improved by employing sandblasted n-Si as a substrate, compared with a nonsand-blasted n-Si substrate. Based on these results, junction formation is described as the evolution of covalent bond formation between hydroxy groups on the n-Si surface and a polymer film. The results are supported by FT-IR measurements of the sandblasted n-Si surface. A covalent bond destruction model is used to describe degradation behavior of the P3MeT/sandblasted n-Si heterojunction.

Mechanism of Memory Effect in an Organic Photoreceptor Coated on an Organic Polymer Electrode

A photoinduced memory effect in an electrophotographic receptor consisting of an iodine-doped conductive polymer electrode and a poly(N-vinylcarbazole) (PVK)/trinitrofluorenone (TNF) photoreceptor was investigated by means of xerographic, voltage-current and electrochemical measurements. The results showed that activation energy for memory formation was about 0.23 eV and was associated with the energy for CT-complex formation of PVK and iodine. This led us to propose a mechanism of memory formation in this system. Accordingly, it was indicated that the memory lifetime could be controlled by varying the kind of hole-transport material interacting with iodine.

Role of Space Charge in a Memory-Type Organic Photoreceptor Coated on an Organic Polymer Electrode

Role of photo-generated space charges on the memory effect, observed in an iodine-doped conductive polymer / poly(N-vinylcarbazole) (PVK)-trinitrofluorenone (TNF) double-layered system, was investigated by means off voltage-current measurements. The results were consistent with the previous conclusion obtained by the xerographic technique. The memory effect was found to come from space charges formed at the electrode-photoreceptor interface containing iodine. The space charge formation induced apparent barrier height lowering against carrier injection and the magnitude of lowering was about 60 meV. It was also found that injected charges from polymer electrode per unit space charge was more than 2×103.