Hiroshi Tabata

Fabrication of single electron transistors using transfer-printed aligned single walled carbon nanotubes arrays

A technique has been developed to transfer the aligned single-walled carbon nanotubes (SWCNTs) grown on a single-crystal quarz substrate to a SiO2/Si substrate. Aligned single electron transistors (SETs) have been fabricated with the transferred SWCNTs, and the low-temperature transport measurements have been carried out at 1.5 K. Several SETs fabricated in this approach exhibited regular Coulomb oscillations and closed Coulomb diamonds, which indicate the single quantum dot behavior. This suggests that the mechanical transfer technique does not produce serious damage to the SETs and would be useful for future integrated SET devices and circuits.

Atomic ordering in the LaFe0.5Mn0.5O3 solid solution film

LaFe0.5Mn0.5O3 solid solution films have been formed on SrTiO3 (111) substrates using a pulsed laser deposition technique and their magnetic properties have been examined. The films showed ferromagnetic (or ferromagnetic) behavior with a Curie temperature of 380 K and the saturation magnetization was estimated to be about 1.5μB per magnetic ion site (B site). The x-ray photoemission spectra indicated that this behavior was due to the partial ordering of magnetic ions (Fe and Mn ions) which is caused by the charge disproportion between Fe and Mn ions under the film formation conditions.

Photocontrol of spin-glass state in Mg1.5FeTi0.5O4 spinel ferrite films

A spin-glass state up to 210 K has been found in (Mg, Fe){Mg,Fe,Ti}2O4 spinel ferrite thin films formed on α-Al2O3(0001) substrates. The films exhibit long-time relaxation of the magnetization in zero-field-cooled operation below 210 K; also, the ac susceptibility measurements show the presence of frequency-dependent cusp temperature. Both of the above observations are characteristic features of a spin glass. The change of magnetic state in the films from a spin glass to ferrimagnet has been achieved over a wide temperature range below 160 K by means of light irradiation.

Formation of C60 Colloidal Particles Suspended in Poor Solvent by Pulsed Laser Irradiation

We have succeeded in forming C60 colloidal solution by laser irradiation of C60 powder suspended in a poor solvent. The formation of particles with an average diameter in the colloidal range was detected by transmission electron microscopy. A corresponding electron diffraction pattern revealed that the formed nanoparticles are fcc-structured C60 crystals. The mean size and size distribution of the formed C60 nanoparticles depended strongly on the fluence and wavelength of incident laser light.

Soft x-ray magnetic circular dichroism study of weakly ferromagnetic Zn1−xVxO thin film

The authors performed a soft x-ray magnetic circular dichroism (XMCD) study of a Zn1−xVxO thin film, which showed a small ferromagnetic moment. Field and temperature dependences of V 2p XMCD signals indicated the coexistence of Curie-Weiss paramagnetic and antiferromagnetic V ions, quantitatively consistent with the magnetization measurements. The authors attributed the paramagnetic signal to V ions substituting for Zn sites, which are somewhat elongated along the c axis. A possible formation of ferromagnetically dead layers in the surface region of the film is also discussed.

A Three-Dimensional Fluorescence Analysis of the Wings of Male Morpho sulkowskyi and Papilio xuthus Butterflies

Abstract Fluorescence properties from the wings of male M. sulkowskyi and Papilio xuthus butterflies were investigated for the first time over a wide range of excitation and emission wavelengths using a three-dimensional (3-D) fluorescence method. From the 3-D plots of the pale blue region of the wings of M. sulkowskyi, four contour peaks were observed. On the other hand, from the yellow region of the wings of Papilio xuthus, one peak was observed. The origins of these contour peaks are discussed based on a comparison with standard pigments. Of the four contour peaks seen for M. sulkowskyi, a specific peak (A), located at an excitation wavelength of about 325 nm and an emission wavelength of about 410 nm, was thought to be mainly due to a mixture or compound of three pteridine pigments (i.e., biopterin, pterin and isoxanthopterin). The single specific peak observed for Papilio xuthus, located at an excitation wavelength of about 400 nm and an emission wavelength of about 470 nm, was thought to be due to the Papiliochrom II pigment. Based on these results, the possibility of using 3-D fluorescence analysis as a tool for classifying butterflies is briefly described.

FLUORESCENCE FROM WING OF MORPHO SULKOWSKYI BUTTERFLY

Fluorescence from various parts of a wing of a male butterfly, Morpho sulkowskyi ( Morpho species), was investigated using a microspectrophotometer. From the central (blue color) region of the wing, fluorescence was observed for the first time in this species when irradiated with ultraviolet (UV) or visible light. On the other hand, the distal tip (black color) of the wing was not fluorescent. Further microscopic studies also showed that the fluorescence spectra of the upper (dorsal) and the lower (ventral) surfaces of scales, which were obtained from the fluorescent central region of the wing, were different, having fluorescence peaks at 520 nm and 470 nm, respectively.

Formation of YBa2Cu3O7−y/BaTiO3 multistructures by pulsed laser deposition for high‐temperature superconducting device applications

The formation of YBa2Cu3O7−y(YBCO)/BaTiO3(BTO)//SrTiO3(STO) (100) and BTO/ YBCO//STO(100) bilayer structures is demonstrated for the construction of a superconductor ferroelectric field transistor. The resulting films of the bilayers have highly c‐axis oriented structure. Epitaxial YBCO films formed on the BTO//STO(100) have a zero resistance temperature of 88.9 K. The surface morphology of the epitaxial BTO films on the YBCO//STO is very smooth with a mean surface roughness of 32 A. Moreover, the Au/BTO/YBCO structures have been fabricated, and the dielectric constant and remanent polarization of BTO layer are obtained to be 180 and 3.5 μC/cm2 at 77 K, respectively.

Write Strategy for Dual-Layer Digital Versatile Discs

A novel write strategy for rewritable dual-layer digital versatile discs (DVDs) was studied. This new strategy involves the erase top pulse which is included in the conventional write strategy for single-layer DVDs in present market. By thermal calculations, it was confirmed that this erase top pulse has an affect on the rapid heating of recording films. We observed that this new strategy enabled the improvement in data qualities on the layer near the laser incident (L0) effectively in 2 × and 4 ×-speed recordings even if L0 had a high optical transparency. Furthermore we also demonstrated a combination of what with the 2T-period strategy on the layer far from the laser incident (L1) realized a well-balanced signal performance for dual-layer DVD media.

Time-Resolved Fluorescence Studies of the Wings of Morpho sulkowskyi and Papilio xuthusButterflies

Abstract Fluorescence from the wings of male Morpho sulkowskyi and Papilio xuthus butterflies has been investigated for the first time using time-resolved fluorescence spectroscopy. Intensity of emission spectra from the wings of Papilio xuthus decreased with increasing delay time after the application of exciting laser pulse and the intensity peak showed an interesting red shift from 480 to 520 nm. In contrast, such a peak shift was not observed from the wings of Morpho sulkowskyi. The decay times obtained from the wings of Morpho sulkowskyi and Papilio xuthus were given by two components, respectively; those of the former at 510 nm were about 0.545 ns and 2.74 ns and those of the latter at 480 nm were about 0.490 ns and 2.10 ns. Based on these results, the possibility of using time-resolved spectroscopy as a tool for the classification of butterflies is described along with a brief discussion of the origin of the 520 nm peak observed for Papilio xuthus.