Biomedical subjects

Yoshizo Takai

Publications and source records attributed to Yoshizo Takai.

6 recordsLinked to original sources

PubMed2006

Viologen-modified platinum clusters acting as an efficient catalyst in photocatalytic hydrogen evolution.

A highly efficient photocatalytic system for hydrogen evolution with dihydronicotinamide coenzyme (NADH) as a sacrificial agent in an aqueous solution has been constructed by using water-soluble platinum clusters functionalized with methyl viologen-alkanethiol (MVA2+) and a simple electron-donor dyad, 9-mesityl-10-methylacridinium ion (Acr+-Mes), which is capable of fast photoinduced electron transfer but extremely slow back electron transfer. The mean diameter of the platinum core was determined as R(CORE) = 1.9 nm with a standard deviation sigma = 0.5 nm by transmission electron microscopy (TEM). As a result, the hydrogen-evolution rate of the photocatalytic system with MVA2+-modified platinum clusters (MVA2+-PtC) is 10 times faster than the photocatalytic system with the mixture of the same amount of MVA2+ and platinum clusters as that of MVA2+-PtC under otherwise the same experimental conditions. The radical cation of NADH has been successfully detected by laser flash photolysis experiments. The decay of the absorbance due to NAD*, produced by the deprotonation from NADH*+, coincides with the appearance of the absorption band due to Acr*-Mes. This indicates electron transfer from NAD* to Acr+-Mes to give Acr*-Mes, which undergoes the electron-transfer reduction of MVA2+-PtC, leading to the efficient hydrogen evolution.

Journal Article↗

PubMed2006

Development of computer-assisted minimal-dose system with beam blanker for TEM.

A computer-assisted minimal-dose system has been developed for the high-resolution observation of radiation-sensitive samples using a transmission electron microscope (TEM). This system consists of a CCD camera, a beam blanker and a control computer (PC) that also controls the TEM. A sample is illuminated by an electron beam only when the CCD camera takes images; otherwise, the beam blanker cuts off the electron beam. Emulated images, which are calculated from the images taken and the variable parameters of the TEM, such as magnification and sample stage position, are displayed on the control PC display. After a few times of repetition of exposures and emulations, the sample is positioned to final observation area. Subsequently to select the observation area, the system automatically adjusts the focus position from two different illuminating angle images and the TEM conditions are appropriate for taking a final image. The total electron dose before the final image is taken can be markedly decreased because the sample is irradiated by an electron beam only when images are taken. For the final image, a three-dimensional Fourier filtering method (3DFFM), which corrects the spherical aberration for the through-focus image series and enables the selection of the optimum focus condition later, is also included in our system.

Journal Article↗

PubMed2004

Development of coincidence transmission electron microscope. III. Incorporation with gamma-type imaging energy filter.

We have developed a new analytical transmission electron microscope (TEM), called coincidence TEM, which, in principle, enables observation of elemental mapping images at a high signal-to-noise ratio. We have previously reported the successful observation of an elemental mapping image of a specimen, but over a very long period of time (168 h). To solve this inefficiency, we installed a gamma-type imaging energy filter in the coincidence TEM to remove the no-loss electrons, which are mainly transmitted electrons. This has enabled the intensity of the background signals in the coincidence measurement to be markedly reduced. The coincidence TEM with a gamma-type imaging energy filter allows the coincidence image to be observed in 3 h, thus, the measurement time is shortened by two orders of magnitude. Moreover, the use of a silicon drift detector (SDD) will shorten the measurement time.

Gamma Rays↗

PubMed2004

Practical method to determine the filter shape function used in the three-dimensional Fourier filtering method.

The procedure to determine the appropriate filter shape function used in the three-dimensional Fourier filtering method (3D-FFM) is discussed from a practical point of view, so as to reduce the artificial contrast induced by the processing and to achieve a high signal-to-noise ratio. The effects of cutting off the high spatial frequency of the filter shape function and damping at low spatial frequency were investigated by using through-focus images of a gold (110) thin film. In addition, the effect of the width of the filtered area was discussed using through-focus images of a carbon nanotube. For reliable image processing, the filter shape function should be cut off beyond the information limit and attenuated with damping at low spatial frequency. Furthermore, the extraction area should include the distributed area of the relevant structural components appearing in the 3-D Fourier spectrum.

Algorithms↗

PubMed2004

Separation of linear and non-linear imaging components in high-resolution transmission electron microscope images.

Linear and non-linear image components in high-resolution transmission electron microscope images were successfully separated by applying a bandpass filter to the three-dimensional Fourier spectrum of its through-focus series of images. In the observed lattice image of a wedgeshaped Si [110] crystal, we determined the magnitude of the contribution of the non-linear imaging components to the total image intensity distribution. The contribution was proved to become sometimes larger than that of the linear imaging component, even at a thickness of 13 nm.

Fourier Analysis↗

PubMed2003

Quantitative analysis of surface atom positions in a thick crystal as determined by a reconstructed exit wave.

Atomic structures of an Au (110) 2 x 1 reconstructed surface were analysed quantitatively using an exit wave reconstructed by the three-dimensional Fourier filtering method in high-resolution transmission electron microscopy. To reconstruct the exit wave in a relatively thick crystal, a practical criterion was proposed in the present analysis. In the 'pseudo-exit wave' obtained by the proposed criterion, relaxation of surface atoms was clearly visible in the top three layers. The atoms' displacement was measured to be about 5-20 pm. For quantitative analysis of the atom column positions, image contrast calculations were performed using a structural model of the Au (110) reconstructed surface. Calculations confirmed that the reconstructed pseudo-exit wave could represent the atom column positions directly with an accuracy of several pm, even for a relaxed surface, provided the sample thickness was <7 nm.

Journal Article↗