Kazuo Satoh

Dependence of spontaneous polarization on orientation and position of several bond moments near chiral parts in ferroelectric liquid crystals

Abstract New series of ferroelectric liquid crystals with several bond moments near the chiral part have been prepared. The position and the orientation of those bond moments are found to strongly influence the magnitude of the spontaneous polarization in these ferroelectric liquid crystals, and the spontaneous polarization as high as 240 nC/cm2 has been obtained.

Room-temperature epitaxial growth of NiO(1 1 1) thin films by pulsed laser deposition

The room-temperature epitaxial growth of NiO(111) thin films was successfully achieved on α-Al 2 O 3 (0001) substrates using a pulsed laser deposition method. The epitaxial growth mechanism and the effect of oxygen pressure on the film quality were investigated using X-ray diffraction, X-ray pole figure, reflection high-energy electron diffraction and atomic force microscopy. The orientation relationships of the films with respect to the substrates were NiO[111]∥α-Al 2 O 3 [0001], NiO[101]∥α-Al 2 O 3 [1010], and NiO[211]∥α-Al 2 O 3 [1120]. The films consisted of a lot of domains and showed sixfold symmetry. These results can be explained by the higher-order epitaxy mechanism enabling the fourfold longer in-plane lattice parameters of NiO(111) to match the threefold longer parameters of α-Al 2 O 3 (001) with <4.5% misfit. The crystallinity of the epitaxial films was significantly improved by expanding the in-plane lattice parameter. This is due to the relaxation of the lattice misfit between the film and the substrate at the initial growth.

Novel Ferroelectricity in Fluorinated Ferroelectric Liquid Crystal

Ferroelectric liquid crystals with spontaneous polarization exceeding 10-7 C/cm2 have been prepared by introducing a fluorinated carbon. The liquid crystals show anomalous dielectric behaviour due to the wall and field effects.

Influence of Oxygen Flow Ratio on Properties of Zn2SnO4 Thin Films Deposited by RF Magnetron Sputtering

Zinc stannate (Zn2SnO4) thin films were deposited by RF magnetron sputtering on silica substrates at various [O2/(Ar+O2)] flow ratios. The influences of the [O2/(Ar+O2)] flow ratio on the crystalline structure, and the optical and electrical properties have been investigated. No sharp X-ray diffraction (XRD) peaks were observed in as-deposited thin films. After postdeposition annealing in air at 750°C, the thin films showed a preferred orientation of (111). The thin films exhibited a high transmittance in the visible spectrum irrespective of the [O2/(Ar+O2)] flow ratio or postdeposition annealing. The optical band gap was estimated to be 4.1 eV by analyzing the optical spectra of thin films annealed at 750°C. The composition ratio of Zn/Sn for thin films deposited in an Ar/O2 mixture was 2.0 and their electrical resistivity was on the order of 105 Ωcm. In contrast, the composition ratio of Zn/Sn for a thin film deposited in pure Ar was 1.5 and an electrical resistivity of 4.1 ×10-2 Ωcm was observed.

Design of neutron detector by using a novel superconductor MgB2

Abstract It is difficult to detect neutrons compared to charged particles. A novel metallic superconductor MgB 2 has a high T c of 40 K. It is well known that the 10 B has a huge cross-section for the nuclear reaction of 10 B( n , α ) 7 Li. It reaches 3800 barns for thermal neutrons. The Li particle has 0.84 MeV while α particle has 1.47 MeV. We propose to use the MgB 2 as a superconducting neutron detector. We design a prototype of a MgB 2 neutron detector from an MgB 2 film where the electron beam lithography is employed to fabricate a meandering MgB 2 stripe line of the 1-μm width. The hot spot caused by the nuclear reaction is responsible for detecting neutrons.

Magnitude and direction of the spontaneous polarization of ferroelectric liquid crystals with several bond moments

Abstract The magnitude and direction of the spontaneous polarization in most ferroelectric liquid crystals have been confirmed to be determined by the location and magnitude of the bond moment around the chiral carbon and the core. In compounds with several bond moments their relative orientation is very important for obtaining a large spontaneous polarization. Compounds with benzene rings in the core substituted with OH also have a large spontaneous polarization, perhaps due to the formation of hydrogen bonds. Reversal of the direction of the spontaneous polarization with temperature has been found for EFPPOPB. This anomalous behaviour has been explained tentatively in terms of a conformation change due to the existence of a flexible -CH2- unit between the chiral carbon and the dipole moment.

Planar reflection grating lens for compact spectroscopic imaging system

A compact spectroscopic imaging device consisting of a planar reflection grating lens, a probe fiber array, and a two-dimensional image sensor was proposed and discussed. Reflected or luminescent lights from a subject are coupled to the probe fibers, guided to fiber output ends, radiated into the air, diffracted by the grating lens with wavelength-dependent angle, and focused onto lines on the image sensor. Two-dimensional intensity distribution on the image sensor can give one-dimensional spectrum distribution along a specified direction. A grating lens was designed with a fiber array and a CCD image sensor for 100-nm wavelength range and 10-mm fiber array width. A spectral resolution of 5 nm and a spatial resolution of 0.25 mm were experimentally confirmed.

Epitaxial growth of CuScO2 thin films on sapphire a-plane substrates by pulsed laser deposition

An epitaxial film of CuScO2, a transparent oxide semiconductor with a delafossite structure, was grown on an α−Al2O3(112¯0) substrate by a pulsed laser deposition method using a single-phase Cu2Sc2Oδ target. A two-dimensional x-ray reciprocal space mapping measurement revealed that the film was single phase with a rhombohedral crystal structure. The film showed six-fold rotational symmetry in the basal plane, indicating that the film had a twinned domain structure. The epitaxial growth of CuScO2[3R](0001) thin films on α−Al2O3(112¯0) substrates is caused by the uniaxial locked epitaxy mechanism along the ⟨1¯21¯0⟩ direction of the film, and the orientation relationships of the film with respect to the substrate were CuScO2[3R](0001)∕∕α−Al2O3(112¯0) and CuScO2[3R][1¯21¯0]∕∕α−Al2O3[88¯01]. The optical transmittance of the film was larger than 65% in the visible/near-infrared regions, while the energy gap for direct allowed transition was estimated as 3.7 eV. The resistivity of the film, 9.3×106Ωcm at room te...

Effect of the Molecular Structure of the Chiral Part on Spontaneous Polarization and Dielectric Properties of Ferroelectric Liquid Crystals

The magnitude and direction of spontaneous polarization in ferroelectric liquid crystals with several bond moments in the chiral parts are found to be influenced strongly by the position and the orientation of those bond moments. By designing appropriate structures in the chiral parts, a spontaneous polarization and dielectric constant exceeding 200 nC/cm2 and 1000, respectively have been obtained.

Systematic characterization of upper critical fields for MgB2 thin films by means of the two-band superconducting theory

We present experimental results for the upper critical fields Hc2 of various MgB2 thin films prepared by molecular beam epitaxy, multiple-targets sputtering, and co-evaporation deposition. Experimental data for the Hc2(T) are successfully analyzed by applying the Gurevich theory of dirty two-band superconductivity in the case of Dπ/Dσ>1, where Dπ and Dσ are the intraband electron diffusivities for the π and σ bands, respectively. We find that the parameters obtained from the analysis are strongly correlated to the superconducting transition temperature Tc of the films. We also discuss the anomalous narrowing of the transition width at intermediate temperatures confirmed by the magnetoresistance measurements.