Tadanori Sei

Preparation and electrical properties of ITO thin films by dip-coating process

Indium tin oxide (ITO) thin films were prepared on quartz glass substrates by a dip-coating process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. The ITO thin films containing 0 ∼ 20 mol% SnO2 were successfully prepared by heat-treatment at above 400 °C. Chemical stability of sol were investigated by using a FTIR spectrometer. The electrical resistivity of the thin films decreased with increasing heat-treatment temperature, that is carrier concentration increased, and mobility decreased with increasing SnO2 content. The ITO thin films containing 12 mol% SnO2 showed the minimum resistivity of ρ=1.2 × 10−3 (Ω cm). It also showed high carrier concentration of N=1.2 × 1020(cm−3) and mobility μH=7.0(cm2 V−1 s−1).

Preparation and properties of transparent conductive thin films by the sol-gel process

Abstract Highly transparent and conducting Al-doped ZnO films were prepared by a dip-coating method. The conditions of preparation and electrical properties of the thin films were examined. The thin films were formed on quartz glass substrates by dipping into a selected solution and calcining at 500°C for 5 h. The conductivities of thin films were measured as a function of doped Al content. The thin films had a conductivity of log σ (S/cm) = +2.7 and a transmission of about 90% in the visible light region. The difference of the conductivities from two raw materials (solution A and solution B) was attributed to an accelerated reaction between the Al-doped ZnO thin film and the SiO2 substrate at high temperatures (solution A system).

The growth mechanism and the habit change of ice crystals growing from the vapor phase

Polyhedral ice crystals are formed at a few % supersaturation in order to clarify experimentally the growth mechanism and the habit change of ice crystals growing in low air pressure at a temperature of 0 to −30°C. On the basis of the normal growth rates versus supersaturation, in situ observation of ice crystal surface and the advance rates of steps versus supersaturation, it is concluded that the {0001} and {1010} faces of ice crystals grow by the vapor-quasi-liquid-solid (V-QL-S) mechanism at a temperature of 0 to −2°C, while they grow by the BCF mechanism at a temperature of −2 to −30°C. The habit change with temperature of ice crystals growing in low air pressure is explained by the temperature dependence of the condensation coefficient α1 of the {0001} and {1010} faces.

Preparation of highly oriented thin film exhibiting transparent conduction by the sol-gel process

Highly oriented thin films exhibiting transparent conduction aluminium-doped ZnO (AZO), were prepared by a spin-coating method. The effects of the solvents on the preparation and electrical properties of the thin films were examined. The thin films were formed on quartz glass substrates by spin-coating into a selected solution and calcining at 700 °C for 5 h. The thin films had a resistivity of ρ (Ω cm)=1.5 after heat treatment in an air atmosphere, and 1.5 × 10−3 Ω cm in a reducing atmosphere, and a transmission of about 85% in the visible light region. The differences in the high orientation and the conductivities were attributed to a chelate formation in the aluminium-doped ZnO due to the solvent effect.

Preparation of spinel-type ferrite thin films by the dip-coating process and their magnetic properties

Films of spinel-type ferrite, MFe2O4 (M=Ni, Co, Mg, Li0.5Fe0.5) have been prepared by a dip-coating method from the sol-gel process. Ferric nitrate, nickel nitrate, cobalt nitrate and lithium nitrate were used as raw materials, and glycerol and formamide were used as solvents. A film was prepared by dipping a silica glass plate. The spinel-type ferrite was obtained by heat-treatment at 700–900°C for 2 h in air. The film thickness was about 0.8 μm. The saturation magnetization, σr, of the film and powder with composition 50NiO·50Fe2O3 was 196 emu cm−3 and 29.1 emu g−1, respectively, and the coercive force,Hc, was 140 and 95 Oe, respectively, after heat-treatment at 800°C for 2 h. In particular, the films were shown to have a much largerHc than the powder. The grain growth of spinel ferrite may be subject to restriction because it is in progress above an amorphous base-plate. The crystals are therefore aligned with the base-plate and have uniaxial anisotropy.

Growth rate and morphology of ice crystals growing in a solution of trehalose and water

In-situ observations have been made of ice crystals growing in solutions of trehalose and water in order to investigate how trehalose suppresses the growth of ice crystals and protects organisms from the freezing of their cellular water. In the range of trehalose concentration below 41.7 wt% the growth rate along the a-axis was found to increase proportionally to the second power of the supercooling and to be suppressed by 75% when the trehalose concentration was doubled. In this manner, trehalose proved to be approximately twice as effective as sucrose in suppressing the growth rate of ice crystals. It was also more effective than sucrose in suppressing the morphological instability of ice crystals. This effectiveness is believed to be related to the fact that trehalose binds more water molecules than does a sucrose molecule.

Preparation of Ferroelectric (Pb, La)(Zr, Ti)O3 Thin Films by Sol-Gel Process and Dielectric Properties

Crack-free transparent ferroelectric polycrystalline PLZT (Pb, La)(Zr, Ti)O3 thin films with perovskite structure were prepared by dipcoating from a sol-gel process. Lead acetate, lanthanum-acetate, zirconyl nitrate and titanium tetrabutoxide were used as the raw materials. Acetic acid and triethylene glycol were used as solvents. Ferroelectric polycrystalline PLZT thin films with perovskite structure were obtained between 400°C and 850°C in air. The thin films deposited on platinum substrates and on silica glass substrates with sputtered ITO thin film were smooth and uniform. The dielectric constant of PLZT (7/65/35) thin film on the platinum substrate was about 788 at room temperature for 10 kHz and the loss tangent was about 0.03. The spontaneous polarization of PLZT (7/65/35) thin film was 8.0 µCcm-2 and the coercive field was 20 kV/cm. The optical transmittance was above 60% in the range from 400 nm to 900 nm.

Preparation of ZnGa2O4 thin film by sol—gel process and effect of reduction on its electric conductivity

Abstract Spinel oxide ZnGa 2 O 4 thin films were prepared on SiO 2 glass substrates by a sol—gel process using inorganic salts as raw materials. The conduction path in the crystal was confirmed by measurement of the photo-current of the film. Reduction of the films in H 2 , at 625°C and above, resulted in the sublimation of Zn and the formation of β-Ga 2 O 3 at the surfaces of ZnGa 2 O 4 crystals. Reduction above 650°C caused pores, cracks and separation of the film from the substrate. These increased the resistivity of the film.

The role of boron in low-temperature synthesis of indialite (α-Mg2Al4Si5O18) by sol–gel process

Powder and pellets composed mainly of indialite (α-Mg2Al4Si5O18) with 2.1 wt% added B2O3 were prepared by a sol–gel process using metal salts as raw materials. When heated at 900°C for 6 h, the pellets showed a relative density of 91.4% of ideal cordierite (β-Mg2Al4Si5O18), a Vickers hardness of 1080 and a relative dielectric constant of 5.0 (at 1 MHz), which was the same value as that of cordierite. Magic angle spinning nuclear magnetic resonance measurements of 29Si, 27Al and 11B showed that boron disturbed the formation of the Si–O–Al network below 300°C and broke the network between 700 and 800°C. The high homogeneity and fluidity caused by the melting helped indialite to crystallize directly from the amorphous state between 800 and 850°C.

In situ observation of vapor-grown ice crystals by laser two-beam interferometry

Abstract In situ observation of vapor-grown ice crystals was carried out using laser two-beam interferometry, and the growth mechanism of vapor-grown ice crystals at the temperature range of -7 to -28.5°C and at low supersaturation was investigated.