Thermoelectric properties of porous SiC/C composites

We developed a porous SiC/C composite by oxidizing a SiC/C composite made from a mixed powder of wood charcoal and SiO₂ (32–45 μm) by pulse current sintering at 1600 and 1800 °C under a N₂ atmosphere. The microstructures of the porous SiC/C composites with oxidation and the SiC/C composites without oxidation were analyzed by Raman spectroscopy and scanning electron microscopy (SEM). Raman spectra revealed the disappearance of excess carbon and the presence of β-SiC. The porous microstructure was monitored by SEM observation as a function of the heat treatment temperature. The thermoelectric properties of porous SiC/C composites with oxidation and SiC/C composites without oxidation were investigated by measuring the Seebeck coefficient, the electrical conductivity and thermal conductivity. The Seebeck coefficient of all samples revealed n-type conduction, and the absolute value of the Seebeck coefficient for the porous SiC/C samples with oxidation was much larger than that for the SiC/C samples without oxidation. For the electrical conductivity the reverse is true. Only the thermal conductivity of the SiC/C sample heated to 1800 °C without oxidation was high initially and stayed rather high. In general, the thermoelectric properties improved at higher measurement temperatures indicating their suitability for high-temperature thermoelectric conversion. A maximum figure of merit of 2.01×10⁻⁵ K⁻¹ was obtained at 700 °C in porous SiC/C samples sintered at 1800 °C with oxidation.     

Preparation of Fluorine-Containing Indium Tin Oxide Sputtering Targets using Spark Plasma Sintering Process

Fluorine-containing indium tin oxide (F-ITO) sputtering targets were prepared using spark-plasma-sintering (SPS) process. The initial powder, which was prepared by reacting ITO with HF, was sintered to the 10 cm-disks with nearly 90% of the theoretical density by the SPS process. The resulting disks were consisted of ITO and InOF, and the fluorine content was about 4 at.%. Using the F-ITO disks as sputtering target, thin films were deposited on the glass substrates. The electrical conductivity and optical transmission of the deposited films were comparable to those of the conventional ITO films, while the surface roughness of the films was much improved.     

Writable and erasable PPV medium by irradiation at 365 nm

Dopings of vaporized cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethane (CMTE) into poly(methyl methacrylate) (PMMA), polystyrene, and polycarbonate were performed by a vacuum process, and the doping behaviors of CMTE were evaluated. Among the matrix polymers, PMMA was dispersed CMTE densely in its surface region. By using the CMTE-doped PMMA, we could fabricate a novel rewritable medium: a multi-layered film was prepared from over-coating of CMTE-doped PMMA onto poly(p-phenylene vinylene) (PPV) film, which set on a transparent substrate. Image storage could be performed upon irradiation at 365 nm at the side of CMTE/PMMA layer: color of the irradiated area changed a light yellow to a red due to photo-isomerization of CMTE. Next, upon irradiation at 365 nm at the side of the transparent substrate, PPV emitted a green fluorescence at around 530 nm, and the CMTE absorbed the emission from PPV causing image-erasure based on back-isomerization of CMTE.     

Reproducible on-off switching of the light emission from the electroluminescent device containing a spin crossover complex

To examine the mechanism of a reproducible on-off switching of light emission from a novel organic electroluminescent (EL) device consisting of a spin crossover complex of [Fe(dpp)₂](BF₄)₂ (dpp = 2,6-di(pyrazol-1-yl)pyridine) and chlorophyll a, we have investigated the EL properties of an ITO/chlorophyll a:[Fe(dpp)₂](BF₄)₂/Al device. The comparison with a reference device not containing [Fe(dpp)₂](BF₄)₂ revealed that the introduction of [Fe(dpp)₂](BF₄)₂ results in small threshold voltage and large external quantum efficiency. Moreover, the EL spectra in the low-temperature region, where [Fe(dpp)₂](BF₄)₂ is in the low-spin state, showed the emission from the ITO electrode, suggesting that injected electrons pass through the active layer via [Fe(dpp)₂](BF₄)₂.     

Crystal shape of GaAs nanocrystals deposited on Si(100) by molecular beam epitaxy

The shape changes in GaAs nanocrystals deposited on Si substrate have been studied as a function of the coverage by transmission electron microscopic observations in order to see the growth mechanism from the viewpoint of the surface energy and the lattice strain energy between the nanocrystal and the substrate. When GaAs was deposited on the Si(100) surface, the shape of the GaAs nanocrystals changes from stepped mound, hut cluster to dome structure with increasing the coverage. The shape changes are responsible for decreasing the total free energy caused by the lattice strain energy with the substrate and surface energy depending on the crystal size.