Faculty Profiles - KIWA Toshihiko

Papers - KIWA Toshihiko

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Characterization of the magnetic moment distribution in low-concentration solutions of iron oxide nanoparticles by a high- T <inf>c</inf> superconducting quantum interference device magnetometer Reviewed

M. M. Saari, K. Sakai, T. Kiwa, T. Sasayama, T. Yoshida, K. Tsukada

Journal of Applied Physics 117 ( 17 ) 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

© 2015 AIP Publishing LLC. We developed a highly sensitive AC/DC magnetometer using a high-temperature superconductor superconducting quantum interference device for the evaluation of magnetic nanoparticles in solutions. Using the developed system, we investigated the distribution of magnetic moments of iron oxide multi-core particles of 100 nm at various iron concentrations that are lower than 96 μg/ml by analyzing the measured magnetization curves. Singular value decomposition and non-regularized non-negative least-squares methods were used during the reconstruction of the distribution. Similar distributions were obtained for all concentrations, and the iron concentration could be determined from the measured magnetization curves. The measured harmonics upon the excitation of AC and DC magnetic fields curves agreed well with the harmonics simulated based on the reconstructed magnetization curves, implying that the magnetization curves of magnetic nanoparticles were successfully obtained as we will show in the article. We compared the magnetization curves between multi-core particles of 100 nm and 130 nm, composed of 12-nm iron oxide nanoparticles. A distinctive magnetic property between the 100 nm and 130 nm particles in low-concentration solutions was successfully characterized. The distribution characteristic of magnetic moments suggests that the net magnetic moment in a multi-core particle is affected by the size of the magnetic cores and their degree of aggregation. Exploration of magnetic properties with high sensitivity can be expected using the developed system.

DOI： 10.1063/1.4919043

Time of flight measurements of polymer films by a terahertz chemical microscopy

T. Arisawa, H. Nino, K. Sakai, T. Kiwa, K. Tsukada

Optics InfoBase Conference Papers Part F132-JSAP 2019 2015

Ion sensing for nano liter level solution by a terahertz chemical microscopy

Y. Zhou, K. Akimune, K. Sakai, T. Kiwa, K. Tsukada

Optics InfoBase Conference Papers Part F132-JSAP 2019 2015

Multi-ion sensing of buffer solutions using terahertz chemical microscopy Reviewed

Kosuke Akimune, Yuki Okawa, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Applied Physics Express 7 ( 12 ) 122401 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

© 2014 The Japan Society of Applied Physics Terahertz chemical microscopy (TCM) has been proposed and developed to visualize electric potential and/or chemical changes in water solutions. To simultaneously detect two types of ions mixed in buffer solutions, five membranes for sodium ions and four membranes for potassium ions were integrated on a sensing plate, and the selectivity to each ion was evaluated. The results suggest that TCM can be used for multi-ion sensing in mixed solutions.

DOI： 10.7567/APEX.7.122401

A terahertz chemical microscopy for an agar culture medium Reviewed

H. Nino, A. Nakamura, K. Omura, K. Sakai, T. Kiwa, K. Tsukada

2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 2014.10

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

© 2014 IEEE. In the field of life science, the research trends are to visualize 'living' materials as it is, whereas most of conventional imaging methods require pre-treatments to living samples. In our group, a terahertz chemical microscope (TCM) has been proposed and developed to investigate metabolism by the cell activity. Here the agar medium, which was generally used to cultivate cells, was immobilized on the sensing plate of TCM and the concentration of the glucose in the buffer solutions on it was detected as the terahertz amplitude shift. This result suggests that the TCM can detect the glucose in the solutions and it may possible to detect the cell activity cultivated on the agar mediums.

DOI： 10.1109/URSIGASS.2014.6930088

Label-free detection of proteins using a terahertz chemical microscopy Reviewed

M. Ogawa, A. Nakamura, K. Omura, K. Sakai, T. Kiwa, K. Tsukada

2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 2014.10

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

© 2014 IEEE. A terahertz chemical microscopy (TCM) has been proposed and developed to visualize the distribution of chemical reactions such as antigen-antibody reaction on the sensing plate without any labels on the analyte. The TCM utilize the semiconductor-based device named a sensing plate. The sensing plate can convert the shift of the chemical potential in the magnitude on the surface of sensing plate into the amplitude of generated terahertz (THz) in the sensing plate. Thus, it enables to get images of the potential distribution on the surface of the sensing plate as the distribution of THz amplitude. Here, we demonstrate the detection of the immune reactions between the mouse immunoglobulin G (IgG) and the anti-mouse immunoglobulin G (anti-IgG). IgG was immobilized on the sensing plate and reacted with anti-IgG in the solutions with various concentrations. We also fabricated the sample wells on the sensing plate and quantitative evaluation of immune reactions were demonstrated with the anti-IgG concentration of between 5 nM and 100 nM. As a result, the change in the THz amplitude during the reaction showed the proportional relation with the concentration of reacted anti-IgG.

DOI： 10.1109/URSIGASS.2014.6930087

Multi-ion sensing in solutions by a terahertz chemical microscopy Reviewed

K. Akimune, Y. Okawa, T. Hagiwara, K. Sakai, T. Kiwa, K. Tsukada

2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 2014.10

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

© 2014 IEEE. A terahertz chemical microscopy (TCM) has been proposed and developed in order to visualize the chemical potential changes in the water solution. In this paper, ion sensing in solutions, as an application of terahertz chemical microscopy, are introduced, and we observed the variation of amplitude of THz wave. In TCM, we detect the change in the amplitude of radiated THz wave from a THz sensing plate. The sensing plate is that the amplitude of radiated THz wave changes when chemical reactions are undergo on the THz sensing plate. We immobilized ion sensitive membranes, which can take the certain ion, on the surface of SiO2side of THz sensing plate. We dropped the sodium solution of 10-4M and 10-1M. The amplitude of radiated THz wave as the concentration of 10-1M was large in magnitude than the concentration of 10-4M where the ion sensitive membrane was immobilized. We can also visualize the concentration of ions to get image. From these results, we can detect ions in solution using TCM.

DOI： 10.1109/URSIGASS.2014.6930079

Visualization of ion transportation in an electrolyte using an HTS-SQUID gradiometer Reviewed

Toshihiko Kiwa, Shinogo Miyazaki, Mohd M. Saari, Kenji Sakai, Akira Tsukamoto, Seiji Adachi, Tsunehiro Hato, Keiichi Tanabe, Keiji Tsukada

Physica C: Superconductivity and its Applications 504 84 - 87 2014.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Direct detection of magnetic fields generated by the ion currents in electrolytic cells was performed and the ion currents were mapped during a cyclic voltammetry experiment. A high-Tc superconducting quantum interference device (SQUID) gradiometer with ramp-edge Josephson junctions was used as the detector and thus the first derivative of the magnetic field along the electrolytic cell surface was obtained. The electric potential vs. the reference electrode was measured between -0.3 V and 0.8 V and the hysteresis signals caused by the redox reactions of the electrolyte were observed. The vector component of the ion current during cyclic voltammetry was mapped along the electrolytic cell. As a demonstration of visualization of ion transportation, the magnetic signal was also measured at various positions above the electrolytic cell surface. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2014.04.024

Ultrathin-film hydrogen gas sensor with nanostructurally modified surface Reviewed

Keiji Tsukada, Shuzo Takeichi, Kenji Sakai, Toshihiko Kiwa

Japanese Journal of Applied Physics 53 ( 7 ) 2014.7

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

The change in electrical resistance of Pt thin films on glass substrates upon exposure to hydrogen gas at room temperature was studied. The effect was detectible only for film thicknesses of less than 40 nm, and increased with decreasing thickness. Samples were also produced with a Ti film inserted between the Pt film and the glass substrate as an adhesive layer. Although the Ti film did not react with the hydrogen gas, its presence reduced the resistance change effect because it acted as a parallel resistance. To overcome this problem, the surface of the glass substrate was nanostructurally modified using porous SiO2, which led to a larger resistance change ratio. To improve the recovery time, heating by pulsed current injection was carried out. A structure consisting of Pt (5nm)/Ti (3 nm)/porous SiO2/glass was found to show a clear response to hydrogen concentrations down to about 100 ppm at room temperature. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.076701

Magnetic susceptibility and magnetic resonance measurements of the moisture content and hydration condition of a magnetic mixture material Reviewed

K. Tsukada, T. Kusaka, M. M. Saari, R. Takagi, K. Sakai, T. Kiwa, Y. Bito

Journal of Applied Physics 115 ( 17 ) 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

We developed a magnetic measurement method to measure the moisture content and hydration condition of mortar as a magnetic mixture material. Mortar is a mixture of Portland cement, sand, and water, and these materials exhibit different magnetic properties. The magnetization-magnetic field curves of these components and of mortars with different moisture contents were measured, using a specially developed high-temperature-superconductor superconducting quantum interference device. Using the differences in magnetic characteristics, the moisture content of mortar was measured at the ferromagnetic saturation region over 250 mT. A correlation between magnetic susceptibility and moisture content was successfully established. After Portland cement and water are mixed, hydration begins. At the early stage of the hydration/gel, magnetization strength increased over time. To investigate the magnetization change, we measured the distribution between bound and free water in the mortar in the early stage by magnetic resonance imaging (MRI). The MRI results suggest that the amount of free water in mortar correlates with the change in magnetic susceptibility. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4852075

Compact AC/DC susceptometer using a high-temperature superconductor superconducting quantum interference device Reviewed

Ryuki Takagi, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEJ Transactions on Fundamentals and Materials 134 ( 6 ) 369 - 374 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical Engineers of Japan

We developed a compact susceptometer employing a high-temperature superconductor (HTS) superconducting quantum interference device (SQUID) that can measure M-H characteristics and harmonic components induced in the AC magnetic field response from a sample. In the DC function for measuring M-H characteristics, the sample was vibrated in the DC magnetic field, and the secondary magnetic field generated from the sample was detected by a DC pickup coil. In the AC function for measuring harmonic components, the sample is placed in the AC magnetic field, and the AC response was detected by an AC pickup coil. The pickup coil is connected in series with the input coil, which is inductively connected to the HTS-SQUID. Signal from the HTS-SQUID was transmitted to the lock-in amplifier, and was analyzed as the intensity and phase of the measured magnetic field. In order to clarify the basic properties of the system, we measured the AC magnetic field response from a sample in the case of changing the position between the sample and the pickup coil, and M-H characteristics when changing the DC bias magnetic field intensity. Furthermore, by analyzing the harmonic components of AC/DC magnetic field response, the system is able to measure the magnetic properties with high sensitivity and high speed. © 2014 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejfms.134.369

DC current distribution mapping system of the solar panels using a HTS-SQUID gradiometer Reviewed

Shingo Miyazaki, Syohei Kasuya, Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Akira Tsukamoto, Seiji Adachi, Keiichi Tanabe, Keiji Tsukada

Journal of Physics: Conference Series 507 ( PART 4 ) 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

Solar panels are expected to play a major role as a source of sustainable energy. In order to evaluate solar panels, non-destructive tests, such as defect inspections and response property evaluations, are necessary. We developed a DC current distribution mapping system of the solar panels using a High Critical Temperature Superconductor Superconducting Quantum Interference Device (HTS-SQUID) gradiometer with ramp edge type Josephson junctions. Two independent components of the magnetic fields perpendicular to the panel surface (∂Bz/∂x, ∂Bz/∂y) were detected. The direct current of the solar panel is visualized by calculating the composition of the two signal components, the phase angle, and mapping the DC current vector. The developed system can evaluate the uniformity of DC current distributions precisely and may be applicable for defect detection of solar panels. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/507/4/042026

Development of integrated AC-DC magnetometer using high-T<inf>c</inf> SQUID for magnetic properties evaluation of magnetic nanoparticles in solution Reviewed

Mohd Mawardi Saari, Ryuki Takagi, Toki Kusaka, Yuichi Ishihara, Yuya Tsukamoto, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Journal of Physics: Conference Series 507 ( PART 4 ) 2014

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-Tc SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The flux-transformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibrating-sample and harmonic detection techniques were used to reduce interference from excitation magnetic fields in the static and dynamic magnetization measurements, respectively. Static and dynamic magnetization measurements were performed on commercially available iron oxide nanoparticles in diluted solutions. The magnetic responses increased with the increase in concentration of the solutions in both measurement results. The magnetization curves showed that the diamagnetic signal due to the carrier liquid of the iron oxide nanoparticles existed in a dilute solution. Biasing with a proper DC magnetic field in the dynamic magnetization measurement resulted in improved signals of the second and third harmonics. Therefore, highly sensitive magnetic characterizations of MNPs utilizing the static and dynamic magnetization measurement are possible via the developed system. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/507/4/042035

FET hydrogen sensor by direct heating of platinum metal gate for fast response time Reviewed

Takahiro Okuir, Yuki Usita, Shuzo Takeichi, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEJ Transactions on Sensors and Micromachines 134 ( 8 ) 264 - 269 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical Engineers of Japan

© 2014 The Institute of Electrical Engineers of Japan. Improvement of the response time by direct heating of the gate catalytic metal of an FET sensor was investigated. The FET hydrogen sensor that has an adhesion layer (Ti) between the catalytic metal (Pt) and the gate insulator was fabricated. In a previous study, there was a problem in the reproducibility as some of the FET sensors displayed long recovery characteristics caused by hydrogen atoms diffused into the Pt thin film. To improve the response characteristics, two electrodes were connected to the gate metal, then, a pulse current was applied to the gate metal, having a resistance element. When applying the pulse current to the gate portion, desorption of the hydrogen remaining in the platinum thin film was accelerated because the platinum was instantaneously heated. Consequently, the hysteresis of the hydrogen was improved. Furthermore, reproducible response, fast response time and recovery time were achieved.

DOI： 10.1541/ieejsmas.134.264

Catalytic reactions of the fuel cells visualized by THz chemical microscope

T. Kusaka, K. Koiso, K. Sakai, T. Kiwa, K. Tsukada

Optics InfoBase Conference Papers 2014

Magnetic nondestructive test for resistance spot welds using magnetic flux penetration and eddy current methods Reviewed

Keiji Tsukada, Kousuke Miyake, Daichi Harada, Kenji Sakai, Toshihiko Kiwa

Journal of Nondestructive Evaluation 32 ( 3 ) 286 - 293 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER/PLENUM PUBLISHERS

Resistance spot welding technologies are widely used in industry. A highly reliable monitoring method is needed to effectively weld and create a robust structure. We developed a combined technique using magnetic flux penetration and an eddy current test (ECT). The magnetic measuring system consists of a pair of magnetic probes having an induction coil and detection coil, a lock-in amplifier, a current source, and a personal computer. The magnetic flux penetration through both surfaces at the weld was measured at low frequency. The ECT was performed at each surface with multiple frequencies. The magnetic flux penetration method showed good correlation with the destructive shear test because of the change in permeability due to the formation of the nugget. The ECT method reflected the depth profile of the nugget and was effective for determining a defective product. © 2013 Springer Science+Business Media New York.

DOI： 10.1007/s10921-013-0181-0

Evaluation of work function of the catalytic electrode in the fuel cells Reviewed

Toshihiko Kiwa, Takafumi Hagiwara, Tetsuya Kusaka, Kenji Sakai, Keiji Tsukada

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

The fuel cell was fabricated on the sensing plate and the catalytic reaction of the electrode was measured using terahertz chemical microscope. Change in the amplitude of THz at the catalytic cathode and anode could be observed. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600102

Hydrogen gas response of meta-materials made from the catalytic metal Reviewed

Takuya Sono, Mitsuhiro Shinomiya, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

The meta-materials with a catalytic metal are fabricated on Si substrate and the hydrogen gas reaction in the THz transmittance was measured. The results suggest that two different catalytic mechanisms contribute the change in transmittance in different frequency region. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600256

Nondestructive inspection of SiGe films using laser terahertz emission microscopy Reviewed

Akihiro Nakamura, Ken Omura, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Laser terahertz emission microscopy was applied to investigate the SiGe film on the Si substrate. In this study, as the initial experiment to apply LTEM to non-destructive evaluation of the strained SiGe films, the THz emission properties of the strained-SiGe were measured. © 2013 IEEE.

DOI： 10.1109/CLEOPR.2013.6600524

Terahertz properties from the surface of strained SiGe on Si multilayered structure Reviewed

K. Omura, A. Nakamura, T. Kiwa, Y. Yamashita, K. Sakai, K. Tsukada

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

A Large-scale integration (LSI) has been improved by scaling contraction. Strained Si has been proposed as a higher carrier mobility than usual. We have evaluated the strained SiGe wafer by LTEM, which is a method of analyzing to detect THz waves generated by fs laser irradiated into the sample. © 2013 IEEE.

DOI： 10.1109/IRMMW-THz.2013.6665819

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