Showing papers by "Tsuyoshi Kawai published in 1995"

Optical and dielectric properties of photochromic dye in amorphous state and its application

Abstract: Preparation of amorphous phase of a photochromic dye, cis‐1,2‐dicyano‐1,2‐ bis(2,4,5‐trimethyl‐ 3‐thienyl) ethene, has been investigated and its photochromic properties have been studied. This photochromic dye shows clear photochromism in the amorphous solid state accompanying reversible changes in absorption spectrum, refractive index, and dielectric properties. Clear optical pattern formation has been achieved on the amorphous dye layer.

Photoluminescence Quenching in Polysilanes by Fullerene Doping and Effective Photoinduced Charge Transfer Depending on Aromatic Side Group

Abstract: Photoluminescence of polysilanes with aromatic side groups has been found to be strongly quenched upon C60 doping, in contrast to the case of polysilanes with saturated hydrocarbon side groups in which a clear quenching effect has not been observed. These results have been interpreted by considering the role of the aromatic side group as a mediator for photoinduced electron transfer from electronic states of the main chain polysilanes to the C60 molecule.

Persistent Photoconductivity in C60-Doped Poly(3-alkylthiophene)

Abstract: Persistent photoconductivity (PPC) has been observed in C60-doped poly(3-alkylthiophene) (PAT). PPC increases with increasing irradiation time, tending toward saturation. PPC also increases with C60 concentration, tending toward saturation or even decrease at high concentration. Novel temperature dependence of PPC has been observed. This PPC has been discussed in terms of enhanced photoexcited carrier density in C60 doped PAT and the suppression of the recombination of primary negative and positive carriers due to the stabilization of trapped electrons in C60 and defect states in PAT.

Novel photomemory effects in an amorphous photochromic dye

Abstract: The stable amorphous state of a photochromic dye, cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene, has been prepared and its optical and electrical properties have been studied. In this stable amorphous dye, changes of the optical and electrical properties upon photoisomerization are found, with which novel photomemory effects have been realized.

Unique Liquid Crystalline Behavior of Conducting Polyacetylene Derivatives

Abstract: Unique liquid crystalline behaviors have been observed in polyacetylene derivatives substituted with long side chains containing mesogen unit such as poly [5- (p- (trans -4′- n- octylcyclohexyl) phenoxy) -1- pentyne] (PPCH803A) with phenylcyclohexyl mesogenic moiety. Texture typical to smectic liquid crystal has been confirmed by optical microscopic observation. Smectic structure has also been confirmed by X-ray diffraction. Anisotropy of optical absorption spectrum consistent with X-ray diffraction has been observed, from which the band gap of PPCH803A has also been evaluated to be 2.7 eV. Dielectric constant of PPCH803A in the smectic phase (90-150°C) is about 2.8 and changes at phase transition temperature in step wise. The mixture of PPCH803A with ferroelectric liquid crystal of low molecular weight exhibits large dielectric constant and unique ferroelectric behavior in the temperature range of the smectic phase of PPCH803A.

Characteristics of junction devices utilizing C 60 doped conducting polymer

Abstract: Schottky diodes and Schottky gated field effect transistors (FET) were fabricated utilizing C 60 doped conducting polymers. Their characteristics are strongly dependent on the C 60 concentration, and marked photo-irradiation effects exist. These results have been discussed taking into account photoinduced charge transfer between C 60 and conducting polymer.

In Situ Studies on X-Ray Diffraction and Resistance of Graphitelike Film during the First Redox Cycle and the Effect of 12 Crown 4

Abstract: Two characteristic X-ray diffraction peaks originated from electrolyte decomposition in graphitelike pyrolytic polymer prepared by pyrolysis at 2800° C. These peaks were clearly observed, with in situ X-ray diffraction measurements using a beryllium window, during the first discharge but they did not appear during the subsequent charge and discharge cycles. Upon addition of crown ether (12 crown 4) into the electrochemical cells, the two diffraction peaks attributed to the excessive electrolyte decomposition during discharge due to the cointercalation of solvent and lithium ions disappeared completely. The reversibilities of change in resistance and structure of graphitelike material (cathode) and also the capacity of the cell have been greatly improved.

Variations of electronic states in La 2-x Sr x CuO 4 (x=0 to 0.30) investigated by scanning tunneling spectroscopy

Abstract: Scanning-tunneling-spectroscopy measurements have been performed on as-grown and oxygen-annealed ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ thin films with 0\ensuremath{\le}x\ensuremath{\le}0.30 and the variations of the density of states (DOS) near the Fermi level (${\mathit{E}}_{\mathit{F}}$) have been systematically investigated. Each spectrum has a characteristic shape in each doping: semiconductor, superconductor, and metal. The shape of the DOS directly correlates with the carrier concentration rather than Sr concentration or oxygen content. The DOS around the Fermi level gradually appears with tailing both from the conduction-band and the valence-band edges accompanied with the increase of carrier concentration. The change of DOS above ${\mathit{E}}_{\mathit{F}}$ is noticeable compared to that below ${\mathit{E}}_{\mathit{F}}$ within the underdoped region.

Novel Characteristics of Poly(1,6-Heptadiyne) Derivatives with Long Side Chains in Liquid Crystalline Phase

Abstract: Poly (1,6-heptadiyne) derivatives substituted with long side chains containing mesogen units such as poly(bis(4-methoxy-4′-hexyloxybiphenyl)- dipropargyl malonate) (PMHBDPM) exhibit unique characteristics typical to both liquid crystal and conducting polymer. PMHBDPM exhibits smectic A phase in consistent with temperature dependence of X-ray diffraction. Two stages of electrochemical doping corresponding to the charge transfers between dopants and polymer main chain and also between dopants and the core of the mesogen unit in the side chain are observed. Diffusion coefficient of dopants also exhibits drastic change at the phase transition between smectic A phase and isotropic phase. These characteristics have been discussed in terms of molecular orientations of both polymer main chains and substituted side chains. Unique dielectric properties and X-ray diffraction characteristics have been observed in a mixture of PMHBDPM with ferroelectric liquid crystal of low molecular weight.

Laser Ablation Process and Growth Control of Oxide Thin Films in Laser Molecular Beam Epitaxy

Abstract: In order to study mechanism of laser ablation, the time-of-flight spectra of monovalent ions generated by ablation of alkaline earth metals are measured. The obtained spectra show that the ion generation is caused by 5-, 4- and 3-photon processes for Ca, Sr and Ba, respectively, when ArF excimer laser is used as a light source. This behavior suggests that laser ablation of alkaline earth metals is triggered by excitation of electrons at the highest inner-core level. Control of layer-by-layer growth processes by monitoring emission from the ablation plume is also reported. The emission measurement is utilized for estimation of each layer thickness in layer-by-layer growth. This conventional technique is very effective for automatic control of layer-by-layer growth.

Novel photomemory effects in conductivity and photoconductivity of photochromic dye-doped conducting polymer

Abstract: We studied photoinduced changes in electrical and optical properties of two photochromic dye-doped conducting polymer systems which are composed of conducting polymers, poly(3-alkylthiophene)s (PAT-12 and PAT-18) and photochromic dyes of a diarylethene derivative (CMTE) and a spiropyran derivative (MINS). The CMTE-doped PAT-18 system showed unique photoisomerization-induced changes in the properties in the photo-excited states, while the MINS-doped PAT-12 system indicated a photoinduced change in the dark conductivity. The origins of these phenomena can be explained tentatively on the basis of photoisomerization-induced changes in probability of photoinduced charge and energy transfers and photoisomerization-induced change in the scattering efficiency for the charge carriers.