Akihiro Takeichi

WO3/metal thin-film bilayered structures as optical recording materials

Interface reactions in WO3∕metal thin-film bilayered structures were examined for applications to optical recording materials. Decreases in the reflectance of the structures caused by temperature elevation were observed and were attributed to (i) coloration of the WO3 layers, and (ii) decreases in the reflectance of the metal layers resulting from redox reactions between the WO3 and the metals. The reflectance spectra of the structures before temperature elevation showed moderate wavelength dependence over a wide range, from the visible to the near infrared. Decreases in the reflectance due to temperature elevation occurred over a wide wavelength range. Examination of the WO3∕Al–Ti bilayered structures as potential optical disk memories revealed that the redox reactions occurred within submicrosecond time periods during irradiation with the recording laser. The results indicate that these structures possess promising properties for applications to optical recording materials that can be used over a wide w...

Improved Performance of Solid-State Dye-Sensitized Solar Cells with CuI: Structure Control of Porous TiO2 Films

By increasing the pore and particle size of porous TiO2 films, the photovoltaic properties of solid-state dye-sensitized solar cells were dramatically improved. We analyzed the relation between the photovoltaic property and the microstructure of TiO2/Dye/CuI measured by scanning electron microscopy of the cross section of the cells. The larger pore size of the TiO2 films improved the CuI filling and the high degree of filling improved the short-circuit current density. Multilayered TiO2 films consisting of a TiO2 layer with small TiO2 particles and a second layer with larger TiO2 particles gave a power conversion efficiency under 1 sun of 6.0%.

GeS2/metal thin film bilayered structures as write-once-type optical recording materials

GeS2/metals thin film bilayered structures were examined for write-once-type optical recording materials. Decreases in the reflectance of GeS2∕Ag and GeS2∕Cu structures at a certain elevated temperature were observed. The phenomena were attributed to the formation of metal sulfides with high optical absorption coefficients by the interface reaction between transparent GeS2 and highly reflective metals. In contrast to GeS2∕Ag or GeS2∕Cu, an increase in the reflectance was observed in GeS2∕Au, which was presumably due to the change of optical interference conditions caused by the decrease in the GeS2 film thickness and the improvements of the crystallinity of Au caused by the decrease of the lattice defects along the grain boundaries of Au. Examination of the GeS2/metals bilayered structures as optical disc memories revealed that the reactions occurred within submicrosecond during the recording laser irradiations. The recording sensitivities of GeS2∕Ag or GeS2∕Cu which corresponded to the reaction temperatu...

Thermally Induced Structural Modification of Nanometer-Order Mo/Si Multilayers by the Spectral Reflectance of Laser-Plasma Soft X-Rays

Thermally induced structural modification of a nm-order multilayer of Mo/Si was investigated by spectral reflect-ance of soft X-rays from laser-produced plasma. Dependence of reflectivity of the nm-order multilayers on the incidence angle of soft X-rays indicated that some structural changes start to occur at 300°C and that the nm-order multilayer structures shrink at 500°C because of the formation of Mo-silicide. These results were found to be consistent with the cross-sectional transmission electron microscope observations. It is clearly shown that measurement of spectral reflectance of soft X-rays from laser plasma is a powerful method for analyzing nm-order structural modifications of multilayers.

Laser Plasma Soft X-Ray Contact Microscopy of Polymer Composites

Microstructures of polymer composites are observed with a good contrast and with a submicron spatial resolution by contact soft X-ray microscopy with a laser plasma as a soft X-ray source. An iron target was irradiated by a YAG laser ( 2ω=532 nm, 0.4 J) at laser power density of 2.5×1012 W/cm2 and the emitted soft X-rays were filtered with a thin aluminum foil. For a 0.1-µ m-thick poly acrylonitrile-butadiene-styrene specimen, poly-butadiene or copolymer of butadiene spheres of about 500 nm diameter, which are selectively stained with osmium, is observed with soft X-rays in the wavelength region between 17 and 20 nm. For a 4-µ m-thick polyvinyl chloride film specimen formed by polymer powder compaction, peripheral areas of holes, grain boundaries, and areas probably degraded by HCl reduction are observed with soft X-rays in the wavelength region mainly around 2 nm.

Higher order structure analysis of nano‐materials by spectral reflectance of laser‐plasma soft x‐ray

We have proposed a new experimental arrangement to measure spectral reflectance of nano‐materials for analyzing higher order structure with laser‐plasma soft x‐rays. Structure modification of annealed Mo/Si multilayers and a nylon‐6/clay hybrid with poor periodicity was investigated. The measurement of the spectral reflectance of soft x‐rays from laser‐produced plasma was found to be a useful method for the structure analysis of nano‐materials, especially those of rather poor periodicity.

Observation of polymer alloy by spectral soft X-ray microscopy with a laser plasma X-ray source

Abstract A polymer alloy film on a photographic plate (ILFORD, Q-plate) was exposed to the dispersed soft X-rays in the wavelength region between 8.1 nm and 33.6 nm. The image on Q-plate was magnified by an optical microscope. In the microscopic images of the polymer alloy containing silicon, circular spots of about 30 μm in diameter scattered in a matrix was observed with certain wavelengths of soft X-rays. The image contrast between the spots and the matrix was reversed at around the wavelengths of 12.6 nm and 17.5 nm. This reversal of contrast suggests that these circular spots, or islands, are silicon-rich phases because the L-absorption edge of silicon is 12.3 nm.

Observation of Polymer Alloy by Spectral Soft X-Ray Microscopy with Laser Plasma X-Ray Source.

A polymer alloy film on a photographic plate (ILFORD, Q-plate) was exposed to the dispersed soft X-rays in the wavelength region between 8.1 nm and 33.6 nm. A direct image recorded on the Q-plate was magnified by means of an optical microscope. The microscopic images for one of the component polymers in the polymer alloy containing silicon had circular spots of about 50 µ m in diameter scattered in a matrix with certain wavelengths of soft X-rays. A change in image contrast of the microstructure was observed in the wavelength range between 8.6 nm and 13.2 nm. This reversal of contrast suggests that these circular spots, or islands, are silicon-rich phases because the L-absorption edge of silicon is 12.3 nm. Spectral soft X-ray contact microscopy is useful in determining the wavelength region suitable for clear microstructure imaging, as well as in identifying constituent elements.

Structure Analysis of Nylon6-Clay Hybrid by Spectral Reflectance of Laser-Plasma Soft X-Rays

Structure analysis of nylon6-clay hybrid (NCH) was carried out by means of spectral reflectance of soft X-rays between 8 and 17 nm wavelength from laser-produced plasma. Spectral reflectance composed of specular reflectance and Bragg reflectance was measured by a flat field XUV spectrometer equipped with a toroidal mirror. The observed Bragg reflectance was very weak, but it suggested that NCH had a periodicity of about 13 nm. The calculated spectral reflectance, using a sea-and-island model (sea was nylon6 matrix and island was a multilayer whose unit consisted of a silicate layer (0.66 nm thick) and a nylon-6 layer (about 12 nm thick)) agreed with the observed spectral reflectance. The structural feature of NCH thus deduced was consistent with the TEM observation. The present results indicated the spectral reflectance of soft X-rays from laser-produced plasma to be a useful method for the structure analysis of a nanometer-scale composite which has rather poor periodicity.