Taihei Mukaide

In situ observation of water distribution and behaviour in a polymer electrolyte fuel cell by synchrotron X-ray imaging.

In situ visualization of the distribution and behaviour of water in a polymer electrolyte fuel cell during power generation has been demonstrated using a synchrotron X-ray imaging technique. Images were recorded using a CCD detector combined with a scintillator (Gd(2)O(2)S:Tb) and relay lens system, which were placed at 2.0 m or 2.5 m from the fuel cell. The images were measured continuously before and during power generation, and data on cell performance was recorded. The change of water distribution during power generation was obtained from X-ray images normalized with the initial state of the fuel cell. Compared with other techniques for visualizing the water in fuel cells, this technique enables the water distribution and behaviour in the fuel cell to be visualized during power generation with high spatial resolution. In particular, the effects of the specifications of the gas diffusion layer on the cathode side of the fuel cell on the distribution of water were efficiently identified. This is a very powerful technique for investigating the mechanism of water flow within the fuel cell and the relationship between water behaviour and cell performance.

Substituent effects of iridium complexes for highly efficient red OLEDs

This study reports substituent effects of iridium complexes with 1-phenylisoquinoline ligands. The emission spectra and phosphorescence quantum yields of the complexes differ from that of tris(1-phenylisoquinolinato-C2,N)iridium(iii)(Irpiq) depending on the substituents. The maximum emission peak, quantum yield and lifetime of those complexes ranged from 598-635 nm, 0.17-0.32 and 1.07-2.34 micros, respectively. This indicates the nature of the substituents has a significant influence on the kinetics of the excited-state decay. The substituents attached to phenyl ring have an influence on a stability of the HOMO. Furthermore, those substituents have effect on the contribution to a mixing between 3pi-pi* and (3)MLCT for the lowest excited states. Some of the complexes display the larger quantum yield than Irpiq, which has the quantum yield of 0.22. The organic light emitting diode (OLED) device based on tris [1-(4-fluoro-5-methylphenyl)isoquinolinato-C2,N]iridium(iii)(Ir4F5Mpiq) yielded high external quantum efficiency of 15.5% and a power efficiency of 12.4 lm W(-1) at a luminance of 218 cd m(-2). An emission color of the device was close to an NTSC specification with CIE chromaticity characteristics of (0.66, 0.34).

Scanning hard x-ray differential phase contrast imaging with a double wedge absorber

Two-directional differential phase contrast images were measured using an x-ray microbeam and a double wedge absorber. The wedge absorber converts the displacement of an x-ray beam that is refracted by an object into change of x-ray intensity. The double wedge absorber made it possible to detect values of two-directional refraction angle with microrad sensitivity simultaneously. By Fourier integration of two-directional phase gradients calculated from the refraction angle instead of line integration of one-directional phase gradients, we obtained a quantitative phase map without artifacts even when only a part of the boundaries of the object were in the field of view. One of the characteristics of this technique is flexibility in a sensitivity of the phase gradient. By changing of shape or material of the wedge absorber, it is comparatively easy to control the detection limit of the refraction angle.

Quantitative effective atomic number imaging using simultaneous x-ray absorption and phase shift measurement

A scanning type x-ray imaging system which measures the absorption and differential phase shift in a material quantitatively and simultaneously has been developed. The absorption and differential phase are used to obtain the effective atomic number of organic material samples which closely reflects their chemical composition. An effective atomic number map of polymer fibers has been obtained. The experimentally obtained effective atomic numbers of these polymers agree well with the corresponding calculated values.

Three-dimensional visualization of the inner structure of single crystals by step-scanning white X-ray section topography.

Visualization of the three-dimensional distribution of the crystal defects of large single crystals of calcium fluoride has been demonstrated by white X-ray section topography using sheet-like X-rays (BL28B2 at SPring-8). An image of the three-dimensional distribution of the crystal defects was reconstructed by stacking section topographs, which expressed the images of cross sections of the sample. The section topographs were recorded using a CMOS flat-panel imager or a CCD detector combined with scintillator (Gd(2)O(2)S:Tb) and relay lens system. The section topographs were measured by repeating cycles of exposure and sample translation along the direction perpendicular to the top face of the sample. Using high-brilliance and high-energy white X-rays ( approximately 60 keV) efficiently, visualization of the three-dimensional structure of subgrains of a sample of up to 60 mm in diameter was achieved. Furthermore, the three-dimensional distribution of the glide plane in the crystal was visualized by reconstructing the linear contrast of the glide plane.

Local Layer Structures in Ferroelectric Liquid Crystal Cells Filled with a Material Which Exhibits Cholesteric-Chiral Smectic C Phase Transition

We investigated the local layer structures in ferroelectric liquid crystal (FLC) cells which have a monostable switching mode using synchrotron X-ray micro diffraction. The monostable switching mode is realized by the FLC cells filled with a material which has cholesteric–chiral smectic C (Ch–SmC*) phase transition sequences. On cooling these cells from the isotropic phase to the SmC* phase, the texture of domains and stripes was observed. The X-ray micro diffraction study revealed that the smectic layer bending with the layer shrinkage generate the texture.

X-RAY MICRODIFFRACTION STUDY OF THE HALF-V SHAPED SWITCHING LIQUID CRYSTAL

Local layer structures and their formation process in a half-V-shaped switching ferroelectric liquid crystal (HV-FLC) were investigated by means of synchrotron X-ray microdiffraction. The HV-FLC is a FLC that has a cholesteric–chiral smectic C (Ch–SmC * ) phase transition sequences. X-ray microdiffraction measurements revealed that the SmC * phase in the HV-FLC was composed of asymmetric chevron and inclined-bookshelf structures. In addition, temperature-controlled X-ray diffraction measurements showed that the transient layer structures appeared during the Ch to SmC * phase transition.

Quantitative Mass Density Image Reconstructed from the Complex X-Ray Refractive Index

We demonstrate a new analytical X-ray computed tomography technique for visualizing and quantifying the mass density of materials comprised of low atomic number elements with unknown atomic ratios. The mass density was obtained from the experimentally observed ratio of the imaginary and real parts of the complex X-ray refractive index. An empirical linear relationship between the X-ray mass attenuation coefficient of the materials and X-ray energy was found for X-ray energies between 8 keV and 30 keV. The mass density image of two polymer fibers was quantified using the proposed technique using a scanning-type X-ray microbeam computed tomography system equipped with a wedge absorber. The reconstructed mass density agrees well with the calculated one.