Demonstration of Thermal Property Determination for a Suspended Wire Using 3ω Method Acquired by a High buffered Multimeter Applying a Discrete Fourier Transformation and a Window Function Takeshi Takada; Yasuhiro Hasegawa
International Journal of Thermophysics, 2024年09月
研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s10765-024-03397-1DOI ID：10.1007/s10765-024-03397-1,
ORCID：165752608 Comprehensive assessment of thermoelectric properties in modules: Time-domain impedance spectroscopy considering heat leakage via attached lead wires Kotoko Kodama; Yasuhiro Hasegawa
Journal of Applied Physics, 2024年05月
研究論文（学術雑誌）
DOI：https://doi.org/10.1063/5.0196012DOI ID：10.1063/5.0196012,
ORCID：159166398 Temperature profile of the Thomson-effect-induced heat release/absorption in junctionless single conductorsTakahiro Chiba; Ryo Iguchi; Takashi Komine; Yasuhiro Hasegawa; Ken-ichi Uchida
Japanese Journal of Applied Physics, 2023年03月
Abstract
The Thomson effect induces heat release or absorption under the simultaneous application of a charge current and a temperature gradient to conductors. Here, we theoretically investigate the temperature profile due to the Thomson-effect-induced heat release/absorption in junctionless single conductors which can be a simple temperature modulator. We also perform analysis of the temperature profile for realistic conductors. As a result, we find that, for a conductor with a large Thomson coefficient, the temperature derivative of the Seebeck coefficient, the Thomson-effect-induced heat absorption overcomes the Joule heating, resulting in current-induced cooling in the bulk region. We also elucidate that a feedback effect of the Thomson effect stabilizes the system temperature to one-side of the heat bath, which reflects the fact that the Thomson effect is dependent on the position and proportional to the local temperature gradient. This work will be the basis for thermal management utilizing the Thomson effect.
IOP Publishing, 研究論文（学術雑誌）
DOI：https://doi.org/10.35848/1347-4065/acc3e6DOI ID：10.35848/1347-4065/acc3e6,
ISSN：0021-4922,
eISSN：1347-4065 Measuring temperature dependence of dimensionless figure of merit of a thermoelectric module using time-domain impedance spectroscopy Yasuhiro Hasegawa; Mai Takeuchi
Review of Scientific Instruments, 2023年01月
研究論文（学術雑誌）
DOI：https://doi.org/10.1063/5.0124602DOI ID：10.1063/5.0124602,
ORCID：125808203 Proposal of time domain impedance spectroscopy to determine precise dimensionless figure of merit for thermoelectric modules within minutes Yasuhiro Hasegawa; Mai Takeuchi
Scientific Reports,
巻：12,
号：1, 2022年07月
AbstractSeveral techniques exist that use a thermoelectric element (TE) or module (TM) to measure precise dimensionless figure of merit (zT), both qualitatively and quantitatively. The techniques can be applied using both alternating (AC) and direct current (DC). Herein, the transient Harman (TH) and impedance spectroscopy (IS) methods were investigated as direct zT measurement techniques using identical TM, which showed that zT at 300 K was 0.767 and 0.811 within several minutes and several hours, respectively. The zT values differed despite the use of the same TM, which revealed that measuring ohmic resistance using DC and pulse DC is potentially misleading owing to the influence of Peltier heat on current flow. In this study, time domain impedance spectroscopy (TDIS) was proposed as a new technique to measure zT using proper DC and AC. zT obtained using TDIS was 0.811 within several minutes using the time and frequency domains, and was perfectly consistent with the result of the IS method. In conclusion, the TDIS is highly appropriate in estimating zT directly using only proper electrometric measurements, and without any heat measurements.Springer Science and Business Media {LLC}, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1038/s41598-022-15947-4DOI ID：10.1038/s41598-022-15947-4,
ISSN：2045-2322,
ORCID：115982983 Analysis of temperature dependencies of transport coefficients for a single-crystal bismuth wire with a 1.90-μm diameter Mioko Otsuka; Hiroyuki Morita; Taichi Arisaka; Yasuhiro Hasegawa
Journal of Applied Physics, 2022年06月
研究論文（学術雑誌）
DOI：https://doi.org/10.1063/5.0094649DOI ID：10.1063/5.0094649,
ORCID：113958813 Temperature dependence of resistivity and temperature coefficient of a single-crystal bismuth nanowire based on the varying scattering mechanism Yasuhiro Hasegawa; Daisuke Yamashita
Japanese Journal of Applied Physics, 2022年06月
{IOP} Publishing, 研究論文（学術雑誌）
DOI：https://doi.org/10.35848/1347-4065/ac646cDOI ID：10.35848/1347-4065/ac646c,
ORCID：111297315 Observing variations in carrier-scattering mechanisms of polycrystalline bismuth through its temperature-dependent properties Shinya Hirabayashi; Yasuhiro Hasegawa
Japanese Journal of Applied Physics,
巻：60,
号：11, 2021年11月
This study has investigated variations in the carrier scattering mechanisms of polycrystalline bismuth based on the temperature dependence of its transport coefficients across a range of temperatures from 10 to 300 K. A measurement of the continuous temperature dependence of the Hall coefficient revealed the characteristic extremes of its temperature-based parameters to be less than 50 K. The results demonstrated a clear variation in the component of the scattering mechanism pertaining to acoustic deformation. Furthermore, the temperature dependencies of carrier density, mobility, chemical potential, and band gap energy were also comprehensively investigated to determine their influence on carrier transport. The information obtained in this study is quite relevant for the realization of the carrier transport of Bi nanowire. The carrier transport of the wire exhibits a mean free path that is equivalent to the wire diameter and has been expected to introduce a quantum effect, thus enhancing the thermoelectric performance.
IOP Publishing Ltd, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.35848/1347-4065/ac21dcDOI ID：10.35848/1347-4065/ac21dc,
ISSN：1347-4065,
SCOPUS ID：85118643890 Influence of contact resistance and heat leakage in the determination of the dimensionless figure of merit via duo-impedance spectroscopy Shinya Hirabayashi; Yasuhiro Hasegawa
Japanese Journal of Applied Physics,
巻：60,
号：10, 2021年10月
The influence of contact resistance between a polycrystalline bismuth as a basic thermoelectric material and electrodes made of copper using binders of Ag epoxy and conventional solder was investigated to estimate the dimensionless figure of merit (zT) via impedance spectroscopy (IS). The frequency dependence of the impedance using both binders was measured at 300 K under an appropriate alternating current because a considerably larger Peltier heat was required, relative to Joule heat, for estimating the zT precisely. Through the duo-IS method, zT at 300 K was estimated to be 0.126 0.004 and 0.130 0.002 using the Ag epoxy and solder, respectively. The temperature dependence of zT from 300 to 30 K was also estimated, and zT >
0.01 was a practical based on this technique, owing to its signal-noise ratio. The duo-IS method is invaluable for estimating zT in the entire temperature region based on an appropriate configuration.
IOP Publishing Ltd, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.35848/1347-4065/ac1f48DOI ID：10.35848/1347-4065/ac1f48,
ISSN：1347-4065,
SCOPUS ID：85115995234 Determination of dimensionless figure of merit in time and frequency domains Yasuhiro Hasegawa; Mai Takeuchi
Review of Scientific Instruments,
巻：92,
号：8, 2021年08月
We propose an impedance spectroscopy (IS)-based model to determine the dimensionless figure of merit (zT) of a commercialized BiTe-based thermoelectric module in the time and frequency domains. In this method, the transient response of the resistance is measured for different current ranges and an apparent current dependence of the measured resistance is observed in the steady state. We successfully explain the experimental results using the model wherein the dependence is caused by the heat balance between the Peltier heat and Joule heat. In addition, a necessary condition of the balance is required to reproduce the experimental value of zT theoretically. Furthermore, we experimentally determined zT using the measured resistance in the time domain and we applied the IS-based model in the frequency domain for comparison. In the time and frequency domains, we obtained zT = 0.842 ± 0.006 and 0.834 ± 0.001, respectively, by applying the appropriate current for neglecting the influence of the Joule heat
a negligible difference was obtained in the results, as verified via temperature dependent estimation. Through this method and the corresponding analysis, we achieved a comprehensive understanding on how to measure zT and the associated error in the measurement, accurately and precisely, during the experiment. We conclude that zT can be determined precisely in the time domain within several minutes using the proposed method that applies an appropriate current across identical thermoelectric modules and elements.
American Institute of Physics Inc., 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/5.0045108DOI ID：10.1063/5.0045108,
ISSN：1089-7623,
PubMed ID：34470373,
SCOPUS ID：85111902314 Evaluation of a thermoelectric material using duo-frequency impedance spectroscopy method Mioko Otsuka; Taichi Arisaka; Yasuhiro Hasegawa
Materials Science and Engineering B: Solid-State Materials for Advanced Technology,
巻：261, 2020年11月
The impedance spectroscopy (IS) method is an efficient technique to evaluate the dimensionless figure of merit (zT) of thermoelectric materials by measuring some impedance values at a wide frequency range. The conventional IS method uses the technique of fitting measured data to estimate zT
however, in our previous work, we showed that zT can also be directly calculated using the measured thermoelectric resistance and ohmic resistance of a sample. Although we successfully estimated zT from two points of impedances whose imaginary components are 0 mΩ, we needed to measure many points of impedances to determine the trend of frequency dependence of impedances and determine specific frequencies. Moreover, discussions on the error of the measured zT caused by the setting values of current frequencies were insufficient. In this paper, we propose the duo-frequency IS method to evaluate the error of the measured zT by relating the phase angle of the measured impedance to the error of zT. Furthermore, appropriate current frequencies are predicted using the proposed method to reduce the measurement time by reducing the data points for calculating zT. The proposed duo-frequency IS method was used to measure the temperature dependence of zT, resistivity, thermal conductivity, and specific heat of a Bi2Te3 bulk material from 125 K to 300 K
the method yielded an error of less than 1% for the measured zT. The results of this study were in good agreement with those obtained in previous studies by using the steady-state method. The proposed duo-frequency IS method simplifies the evaluation of the thermoelectric properties of thermoelectric materials and elucidates the measurement errors caused by the setting frequencies.
Elsevier Ltd, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1016/j.mseb.2020.114620DOI ID：10.1016/j.mseb.2020.114620,
ISSN：0921-5107,
SCOPUS ID：85088920256 Dimensionless figure of merit of constantan estimated using impedance spectroscopy Ryo Shinozaki; Shinya Hirabayashi; Yasuhiro Hasegawa
Applied Physics Express,
巻：13,
号：10, 2020年10月
Commercialized bulk constantan with a low dimensionless figure of merit and its film fabricated by electroplating were prepared to demonstrate the feasibility of impedance spectroscopy for estimating thermoelectric parameters. From the frequency dependence of the impedance, the resistivity and dimensionless figure of merit were directly estimated as 5.3 × 10-7 Ωm and 0.026 for the bulk and 3.8 × 10-7 Ωm and 0.0098 for the film at room temperature (302 K), respectively. We concluded that impedance spectroscopy is a suitable technique for estimating the thermoelectric parameters of any material with an apparent Seebeck coefficient.
IOP Publishing Ltd, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.35848/1882-0786/abb285DOI ID：10.35848/1882-0786/abb285,
ISSN：1882-0786,
SCOPUS ID：85091705922 Temperature dependence of carrier scattering in polycrystalline bismuth Taichi Arisaka; Mioko Otsuka; Masayuki Tokitani; Yasuhiro Hasegawa
Journal of Applied Physics,
巻：126,
号：8, 2019年08月,
［査読有り］The dependence of the scattering process on temperatures ranging from 50 to 300 K was comprehensively investigated by measuring five transport coefficients (resistivity, magnetoresistivity, Seebeck coefficient, Hall coefficient, and Nernst coefficient) using polycrystalline bulk bismuth. The values of five physical properties (carrier density, electron and hole mobilities, and electron and hole Fermi energies) were calculated assuming that carrier scattering ranged from acoustic deformation potential scattering to ionized impurity scattering. The accompanying mean-free paths of carriers were also evaluated using the calculated Fermi energy and the effective mass tensor. The mean-free path and grain size (typically several micrometers) obtained from electron backscattered diffraction helped narrow the distribution range of the different scattering processes. Thus, the physical properties, including temperature dependence of the scattering processes, were recalculated, and realistic temperature dependence of the electron mobility was assumed. Quantitative and qualitative analyses showed that near room temperature, acoustic deformation potential scattering dominated, which changed to ionized impurity scattering when the estimated mean-free path exceeded 1 mu m. This indicated that the scattering process of polycrystalline bulk bismuth depends on the grain size when the measurement results of the Nernst coefficient related to the scattering process are directly used. The bandgap energy of bismuth was also calculated, and the temperature dependence of the scattering process was estimated. The results showed that the temperature dependence tendency of bandgap energy is similar to that described in the literature. Finally, this study provides the temperature dependence of the physical properties of polycrystalline bismuth. Published under license by AIP Publishing.
AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.5110254DOI ID：10.1063/1.5110254,
ISSN：0021-8979,
eISSN：1089-7550,
ORCID：60805755,
Web of Science ID：WOS:000483884600046 Investigation of carrier scattering process in polycrystalline bulk bismuth at 300 KTaichi Arisaka; Mioko Otsuka; Yasuhiro Hasegawa
Journal of Applied Physics,
巻：123,
号：23,
開始ページ：235107, 2018年06月,
［査読有り］A carrier scattering process in polycrystalline bismuth at 300 K has been investigated by measuring its Seebeck coefficient, electrical resistivity, magneto-resistivity, Hall coefficient, and Nernst coefficient and solving the Boltzmann equation under the relaxation time and low magnetic field approximations. All measurements were performed using identical bulk bismuth samples
as a result, the scattering process, carrier density, carrier mobility, and Fermi energy were estimated. It was found that acoustic deformation potential scattering was a dominant process even at a temperature of 300 K. In addition, a new measurement method (called a quasi-AC method) was proposed to determine the Nernst coefficient more quickly as compared to the conventional method. It was also shown that the difference in the Nernst coefficients estimated by the two methods affected other material parameters (such as carrier density, mobility, and Fermi energy) only slightly
however, the accurate determination of the Nernst coefficient was required for elucidating the scattering mechanism and estimating the Fermi energy of the studied material.
American Institute of Physics Inc., 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.5032137DOI ID：10.1063/1.5032137,
ISSN：1089-7550,
ORCID：49697721,
SCOPUS ID：85048938293 Dimensionless figure of merit and its efficiency estimation for transient response of thermoelectric module based on impedance spectroscopy Mioko Otsuka; Yasuhiro Hasegawa; Taichi Arisaka; Ryo Shinozaki; Hiroyuki Morita
APPLIED PHYSICS EXPRESS,
巻：10,
号：11,
開始ページ：115801, 2017年11月,
［査読有り］The dimensionless figure of merit and its efficiency for the transient response of a Pi-shaped thermoelectric module are estimated according to the theory of impedance spectroscopy. The effective dimensionless figure of merit is described as a function of the product of the characteristic time to reduce the temperature and the representative angular frequency of the module, which is expressed by the thermal diffusivity and the length of the elements used. The characteristic time required for achieving a higher dimensionless figure of merit and efficiency is derived quantitatively for the transient response using the properties of a commercial thermoelectric module. (C) 2017 The Japan Society of Applied Physics
IOP PUBLISHING LTD, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.7567/APEX.10.115801DOI ID：10.7567/APEX.10.115801,
ISSN：1882-0778,
eISSN：1882-0786,
Web of Science ID：WOS:000413839200001 Fabrication of a Nanoscale Electrical Contact on a Bismuth Nanowire Encapsulated in a Quartz Template by Using FIB-SEM Masayuki Murata; Atsushi Yamamoto; Yasuhiro Hasegawa; Takashi Komine
JOURNAL OF ELECTRONIC MATERIALS,
巻：46,
号：5,
開始ページ：2782,
終了ページ：2789, 2017年05月,
［査読有り］A method to fabricate an electrode on a 110-nm-diameter Bi nanowire, encapsulated in a quartz template, was established using a dual beam instrument equipped with a focused ion beam and a scanning electron microscope. A fabrication method has already been successfully developed to obtain suitable Ohmic contact on both ends of Bi nanowires (several hundred nanometers in diameter) by first polishing the ends of the nanowires, and then depositing titanium/copper thin-films via an ion-plating method. However, with this method, it was difficult to obtain suitable electrodes on Bi nanowires with diameters less than 300 nm. Therefore, in order to understand why it was not possible to establish an electrical contact in small-diameter Bi nanowires, the vertical section of the fabricated electrode and the end of a 110-nm-diameter Bi nanowire were observed using a focused ion beam scanning electron microscope. A vacant area was observed between the end of the nanowire and the titanium thin-film, indicating a possible cause for the electrical contact failure. This implies that the quartz-encapsulated Bi nanowire is selectively removed when it undergoes polishing due to the great difference in hardness between Bi and quartz. A local electrode, which would connect the exposed area of the Bi nanowire and the metal thin-films on the surface of the quartz template, was fabricated by tungsten deposition using an electron beam. After fabrication of the opposite-end electrode by the same method, an electrical connection was successfully confirmed by measuring the voltage between both ends of the metal thin-films with a circuit tester. Ohmic contact was confirmed by measuring the current-voltage characteristics between the fabricated electrodes. As a result, the electrical resistivity and Seebeck coefficient were successfully measured at 300 K.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-016-4968-5DOI ID：10.1007/s11664-016-4968-5,
ISSN：0361-5235,
eISSN：1543-186X,
Web of Science ID：WOS:000398937900033 Estimation of Phonon and Carrier Thermal Conductivities for Bulk Thermoelectric Materials Using Transport Properties Mioko Otsuka; Ryoei Homma; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：46,
号：5,
開始ページ：2752,
終了ページ：2764, 2017年05月,
［査読有り］The phonon and carrier thermal conductivities of thermoelectric materials were calculated using the Wiedemann-Franz law, Boltzmann equation, and a method we propose in this study called the Debye specific heat method. We prepared polycrystalline n-type doped bismuth telluride (BiTe) and bismuth antimony (BiSb) bulk alloy samples and measured six parameters (Seebeck coefficient, resistivity, thermal conductivity, thermal diffusivity, magneto-resistivity, and Hall coefficient). The carrier density and mobility were estimated for calculating the carrier thermal conductivity by using the Boltzmann equation. In the Debye specific heat method, the phonon thermal diffusivity, and thermal conductivity were calculated from the temperature dependence of the effective specific heat by using not only the measured thermal conductivity and Debye model, but also the measured thermal diffusivity. The carrier thermal conductivity was also evaluated from the phonon thermal conductivity by using the specific heat. The ratio of carrier thermal conductivity to thermal conductivity was evaluated for the BiTe and BiSb samples, and the values obtained using the Debye specific heat method at 300 K were 52% for BiTe and < 5.5% for BiSb. These values are either considerably larger or smaller than those obtained using other methods. The Dulong-Petit law was applied to validate the Debye specific heat method at 300 K, which is significantly greater than the Debye temperature of the BiTe and BiSb samples, and it was confirmed that the phonon specific heat at 300 K has been accurately reproduced using our proposed method.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-016-4955-xDOI ID：10.1007/s11664-016-4955-x,
ISSN：0361-5235,
eISSN：1543-186X,
Web of Science ID：WOS:000398937900029 Temperature Dependence of the Resistivity and Seebeck Coefficient of Individual Single-Crystal Bismuth Nanowires of 345-nm and 594-nm Diameters Encased in a Quartz Template Mioko Otsuka; Ryoei Homma; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：46,
号：5,
開始ページ：2976,
終了ページ：2985, 2017年05月,
［査読有り］Temperature dependence measurements of resistivity and the Seebeck coefficient were performed using individual bismuth nanowires of 345-nm and 594-nm diameters encased in a quartz template. Each nanowire was confirmed as a single crystal by Laue measurement, and an advanced mean free path model was utilized to explain both temperature dependencies. The model successfully explains the dependence over 100 K, which occurs because the carrier mobility is restricted by boundary scattering at the nanowire surface considering the crystal orientation along the wire length direction, band structure, and isotropic Fermi surface. However, it is difficult to determine the temperature dependence of the resistivity in the low-temperature region, in which a much higher temperature coefficient is indicated, especially at temperatures lower than 50 K. Although we calculated the temperature dependence of the resistivity with the influence of p-type contamination in the nanowire because a positive Seebeck coefficient at low temperatures was observed, an explanation of the resistivity in the low-temperature region has not been developed. Therefore, a hypothesis was introduced in which the hole mobility was not restricted in the nanowire, and the hole mobility was estimated by the mobility ratio from the Seebeck coefficient, the measured resistivity, and the electron mobility using the model. Lastly, the temperature dependence of the resistivity can be explained over the entire temperature region. This result suggests that the scattering mechanism between holes and electrons in the nanowire differs and depends on the crystal orientation in the low-temperature region.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-016-5087-zDOI ID：10.1007/s11664-016-5087-z,
ISSN：0361-5235,
eISSN：1543-186X,
Web of Science ID：WOS:000398937900061 Theoretical modeling of electrical resistivity and Seebeck coefficient of bismuth nanowires by considering carrier mean free path limitation Masayuki Murata; Atsushi Yamamoto; Yasuhiro Hasegawa; Takashi Komine; Akira Endo
JOURNAL OF APPLIED PHYSICS,
巻：121,
号：1,
開始ページ：10, 2017年01月,
［査読有り］In this study, the electrical resistivity and Seebeck coefficient of bismuth nanowires, several hundred nanometers in diameter, are calculated using the Boltzmann equation in the relaxation time approximation. The three-dimensional density of states and properties of single-crystalline bulk bismuth, such as carrier density, effective mass, and mobility, are used in the calculation without considering the quantum size effect. The relaxation times of the electrons and holes are calculated using Matthiessen's rule considering the carrier collisions at the wire boundary. The temperature, crystal orientation, and diameter dependence of the electrical resistivity and Seebeck coefficient are investigated. The calculation demonstrates that the electrical resistivity increases gradually with decreasing wire diameter, and the temperature coefficient of the electrical resistivity varies from positive to negative at low temperatures for thin wires with diameters less than approximately 500 nm. The diameter dependence of the electrical resistivity varies with the crystal orientation; the increase along the bisectrix axis is larger than that along the binary and trigonal axes. The temperature dependence of the Seebeck coefficient also strongly depends on the crystal orientation. The absolute value of the negative Seebeck coefficient along the bisectrix axis rapidly decreases with decreasing diameter and even changes sign from negative to positive at low temperatures despite the charge neutrality condition, while the Seebeck coefficients along the binary and trigonal axes do not differ significantly from those of single-crystalline bulk bismuth. We conclude that the thermoelectric properties of bismuth nanowires strongly depend not only on the wire diameter but also on the crystal orientation. Published by AIP Publishing.
AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.4973191DOI ID：10.1063/1.4973191,
ISSN：0021-8979,
eISSN：1089-7550,
ORCID：45323566,
Web of Science ID：WOS:000392839400023 Experimental and Theoretical Evaluations of the Galvanomagnetic Effect in an Individual Bismuth Nanowire Masayuki Murata; Atsushi Yamamoto; Yasuhiro Hasegawa; Takashi Komine
NANO LETTERS,
巻：17,
号：1,
開始ページ：110,
終了ページ：119, 2017年01月,
［査読有り］The galvanomagnetic effect is evaluated experimentally and theoretically in an individual bismuth nanowire encapsulated within a quartz template. A small section of the side surface of the encapsulated bismuth nanowire is exposed using focused ion beam processing, and a total of six carbon film electrodes are fabricated on the exposed nanowire surface by in situ deposition in order to be able to perform electrical measurements on the nanowire. The results show that the galvanomagnetic effect in the nanowire is affected by carrier collisions at the nanowire boundary; this is particularly the case at low temperatures. The Hall mobilities of electrons and holes are determined based on the measured Hall coefficient and magnetoresistivity values. It is found that the carrier mobility in the bismuth nanowire is lower than that in bulk bismuth and that it plateaus at low temperatures, as predicted by the calculation model used in the study, which takes into account the carrier mean free path limitation imposed by the small diameter of the nanowire.
AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1021/acs.nanolett.6b03592DOI ID：10.1021/acs.nanolett.6b03592,
ISSN：1530-6984,
eISSN：1530-6992,
Web of Science ID：WOS:000392036600017 Thermal diffusivity measurement using thermographic method and performance evaluation by impedance spectroscopy for thermoelectric module Mioko Otsuka; Hiroki Terakado; Ryoei Homma; Yasuhiro Hasegawa; Md. Zahidul Islam; Georg Bastian; Alexander Stuck
JAPANESE JOURNAL OF APPLIED PHYSICS,
巻：55,
号：12, 2016年12月,
［査読有り］The thermal diffusivity of two bulk thermoelectric elements and a thermoelectric module was measured by an infrared camera using a thermographic method without any contact in air at room temperature. The estimated values for the elements (3.45 x 10(-6)m(2)/s for a BiSb sample and 1.60 x 10(-6)m(2)/s for a BiTe sample) were slightly larger than those measured in vacuum. The difference was explained as the effect of heat convection on the surface of the samples by solving the one-dimensional heat conduction equation numerically. The thermal diffusivity of thermoelectric elements in a thermoelectric module was also estimated using the thermographic method, and values of (1.1-1.7) x 10(-6)m(2)/s in air were obtained, depending on the element. On the basis of the measurement results, the performance of the module was estimated using impedance spectroscopy, which can estimate not only the dimensionless figure of merit but also the thermal loss and response. The thermal response and thermal loss in air were similar to those in vacuum; however, the dimensionless figure of merit was 0.82 in vacuum and 0.70 in air. (C) 2016 The Japan Society of Applied Physics
IOP PUBLISHING LTD, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.7567/JJAP.55.126601DOI ID：10.7567/JJAP.55.126601,
ISSN：0021-4922,
eISSN：1347-4065,
Web of Science ID：WOS:000403936200001 Anomalous Nernst Effect of Perpendicularly Magnetic Anisotropy TbFeCo Thin Films Ryo Ando; Takashi Komine; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：45,
号：7,
開始ページ：3570,
終了ページ：3575, 2016年07月,
［査読有り］In this study, we investigated anomalous Nernst effect (ANE) of perpendicularly magnetized TbFeCo thin films with various Tb content, and especially studied the relation between ANE and anomalous Hall effect. As a result, the hysteresis of anomalous Nernst coefficient showed the same behavior as that of anomalous Hall resistivity, and the sign of anomalous Nernst coefficient was consistent with that of anomalous Hall voltage in any Tb content, whereas the Seebeck coefficient and the resistivity were almost constant even if the applied magnetic field was varied. Taking into account of thermoelectric coefficient tensor, it was revealed that the off-diagonal thermopower corresponding to the ANE in TbFeCo thin films is the product of Hall angle and Seebeck coefficient.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-016-4537-yDOI ID：10.1007/s11664-016-4537-y,
ISSN：0361-5235,
eISSN：1543-186X,
Web of Science ID：WOS:000377434100042 Thermoelectric Module Performance Estimation Based on Impedance Spectroscopy Yasuhiro Hasegawa; Ryoei Homma; Mioko Ohtsuka
JOURNAL OF ELECTRONIC MATERIALS,
巻：45,
号：3,
開始ページ：1886,
終了ページ：1893, 2016年03月,
［査読有り］The performance of a thermoelectric module is studied using impedance spectroscopy. We propose the simplest approximation using a least-squares method to estimate not only the dimensionless figure of merit but also the thermal loss and time constant more easily than would be possible using an exact solution. The frequency dependence of the impedance from 1 mHz to 10 kHz is measured at room temperature for a commercially available thermoelectric module, and the dimensionless figure of merit is evaluated to be 0.82, including the influence of the electrodes, isolation plate, and binding agent on the module. The thermal diffusivity of the thermoelectric element is shown to be important for evaluating the thermoelectric module performance, and the thermal loss and time constant are estimated to be less than 1% and 11 s, respectively. From the experimental results, we devise a strategy for creation of an ideal thermoelectric module.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-015-4271-xDOI ID：10.1007/s11664-015-4271-x,
ISSN：0361-5235,
eISSN：1543-186X,
Web of Science ID：WOS:000371163400092 Enhancement of Seebeck Coefficient in Bi Nanowires by Electric Field Effect Takashi Komine; Tomosuke Aono; Yuta Nabatame; Masayuki Murata; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：45,
号：3,
開始ページ：1555,
終了ページ：1560, 2016年03月,
［査読有り］In this study, we investigated the electric field effect on the transport properties of a Bi nanowire. These effects were modeled by a surface potential. The electron states of Bi nanowires were numerically analyzed by effective mass equations at the T-point and L-point taking into account surface potential due to an external electric field. The Seebeck coefficients of Bi nanowires were calculated by using the Boltzmann equation with a constant relaxation time. It was found that the Seebeck coefficients increased when the sign of the surface potential parameter was negative. In particular, when the surface potential parameter was -1 eV and the skin depth was 10 nm in a 20-nm-diameter nanowire, the maximum absolute value of the Seebeck coefficient was larger than 1 mV/K, which was greatly improved compared to that without an external electric field.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-015-4113-xDOI ID：10.1007/s11664-015-4113-x,
ISSN：0361-5235,
eISSN：1543-186X,
ORCID：45323567,
Web of Science ID：WOS:000371163400050 Magnetic-Field Dependence of Thermoelectric Properties of Sintered Bi90Sb10 Alloy Masayuki Murata; Atsushi Yamamoto; Yasuhiro Hasegawa; Takashi Komine
JOURNAL OF ELECTRONIC MATERIALS,
巻：45,
号：3,
開始ページ：1875,
終了ページ：1885, 2016年03月,
［査読有り］The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit (ZT) of a sintered Bi90Sb10 alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered Bi90Sb10 alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77-300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the Bi90Sb10 alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L-and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-015-4270-yDOI ID：10.1007/s11664-015-4270-y,
ISSN：0361-5235,
eISSN：1543-186X,
ORCID：45323568,
Web of Science ID：WOS:000371163400091 Simultaneous measurement of the Seebeck coefficient and thermal diffusivity for bulk thermoelectric materials Ryoei Homma; Yasuhiro Hasegawa; Hiroki Terakado; Hiroyuki Morita; Takashi Komine
JAPANESE JOURNAL OF APPLIED PHYSICS,
巻：54,
号：2, 2015年02月,
［査読有り］We simultaneously measured the Seebeck coefficient and thermal diffusivity of a rectangular parallelepiped bulk thermoelectric material. We used one-dimensional heat conduction equation to show that a periodic heat cycle produces not only the thermoelectromotive force but also a certain phase shift angle between the edge and intermediate points of a sample along the length of the material. Based on the equation of the modified Angstrom method, an experiment at 300K was performed using NIST standard material (SRM 3451, Bi2Te3 material) to measure the Seebeck coefficient and thermal diffusivity. The measured Seebeck coefficient was -231 +/- 3 mu V/K, which corresponds to the published value. Using the same experimental setup as that for the thermal diffusivity measurement, the dependence of the phase shift angle on frequency was measured from 5 mHz to 10 Hz for the phase shift angle from -8.2 to -450 degrees. The estimated thermal diffusivity was (1.53 +/- 0.05) x 10(-6) m(2)/s. We conclude that the modified Angstrom method can be used to measure the Seebeck coefficient and thermal diffusivity simultaneously. (C) 2015 The Japan Society of Applied Physics
IOP PUBLISHING LTD, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.7567/JJAP.54.026602DOI ID：10.7567/JJAP.54.026602,
ISSN：0021-4922,
eISSN：1347-4065,
Web of Science ID：WOS:000350091000024 Focused ion beam processing to fabricate ohmic contact electrodes on a bismuth nanowire for Hall measurements Masayuki Murata; Yasuhiro Hasegawa
NANOSCALE RESEARCH LETTERS,
巻：8, 2013年09月,
［査読有り］Ohmic contact electrodes for four-wire resistance and Hall measurements were fabricated on an individual single-crystal bismuth nanowire encapsulated in a cylindrical quartz template. Focused ion beam processing was utilized to expose the side surfaces of the bismuth nanowire in the template, and carbon and tungsten electrodes were deposited on the bismuth nanowire in situ to achieve electrical contacts. The temperature dependence of the four-wire resistance was successfully measured for the bismuth nanowire, and a difference between the resistivities of the two-wire and four-wire methods was observed. It was concluded that the two-wire method was unsuitable for estimation of the resistivity due to the influence of contact resistance, even if the magnitude of the bismuth nanowire resistance was greater than the kilo-ohm order. Furthermore, Hall measurement of a 4-mu m-diameter bismuth microwire was also performed as a trial, and the evaluated temperature dependence of the carrier mobility was in agreement with that for bulk bismuth, which indicates that the carrier mobility was successfully measured using this technique.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1186/1556-276X-8-400DOI ID：10.1186/1556-276X-8-400,
ISSN：1931-7573,
Web of Science ID：WOS:000325248300001 Thermal conductivity of an individual bismuth nanowire covered with a quartz template using a 3-omega technique Yasuhiro Hasegawa; Masayuki Murata; Fumiaki Tsunemi; Yusuke Saito; Katsuhito Shirota; Takashi Komine; Chris Dames; Javier E. Garay
Journal of Electronic Materials,
巻：42,
号：7,
開始ページ：2048,
終了ページ：2055, 2013年07月,
［査読有り］Thermal conductivity is estimated using a 3-omega technique for an individual bismuth nanowire (diameter: 595 nm, length: 2.24 mm) covered with a quartz template. To evaluate the thermal conductivity of the nanowire, we propose a simple model of thermal and electrical transfer functions for the nanowire that assumes a linear combination of that of the line heater on the substrate and a suspended wire. Since the out-of-phase third-harmonic component of the electrical transfer function depends only on the thermal diffusivity of the nanowire, measurement of the frequency dependence is carried out. A distinct extreme value of the frequency has been observed, as expected and estimation of the thermal conductivity of the nanowire covered with the quartz is attempted. Although the thermal conductivity at 300 K is 9.8 W/mK, somewhat smaller than that of bulk bismuth, the temperature dependence of the thermal conductivity is quite different from that of bulk bismuth and decreased linearly with decreasing temperature. In particular, this shows that the thermal conductivity obtained is suppressed in the low-temperature region by phonon confinement in the nanowire. © 2013 TMS.
英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-013-2520-4DOI ID：10.1007/s11664-013-2520-4,
ISSN：0361-5235,
ORCID：45323573,
SCOPUS ID：84879794957,
Web of Science ID：WOS:000320890800122 Current-induced cooling phenomenon in a two-dimensional electron gas under a magnetic field Naomi Hirayama; Akira Endo; Kazuhiro Fujita; Yasuhiro Hasegawa; Naomichi Hatano; Hiroaki Nakamura; Ryoen Shirasaki; Kenji Yonemitsu
Journal of Low Temperature Physics,
巻：172,
号：1-2,
開始ページ：132,
終了ページ：153, 2013年07月
We investigate the spatial distribution of temperature induced by a dc current in a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field. We numerically calculate the distributions of the electrostatic potential φ and the temperature T in a 2DEG enclosed in a square area surrounded by insulated-adiabatic (top and bottom) and isopotential-isothermal (left and right) boundaries (with φ left<φ right and T left=T right), using a pair of nonlinear Poisson equations (for φ and T) that fully take into account thermoelectric and thermomagnetic phenomena, including the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. We find that, in the vicinity of the left-bottom corner, the temperature becomes lower than the fixed boundary temperature, contrary to the naive expectation that the temperature is raised by the prevalent Joule heating effect. The cooling is attributed to the Ettingshausen effect at the bottom adiabatic boundary, which pumps up the heat away from the bottom boundary. In order to keep the adiabatic condition, downward temperature gradient, hence the cooled area, is developed near the boundary, with the resulting thermal diffusion compensating the upward heat current due to the Ettingshausen effect. © 2013 Springer Science+Business Media New York.
研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s10909-012-0852-8Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84879893161&origin=inwardScopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84879893161&origin=inwardDOI ID：10.1007/s10909-012-0852-8,
ISSN：0022-2291,
eISSN：1573-7357,
SCOPUS ID：84879893161 Temperature Coefficient of Electrical Resistivity in Individual Single-Crystal Bismuth Nanowires Masayuki Murata; Fumiaki Tsunemi; Yusuke Saito; Katsuhito Shirota; Keisuke Fujiwara; Yasuhiro Hasegawa; Takashi Komine
JOURNAL OF ELECTRONIC MATERIALS,
巻：42,
号：7,
開始ページ：2143,
終了ページ：2150, 2013年07月,
［査読有り］The temperature dependence of electrical resistivity and the crystal orientation of single-crystal bismuth nanowires each encapsulated in a quartz template were studied. The electrical resistivities of four bismuth nanowires with diameter of 356 nm, 376 nm, 622 nm, and 633 nm were measured in the temperature range from 4.2 K to 300 K. The temperature coefficient of resistivity of 376-nm- and 633-nm-diameter nanowires was negative in the low-temperature region. On the other hand, a positive temperature coefficient appeared in 356-nm- and 622-nm-diameter nanowires. The positive temperature coefficient was not explained by carrier mean free path limitation. Thus, the crystal orientation of the bismuth nanowires was observed by x-ray diffraction measurements to study the relationship between electrical resistivity and crystal orientation. It was confirmed that the temperature dependence of electrical resistivity strongly depended on the crystal orientation of the bismuth nanowire.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-013-2552-9DOI ID：10.1007/s11664-013-2552-9,
ISSN：0361-5235,
eISSN：1543-186X,
ORCID：45323572,
Web of Science ID：WOS:000320890800136 Numerical Analysis of the Boundary Scattering Effect on Transport Properties in Bi-Sb Nanowires Yuta Nabatame; Tsuyoshi Matsumoto; Yuki Ichige; Takashi Komine; Ryuji Sugita; Masayuki Murata; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：42,
号：7,
開始ページ：2172,
終了ページ：2177, 2013年07月,
［査読有り］In this study, we have numerically analyzed the transport properties of Bi-Sb nanowires, taking into account wire boundary scattering. Wire boundary scattering slightly decreased the Seebeck coefficient of Bi-Sb nanowires. This effect is due to the observation that boundary scattering and the mobility ratio of L-point electrons to T-point holes in the nanowires are smaller than those in bulk Bi-Sb because the wire boundary scattering suppresses the mobilities of L-point electrons and heavy holes. The largest Seebeck coefficient for all wire diameters was obtained when the Sb concentration was 5 at.%. The effective mass approached zero near 5 at.% Sb, and the small effective mass led to a large subband shift in each band. Thus, a small effective mass enhances the quantum effect at a fixed wire diameter, even if wire boundary scattering is taken into account.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-013-2564-5DOI ID：10.1007/s11664-013-2564-5,
ISSN：0361-5235,
ORCID：45323570,
Web of Science ID：WOS:000320890800140 Shubnikov--de Haas Oscillations in Single-Crystal Bismuth Nanowires Encased in Quartz Template Tsunemi Fumiaki; Murata Masayuki; Saito Yusuke; Shirota Katsuhito; Hasegawa Yasuhiro; Komine Takashi
Applied physics express,
巻：6,
号：4,
開始ページ：45002,
終了ページ：045002-4, 2013年04月
Shubnikov--de Haas (SdH) oscillations were measured at 0.3 K in bismuth nanowires with diameters of 393, 548, and 622 nm, and lengths of over 1 mm, which were encased in quartz templates. The magnetoresistance was measured up to a magnetic field of 17 T. Distinct SdH oscillations were observed, and the nanowire samples were rotated in the magnetic field to determine the contribution due to holes, electrons, and spin--orbit interactions. For the 622-nm-diameter nanowire, for example, values of 30.7 meV and 1.66\times 10^{17} cm
-3were obtained for the Fermi energy and carrier density, respectively, which were similar to the values for bulk bismuth.
The Japan Society of Applied Physics, 英語
DOI：https://doi.org/10.7567/APEX.6.045002DOI ID：10.7567/APEX.6.045002,
ISSN：1882-0778,
CiNii Articles ID：10031166429,
CiNii Books ID：AA12295133 Preparation of bismuth nanowire encased in quartz template for Hall measurements using focused ion beam processing Masayuki Murata; Yasuhiro Hasegawa; Takashi Komine; Tomohiro Kobayashi
NANOSCALE RESEARCH LETTERS,
巻：7,
開始ページ：1,
終了ページ：6, 2012年09月,
［査読有り］Forming electrodes on opposite sides of an individual bismuth nanowire was attempted to prepare for Hall measurements. Although a 1-mm-long bismuth nanowire which is completely covered with a quartz template has been successfully fabricated to prevent oxidation, it is very difficult to attach Hall electrodes on the opposite sides of the nanowire due to the quartz covering. One side of the cylindrical quartz template was removed by polishing without exposure of the nanowire to the atmosphere; the thickness between the polished template surface and the nanowire was estimated to be several micrometers. Focused ion beam processing was successfully employed to expose both surfaces of the nanowire under high vacuum by removing part of the quartz template. A carbon thin film was then deposited in situ on the wire surface to fabricate an electrical contact on the bismuth nanowire sample. Furthermore, the energy dispersive X-ray analysis was performed to the area processed by focused ion beam, and the bismuth component of the nanowire was successfully detected. It was confirmed that the focused ion beam processing was applicable to attach electrodes to bismuth nanowire for Hall measurement.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1186/1556-276X-7-505DOI ID：10.1186/1556-276X-7-505,
ISSN：1931-7573,
Web of Science ID：WOS:000311319400001 Transport-coefficient dependence of current-induced cooling effect in a two-dimensional electron gas Naomi Hirayama; Akira Endo; Kazuhiro Fujita; Yasuhiro Hasegawa; Naomichi Hatano; Hiroaki Nakamura; Ryoen Shirasaki; Kenji Yonemitsu
Journal of Electronic Materials,
巻：41,
号：6,
開始ページ：1535,
終了ページ：1539, 2012年06月
The dependence of the current-induced cooling effect on the electron mobility μ e is explored for a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field. We calculate the distributions of the electrochemical potentials and the temperatures under a magnetic field, fully taking account of thermoelectric and thermomagnetic phenomena. Whereas the electrochemical potential and the electric current remain qualitatively unchanged, the temperature distribution exhibits drastic mobility dependence. The lower-mobility system has cold and hot areas at opposite corners, which results from the heat current brought about by the Ettingshausen effect in the vicinity of the adiabatic boundaries. The cooling effect is intensified by an increase in μ e. Intriguingly, the cold and hot areas change places with each other as the mobility μ e is further increased. This is because the heating current on the adiabatic edges due to the Righi-Leduc effect exceeds that due to the Ettingshausen effect in the opposite direction. © 2011 TMS.
研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-011-1850-3Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84862167887&origin=inwardScopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84862167887&origin=inwardDOI ID：10.1007/s11664-011-1850-3,
ISSN：0361-5235,
SCOPUS ID：84862167887 Four-Wire Resistance Measurements of a Bismuth Nanowire Encased in a Quartz Template Utilizing Focused Ion Beam Processing
M. Murata; H. Yamamoto; F. Tsunemi; Y. Hasegawa; T. Komine
J. Elec. Mater., 巻：41, 号：6, 開始ページ：1442-1449, 2012年06月, ［査読有り］
英語, 研究論文（学術雑誌）
Thermoelectric propeties for single crystal bismuth nanowires using a mean free path limitation model
D. Nakamura; Y. Hasegawa; M. Murata; H. Yamamoto; T. Komine
J. Appl. Phys., 巻：110, 開始ページ：053702/pp.1-6, 2011年08月, ［査読有り］
英語, 研究論文（学術雑誌）
Temperature distribution in two-dimensional electron gases under a strong magnetic field Naomi Hirayama; Akira Endo; Kazuhiro Fujita; Yasuhiro Hasegawa; Naomichi Hatano; Hiroaki Nakamura; Ryoen Shirasaki; Kenji Yonemitsu
Journal of Electronic Materials,
巻：40,
号：5,
開始ページ：529,
終了ページ：532, 2011年05月
Two-dimensional electron gases having an electrochemical potential gradient under a magnetic field are numerically examined using the finite-difference method. The temperature, voltage, electric current, and heat flux are calculated from transport equations describing thermoelectric and thermomagnetic effects, namely the Hall, Nernst, Ettingshausen, and Righi-Leduc effects. The results show that a magnetic field distorts equipotential lines and generates an uneven temperature distribution. In particular, a part of the system is found to become colder than the temperature of the heat baths. The cooling effect under a strong magnetic field is due primarily to the Ettingshausen and Hall effects. © 2010 TMS.
研究論文（国際会議プロシーディングス）
DOI：https://doi.org/10.1007/s11664-010-1427-6Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=79955880928&origin=inwardScopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=79955880928&origin=inwardDOI ID：10.1007/s11664-010-1427-6,
ISSN：0361-5235,
SCOPUS ID：79955880928 Numerical Study of Effects of Scattering Processes on Transport Properties of Bi Nanowires Yuki Ichige; Tsuyoshi Matsumoto; Takashi Komine; Ryuji Sugita; Tomosuke Aono; Masayuki Murata; Daiki Nakamura; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：40,
号：5,
開始ページ：523,
終了ページ：528, 2011年05月,
［査読有り］In this study, we investigated the effects of scattering on the transport properties of Bi nanowires. The electrical conductivities and Seebeck coefficients of Bi nanowires were calculated using the Boltzmann equation, with an energy-dependent relaxation time corresponding to the scattering process. Decreasing the wire diameter increased the Seebeck coefficient for all of the scattering processes examined, because a semimetal-semiconductor transition occurred. In 80-nm-diameter nanowires, the Seebeck coefficient for ionized impurity scattering was larger than that of the acoustic deformation potential. On the other hand, in 20-nm-diameter nanowires, the dependence of the Seebeck coefficient on the scattering process was negligible, compared with the influence of wire diameter.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-010-1426-7DOI ID：10.1007/s11664-010-1426-7,
ISSN：0361-5235,
ORCID：45323578,
Web of Science ID：WOS:000289901700010 Numerical Study of Effect of Surface Potential on Transport Properties of Bi Nanowires Tsuyoshi Matsumoto; Yuki Ichige; Takashi Komine; Ryuji Sugita; Tomosuke Aono; Masayuki Murata; Daiki Nakamura; Yasuhiro Hasegawa
JOURNAL OF ELECTRONIC MATERIALS,
巻：40,
号：5,
開始ページ：1260,
終了ページ：1265, 2011年05月,
［査読有り］We numerically investigated the effect of the surface on the transport properties of Bi nanowires. The effect of the surface was modeled using the surface potential. The energy shift in each band due to the surface potential was calculated by a perturbation method. The effect of the surface potential on the transport properties was estimated using the Boltzmann equation with a constant relaxation time. The results reveal that the surface potential dramatically alters the density of states of T-point holes, whereas it has very little effect on the density of states of L-point holes. This is because the wavefunctions at the L- and T-points have different symmetries. The electrical conductivity increases and the Seebeck coefficient decreases with increasing surface potential. The maximum absolute value of the Seebeck coefficient decreases drastically with increasing surface potential. The Seebeck coefficient has a much stronger dependence on the surface potential than on the wire diameter. These results demonstrate that the transport properties of Bi nanowires are very sensitive to the surface potential.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-010-1406-yDOI ID：10.1007/s11664-010-1406-y,
ISSN：0361-5235,
ORCID：45323577,
Web of Science ID：WOS:000289901700142 Crystal Orientation and Transport Properties of a 633-nm-Diameter Bismuth Nanowire Yasuhiro Hasegawa; Daiki Nakamura; Masayuki Murata; Hiroya Yamamoto; Takashi Komine; Takashi Taguchi; Shinichiro Nakamura
JOURNAL OF ELECTRONIC MATERIALS,
巻：40,
号：5,
開始ページ：1005,
終了ページ：1009, 2011年05月,
［査読有り］The crystal orientation and resistivity of a bismuth nanowire (diameter 633 nm, length 1.91 mm) encased in quartz were measured. The nanowire surface was irradiated with a high-intensity, collimated x-ray beam through the quartz template, and several Laue spots were observed with no streak patterns. Therefore, we concluded that the nanowire was a single crystal. The crystal orientation could be determined by measuring the relationship between the Laue spot distribution and the location of the nanowire fixed by a goniometer. The direction along the wire length was strongly directed toward the bisectrix axis of bismuth. The temperature dependence of the nanowire resistivity was measured; the resistivity at 300 K was 1.40 mu Omega m, which is somewhat greater than that of the bulk sample due to the lower mobility of the nanowire. The temperature coefficient of resistivity was positive in the temperature range from 300 K to 165 K, and it became negative below 165 K. The temperature dependence can be modeled by accounting for the limited electron mean free path in the bismuth nanowire based on the crystal orientation determined by the Laue measurements.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-010-1480-1DOI ID：10.1007/s11664-010-1480-1,
ISSN：0361-5235,
ORCID：45323576,
Web of Science ID：WOS:000289901700097 Numerical Analysis of Effect of Scattering Process on Transport Properties in Bi Nanowires
Y. Ichige; T. Matsumoto; T. Komine; R. Sugita; T. Aono; Y. Hasegawa; M. Murata; D. Nakamura
J. Elec. Mater., 巻：40, 号：5, 開始ページ：523-528, 2011年05月, ［査読有り］
英語, 研究論文（学術雑誌）
Reduction of temperature fluctuation within low temperature region using a cryocooler Daiki Nakamura; Yasuhiro Hasegawa; Masayuki Murata; Hiroya Yamamoto; Fumiaki Tsunemi; Takashi Komine
REVIEW OF SCIENTIFIC INSTRUMENTS,
巻：82,
号：4,
開始ページ：4, 2011年04月,
［査読有り］Modeling and experiments are performed to decrease temperature fluctuation generated by the periodic motion of the displacer in a Gifford-McMahon (GM) type cryocooler within the low-temperature region. The one-dimensional heat equation allows us to show that thermal diffusivity is an essential factor to achieve much smaller temperature fluctuation, and fiber-reinforced plastic (FRP) with low thermal diffusivity makes it possible to reduce the temperature fluctuation dramatically. Based on the model, experiments are performed to vary the thickness of two FRP dampers, on the cryohead of the cryocooler and on the sample stage. As a result, the FRP dampers enable us to achieve the temperature fluctuations of only 0.7 mK, corresponding to a standard deviation of 0.25 mK, when the sample stage is maintained at 4.2000 K, even if a GM cryocooler is utilized for cooling the temperature, which introduces an initial temperature fluctuation of 282 mK at the cryohead. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581211]
AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.3581211DOI ID：10.1063/1.3581211,
ISSN：0034-6748,
ORCID：45323579,
Web of Science ID：WOS:000290051500044 Temperature distribution in nano-devices under a strong magnetic field Naomi Hirayama; Akira Endo; Kazuhiro Fujita; Yasuhiro Hasegawa; Naomichi Hatano; Hiroaki Nakamura; Ryoen Shirasaki
Computer Physics Communications,
巻：182,
号：1,
開始ページ：90,
終了ページ：92, 2011年01月
The thermoelectric and thermomagnetic phenomena of two-dimensional electron gases at low temperatures are numerically examined using the finite-difference method. The temperature and the voltage are calculated from transport equations describing thermoelectric and thermomagnetic effects. The results demonstrate that a magnetic field distorts equipotential lines and generates an uneven distribution of the temperature, which can cause inhomogeneous heating of experimental systems. In particular, a part of the system is found to be colder than the temperature of the heat baths. © 2010 Elsevier B.V. All rights reserved.
研究論文（国際会議プロシーディングス）
DOI：https://doi.org/10.1016/j.cpc.2010.07.043Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=78149360259&origin=inwardScopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=78149360259&origin=inwardDOI ID：10.1016/j.cpc.2010.07.043,
ISSN：0010-4655,
SCOPUS ID：78149360259 High-precision temperature control and stabilization using a cryocooler Yasuhiro Hasegawa; Daiki Nakamura; Masayuki Murata; Hiroya Yamamoto; Takashi Komine
REVIEW OF SCIENTIFIC INSTRUMENTS,
巻：81,
号：9,
開始ページ：4, 2010年09月,
［査読有り］We describe a method for precisely controlling temperature using a Gifford-McMahon (GM) cryocooler that involves inserting fiber-reinforced-plastic dampers into a conventional cryosystem. Temperature fluctuations in a GM cryocooler without a large heat bath or a stainless-steel damper at 4.2 K are typically of the order of 200 mK. It is particularly difficult to control the temperature of a GM cryocooler at low temperatures. The fiber-reinforced-plastic dampers enabled us to dramatically reduce temperature fluctuations at low temperatures. A standard deviation of the temperature fluctuations of 0.21 mK could be achieved when the temperature was controlled at 4.200 0 K using a feedback temperature control system with two heaters. Adding the dampers increased the minimum achievable temperature from 3.2 to 3.3 K. Precise temperature control between 4.200 0 and 300.000 K was attained using the GM cryocooler, and the standard deviation of the temperature fluctuations was less than 1.2 mK even at 300 K. This technique makes it possible to control and stabilize the temperature using a GM cryocooler. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3484192]
AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.3484192DOI ID：10.1063/1.3484192,
ISSN：0034-6748,
ORCID：45323582,
Web of Science ID：WOS:000282440900031 Numerical Analysis of Effective Thermal Conductivity of Microwire Array Element Takashi Komine; Masahiro Kuraishi; Takayuki Teramoto; Ryuji Sugita; Yasuhiro Hasegawa; Masayuki Murata; Daiki Nakamura
JOURNAL OF ELECTRONIC MATERIALS,
巻：39,
号：9,
開始ページ：1606,
終了ページ：1610, 2010年09月,
［査読有り］We have used the finite-element method to calculate numerically the equations of electrical and thermal transport. The thermal conductivity of a wire array is analyzed. The influence of the wire array on the effective thermal conductivity of the element is discussed. The effective thermal conductivity decreases as the wire diameter is reduced. Decreasing the packing density significantly reduces the effective thermal conductivity. In the classical regime, the ratio of the effective electrical conductivity to the effective thermal conductivity of the wire array can be expressed as a function of packing density; this ratio decreases as the packing density decreases. The ratio for a wire array with realistic parameters is similar to that of bulk bismuth. Therefore, to improve the thermoelectric figure of merit, it is critical to enhance the intrinsic power factor in a wire by exploiting thermomagnetic or quantum effects.
SPRINGER, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-010-1266-5DOI ID：10.1007/s11664-010-1266-5,
ISSN：0361-5235,
ORCID：45323583,
Web of Science ID：WOS:000281393000043 Electrical nanocontact between bismuth nanowire edges and electrodes
M. Murata; D. Nakamura; Y. Hasegawa; T. Komine; D. Uematsu; S. Nakamura; T. Taguchi
J. Elec. Mater., 巻：39, 号：9, 開始ページ：1536-1542, 2010年06月, ［査読有り］
英語, 研究論文（学術雑誌）
Thermoelectric properties of a 593 nm individual bismuth nanowire prepared using a quartz template D. Nakamura; M. Murata; Y. Hasegawa; T. Komine; D. Uematsu; S. Nakamura; T. Taguchi
J. Elec. Mater.,
巻：39,
号：9,
開始ページ：1960-1965, 2010年05月,
［査読有り］英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-009-1045-3DOI ID：10.1007/s11664-009-1045-3 Reducing thermal conductivity of thermoelectric materials by using a narrow wire geometry
Y. Hasegawa; M. Murata; D. Nakamura; T. Komine; T. Taguchi; S. Nakamura; D. Uematsu
J. Appl. Phys., 巻：106, 開始ページ：063703/pp.1-7, 2009年09月, ［査読有り］
英語, 研究論文（学術雑誌）
Mobility estimation in micro-sized bismuth wire arrays Y. Hasegawa; M. Murata; D. Nakamura; T. Komine; T. Taguchi; S. Nakamura
J. Appl. Phys.,
巻：105,
開始ページ：103715/pp.1-7, 2009年05月,
［査読有り］英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.3133136DOI ID：10.1063/1.3133136 Thermoelectric properties of bismuth nanowires in a quartz template Y. Hasegawa; M. Murata; D. Nakamura; T. Komine; T. Taguchi; S. Nakamura; V. Jovovic; J. P. Heremans
Appl. Phys. Lett.,
巻：94,
開始ページ：192104, 2009年05月,
［査読有り］英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.3133355DOI ID：10.1063/1.3133355 Thermoelectric properties of bismuth micro/nano-wire array elements pressured into a quartz template mold Y. Hasegawa; H. Morita; T. Komine; T. Taguchi; S. Nakamura
J. Elec. Mater.,
巻：38,
号：7,
開始ページ：944-947, 2009年04月,
［査読有り］英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1007/s11664-009-0781-8DOI ID：10.1007/s11664-009-0781-8 Thermoelectric property of Cu2O thin film deposited by Reactive Ion Plating method
H. Uchiyama; Y. Hasegawa; H. Morita; A. Kurokouchi; K. Wada; T. Komine
Proceedings of International Conference on Thermoelectrics, 開始ページ：379-381, 2006年08月, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）
First-principles calculation of atomic-sized Ni nanocontacts T. Takahashi; T. Komine; R. Sugita; Y. Hasegawa
INTERMAG 2006 - IEEE International Magnetics Conference,
開始ページ：472, 2006年,
［査読有り］We calculated the electronic structures of Ni nanocontact by using the first-principles band calculation, and investigated the dependence of the electronic structure on the nanocontact shape. It is expected that the large spin polarization at the center of nanocontact can be obtained in the large contact length. The small contact length can easily switch from P state to AP state in spin configuration of two ferromagnetic electrodes.
英語, 研究論文（国際会議プロシーディングス）
DOI：https://doi.org/10.1109/INTMAG.2006.376196DOI ID：10.1109/INTMAG.2006.376196,
SCOPUS ID：50249115135 Numerical analysis of effective thermal conductivity in microwire array element
M. Kuraishi; T. Komine; T. Teramoto; R. Sugita; Y. Hasegawa
ICT'06: XXV INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS, 開始ページ：582, 終了ページ：+, 2006年, ［査読有り］
In this study, we have developed a three-dimensional finite element method for solving the equations of electrical and thermal flows. The 3D analysis of bulk material and wire array element was demonstrated, and electrical potential and temperature distributions were calculated in thermoelectric elements of bulk bismuth and wire array structures for various boundary conditions. The influence of wire array structure on effective thermal. conductivity of the element was discussed in this study. It was clarified that thermal exchange between bismuth wire and glass template in wire array element plays a very important role for reduction of thermal conductivity.
IEEE, 英語, 研究論文（国際会議プロシーディングス）
Web of Science ID：WOS:000245921800138
Geometrical dependence of magneto resistivity in bismuth microwire arrays
Hirofumi Nakano; Yoshiaki Ishikawa; Yasuhiro Hasegawa; Hiroyuki Morita; Takashi Komine
ICT'06: XXV INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS, 開始ページ：375, 終了ページ：+, 2006年, ［査読有り］
Geometrical dependence of the magnetoresistivity using polycrystalline bismuth microwire array was measured under magnetic fields of 0-2 T at temperatures of 50-300 K, and its diameter of prepared microwire arrays were 10 and 25 mu m. Aspect ratio, defined by wire length divided by the diameter, was determined for the wire array since both edges of all wires were attached to Ti thin film layer in order to avoid contact resistance. The attachment of the layer makes it possible to estimate the resistivity of the wire arrays. Both resistivities of the wire arrays at 300 K were equal to approximately 1.35 mu Omega m and were good agreement not only at 300 K but also in temperature region of 50-300 K in the absence of a magnetic field. Although the magnetoresistivities of both samples increased in the presence of the magnetic field, the behavior of magnetoresistivity depended on wire diameter. The magnetoresistivity of the wire array with higher aspect ratio was suppressed even if the resistivities of both samples without magnetic field are equal. The difference of magnetoresistivities was remarkable in high magnetic field and low temperature region. Therefore, the thermoelectric element with high aspect ratio such as micro- and nano-wire array leads suppression of magnetoresistivity increase more than that of bulk material.
IEEE, 英語, 研究論文（国際会議プロシーディングス）
Web of Science ID：WOS:000245921800086
Reduction of contact resistance at terminations of bismuth wire arrays
Yasuhiro Hasegawa; Hiroyuki Morita; Akio Kurokouchi; Kentarou Wada; Takashi Komine
ICT'06: XXV INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS, 開始ページ：372, 終了ページ：+, 2006年, ［査読有り］
Contact resistance at the terminations of bismuth wire array of 25 mu m diameter is reduced by ion plating of a titanium interlayer 100 nm upon the wire ends. 1,000 nm-thick copper electrodes are ion plated upon the titanium. Copper probe electrodes are then attached using Pb-Sn solder. The temperature dependence of the Seebeck coefficient and resistance are measured upon heating from 25 K to 300 K and the results compared with those for the polycrystalline bulk bismuth sample. The resistivity of the micro-wire array is found to be 1.37 mu Omega m at 300 K. Based on the similarities between the temperature dependences of resistivity and Seebeck coefficient for the wire and bulk samples, contact resistance of the wires is considered to have been completely eliminated. This technique makes it possible to simultaneously estimate the resistivity and Seebeck coefficient for nano-wire arrays of thermoelectric materials.
IEEE, 英語, 研究論文（国際会議プロシーディングス）
Web of Science ID：WOS:000245921800085
Synthesis of silicon nanocones using rf microplasma at atmospheric pressure H Shirai; T Kobayashi; Y Hasegawa
APPLIED PHYSICS LETTERS,
巻：87,
号：14, 2005年10月,
［査読有り］We report the synthesis of silicon nanocones using the rf microplasma discharge at atmospheric pressure. The products formed underneath the tube electrode on Fe-coated crystalline silicon were constituted mainly of silicon and silicon oxide despite the use of a methane-argon mixture. Carbon nanotubes and silicon nanowires were also formed around the silicon nanocones. The number density and average size of silicon nanocones increased with the plasma exposure time accompanied by the enlargement of their surface distribution. The growth mechanism of silicon nanocones is discussed in terms of the catalytic growth via diffusion of silicon with nanocrystalline Si particle through FeSix nanoclusters, and enhanced Si oxidation by the plasma heating. (C) 2005 American Institute of Physics.
AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.2084342DOI ID：10.1063/1.2084342,
ISSN：0003-6951,
Web of Science ID：WOS:000232225700061 Electronic transport properties of a bismuth microwire array in a magnetic field Y Hasegawa; Y Ishikawa; H Morita; T Komine; H Shirai; H Nakamura
JOURNAL OF APPLIED PHYSICS,
巻：97,
号：8, 2005年04月,
［査読有り］The magneto-Seebeck coefficient and magnetoresistivity of a polycrystalline bismuth microwire array were measured under magnetic fields of 0-2 T and at temperatures of 50-300 K. To avoid the influence of contact resistance between the wire array and the electrodes, bulk bismuth was used for the electrodes. In the absence of a magnetic field, the Seebeck coefficient and resistivity were -76 mu V/K and 1.8 mu Omega m at 300 K, respectively. The magneto-Seebeck coefficient for the wire array increased with the application of an external magnetic field, attributable to the precise control of impurities and carrier scattering process in the fabrication of the wire array. The phonon drag effect was observed below 100 K, with a corresponding increase in the magneto-Seebeck coefficient under high magnetic fields. However, the magnetoresistivity was also raised under higher magnetic fields, detracting from the thermoelectric properties. Through analysis of the power factor, the optimum magnetic field was determined for each temperature, revealing a trend for the optimum magnetic field to increase with temperature. The power factor was improved by a maximum factor of 1.12, achieved at 200 K and 0.25 T. Further improvements appear to be possible by eliminating the bulk bismuth employed for the electrodes. (C) 2005 American Institute of Physics.
AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1063/1.1865342DOI ID：10.1063/1.1865342,
ISSN：0021-8979,
Web of Science ID：WOS:000228729500070 有限要素法を用いたフラックスガイド型半導体磁気抵抗素子の解析 高山裕樹; 小峰啓史; 杉田龍二; 村野井徹夫; 長谷川靖洋
日本応用磁気学会誌,
巻：29,
号：3,
開始ページ：278-281,
終了ページ：281, 2005年03月,
［査読有り］We investigate the magnetoresistance of a magnetoresistive element consisting of a nonmagnetic semiconductor, four electrodes, and a metallic shunt, with varying locations of the voltage electrodes. The optimum location of the voltage electrodes is estimated from MR ratios calculated by using the finite element method. The MR ratio of 6.9%, which was obtained at an applied magnetic field of 0.005 T for an MR element with asymmetrical voltage electrodes separated by a distance of 25 nm, is higher than that for the MR element with symmetrical electrodes. In order to improve the MR ratio at a low applied field, a flux-guide-type MR element is proposed in this study. An MR ratio of 124% at an applied field of 0.005 T was obtained for a flux-guide-type element with asymmetrical electrodes.
The Magnetics Society of Japan, 日本語, 研究論文（学術雑誌）
DOI：https://doi.org/10.3379/jmsjmag.29.278DOI ID：10.3379/jmsjmag.29.278,
ISSN：0285-0192,
CiNii Articles ID：110002811784,
CiNii Books ID：AN0031390X 磁性体ナノ接合部における磁壁構造の数値解析 小峰啓史; 高橋朋広; 杉田龍二; 村野井徹夫; 長谷川靖洋
日本応用磁気学会誌,
巻：29,
号：2,
開始ページ：116-119,
終了ページ：119, 2005年02月,
［査読有り］強磁性体ナノ接合の磁壁構造をマイクロマグネティックスにより解析し，Ｈ型強磁性体の接合形状と磁壁幅の関係を明らかにした．
The Magnetics Society of Japan, 日本語, 研究論文（学術雑誌）
DOI：https://doi.org/10.3379/jmsjmag.29.116DOI ID：10.3379/jmsjmag.29.116,
ISSN：0285-0192,
CiNii Articles ID：110002811869,
CiNii Books ID：AN0031390X Numerical Analysis of Thermoelectric Properties of Bismuth Under Magnetic Field
T. Komine; Y. Hasegawa; Y. Ishikawa; H. Morita; H. Shirai; R. sugita; T. Muranoi
The 23rd International Conference on Thermoelectrics, 2004年07月
英語, 研究論文（国際会議プロシーディングス）
Polarity change switch for peltier current leadMasato Moriguchi; Susumu Mizutani; Satoshi Miwa; Tosin Famakinwa; Takayuki Yamaguchi; Makoto Hamabe; Hideaki Takahashi; Keiji Nakamura; Satarou Yamaguchi; Haruhiko Okumura; Yasuhiro Hasegawa
IEEE Transactions on Applied Superconductivity,
巻：14,
開始ページ：1786,
終了ページ：1789, 2004年06月
Peltier current lead is a promising method to reduce heat leakage from current lead. This paper reports development of Peltier current lead (PCL) with switching facilities to adopt the PCL to polarity-reversible superconducting magnet. In the present work, two types of the PCL were discussed. We mainly investigated the PCL with switching element installed in the copper part. Numerical analysis revealed that it is preferable to reduce heat leakage at the low temperature end of Peltier element. With switch resistance of ∼ 100 μΩ, which enabled switch induced increment of the heat leakage to be suppressed by less than 10%. A transistor switching module with appropriate resistance were manufactured. We demonstrated that a temperature gradient at the end of the lead, corresponding to the heat leakage, could be reduced compared to a conventional current lead (CCL) even when the module was installed with the PCL.
DOI：https://doi.org/10.1109/TASC.2004.831096DOI ID：10.1109/TASC.2004.831096,
ISSN：1051-8223,
SCOPUS ID：4344638499 Seebeck coefficient and resistivity measurement of polycrystalline Bi in a magnetic field
Y. Ishikawa; A. Suzuki; T. Komine; H. Shirai; Y. Hasegawa
The 22nd International Conference on Thermoelectrics, 開始ページ：286- 289, 2003年08月
英語, 研究論文（国際会議プロシーディングス）
Investigation on binder for thermoelectric module
A. Suzuki; Y. Ishikawa; T. Komine; H. Shirai; Y. Hasegawa
The 22nd International Conference on Thermoelectrics, 開始ページ：537- 540, 2003年08月
英語, 研究論文（国際会議プロシーディングス）
Thermoelectric property measurement for a Peltier current lead
Y. Hasegawa; T. Oike; H. Okumura; K. Sato; K. Nakamura; T. Yamaguchi; A. Iiyoshi; S. Yamaguchi; K. Asano; T. Eura
International Conference on Thermoelectrics, ICT, Proceedings, 開始ページ：507, 終了ページ：510, 2001年12月
Peltier current lead (PCL) has been studied since it was proposed as one of thermoelectric applications. Due to the Peltier effect, it is expected the PCL reduces the heat leak from room temperature side to the low temperature side of a cryogenic system. Thermoelectric materials are installed into the copper (or aluminum) leads at room temperature side and the copper leads are connected to super-conducting magnet. Present performance of the thermoelectric material can achieve such a high current with a relatively small Peltier element. We measure temperature dependence of Seebeck coefficient and resistivity with BiTe thermoelectric materials. Optimum current is determined when PCLs apply to a super-conducting system with simplest model. The heat leak reduction at the optimum current operation is estimated with several thermoelectric elements, and it is expected about that the heat leak reduce about 25%.
SCOPUS ID：0035705703
Thermal resistance measurements of the surfaces of various materials in room temperature to 50 K
T. Oike; Y. Hasegawa; S. Takayama; S. Yamaguchi
International Conference on Thermoelectrics, ICT, Proceedings, 開始ページ：511, 終了ページ：514, 2001年12月
Measurements of transport parameters of thermoelectric semiconductors need to control the temperature profile of the samples. Therefore, the appropriate materials should be employed for the sample-base and the electrodes in the different experiments. Similar problems occur when a thermoelectric element is set into an instrument. We measured the thermal resistances of the interfaces on various conditions from room temperature to 50 K. Furthermore, we separated the thermal resistances into two parts: those of the material itself and its pure interfaces.
SCOPUS ID：0035707126
Relation between impedance distribution and current imbalance in an insulated multi-strand superconducting cable conductorAkira Ninomiya; Takeshi Ishigohka; Satarou Yamaguchi; Keiji Nakamura; Toshiharu Sato; Satoshi Hanai; Yasuhiro Hasegawa; Haruhiko Okumura; Sadatsugu Takayama; Ryuichi Shimada
IEEE Transactions on Applied Superconductivity,
巻：11,
開始ページ：1466,
終了ページ：1469, 2001年03月
We have been investigating the current imbalance problem comparing the calculated result obtained by the measurement of inductance distribution in multi-strand superconducting cable conductor using high accuracy LCR meter and the measured actual current distribution in it. So far, the measurement of inductance and that of actual current had been carried out at 1kHz and at few Hz, respectively. As a result, the experimental result did not agree well with the calculated one. It was estimated that the discrepancy between both results was due to the error in the inductance measurement. So, this time, we have carried out inductance measurement more precisely at 100Hz. And, we have also measured actual current at wider frequency range. From these results, it is concluded that the current distribution is very sensitive to the inductance distribution. Particularly, in multi-stranded conductors with higher magnetic coupling among the strands, such as a large scale and multi twisted cable conductor, the current distribution shows a very dynamic change with the frequency.
DOI：https://doi.org/10.1109/77.920049DOI ID：10.1109/77.920049,
ISSN：1051-8223,
SCOPUS ID：17844374322 Bismuth-tellurium alloy for Peltier current lead
S Yamaguchi; K Nakamura; Y Hasegawa; H Okumura; K Sato
PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II, 開始ページ：2173, 終了ページ：2176, 2001年, ［査読有り］
Superconductivity is non-dissipative system originally because of zero resistance, however, we should spend electric power to keep low temperature. Therefore, beat leak should be reduced as possible as we can to realize the superconducting system as an actual system Peltier current lead (PCL) was proposed to reduce beat leak from the electric circuit for superconducting low temperature system. PCL is composed of thermoelectric materials, metal leads and high temperature superconducting leads. The thermoelectric material is based on bismuth-tellurium alloy in the present design, and this is set at the room temperature side. Optimum design of the PCL is derived to solve a heat leak equation, and depends on the transport parameters, thermal conductivity, electric resistivity and Seebeck coefficient. Cold-end temperature of the thermoelectric material is calculated to be around 200 K by using the parameters of the market materials of bismuth-tellurium alloy. The experiment has been done and the principle was proven by the experiment We also measured the temperature dependence of the transport parameters of the materials. Finally, we propose two-stage PCL in this paper.
JAPAN INST METALS, 英語, 研究論文（国際会議プロシーディングス）
Web of Science ID：WOS:000178391600551
Effect of impedance distributions on current imbalance in insulated multi-stranded superconducting conductorT Ishigohka; A Ninomiya; S Yamaguchi; Nomura, I; T Sato; S Hanai; Y Hasegawa; H Okumura; R Shimada
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY,
巻：10,
号：1,
開始ページ：1216,
終了ページ：1219, 2000年03月
We have been investigating a current imbalance in multi-strand cable conductor using several types of solenoid coils wound by insulated multi-stranded copper cable, and obtained a result that the current distribution in the multi-stranded conductor is strongly affected by the magnetic coupling coefficient between strands. This time, we have carried out an experiment to investigate the current imbalance problem using a superconducting cable conductor. The main purpose of this investigation is to make clear the relation between the current imbalance and the impedance distributions among the strands. The experiment was carried out on (1) DC test, and (2) AC test. The calculation results show that the resistance component becomes dominant in the frequency region lower than 0.1 Hz. On the other hand, inductance component becomes dominant in the frequency region higher than 1Hz. For the experimental results lower than 1Hz, the amplitude and the phase characteristics of the current in each strand coincide well with the calculated results based on the measured resistance and impedance distribution. From these results, it can be concluded that a precise impedance measurement utilizing high accuracy LCR meter can estimate the current imbalance in insulated multi-stranded superconducting cable conductor before actual superconducting operation.
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 英語, 研究論文（学術雑誌）
ISSN：1051-8223,
SCOPUS ID：33747602525,
Web of Science ID：WOS:000085950700284 New proposal of medium temperature thermoelectric conversion in power plant
N. Kondo; S. Yamaguchi; I. Nomura; Y. Hasegawa; T. Eura
International Conference on Thermoelectrics, ICT, Proceedings, 開始ページ：88, 終了ページ：91, 1999年12月
There exists a large amount of unused energy in power generation plants, such as condenser waste heat which accounts about 50% of plant thermal output. However, it consists of relatively low temperature energy, so it is difficult to generate electricity by the conventional water-steam cycle. In order to raise the efficiency, we have to install energy recovering system to heat exchangers which have high entropy production as the boiler and the feed water heaters instead of the condenser. A new concept of electricity generating system for the feed water heater has been proposed. In this concept, the total generation efficiency is improved by applying the medium temperature thermoelectric generation module into heat exchanging walls or tubes in the feed water heaters focusing on the reduction of the entropy production. The efficiency improvement of the proposed system is 1% and the allowed cost of the proposed system is proportional to the net increase of the electric power.
ISSN：1094-2734, SCOPUS ID：0033298451
Computational model of thermoelectric and thermomagnetic semiconductors
H. Okumura; Y. Hasegawa; H. Nakamura; S. Yamaguchi
International Conference on Thermoelectrics, ICT, Proceedings, 開始ページ：209, 終了ページ：212, 1999年12月
We present a theoretical and computational framework for calculating transport properties of thermoelectric and thermomagnetic semiconductors and relating them to measurements. Assuming a multiple-band model with generally nonparabolic band structures, we numerically integrate the Boltzmann equation with a relaxation time approximation to obtain the electric conductivity and the Hall, Seebeck, Nernst, and Righi-Leduc coefficients under magnetic fields. These `bare' (microscopic) transport coefficients are used to calculate quantities that can be compared with measurements by numerically solving macroscopic differential equations in two dimensions with appropriate boundary conditions. It is shown that, for finite-geometry samples, there is considerable coupling between thermoelectric and thermomagnetic effects, which can make the magnetic-field dependence profile of measured values quite different from that of bare values.
ISSN：1094-2734, SCOPUS ID：0033299890
Real Time Boroniqation Experiments in CHS and Scaling for LHD A.Sagara; Y.Hasegawa; K.Tsuzuki; N.Inoue; H.Suzuki; T.Morisaki; N.Noda; O.Motojima; K.Matsuoka; R.Akiyama; K.Ida; H.Idei; K.Iwasaki; S.Kubo; T.Minami; S.Morita; K.Narihara; T.Ozaki; K.Sato; C.Takahashi; K.Tanaka; K.Toi; I.Yamada
Journal of Nuclear Materials,
巻：241/243,
開始ページ：972,
終了ページ：976, 1997年,
［査読有り］英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1016/S0022-3115(96)00642-3DOI ID：10.1016/S0022-3115(96)00642-3,
ISSN：0022-3115,
CiNii Articles ID：30002371622 Control of discharge conditions to reduce hydrogen content in boron films coating M Natsir; A Sagara; K Tsuzuki; B Tsuchiya; Y Hasegawa; O Motojima
VACUUM,
巻：47,
号：6-8,
開始ページ：997,
終了ページ：999, 1996年06月,
［査読有り］Boronization at near room temperature has been performed in plasma processing teststand (PPT) by using a 5% diborane gases B2H6 in He on electrically floating or cathode potential Al samples under various DC glow discharge conditions as a function of power or total gas pressure. The hydrogen concentration was analyzed by using elastic recoil defection method (ERD) and a new modified normalizing technique with Rutherford back scattering (RBS). Results showed that a high growth rate of film formation and floating surface were effective in reducing hydrogen concentration in B films. This result was in good agreement with earlier measurements of H with flash filament (FF) desorption method. In particular it was presumed from the experiments that the H/B ratio was reduced by decreasing energetic ions but increasing radicals for B film formation. Copyright (C) 1996 Published by Elsevier Science Ltd.
PERGAMON-ELSEVIER SCIENCE LTD, 英語, 研究論文（学術雑誌）
DOI：https://doi.org/10.1016/0042-207X(96)00110-8DOI ID：10.1016/0042-207X(96)00110-8,
ISSN：0042-207X,
Web of Science ID：WOS:A1996UV26200114
バルク熱電材料のゼーベック係数・抵抗率・熱拡散率の同時測定
本間亮英; 寺門宏樹; 長谷川靖洋; 村田正行; 山本淳; 小峰啓史; 森田寛之
応用物理学会春季学術講演会講演予稿集(CD-ROM), 巻：62nd, 2015年
ISSN：2436-7613, J-Global ID：201502201739113770
焼結法により作製したBi-Sb合金の磁場中の熱電物性
村田正行; 山本淳; 長谷川靖洋; 小峰啓史
応用物理学会春季学術講演会講演予稿集(CD-ROM), 巻：62nd, 2015年
ISSN：2436-7613, J-Global ID：201502214783666234
石英ガラスを利用したBiナノワイヤーの作製と熱電物性の評価
村田正行; 山本淳; 長谷川靖洋; 小峰啓史
日本機械学会マイクロ・ナノ工学シンポジウム講演論文集(CD-ROM), 巻：6th, 2014年
ISSN：2432-9495, J-Global ID：201502234799079089
直径700nm Biナノワイヤーのホール係数測定とキャリア移動度評価
村田正行; 山本淳; 長谷川靖洋; 小峰啓史
応用物理学会秋季学術講演会講演予稿集(CD-ROM), 巻：75th, 2014年
ISSN：2758-4704, J-Global ID：201402204249733225
Bi-Sb系バルク材料の作製と熱電物性の評価
村田正行; 山本淳; 長谷川靖洋; 小峰啓史
応用物理学会秋季学術講演会講演予稿集(CD-ROM), 巻：75th, 2014年
ISSN：2758-4704, J-Global ID：201402235556616352
23aTL-2 単結晶ビスマスナノワイヤーのShubnikov-de Haas振動(23aTL 量子ホール効果(整数量子ホール効果),領域4(半導体,メゾスコピック系・局在))
常見 文昭; 村田 正行; 長谷川 靖洋; 小峰 啓史; 遠藤 彰
日本物理学会講演概要集, 巻：66, 号：2, 開始ページ：687, 終了ページ：687, 2011年08月24日
一般社団法人日本物理学会, 日本語
ISSN：1342-8349, CiNii Articles ID：110008759757, CiNii Books ID：AA11439205
25pHG-15 電流加熱時の磁場中極低温2次元電子系の冷却効果(25pHG 量子ホール効果(整数量子ホール効果),領域4(半導体,メゾスコピック系・局在))
平山 尚美; 遠藤 彰; 藤田 和博; 長谷川 靖洋; 羽田野 直道; 中村 浩章; 白崎 良演; 米満 賢治
日本物理学会講演概要集, 巻：66, 号：1, 開始ページ：704, 終了ページ：704, 2011年
一般社団法人 日本物理学会, 日本語
DOI ID：10.11316/jpsgaiyo.66.1.4.0_704_2, ISSN：1342-8349, J-Global ID：201102228594893914, CiNii Articles ID：110008714789, CiNii Books ID：AA11439205
23aTL-3 ビスマスナノワイヤーの量子化磁場下での熱電特性の理論計算(23aTL 量子ホール効果(整数量子ホール効果),領域4(半導体,メゾスコピック系・局在))
平山 尚美; 遠藤 彰; 藤田 和博; 長谷川 靖洋; 羽田野 直道; 中村 浩章; 白崎 良演; 米満 賢治
日本物理学会講演概要集, 巻：66, 号：2, 開始ページ：688, 終了ページ：688, 2011年
一般社団法人 日本物理学会, 日本語
DOI ID：10.11316/jpsgaiyo.66.2.4.0_688_1, ISSN：1342-8349, J-Global ID：201102252418028059, CiNii Articles ID：110008759758, CiNii Books ID：AA11439205
熱電材料の磁場効果
小峰 啓史; 長谷川 靖洋; 中村 浩章
日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan, 巻：173, 開始ページ：19, 終了ページ：25, 2010年08月03日
日本磁気学会, 日本語
ISSN：1882-2940, CiNii Articles ID：10026602073, CiNii Books ID：AA12326521
電流加熱時の磁場中極低温2次元電子系の温度分布と電位分布 平山尚美; 遠藤彰; 藤田和博; 長谷川靖洋; 羽田野直道; 中村浩章; 白崎良演
日本物理学会講演概要集,
巻：65,
号：2,
開始ページ：661,
終了ページ：661, 2010年
一般社団法人 日本物理学会, 日本語
DOI：https://doi.org/10.11316/jpsgaiyo.65.2.4.0_661_1DOI ID：10.11316/jpsgaiyo.65.2.4.0_661_1,
ISSN：1342-8349,
J-Global ID：201002231735405416,
CiNii Articles ID：110008098952 Mean free path limitation of thermoelectric properties of bismuth nanowire Masayuki Murata; Daiki Nakamura; Yasuhiro Hasegawa; Takashi Komine; Takashi Taguchi; Shinichiro Nakamura; Christopher M. Jaworski; Vladimir Jovovic; Joseph P. Heremans
巻：105,
号：11,
開始ページ：113706, 2009年06月
A limiting mean free path was considered in order to better understand the temperature and wire diameter dependence of the resistivity and Seebeck coefficient of bismuth microwire and nanowire samples. The mean free path limited mobility was numerically calculated from experimentally measured mobility in a bulk bismuth sample, and the electron and hole mobilities were dramatically decreased to a 10 mu m mean free path. Therefore, the temperature dependence of resistivity in very thin wire was quite different from that of a bulk sample, which had a positive temperature coefficient. The calculations showed that the temperature coefficient decreased gradually with decreasing mean free path, and the coefficient became negative for a mean free path of less than 1 mu m at about 150 K. The Seebeck coefficient was also calculated, but showed only a weak dependence on mean free path compared with the resistivity. Experimental comparisons were made to previous measurements of bismuth microwire or nanowire samples, and the temperature and wire diameter dependencies of the resistivity and Seebeck coefficient were qualitatively and quantitatively in very good agreement. Therefore, the temperature dependencies of nanowire samples over 850 nm in diameter were well described using the mean free path limitation. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3131842]
英語
DOI：https://doi.org/10.1063/1.3131842DOI ID：10.1063/1.3131842,
ISSN：0021-8979,
CiNii Articles ID：80020439521,
Web of Science ID：WOS:000267053200072 28pTX-5 ビスマスの量子ネルンスト効果 : 電子・ホール共存とフォノンドラッグの寄与(28pTX 量子ホール効果,領域4(半導体,メゾスコピック系・局在))
松尾 まり; 遠藤 彰; 白崎 良演; 杉原 硬; 中村 浩章; 長谷川 靖洋; 羽田野 直道
日本物理学会講演概要集, 巻：64, 号：1, 開始ページ：702, 終了ページ：702, 2009年03月03日
一般社団法人日本物理学会, 日本語
ISSN：1342-8349, CiNii Articles ID：110007372346, CiNii Books ID：AA11439205
Influence of the band structure of BiSb alloy on the magneto-Seebeck coefficient Takayuki Teramoto; Takashi Komine; Shinji Yamamoto; Masahiro Kuraishi; Ryuji Sugita; Yasuhiro Hasegawa; Hiroaki Nakamura
巻：104,
号：5,
開始ページ：053714, 2008年09月
The influence of the band structure of BiSb alloys on the magneto-Seebeck coefficient was estimated by the Boltzmann equation using an energy-dependent relaxation time approximation at 100 K. The magneto-Seebeck coefficient along the trigonal direction was calculated under a magnetic field along the bisectrix direction. The scattering factor was supposed as being an acoustic deformation potential scattering. In order to estimate the influence of band structure on the magneto-Seebeck coefficient, both two band and three band models were utilized. The two band model consists of an electron surface at the L-point and a hole surface at the T-point. The influence of the change in band overlap and the effective electron mass was investigated using the two band model. The three band model consists of an electron surface at the L-point and a hole surface at the T-point. The influence of change in the Sb concentration of BiSb alloy was also investigated using the three band model. As a result, the Seebeck coefficient was observed to increase as the band overlap decreased. The band overlap has little influence on the improvement of the magneto-Seebeck coefficient. The Seebeck coefficient decreases as the effective mass decreases; however, improvement in the magneto-Seebeck coefficient increases as the effective mass decreases. The magneto-Seebeck coefficient of Bi(95)Sb(5) was effectively improved under a low maonetic field. (C) 2008 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.2975387DOI ID：10.1063/1.2975387,
ISSN：0021-8979,
eISSN：1089-7550,
CiNii Articles ID：80019908829,
Web of Science ID：WOS:000259853600068 Evaluation of Thermoelectric Properties in Bi-Microwires by the Harman Method Hideo Iwasaki; Hiroyuki Morita; Yasuhiro Hasegawa
巻：47,
号：5,
開始ページ：3576,
終了ページ：3580, 2008年05月
We have improved the Harman method to evaluate all thermoelectric properties related to the figure of merit, ZT, not only in bulk materials but also in mesoscopic ones. By this method, the ZT of single microwires can also be determined. The minimum sample size is currently similar to 0.25 mm in length and similar to 10 mu m in diameter. The fabrication of our equipment based on the Harman method is described in detail. The enhancement of ZT can be achieved in the Bi-microwire array because of the homogeneous arrangement of the crystal orientation in each microwire. The results obtained in the Bi-microwire arrays are consistent with ZT behavior in the single microwires extracted from the arrays. [DOI: 10.1143/JJAP.47.3576]
英語
DOI：https://doi.org/10.1143/JJAP.47.3576DOI ID：10.1143/JJAP.47.3576,
ISSN：0021-4922,
Web of Science ID：WOS:000256462500058 Numerical analysis of the magneto-Seebeck effect of bismuth with anisotropic band structure Takayuki Teramoto; Takashi Komine; Masahiro Kuraishi; Ryuji Sugita; Yasuhiro Hasegawa; Hiroaki Nakamura
巻：103,
号：4,
開始ページ：043717, 2008年02月
We studied the influence of band structure on the Seebeck coefficient of bismuth under a magnetic field. In this study, the magneto-Seebeck coefficient was calculated by solving the Boltzmann equation with an energy-dependent relaxation-time approximation and by assuming the Lax model of the bismuth band structure, which contains the anisotropy of bismuth. The influence of the scattering factor on the magneto-Seebeck effect was also investigated in the anisotropic band structure. The magneto-Seebeck coefficient varies with the magnetic field direction. Improvement of the Seebeck coefficient under a transverse magnetic field is higher than that under a longitudinal magnetic field. For the acoustic deformation potential scattering, the Seebeck coefficient is improved in a low magnetic field. For other types of scattering, the absolute values of the Seebeck coefficient are decreased in the low magnetic field. Moreover, for scattering factor r of 0, the magneto-Seebeck coefficient for a parabolic band does not vary, while the magneto-Seebeck coefficient for a nonparabolic band decreases. The sign of the Seebeck coefficient was changed under a high magnetic field because of the increase in magnetoresistivity due to high electron mobility. The effect of impurity addition was also investigated by changing the Fermi energy. With increasing Fermi energy, the Seebeck coefficient is more easily affected by an applied magnetic field, because the electron density is increased.
英語
DOI：https://doi.org/10.1063/1.2840060DOI ID：10.1063/1.2840060,
ISSN：0021-8979,
eISSN：1089-7550,
CiNii Articles ID：80019378975,
Web of Science ID：WOS:000254191300039 20aYF-12 量子ホール系における拡散熱電能の測定(20aYF 量子ドット・量子ホール効果,領域4(半導体,メゾスコピック系・局在)) 藤田 和博; 家 泰弘; 遠藤 彰; 白崎 良演; 杉原 硬; 中村 浩章; 長谷川 靖洋; 羽田野 直道; 松尾 まり; 勝本 信吾
日本物理学会講演概要集,
巻：63,
号：0,
開始ページ：585,
終了ページ：585, 2008年
一般社団法人 日本物理学会, 日本語
DOI：https://doi.org/10.11316/jpsgaiyo.63.2.4.0_585_3DOI ID：10.11316/jpsgaiyo.63.2.4.0_585_3,
CiNii Articles ID：110006984665 量子効果を期待したナノワイヤー構造熱電変換素子の特性評価
長谷川靖洋
総合研究機構研究プロジェクト研究成果報告書, 巻：6 (平成19年度), 2008年
量子効果を期待したナノワイヤー構造熱電変換素子の特性評価
長谷川靖洋
巻：6 (平成19年度), 2008年
Power factor enhancement in a magnetic field using polycrystalline bismuth microwire arrays Yasuhiro Hasegawa; Hirofumi Nakano; Hiroyuki Morita; Takashi Komine; Haruhiko Okumura; Hiroaki Nakamura
巻：102,
号：7,
開始ページ：073701, 2007年10月
Measurements of the magneto-Seebeck coefficient and magnetoresistivity of two bismuth microwire arrays having different diameters and a bulk sample were performed for applied magnetic fields between 0 and 2 T and temperatures between 50 and 300 K. The magneto-Seebeck coefficients were always enhanced as a result of controlling the phonon scattering process and the magnetoresistivity also invariably increased. The power factors in an applied magnetic field were estimated, and the power factors of the microwire arrays were found to be enhanced over the whole measurement range. By contrast, the power factor of the bulk sample was not enhanced at temperatures under 200 K. The difference in the responses of the bulk sample and the microwire arrays is strongly related to suppression of the magnetoresistivity; the suppression ratios of the magnetoresistivity of the bulk sample, which has a low aspect ratio, are smaller than those of the microwire arrays. It was experimentally demonstrated that there is an optimum magnetic field that maximizes the power factor and that the enhancement ratio of the power factor is much greater for structures that have a high aspect ratio, such as microwire arrays. This suggests that microwire arrays are suitable for enhancing the power factor by applying a magnetic field. (C) 2007 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.2785003DOI ID：10.1063/1.2785003,
ISSN：0021-8979,
eISSN：1089-7550,
CiNii Articles ID：80018073828,
Web of Science ID：WOS:000250147700059 Aspect ratio dependence of magnetoresistivity in polycrystalline bismuth microwire arrays Yasuhiro Hasegawa; Hirofumi Nakano; Hiroyuki Morita; Akio Kurokouchi; Kentarou Wada; Takashi Komine; Hiroaki Nakamura
巻：101,
号：3,
開始ページ：033704 1-5, 2007年02月
Magnetoresistivity measurements of polycrystalline bismuth microwire arrays having a range of different diameters and a bulk sample were performed under applied magnetic fields between 0 and 2 T and temperatures from 50 to 300 K. A thin film layer was deposited on the terminations of the microwire arrays in order to completely eliminate contact resistance. The measured resistivities were in very good agreement with those of polycrystalline bulk bismuth over the entire measured temperature range, even when the resistances had different values. The magnetoresistivities increased when a magnetic field was applied, and the rate of increase of the magnetoresistivities with applied magnetic field varied in samples having different aspect ratios. It was conjectured that this variation in the rate of increase is related to the aspect ratio. Suppression of magnetoresistivity in the microwire arrays was confirmed experimentally using bulk bismuth since the aspect ratio of the microwire arrays was much larger than that of the bulk sample. The geometrical contribution of the high aspect ratio on the magnetic effect in microwire and nanowire arrays makes it possible to enhance the thermoelectric performance of materials by suppressing the magnetoresistivity and increasing the magneto-Seebeck coefficient. (c) 2007 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.2432876DOI ID：10.1063/1.2432876,
ISSN：0021-8979,
Web of Science ID：WOS:000244250100085 Biナノワイヤー熱電素子の開発
長谷川靖洋; 中野博文; 神戸勇貴; 森田寛之; 小峰啓史; 中村浩章
応用物理学関係連合講演会講演予稿集, 巻：54th, 号：1, 2007年
J-Global ID：200902220150253928
BiSb合金のバンド構造が磁気ゼーベック係数に与える影響
寺本貴之; 山本真司; 倉石正寛; 小峰啓史; 長谷川靖洋; 中村浩章; 杉田龍二
応用物理学関係連合講演会講演予稿集, 巻：54th, 号：1, 2007年
J-Global ID：200902261752004870
ナノワイヤーアレイ構造熱電変換素子開発に向けた基盤整備
長谷川靖洋
総合研究機構研究プロジェクト研究成果報告書, 巻：5 (平成18年度), 開始ページ：155, 終了ページ：156, 2007年
ナノワイヤーアレイ構造熱電変換素子開発に向けた基盤整備
長谷川靖洋
巻：5 (平成18年度), 開始ページ：155, 終了ページ：156, 2007年
熱電材料の磁場効果
小峰 啓史; 長谷川 靖洋; 中村 浩章
まぐね = Magnetics Japan, 巻：1, 号：10, 開始ページ：476, 終了ページ：481, 2006年10月01日
日本応用磁気学会, 日本語
ISSN：1880-7208, CiNii Articles ID：10018781304, CiNii Books ID：AA1211610X
熱電材料の磁場効果
小峰啓史; 長谷川靖洋; 中村浩章
まぐね, 巻：10, 号：1, 開始ページ：476-481, 2006年10月01日
熱電材料の磁場効果及び磁場効果を有効に引き出すためのマイクロワイヤーアレイ素子について解説した．また，低温域で予想される量子ネルンスト効果を紹介した．
日本語, 記事・総説・解説・論説等（学術雑誌）
A method for analysis of carrier density and mobility in polycrystalline bismuth Y Hasegawa; Y Ishikawa; T Saso; H Shirai; H Morita; T Komine; H Nakamura
巻：382,
号：1-2,
開始ページ：140,
終了ページ：146, 2006年06月
Carrier densities and mobilities in polycrystalline bismuth contaminated with 0.01 at% tin are determined by measurement of various electronic transport parameters in low magnetic fields from 50 to 300 K. The parameters measured include the Seebeck coefficient, resistivity, magneto-resistance and Hall coefficient. The present sample exhibits the temperature-dependent variations in electron carrier density seen for single-crystal bismuth. However, due to tin contamination of 0.01 at%, the hole carrier density is invariant below 150 K. The mobilities are somewhat lower due to boundary scattering, with the reduction in electron mobility being prominent. The proposed method allows the temperature dependences to be determined reliably even in the presence of contamination, and represents a useful technique for the analysis of carrier densities and mobilities in high-mobility materials under low magnetic fields. (c) 2006 Elsevier B.V. All rights reserved.
英語
DOI：https://doi.org/10.1016/j.physb.2006.02.011DOI ID：10.1016/j.physb.2006.02.011,
ISSN：0921-4526,
CiNii Articles ID：80018993197,
Web of Science ID：WOS:000238780100024 Biマイクロワイヤーアレイ素子の抵抗率及びゼーベック係数の計測<論文>石川最朗; 長谷川靖洋
埼玉大学紀要, 工学部, 第1部論文集,
巻：39,
開始ページ：81,
終了ページ：85, 2006年
The resistivity and Seebeck coefficient of a bismuth microwire array (wire diameter: 25μm) were successfully measured from 25 to 300 K. To eliminate the influence of the contact resistance between the wire edges of the microwire array and copper electrodes, the titanium (100 nm) /copper (500 nm) film layers were deposited as interlayer on the wire edge by ion plating method. Copper electrodes were glued by using Pb-Sn solder. The resistivity and the Seebeck coefficient at 300K were approximately 1.8μΩm and -54 μV/K, respectively. The value of the resistivity and the Seebeck coefficient were in good agreement with those of bulk polycrystalline bismuth reported previously. Thus, the effects of the contact resistance for the microwire array were almost resolved, and the chemical reaction of the Pb-Sn solder and bismuth was prevented by using the thin film layer. The technique is expected to be applicable to nanowire arrays as well.
埼玉大学工学部, 日本語
ISSN：1880-4446,
CiNii Articles ID：120001370428 ペルチェ効果を用いたCPU冷却用薄膜の開発
長谷川靖洋
総合研究機構研究プロジェクト研究成果報告書, 巻：4 (平成17年度), 2006年
Biマイクロワイヤーアレイ素子の抵抗率及びゼーベック係数の計測<論文>石川 最朗; 長谷川 靖洋
埼玉大学紀要. 工学部 第1編 第1部 論文集,
巻：39,
開始ページ：81,
終了ページ：85, 2006年
The resistivity and Seebeck coefficient of a bismuth microwire array (wire diameter: 25μm) were successfully measured from 25 to 300 K. To eliminate the influence of the contact resistance between the wire edges of the microwire array and copper electrodes, the titanium (100 nm) /copper (500 nm) film layers were deposited as interlayer on the wire edge by ion plating method. Copper electrodes were glued by using Pb-Sn solder. The resistivity and the Seebeck coefficient at 300K were approximately 1.8μΩm and -54 μV/K, respectively. The value of the resistivity and the Seebeck coefficient were in good agreement with those of bulk polycrystalline bismuth reported previously. Thus, the effects of the contact resistance for the microwire array were almost resolved, and the chemical reaction of the Pb-Sn solder and bismuth was prevented by using the thin film layer. The technique is expected to be applicable to nanowire arrays as well.
埼玉大学工学部, 日本語
ISSN：1880-4446,
CiNii Articles ID：120001370428 ペルチェ効果を用いたCPU冷却用薄膜の開発
長谷川靖洋
巻：4 (平成17年度), 2006年
Reduction of contact resistance at terminations of bismuth wire arrays Y Hasegawa; Y Ishikawa; H Shirai; H Morita; A Kurokouchi; K Wada; T Komine; H Nakamura
巻：76,
号：11,
開始ページ：113902 1-4, 2005年11月
Contact resistance at the terminations of bismuth wire arrays of 25-mu m diam is reduced by ion plating of a titanium interlayer 100 nm upon the wire ends. One-thousand (1000)-nm-thick copper electrodes are ion plated upon the titanium. Copper probe electrodes are then attached using Pb-Sn solder. The temperature dependences of the Seebeck coefficient and resistance are measured upon heating from 25 to 300 K and the results compared with those for the polycrystalline bulk bismuth sample. The resistivity of the microwire array is found to be 1.37 mu Omega m at 300 K. Based on the similarities between the temperature dependences of resistivity and Seebeck coefficient for the wire and bulk samples, contact resistance of the wires is considered to have been completely eliminated. This technique makes it possible to simultaneously estimate the resistivity and Seebeck coefficient for nanowire arrays of thermoelectric materials. (c) 2005 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.2126952DOI ID：10.1063/1.2126952,
ISSN：0034-6748,
Web of Science ID：WOS:000233569800029 Resistivity and Seebeck coefficient measurements of a bismuth microwire array Y Ishikawa; Y Hasegawa; H Morita; A Kurokouchi; K Wada; T Komine; H Nakamura
巻：368,
号：1-4,
開始ページ：163,
終了ページ：167, 2005年11月
The resistivity and Seebeck coefficient of a bismuth microwire array (wire diameter: 25 mu m) were successfully measured from 25 to 300 K. To eliminate the influence of the contact resistance between the wire edges of the microwire array and copper electrodes, the titanium (100 nm)/copper (500 nm) film layers were deposited as interlayer on the wire edge by ion plating method. Copper electrodes were glued by using Pb-Sn solder. The resistivity and the Seebeck coefficient at 300K were approximately 1.8 X 10-6 Omega m and -54 x 10(-6) V/K, respectively. The value of the resistivity and the Seebeck coefficient were in good agreement with those of bulk polycrystalline bismuth reported previously. Thus, the effects of the contact resistance for the microwire array were almost resolved, and the chemical reaction of the Pb-Sn solder and bismuth was prevented by using the thin-film layer. The technique is expected to be applicable to nanowire arrays as well. (c) 2005 Elsevier B.V. All rights reserved.
英語
DOI：https://doi.org/10.1016/j.physb.2005.07.012DOI ID：10.1016/j.physb.2005.07.012,
ISSN：0921-4526,
CiNii Articles ID：80017621253,
Web of Science ID：WOS:000232959400025 Micromagnetic analysis of a magnetic domain wall in 2-D and 3-D nanocontacts T Komine; T Takahashi; S Ishii; R Sugita; T Muranoi; Y Hasegawa
巻：41,
号：10,
開始ページ：2586,
終了ページ：2588, 2005年10月
We have performed micromagnetic calculations of magnetic domain walls in two-dimensional (2-D) and three-dimensional (3-D) nanocontacts and estimate the domain wall widths. The magnetic domain wall in a 3-D nanocontact is smaller than that in a 2-D nanocontact due to the larger magnetic volume available to pin the magnetization in the antiparallel configuration of the electrodes. Therefore, 3-D nanocontacts are more suitable than 2-D nanocontacts for domain wall confinement and large magnetoresistance effects.
英語
DOI：https://doi.org/10.1109/TMAG.2005.854753DOI ID：10.1109/TMAG.2005.854753,
ISSN：0018-9464,
eISSN：1941-0069,
CiNii Articles ID：80017742894,
Web of Science ID：WOS:000232679700010 Micromagnetic calculation of the magnetization process in nanocontacts Takashi Komine; Tomohiro Takahashi; Ryuji Sugita; Tetsuo Muranoi; Yasuhiro Hasegawa
巻：97,
号：10,
開始ページ：10C508 1-3, 2005年05月15日
We report herein the micromagnetic calculations of the magnetic domain walls in nanoconstrictions of various shapes for H -shaped samples and estimate the domain wall widths. The length and width of the nanoconstriction and the exchange stiffness constant in the nanoconstriction was varied for each case. In the case of a uniform exchange stiffness constant at the nanoconstriction, the domain wall width depends on the length and width of the nanoconstriction. Each domain wall width D calculated herein is longer than the constriction length L, and the exchange stiffness constant is 1.05×10-6 ergcm. The small exchange stiffness at the nanoconstriction leads to the small domain wall width. These results imply the possibility of the large domain wall scattering only for nanoconstrictions with a small effective exchange coupling between the two magnetic materials. © 2005 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.1850856DOI ID：10.1063/1.1850856,
ISSN：0021-8979,
SCOPUS ID：20944451577 Micromagnetic calculation of the magnetization process in nanocontacts T Komine; T Takahashi; R Sugita; T Muranoi; Y Hasegawa
巻：97,
号：10,
開始ページ：10C508 1-3, 2005年05月
We report herein the micromagnetic calculations of the magnetic domain walls in nanoconstrictions of various shapes for H-shaped samples and estimate the domain wall widths. The length and width of the nanoconstriction and the exchange stiffness constant in the nanoconstriction was varied for each case. In the case of a uniform exchange stiffness constant at the nanoconstriction, the domain wall width depends on the length and width of the nanoconstriction. Each domain wall width D calculated herein is longer than the constriction length L, and the exchange stiffness constant is 1.05 X 10(-6) erg/cm. The small exchange stiffness at the nanoconstriction leads to the small domain wall width. These results imply the possibility of the large domain wall scattering only for nanoconstrictions with a small effective exchange coupling between the two magnetic materials. (c) 2005 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.1850856DOI ID：10.1063/1.1850856,
ISSN：0021-8979,
eISSN：1089-7550,
Web of Science ID：WOS:000230168300142 Investigation of physical and electric properties of silver pastes as a binder for thermoelectric materials A Suzuki; Y Hasegawa; Y Ishikawa; T Komine; H Morita; H Shirai
巻：76,
号：2,
開始ページ：023907 1-5, 2005年02月
The physical and electric properties of several silver pastes, Pb-Sn solder, and indium were systematically investigated as potential binders for attaching electrodes to bismuth-based bulk or nanowire array thermoelectric elements. Scanning electron microscopy observations and x-ray diffraction surface measurements of the silver pastes were performed and the temperature and magnetic field dependence of the resistance were measured to characterize their electrical properties from 300 K down to 15 K and from 0 to 1 T at 15 K, respectively. The silver pastes were not reactive with bismuth and hence were found to be potentially useful as electrically conductive adhesives with bismuth-based materials. The properties of each of the binders were quite different; the typical size of the particles in the silver pastes before solidification were distributed in the range from 3 nm to 20 mum, and the size strongly affected the resistances of the silver pastes, which were distributed over 2 and 3 orders of magnitude at 300 and 15 K, respectively. Therefore, an appropriate selection of binder must be made for a specific purpose, based on the measurement results. For use with bismuth-based thermoelectric materials, the silver nanopaste is a strong candidate binder because it is far superior to other the binders examined in terms of its resistance properties and magnetic field dependence. (C) 2005 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.1844691DOI ID：10.1063/1.1844691,
ISSN：0034-6748,
Web of Science ID：WOS:000226738400040 マイクロワイヤー熱電素子の開発
長谷川靖洋; 石川最朗; 森田寛之; 小峰啓史; 中村浩章
応用物理学関係連合講演会講演予稿集, 巻：52nd, 2005年
J-Global ID：200902248261964833
磁場中におけるマイクロワイヤーアレイ素子の熱電特性の計測
石川最朗; 長谷川靖洋; 小峰啓史; 森田寛之; 中村浩章
応用物理学関係連合講演会講演予稿集, 巻：52nd, 号：1, 2005年
J-Global ID：200902248976231833
実効的な磁気ゼーベック係数に及ぼす形状効果の数値解析
小峰啓史; 長谷川靖洋; 石川最朗; 森田寛之; 中村浩章; 杉田龍二; 村野井徹夫
応用物理学関係連合講演会講演予稿集, 巻：52nd, 号：1, 2005年
J-Global ID：200902274582409905
Electronic transport properties of a bismuth microwire array in a magnetic field Y Hasegawa; Y Ishikawa; H Morita; T Komine; H Shirai; H Nakamura
巻：97,
号：8,
開始ページ：391,
終了ページ：394, 2005年
The magneto-Seebeck coefficient and magneto-resistivity of a polycrystalline bismuth microwire array were measured under magnetic fields of 0 to 2 Tesla and at temperatures of 50 to 300 K. To avoid the influence of contact resistance between the wire array and the electrodes, bulk bismuth was used for the electrodes. In the absence of a magnetic field, the Seebeck coefficient and resistivity were -76 mu V/K and 1.8 mu Omega m at 300 K, respectively. The rnagneto-Seebeck coefficient for the wire array increased with the application of an external magnetic field, attributable to the precise control of impurities and carrier scattering process in the fabrication of the wire array. The phonon drag effect was observed below 100 K, with a corresponding increase in the rnagneto-Seebeck coefficient under high magnetic fields. However, the magneto-resistivity was also raised under higher magnetic fields, detracting from the thermoelectric properties. Through analysis of the power factor, the optimum magnetic field was determined for each temperature, revealing a trend for the optimum magnetic field to increase with temperature. The power factor was improved by a maximum factor of 1.12, achieved at 200 K and 0.25 Tesla. Further improvements appear to be possible by eliminating the bulk bismuth employed for the electrodes.
英語
DOI：https://doi.org/10.1063/1.1865342DOI ID：10.1063/1.1865342,
Web of Science ID：WOS:000234650600096 強磁性ナノワイヤ構造の第一原理計算
高橋 朋広; 小峰 啓史; 杉田 龍二; 村野井 徹夫; 長谷川 靖洋
日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 巻：28, 開始ページ：136, 終了ページ：136, 2004年09月21日
日本語
CiNii Articles ID：10013769025, CiNii Books ID：AN10269644
磁性体ナノ接合の磁化過程
小峰 啓史; 長谷川 靖洋; 杉田 龍二; 村野井 徹夫
日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 巻：28, 開始ページ：147, 終了ページ：147, 2004年09月21日
日本語
CiNii Articles ID：10013769052, CiNii Books ID：AN10269644
磁性体を組み合わせた半導体磁気抵抗素子
高山 裕樹; 小峰 啓史; 杉田 龍二; 村野井 徹夫; 長谷川 靖洋
日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 巻：28, 開始ページ：247, 終了ページ：247, 2004年09月21日
日本語
CiNii Articles ID：10013769313, CiNii Books ID：AN10269644
Synthesis of novel p-type nanocrystalline Si prepared from SiH2Cl2 and SiCl4 for window layer of thin film Si solar cell Y Ikeda; T Ito; YL Li; M Yamazaki; Y Hasegawa; H Shirai
巻：43,
号：9A,
開始ページ：5960,
終了ページ：5966, 2004年09月
A novel p-type hydrogenated chlorinated nanocrystalline silicon (nc-Si:H:(Cl)) film was fabricated from chlorinated materials, i.e., SiH2Cl2 and SiCl4,by rf plasma-enhanced chemical vapor deposition. These p-type nc-Si:H:(Cl) films showed high conductivities of 10-50 S/cm under 3000-5000 ppm B2H6-mixing concentrations with lower optical absorption in the visible region, while maintaining a high film crystallinity. No marked darkening of the ZnO:Al layer was observed after deposition of the p-type nc-Si:H:(Cl) layer fabricated from SiH2Cl2 and SiCl4 compared to the p-type Si:H film fabricated from SiH4. The origin of the low optical absorption in p-type nc-Si:H:(Cl) is demonstrated along with the performance of a p-i-n structure amorphous silicon solar cell.
英語
DOI：https://doi.org/10.1143/JJAP.43.5960DOI ID：10.1143/JJAP.43.5960,
ISSN：0021-4922,
CiNii Articles ID：150000043804,
Web of Science ID：WOS:000224579000006 Magneto-Seebeck coefficient of a bismuth microwire array in a magnetic field Y Hasegawa; Y Ishikawa; T Komine; TE Huber; A Suzuki; H Morita; H Shirai
巻：85,
号：6,
開始ページ：917,
終了ページ：919, 2004年08月
The enhancement of the magneto-Seebeck coefficient of a bismuth microwire array under a magnetic field is measured at temperatures from 45 to 295 K. The measured magneto-Seebeck coefficient exhibits a peak at a certain magnitude of magnetic field, with the peak shifting to higher magnetic fields and becoming broader with increasing temperature. The results show that the magneto-Seebeck coefficient can be improved by approximately 20% by applying an appropriate external magnetic field and temperature. The Boltzmann equation with a relaxation-time approximation is solved numerically to determine the magnetic field and temperature dependences of the magneto-Seebeck coefficient for the bismuth microwire array. The experimental results are compared with calculations, and the two sets of results are shown to be in very good agreement, clarifying the mechanisms contributing to the magneto-Seebeck coefficient for bismuth. The wire array structure is thus suitable for enhancing the thermoelectric properties of materials in a magnetic field. (C) 2004 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.1781390DOI ID：10.1063/1.1781390,
ISSN：0003-6951,
eISSN：1077-3118,
CiNii Articles ID：80016841411,
Web of Science ID：WOS:000223109500022 Rf microplasma jet at atmospheric pressure: characterization and application to thin film processing T Kikuchi; Y Hasegawa; H Shirai
巻：37,
号：11,
開始ページ：1537,
終了ページ：1543, 2004年06月
A novel rf microplasma jet at atmospheric pressure was successfully generated using a single needle tube electrode. The atmospheric He discharge was characterized using optical emission spectroscopy with the inner hole diameter of the needle electrode and the flow rate of gas as variables. Preliminary results of the application of microplasma jets to thin film processing are given, i.e. silicon oxidation and the synthesis of carbon nanostructures including amorphous carbon, graphite, and nanotubes. A metal-oxide-semiconductor structure using the silicon oxidized layer formed by the O-2/He plasma showed good rectification behaviour. The effects of gas flow velocity and inner diameter of the needle tube electrode on the carbon nanostructure and deposition area are discussed.
This article was due to be published in Volume 36, issue 23 of Journal of Physics D: Applied Physics. To access this special issue please follow this link http://www.iop.org/EJ/toc/0022-3727/36/23.
英語
DOI：https://doi.org/10.1088/0022-3727/37/11/005DOI ID：10.1088/0022-3727/37/11/005,
ISSN：0022-3727,
CiNii Articles ID：80016728477,
Web of Science ID：WOS:000222582500006 Numerical calculation of magneto-seebeck coefficient of bismuth under a magnetic field Y Hasegawa; T Komine; Y Ishikawa; A Suzuki; H Shirai
巻：43,
号：1,
開始ページ：35,
終了ページ：42, 2004年01月
Seebeck and Nernst coefficients were numerically calculated by solving the Boltzmann equation with relaxation time approximation for bismuth under a magnetic field as functions of the products of cyclotron frequency (omega(c)) and relaxation time (tau(0)), taking into consideration the scattering process of carriers as a function of energy. The relationship between omega(c)tau(0) and magnitude of the magnetic field was derived from the definition of mobility, and each coefficient was estimated as a function of the magnetic field. The magneto-Seebeck coefficient was estimated by the addition of the Seebeck coefficient to the Nernst coefficient, and the contribution of thermoelectric effect in the presence of the magnetic field was dominant, being derived from the Seebeck effect. The magnetic field and temperature dependences of the magneto-Seebeck coefficient were evaluated by the use of a two-carrier model and mobility of single-crystal bismuth. The results show that the magneto-Seebeck coefficient can be improved by a factor of 1.3 to 1.4 in the presence of a magnetic field to control the scattering process of the carriers.
英語
DOI：https://doi.org/10.1143/JJAP.43.35DOI ID：10.1143/JJAP.43.35,
ISSN：0021-4922,
CiNii Articles ID：150000042210,
Web of Science ID：WOS:000220092400007 Peltier current lead experiment and their applications for superconducting magnets S Yamaguchi; T Yamaguchi; K Nakamura; Y Hasegawa; H Okumura; K Sato
巻：75,
号：1,
開始ページ：207,
終了ページ：212, 2004年01月
Many applications of superconductivity are studied because they are basically nondissipative systems; however, electric power is spent to keep them at low temperature. If heat leakage is high, the advantage of the superconductivity will be reduced or disappear, and therefore we must reduce the heat leakage as much as we can in the actual system. The Peltier current lead (PCL) was proposed to reduce heat leakage from the electric circuit of the superconducting magnet system. PCL is composed of thermoelectric semiconductors, metal leads, and high temperature superconducting (HTS) leads. Bismuth-tellurium alloys (BiTe) are used as the thermoelectric semiconductors in the experiment, and these are placed on the room temperature side. Optimum design of the PCL is conducted to solve a heat leakage equation, and depends on the transport parameters such as thermal conductivity, electric resistivity, and Seebeck coefficient of the materials of the PCL. The thermal conductivity of the BiTe is about 0.4% of the copper's, and we can expect the Peltier cooling by using this material. Therefore, we can expect the large temperature difference of the BiTe and reduce the heat leakage. The experiment has been done and the cold-end temperature of the thermoelectric BiTe is around 200 K both in the experiment and the numerical calculation. The temperature difference of 4 mm thickness of the BiTe exceeds 70 K for 150 A in both the experiment and the calculation. Therefore, the principle was proven in the experiments, and the reduction of the heat leakage is up to 35% for the current lead included in the HTS current lead. Here, we also mentioned and proposed the various types of the PCL for the different kinds of superconducting magnet systems in this article. (C) 2004 American Institute of Physics.
英語
DOI：https://doi.org/10.1063/1.1633987DOI ID：10.1063/1.1633987,
ISSN：0034-6748,
CiNii Articles ID：80016382541,
Web of Science ID：WOS:000187536500030 極性反転のためのペルチェ電流リード用低温切替えスイッチの検討
森口 正人; 水谷 進; 山口 貴行; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 松岡 良輔; 中村 圭二; 山口 作太郎; 池澤 俊治郎; 飯吉 厚夫; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦; 木村 誠宏
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：69, 開始ページ：210, 終了ページ：210, 2003年12月03日
日本語
ISSN：0919-5998, CiNii Articles ID：10013401274, CiNii Books ID：AA1195143X
ヘリウムフリーマグネットを模擬した真空中でのPCLの適用
水谷 進; 森口 正人; 山口 貴行; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 松岡 良輔; 中村 圭二; 山口 作太郎; 池澤 俊治郎; 飯吉 厚夫; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦; 木村 誠宏
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：69, 開始ページ：212, 終了ページ：212, 2003年12月03日
日本語
ISSN：0919-5998, CiNii Articles ID：10013401277, CiNii Books ID：AA1195143X
超電導コイルにおける偏流特性と鉄芯法によるその抑制 大瀧直浩; 中村圭二; 山口作太郎; 野村新一; 二ノ宮晃; 佐藤利和; 長谷川靖洋; 花井哲
電気学会論文誌B(電力・エネルギー部門誌),
巻：123,
号：6,
開始ページ：759,
終了ページ：764, 2003年
This paper describes characteristics of current imbalance in AC-operated superconducting coil and trial for its suppression with iron core method. Measurements of strand current in the frequency less than −1 Hz revealed that the current imbalance significantly occurred to the frequency increase, and that the critical frequency almost corresponds to a frequency where the coil leakage inductance is comparable to the coil resistive. Such a current imbalance was not seriously affected by ferromagnetic materials set in the coil. The iron core method was effective for suppression of the current imbalance, especially in the low frequency region, and inductance measurements suggested that the suppression effect was attributed to inductance compensation as well as reduction of effective electro-magnetic coupling between coil strands. © 2003, The Institute of Electrical Engineers of Japan. All rights reserved.
英語
DOI：https://doi.org/10.1541/ieejpes.123.759DOI ID：10.1541/ieejpes.123.759,
ISSN：1348-8147,
CiNii Articles ID：130000081175,
SCOPUS ID：85024455614 Characteristics of Current Imbalance on Superconducting Coils and Suppression with Iron Core Method Naohiro Ohtaki; Keiji Nakamura; Sataro Yamaguchi; Shin-ichi Nomura; Akira Ninomiya; Toshikazu Sato; Yasuhiro Hasegawa; Satoshi Hanai
巻：123,
号：6,
開始ページ：759,
終了ページ：764, 2003年
This paper describes characteristics of current imbalance in AC-operated superconducting coil and trial for its suppression with iron core method. Measurements of strand current in the frequency less than −1 Hz revealed that the current imbalance significantly occurred to the frequency increase, and that the critical frequency almost corresponds to a frequency where the coil leakage inductance is comparable to the coil resistive. Such a current imbalance was not seriously affected by ferromagnetic materials set in the coil. The iron core method was effective for suppression of the current imbalance, especially in the low frequency region, and inductance measurements suggested that the suppression effect was attributed to inductance compensation as well as reduction of effective electro-magnetic coupling between coil strands. © 2003, The Institute of Electrical Engineers of Japan. All rights reserved.
英語
DOI：https://doi.org/10.1541/ieejpes.123.759DOI ID：10.1541/ieejpes.123.759,
ISSN：1348-8147,
CiNii Articles ID：130000081175,
SCOPUS ID：85024455614 交流通電における液体窒素用ペルチェ電流リードの動作特性
森口正人; 山口作太郎; 飯吉厚夫; 佐藤利和; 長谷川靖洋; 二ノ宮晃; 石郷岡猛; 奥村晴彦; 浅野克彦
低温工学・超電導学会講演概要集, 巻：67th, 開始ページ：126, 2002年10月30日
日本語
ISSN：0919-5998, J-Global ID：200902184460704630, CiNii Articles ID：10013399840
数値計算による, 低熱侵入ペルチェ電流リードの特性評価
山口 貴行; 水谷 進; 森口 正人; 中村 圭二; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 山口 作太郎; 松岡 良輔; 池澤 俊治郎; 飯吉 厚夫; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：67, 開始ページ：124, 終了ページ：124, 2002年10月30日
日本語
ISSN：0919-5998, CiNii Articles ID：10013399834, CiNii Books ID：AA1195143X
直流通電におけるLN_2用ペルチェ電流リードの動作特性
水谷 進; 森口 正人; 山口 貴行; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 松岡 良輔; 中村 圭二; 山口 作太郎; 池澤 俊治郎; 飯吉 厚夫; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：67, 開始ページ：125, 終了ページ：125, 2002年10月30日
日本語
ISSN：0919-5998, CiNii Articles ID：80015675988, CiNii Books ID：AA1195143X
半波整流電流モードでのペルチェ電流リードによる熱侵入の低減 山口貴行; 大瀧直浩; 長谷川靖洋; 中村圭二; 山口作太郎
低温工学,
巻：37,
号：9,
開始ページ：472,
終了ページ：478, 2002年09月25日
Experiments of Peltier current lead (PCL) were performed by the way of half-wave-rectified current (HWRC) for an evaluation of the PCL system in the drive with the large-rippled current. The current ripple of the HWRC is large, and we discussed the cooling capability of the current ripple. The experimental results revealed that the temperature difference of the thermoelectric-element (TE) increased with the magnitude of the current in the PCL system, despite the large current ripple. Calorimetric measurements revealed that the PCL reduced the heat leak of 60% for the peak current 90A. We compared the PCL systems of the direct current (dc) mode and the HWRC mode. The results showed that the current dependence of the temperature difference in the HWRC mode did not match that of the dc mode, but those of the heat leak matched well. The performance of the Peltier cooling in the HWRC mode is reduced to be 2/πtime of the Seebeck coefficient for the dc mode by using the time-average method.
公益社団法人 低温工学・超電導学会 (旧 社団法人 低温工学協会), 日本語
DOI：https://doi.org/10.2221/jcsj.37.472DOI ID：10.2221/jcsj.37.472,
ISSN：0389-2441,
J-Global ID：200902128024014272,
CiNii Articles ID：10009678571,
CiNii Books ID：AN00333419 Reduction of heat leak in cryogenic system using Peltier current leads Y Hasegawa; K Sato; H Okumura; K Nakamura; S Yamaguchi; K Miyake
巻：42,
号：8,
開始ページ：495,
終了ページ：500, 2002年08月
Peltier current leads (PCLs) for cryogenic systems are investigated in regard to temperature dependence of thermoelectric materials. Due to the Peltier effect on the thermoelectric parts of the current lead, PCLs act as heat pumps. It is expected that PCLs will reduce the amount of heat leak from the room temperature side to the low temperature side of a cryogenic system. Six (three each for p and n type) hot-pressed BiTe samples for PCLs are selected to estimate PCL performance. Our experimental results and analyses indicate that PCLs show a capacity in the order of several hundred Amperes and as much as 20-30% reductions of heat leak. (C) 2002 Published by Elsevier Science Ltd.
英語
DOI：https://doi.org/10.1016/S0011-2275(02)00048-6DOI ID：10.1016/S0011-2275(02)00048-6,
ISSN：0011-2275,
eISSN：1879-2235,
CiNii Articles ID：80015512957,
Web of Science ID：WOS:000178505900008 低熱侵入ペルチェ電流リードの開発(3) : 半波交流通電時での動作特性
中村 圭二; 大瀧 直浩; 山口 貴行; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 山口 作太郎; 松岡 良輔; 池澤 俊治郎; 飯吉 厚夫; 佐藤 堅; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：65, 開始ページ：102, 終了ページ：102, 2001年11月23日
日本語
ISSN：0919-5998, CiNii Articles ID：10013398508, CiNii Books ID：AA1195143X
低熱侵入ペルチェ電流リードの開発(1) : 液体窒素環境での動作特性
中村 圭二; 大瀧 直浩; 山口 貴行; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 山口 作太郎; 松岡 良輔; 池澤 俊治郎; 飯吉 厚夫; 佐藤 堅; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：65, 開始ページ：258, 終了ページ：258, 2001年11月23日
日本語
ISSN：0919-5998, CiNii Articles ID：10013398905, CiNii Books ID：AA1195143X
低熱侵入ペルチェ電流リードの開発(2) : 液体ヘリウム環境での動作特性
山口 貴行; 大瀧 直浩; 中村 圭二; 後藤 英雄; 角 紳一; 林 洋司; 寺田 弘; 馬場 清英; 山口 作太郎; 松岡 良輔; 池澤 俊治郎; 飯吉 厚夫; 佐藤 堅; 佐藤 利和; 長谷川 靖洋; 二ノ宮 晃; 石郷岡 猛; 奥村 晴彦; 浅野 克彦
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：65, 開始ページ：259, 終了ページ：259, 2001年11月23日
日本語
ISSN：0919-5998, CiNii Articles ID：10013398908, CiNii Books ID：AA1195143X
Required accuracy of inductance measurement for current imbalance phenomena S Yamaguchi; S Takayama; Y Hasegawa; A Ninomiya; K Nakamura; H Okumura; R Shimada
巻：41,
号：10,
開始ページ：705,
終了ページ：712, 2001年10月
Current imbalance can be estimated by the solution of the circuit equation, which depends on the result of the measurement of the self- and mutual inductances. Strand circuit is coupled with each other strongly, and therefore the matrix calculation is stiff. This situation leads to enhance the error of the measurement. In order to study this problem, we made a magnet, in which the cable was composed of the nine insulated strands, and measured the inductance matrix of the strand circuits by the LCR-meter. The inductance of the magnet is 11 mH, and the error of the measurement is the order of micro Henry to 10 muH. The average coupling factor of the magnet is 0.9956, and therefore this inductance matrix is almost singular. Finally, we calculated the currents of the strand. The accuracy of the inductance measurement is the order of 5-6 digits. We used (TM)Mathematica to solve the circuit equation, and we tested the accuracy of the calculation precision. Random number method is introduced to estimate the required accuracy of the inductance measurement. The required accuracy of the inductance measurement is the order of micro Henry in this magnet to obtain the accuracy of 5% for the strand currents. (C) 2002 Elsevier Science Ltd. All rights reserved.
英語
DOI：https://doi.org/10.1016/S0011-2275(01)00128-XDOI ID：10.1016/S0011-2275(01)00128-X,
ISSN：0011-2275,
CiNii Articles ID：80012898402,
Web of Science ID：WOS:000173836500002 低温機器への応用に向けた熱電特性の測定長谷川靖洋; 三宅潔; 大池知子; 奥村晴彦; 佐藤堅; 中村圭二; 山口貴行; 山口作太郎; 飯吉厚夫
応用物理学会学術講演会講演予稿集,
巻：62nd,
号：1,
開始ページ：134, 2001年09月11日
日本語
J-Global ID：201202131274320464 磁場中における単結晶BiSb熱電特性長谷川靖洋; 三宅潔; 大池知子; 奥村晴彦; 佐藤堅; 中村圭二; 山口作太郎; 飯吉厚夫
応用物理学会学術講演会講演予稿集,
巻：62nd,
号：1,
開始ページ：133, 2001年09月11日
日本語
J-Global ID：201202161522616533 鉄芯法を用いた超伝導コイルにおける偏流抑制試験大瀧直浩; 中村圭二; 後藤英雄; 寺田弘; 林洋司; 角伸一; 松岡良輔; 池澤俊治郎; 山口作太郎; 二ノ宮晃; 奥村晴彦; 嶋田隆一; 長谷川靖洋; 佐藤利和; 高山定次
電気学会全国大会講演論文集,
巻：2001,
号：5,
開始ページ：1991, 2001年03月21日
日本語
J-Global ID：201302101729352638 超電導コイルにおける偏流特性とその抑制大瀧直浩; 中村圭二; 後藤英雄; 山口作太郎; 二ノ宮晃; 奥村晴彦; 佐藤利和; 長谷川靖洋; 高山定次
電気学会超電導応用電力機器研究会資料,
巻：ASC-01,
号：1-15,
開始ページ：31,
終了ページ：36, 2001年01月25日
日本語
J-Global ID：200902197397874664 Seebeck coefficient measurement of BiSb single crystal in a magnetic field
Y. Hasegawa; T. Oike; H. Okumura; N. Sato; S. Yamaguchi; S. Takayama
IEEE The componets, Packing and Manufacturing Technology Society, Proc. 19th Int. Conf. Thermoelectrics, 開始ページ：356, 終了ページ：359, 2001年
Seebeck coefficient measurement of BiSb single crystal in a magnetic field
Y. Hasegawa; T. Oike; H. Okumura; N. Sato; S. Yamaguchi; S. Takayama
開始ページ：356, 終了ページ：359, 2001年
交流超電導コイルの偏流特性に及ぼす強磁性材の影響
中村 圭二; 大滝 直浩; 後藤 英雄; 寺田 弘; 角 紳一; 馬場 清英; 松岡 良輔; 池澤 俊治郎; 山口 作太郎; 二ノ宮 晃; 奥村 晴彦; 高山 定次; 佐藤 利和; 長谷川 靖洋
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：63, 開始ページ：269, 終了ページ：269, 2000年10月31日
日本語
ISSN：0919-5998, CiNii Articles ID：10013935099, CiNii Books ID：AA1195143X
Shape effect of resistance and thermoelectric power for BiSb in a magnetic field
Y. Hasegawa; H. Okumura; N. Kondo; N. Shuto; S. Yamaguchi; N. Sato
IEEE The componets, Packing and Manufacturing Technology Society, Proc. 18th Int. Conf. Thermoelectrics, 開始ページ：241, 終了ページ：244, 2000年
Shape effect of resistance and thermoelectric power for BiSb in a magnetic field
Y. Hasegawa; H. Okumura; N. Kondo; N. Shuto; S. Yamaguchi; N. Sato
開始ページ：241, 終了ページ：244, 2000年
超伝導撚り線導体の偏流防止対策その2 : 超伝導コイルのインダクタンス及びシャント抵抗の測定
佐藤 利和; 二ノ宮 晃; 石郷岡 猛; 山口 作太郎; 奥村 晴彦; 花井 哲; 長谷川 靖洋; 嶋田 隆一
低温工学・超電導学会講演概要集 = Meetings of Cryogenics and Superconductivity, 巻：61, 開始ページ：125, 終了ページ：125, 1999年11月10日
日本語
ISSN：0919-5998, CiNii Articles ID：10013805402, CiNii Books ID：AA1195143X
LHDにおける直接エネルギー変換 熱電変換の検討 2
山口作太郎; 奥村晴彦; 河本邦仁; 沢田圭司; 長谷川靖洋; 八坂保能; 米永一郎; 丹治やす典; 近藤成仁
プラズマ・核融合学会年会予稿集, 巻：16th, 号：16, 開始ページ：122, 終了ページ：122, 1999年11月
プラズマ・核融合学会, 日本語
J-Global ID：200902141932476546, CiNii Articles ID：110003746998, CiNii Books ID：AN10117056
Study on energy distribution of reflected particles from plasma facing materials Y Hasegawa; S Masuzaki; N Noda; N Ohyabu; A Sagara; H Suzuki; A Komori; T Morisaki; O Motojima; VS Voitsenya
巻：266,
開始ページ：1072,
終了ページ：1077, 1999年03月
Reflection of ions at a tungsten target was investigated experimentally in a linear plasma device. The tungsten target plate was set perpendicular to the magnetic field, and irradiated by hydrogen and helium plasma. The experiment measures a current as a function of sheath potential for a fixed angle. The reflected neutral particles from the target plate are measured by neutral-negative charge convertor made of Cu. The experimental results show good agreement with the results calculated with TRIM Monte-Carlo simulation code. A possibility to estimate the ion temperature is shown through the sheath potential dependence of the ion reflection in the low energy range. (C) 1999 Elsevier Science B.V. All rights reserved.
英語
DOI：https://doi.org/10.1016/S0022-3115(98)00629-1DOI ID：10.1016/S0022-3115(98)00629-1,
ISSN：0022-3115,
CiNii Articles ID：80011050220,
Web of Science ID：WOS:000079725200179 25aB5 半導体中のヘリコン波(プラズマ基礎/炉設計)
津島 晴; 小川 勇; 長谷川 靖洋; 山口 作太郎
プラズマ・核融合学会年会予稿集, 号：16, 開始ページ：117, 終了ページ：117, 1999年
プラズマ・核融合学会, 日本語
CiNii Articles ID：110003746989, CiNii Books ID：AN10117056
EXPERIMENTAL AND THEORETICAL STUDY OF ION REFLECTION FOR NEW DIAGNOSTIC METHOD OF ION ENERGY DISTRIBUTION IN EDGE PLASMA, 共著 Y. Hasegawa; S. Masuzaki
Plasmas Devices and Operation,
巻：7,
号：2,
開始ページ：149,
終了ページ：156, 1999年
A new diagnostic method to measure ion energy distribution using ion reflection on the solid surface, one of the processes of plasma-wall interactions, is proposed. It is well known that the energy distribution of reflected particles is related to the energy distribution of incident ions. This method is used in relatively low ion temperature region such as edge plasma in fusion experimental devices. Incident ions to target plate which is inserted in the edge plasma are mainly reflected as neutral particles, and time-of-flight method is utilized to measure energy distribution of reflected particles. Energy distribution of incident ions is deduced by fitting with calculation using Monte Carlo simulation code TRIM.SP. The sheath potential in front of the target can also be obtained with this method.
英語
DOI：https://doi.org/10.1080/10519999908224467DOI ID：10.1080/10519999908224467,
ISSN：1051-9998,
Web of Science ID：WOS:000079682400009 Experimental and theoretical study of ion reflection for new diagnostic method of ion energy distribution in edge plasma Y Hasegawa; S Masuzaki; N Noda; N Ohyabu; A Sagara; H Suzuki; O Motojima; VS Voitsenya
巻：7,
号：2,
開始ページ：149,
終了ページ：156, 1999年
A new diagnostic method to measure ion energy distribution using ion reflection on the solid surface, one of the processes of plasma-wall interactions, is proposed. It is well known that the energy distribution of reflected particles is related to the energy distribution of incident ions. This method is used in relatively low ion temperature region such as edge plasma in fusion experimental devices. Incident ions to target plate which is inserted in the edge plasma are mainly reflected as neutral particles, and time-of-flight method is utilized to measure energy distribution of reflected particles. Energy distribution of incident ions is deduced by fitting with calculation using Monte Carlo simulation code TRIM.SP. The sheath potential in front of the target can also be obtained with this method.
英語
DOI：https://doi.org/10.1080/10519999908224467DOI ID：10.1080/10519999908224467,
ISSN：1051-9998,
Web of Science ID：WOS:000079682400009 LHDにおける直接エネルギー変換 熱電変換の検討
山口作太郎; 飯吉厚夫; 奥村晴彦; 河本邦仁; 沢田圭司; 長谷川靖洋; 八坂保能; 米永一郎; 新野正之
プラズマ・核融合学会年会予稿集, 巻：15th, 号：16, 開始ページ：212, 終了ページ：122, 1998年11月
プラズマ・核融合学会, 日本語
J-Global ID：200902197537702133, CiNii Articles ID：110003746998, CiNii Books ID：AN10117056
Simulation Study for New Diagnostic Method of Ion Energy Distribution in Edge Plasma
Y. Hasegawa; S. Masuzaki
Journal of Plasma and Fusion Research SERIES, 巻：1, 開始ページ：390, 終了ページ：393, 1998年
Simulation Study for New Diagnostic Method of Ion Energy Distribution in Edge Plasma
Y. Hasegawa; S. Masuzaki
巻：1, 開始ページ：390, 終了ページ：393, 1998年
磁性トポロジカル絶縁体素子の界面制御による低消費電力動作の実現
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2024年04月01日 - 2028年03月31日
小峰 啓史; 青野 友祐; 長谷川 靖洋; 千葉 貴裕, 茨城大学
配分額（総額）：18460000, 配分額（直接経費）：14200000, 配分額（間接経費）：4260000
課題番号：24K00916
1次元量子ナノワイヤー熱電変換素子の巨大ゼーベック効果の実証
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2022年04月01日 - 2026年03月31日
長谷川 靖洋; 遠藤 彰; 小峰 啓史, 埼玉大学
配分額（総額）：17290000, 配分額（直接経費）：13300000, 配分額（間接経費）：3990000
課題番号：22H01805
磁壁移動型メモリの低消費電力動作に向けた界面構造制御
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2020年04月01日 - 2024年03月31日
小峰 啓史; 青野 友祐; 長谷川 靖洋; 千葉 貴裕, 茨城大学
配分額（総額）：17550000, 配分額（直接経費）：13500000, 配分額（間接経費）：4050000
トポロジカル絶縁体として期待されるBi-Sb薄膜を作製するため，Sb用Kセルを導入し，機器の基本特性および成膜条件を精査した．既設のBi用Kセルと合わせて２つのセル温度を調整することで，膜厚および組成制御が可能となった．厚膜の電気特性を測定したところ，従来報告されているバルクの電気抵抗率と同等の膜質のBi-Sb薄膜が得られることを確認した．
前年度までに検討したトポロジカル絶縁体(Topological Insulator, TI)を用いたFET型素子の発展形として，近年，スピン波情報処理で注目されている磁性絶縁体(Ferrimagnetic Insulator, FI)とTIの積層構造において，スピン波の電界制御を検討した．スピン-電荷ポンピングによる散逸トルクが磁化の時間変化に起因するトルクになることに着目して，ダンピング定数の電界制御を試みた．その結果，ゲート電圧によって，大きくダンピング定数を変えられる可能性を示唆した．電界制御したダンピング定数を通じてスピン波伝搬を変調することが可能であり，スピン波を利用した新しい情報処理技術への応用が示唆された．また，磁性絶縁体を利用したスピン波の電界制御は，電流-電圧で制御するこれまでのスピントロニクス素子に比べて，格段の省電力動作が期待できる．
並行してナノワイヤメモリ素子の試作も行った．ナノインプリントリソグラフィによる素子作製を試みて，100nmから2μm幅のナノワイヤを形成するプロセスを構築した．被覆型ナノワイヤの作製過程で複合磁性体の磁気特性を調べた結果，磁気パターンを別の磁性体薄膜に転写する方法を発明して，HDDへの有用性についても成果報告した．
課題番号：20H02196
ビスマスナノワイヤーにおける特異な輸送現象の解明
日本学術振興会, 科学研究費助成事業, 国際共同研究加速基金(国際共同研究強化(B)), 2018年10月09日 - 2023年03月31日
長谷川 靖洋; 伏屋 雄紀; 村田 正行; 小峰 啓史, 埼玉大学
配分額（総額）：17810000, 配分額（直接経費）：13700000, 配分額（間接経費）：4110000
ナノスケール直径とミリスケール長さを同時に実現した単結晶Bi(ビスマス)製ナノワイヤーを用いて、トポロジカル絶縁体に代表されるようなスピン軌道相互作用が輸送現象に与える影響に注目し、1次元状態特有の輸送現象と電子状態を実験・理論の面から解明することを目的とする。研究を遂行するにあたり、世界に先駆けてナノワイヤーの開発と物性測定に成功した日本の研究グループが中心となり、物性測定用ナノワイヤーへのナノ加工と熱電物性測定を進め、伝導率，ゼーベック係数，ホール係数，ネルンスト係数測定を行う。また、バルクBiでの電子状態の解明と、スピン軌道相互作用と熱電物性の研究を推進するため国際共同研究の体制を構築し、量子ネルンスト係数測定を用いた極低温・強磁場における量子物性測定と解析につなげていく。実験結果を元にして、量子効果を完全に取り入れた理論構築を進めていく。
課題番号：18KK0132
ナノ加工を用いた1次元量子ナノワイヤー熱電変換素子の巨大ゼーベック効果機構解明
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2018年04月01日 - 2022年03月31日
長谷川 靖洋; 遠藤 彰; 村田 正行; 小峰 啓史, 埼玉大学
配分額（総額）：17160000, 配分額（直接経費）：13200000, 配分額（間接経費）：3960000
大きなアスペクト比を持つ光ファイバー作製技術にヒントを得て、石英ガラステンプレート中に封入された単結晶Bi製ナノワイヤー熱電変換素子の開発を進めている。また本研究グループによって開発されたナノ加工技術にとって、Biナノワイヤー熱電変換素子側面など任意の場所に数~数十nm角の局所ナノ加工電極を取り付けることが可能となり、４端子測定など精密な電気物性測定が可能となった。これを受け、その物性値のワイヤー直径依存性測定ならびにモデル計算より、巨大ゼーベック効果の実証とそのメカニズムを物理的な見地から解明していく。
課題番号：18H01698
電界制御ラシュバ効果による磁壁移動型メモリの高速化
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2016年04月01日 - 2020年03月31日
小峰 啓史; 青野 友祐; 原 嘉昭; 長谷川 靖洋, 茨城大学
配分額（総額）：16770000, 配分額（直接経費）：12900000, 配分額（間接経費）：3870000
本研究では，磁性膜/ビスマス/絶縁膜の積層構造と輸送特性の電界効果を調べた．ビスマス/絶縁層界面では，ビスマス単層に見られない歪みや界面ミキシングの影響で輸送特性が著しく変化することを見出した．フェリ磁性層/絶縁層界面では，界面歪みやミキシングにより異常ホール効果の符号反転の層厚依存性が観測された．急峻な界面構造を得ることが実験結果を解釈する上で不可欠であることが明らかとなった．ビスマス系合金における電界効果により膜厚方向にpn接合が形成される新奇デバイスの検討を行った．その結果，電界効果による新しい熱電素子の可能性を示唆した．
課題番号：16H04325
ナノスケール制御によるナノワイヤー熱電変換素子の巨大ゼーベック効果発現と機構解明
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2015年04月01日 - 2019年03月31日
長谷川 靖洋; 遠藤 彰; 中村 浩章; 村田 正行; 小峰 啓史, 埼玉大学
配分額（総額）：14820000, 配分額（直接経費）：11400000, 配分額（間接経費）：3420000
高効率エネルギー変換材料創成のため、熱電変換材料の基本材料となっているBiをナノスケール化し、量子効果（１次元状態密度導入）を目指した研究開発であり、それに伴い熱・電気物性を通して巨大ゼーベック効果を実証する研究である。対象としているナノワイヤーは、ワイヤー直径が数百nmと小さく、ワイヤー表面に如何に電極を取り付けるかが大きな問題となり、その物性値を正確に測定することがこれまで困難であった。本研究では、ナノ加工を用いてナノワイヤー熱電変換素子表面に複数本の局所電極を適切に取り付けることに成功し、抵抗率・磁気抵抗・ホール係数測定の同時測定に初めて成功した。
課題番号：15H04142
超高記録密度積層構造ナノワイヤメモリの低電流・高速動作に関する研究
日本学術振興会, 科学研究費助成事業, 基盤研究(C), 2013年04月01日 - 2016年03月31日
小峰 啓史; 杉田 龍二; 青野 友祐; 長谷川 靖洋, 茨城大学
配分額（総額）：5200000, 配分額（直接経費）：4000000, 配分額（間接経費）：1200000
本研究では，電流誘起磁壁移動を用いた超高記録密度積層構造ナノワイヤメモリにおける低電流化と高速化を検討した．磁壁抵抗評価を通じて，低電流化のための候補材料であるTbFeCo薄膜のスピン分極率を評価した．その結果，0.16という磁壁移動に十分なスピン分極率を得た．磁成膜の下地層に流れる駆動電流が磁壁移動に及ぼす影響を調べたところ，駆動電流が作る面ない磁場が磁壁移動を改善することがわかった．積層磁成膜における層間相互作用が磁壁移動に及ぼす影響を調べたところ，反強磁性結合によって磁壁移動速度が大幅に改善すること明らかにした．スピン軌道トルクとの組み合わせでさらなる高速動作が期待出来る．
課題番号：25420318
収束イオンビームを用いたナノワイヤー熱電変換素子へのナノ電極形成・輸送特性の解明
日本学術振興会, 科学研究費助成事業, 基盤研究(C), 2011年 - 2013年
長谷川 靖洋; 小峰 啓史, 埼玉大学
配分額（総額）：5070000, 配分額（直接経費）：3900000, 配分額（間接経費）：1170000
高圧圧入法を用いて長さ1mm以上の単結晶Biナノワイヤー熱電変換素子の開発を行った。収束イオンビームのナノ加工とその場電極形成により、ワイヤー直径４μｍ，700nmのワイヤー両側面に局所電極の形成に成功した。これによって、４端子抵抗測定ならびにホール測定を行うことが出来た。抵抗測定から、ナノワイヤーの抵抗が数ｋΩであったとしても、電極とワイヤー間との接触抵抗が無視できないことが明らかになった。ホール測定から、電子・ホールの各移動度の温度依存性を実験的に明らかにした。その結果、低温領域での抵抗率の上昇は、キャリアの平均自由行程の制限によるものであると結論づけられた。
課題番号：23560828
フェリ磁性積層構造を利用した高密度ナノワイヤメモリの基礎研究
日本学術振興会, 科学研究費助成事業, 基盤研究(C), 2010年 - 2012年
小峰 啓史; 杉田 龍二; 長谷川 靖洋, 茨城大学
配分額（総額）：4160000, 配分額（直接経費）：3200000, 配分額（間接経費）：960000
本研究では,電流誘起磁壁移動を利用したナノワイヤメモリにおいて,磁壁移動のための閾値電流密度低減,及び,高密度化を検討するために,物性値及び素子構造を検討した.物性値が閾値電流密度に及ぼす影響を検討したところ,飽和磁化低減が閾値電流密度低減に有効な手段であることを明らかにし,補償組成近傍のフェリ磁性体がその有力な候補であることを提案した.また,高密度化を実現するための構造として,グラニュラ-磁性膜,連続磁性膜を積層した二層ナノワイヤを提案し,高密度化見通しを示した.
課題番号：22560318
スピン軌道相互作用系におけるスピンネルンスト効果の理論と観測
日本学術振興会, 科学研究費助成事業, 基盤研究(C), 2010年 - 2012年
白崎 良演; 羽田野 直道; 中村 浩章; 遠藤 彰; 長谷川 靖洋, 横浜国立大学
配分額（総額）：4030000, 配分額（直接経費）：3100000, 配分額（間接経費）：930000
固体物質中のキャリアにスピン軌道相互作用が働く場合、その物質に熱伝導を与えると、熱流に垂直にスピン流が現れるスピンネルンスト効果が起こる可能性がある。我々は、スピン軌道相互作用が働くナノスケールの物理系の電子状態を調べ、材料に熱伝導を与えたときの輸送現象に対する不純物の効果とフォノンドラッグ効果を理論的に考察した。また、ワイヤ径が数百nm程度のBi単結晶ナノワイヤを製作し、その電子物性を測定した。
課題番号：22560004
量子熱電効果の非平衡物理と熱駆動ナノデバイスの開拓
日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2008年 - 2011年
中村 浩章; 羽田野 直道; 米満 賢治; 遠藤 彰; 長谷川 靖洋; 白崎 良演; 藤井 達也, 核融合科学研究所
配分額（総額）：18980000, 配分額（直接経費）：14600000, 配分額（間接経費）：4380000
磁場中での量子熱電現象を解明すべく、理論および実験を行った。(1) Biに関して、フォノンドラックを考慮したネルンスト係数の導出、(2)金属-半導体接合面での整流効果の予言、(3) GaAs/AlGaAsの磁場中電子温度勾配下のネルンスト電圧の測定、(4)試料中での温度分布・電位分布を正確に求める輸送方程式の計算機シミュレーション法確立、(5) Biナノワイヤのホール電圧・ネルンスト電圧の測定の研究成果があった。
課題番号：20340101
ガラステンプレートを用いたナノワイヤー熱電変換素子の開発
日本学術振興会, 科学研究費助成事業, 若手研究(A), 2007年 - 2009年
長谷川 靖洋, 埼玉大学
配分額（総額）：18590000, 配分額（直接経費）：14300000, 配分額（間接経費）：4290000
石英ガラステンプレートを用いて長さ1mm以上で、ナノメーターオーダーの直径を持つBi製ナノワイヤー熱電変換素子の開発に成功し、ゼーベック係数・抵抗率の温度依存性を測定することが可能となった。
課題番号：19686041
プラズマジェット法を用いたVOC/ナノ粒子分解技術の展開
日本学術振興会, 科学研究費助成事業, 挑戦的萌芽研究, 2007年 - 2009年
長谷川 靖洋; 関口 和彦, 埼玉大学
配分額（総額）：2800000, 配分額（直接経費）：2800000
近年、様々なナノ材料の研究が行われている。現在、二酸化チタンは光触媒として様々な用途に利用されている。そこで、高い触媒作用のある二酸化チタン粒子が求められている。今年度は、高熱流束マイクロプラズマ(以下MP)の利点を生かして酸化チタン粒子を合成し、その粒子を調べることを目的とする。チタンテトライソプロポキシドをアルゴン:酸素が3:1の混合ガスでバブリング供給した。反応部はMPまたは電気炉(1000℃で使用)を利用した。また、プラズマ生成用ガスとしてアルゴンを供給した。反応後の粒子は、SMPSにより個数を数え、個数濃度、体積濃度、幾何平均径を求めた。今回は、反応部およびプラズマ生成用ガスの流速を変えた場合の粒径分布の違いを比較した。バブリング(反応前)、MP、電気炉それぞれの粒径別体積濃度を比較して、生成濃度は少ないが体積幾何学的平均径の小さい粒子が得られた。濃度が少ない理由として、プラズマ管への壁面沈着やSMPSで測定を行っていない500nm以上の粒子の影響が考えられる。MPを用いることで、粒径の小さい酸化チタン粒子が効率的に得られ、また、流量を増やすことで、さらに小さい粒子を得られることが確認された。
課題番号：19655055
量子ネルンスト効果の理論と実験
日本学術振興会, 科学研究費助成事業, 萌芽研究, 2005年 - 2007年
白崎 良演; 中村 浩章; 羽田野 直道; 町田 友樹; 長谷川 靖洋, 横浜国立大学
配分額（総額）：2900000, 配分額（直接経費）：2900000
我々は、2次元電子系がメゾスケールの大きさである場合、強磁場下で系のネルンスト係数に量子振動が見られる(量子ネルンスト効果)ことを平成17年度から平成18年度にかけて線形応答理論を用いた理論計算で示していた。平成18年度にフランスのグループ(Bhenia, et. al. ESPCI, Paris)から、ビスマス(Bi)単結晶のネルンスト係数およびエッチングスハウゼン係数の測定結果が発表され、ネルンスト係数の量子振動が現実の系で示された。我々はこの実験結果の検討を行い、試料の3次元性の効果を取り入れた理論拡張を行った。我々は磁場中の3次元バリスティック系を考え、運動の自由度を磁場に垂直な2次元面内の自由度と磁場に平行な自由度に分け、2次元面内の運動成分は有限サイズのバリスティックなものと見なしてネルンスト係数を考察した。その結果、3次元系でもネルンスト係数の量子的な振動が現れ、ネルンスト係数のピークは弱磁場側に尾を引く左右非対称の形を持つことが分かった。この形はBiの実験結果と一致する。このように、量子ネルンスト効果が3次元系において理論・実験両面から確認された。一方、Biのネルンスト係数のピークは実験値が理論値に比べ非常に大きい。この原因の理論的解明は今後の課題として残っている。
我々は量子ホール系における輸送係数の基本関係に関しても考察を行った。従来、電気伝導度テンソルの非対角成分の磁場微分と対角成分との間では線形な関係式が提案され、研究が進められていた。我々は線形応答理論を用いて量子ホール系の輸送係数を理論・解析的に導出し、成分間の関係が非対角成分の磁場微分と対角成分の二乗が比例する非線形な関係であることを示した。この理論では、電子の不純物散乱により、ランダウ準位近傍の電子状態密度がローレンツ型になると仮定している。我々はGaAsによる実験結果を用いて、数テスラ程度の磁場のもとでこの関係が良く成立していることを確かめた。
課題番号：17654073
大気圧プラズマジェットによる針状シリコン結晶の作製と成長機構の解明
日本学術振興会, 科学研究費助成事業, 萌芽研究, 2005年 - 2006年
白井 肇; 長谷川 靖洋, 埼玉大学
配分額（総額）：3000000, 配分額（直接経費）：3000000
大気圧マイクロプラズマジェットによるCH4/Ar系からの針状シリコン結晶(SNC)の成長解明を目的として、微細構造の観察、プラズマ診断および基板表面のレーザー光反射率の実時間その場計測を通して診断した。内径700μmのタングステン製筒状電極に高周波電力を供給し、中心部からArを供給することで電極先端にプラズマジェットを生成し、周囲からCH4を供給することで電極直下に設置した金属コートシリコン基板上の生成物を詳細に調べた。その結果電極直下400μm以内の領域で針状生成物の一様な成長を見出した。またその周囲には多層カーボンナノチューブ(CNT)およびシリコンナノワイヤー(SNW)の成長を見出した。そこでこれらの成長機構の詳細を高分解能サーモグラフィーによる表面温度計測、SEM、マイクロラマン分光、電子顕微鏡観察(TEM)、電子放出特性により評価した。シリコン上の表面温度は、数ミリ秒で1400℃以上に達し、シリコンを十分溶融する温度に達していることがわかった。またSNCは主にナノ結晶Si微粒子、クラスターを内包するSiO_2コーンであることがEDX、ラマン分光により明らかになった。特にCH_4供給、金属コートのSNC成長に与える影響を考察した結果、CH4供給はプラズマガス温度の上昇に寄与し、金属シリサイド微粒子の形成を促進していることがわかった。さらに金属の種類を変えてSNC成長を行った結果、Fe, Cr, Ni等の重金属で顕著なSNC成長が観測され、一方融点の低いAu, Ag、Alでは成長が見られなかった。以上の結果はSiより融点の高い金属でSNC成長を促進することを明らかにした。さらに表面形状のプラズマ照射時間に対する観察、レーザー反射率の実時間評価から、熱プラズマジェットの金属コートシリコン基板照射直後のSiの溶融およびその冷却過程において、金属シリサイド液体から相変化に伴うシリコンと金属シリサイドの析出および液体から固化に伴う体積膨張がSNC、SNW等の微細構造を決定していることを明らかにした。
課題番号：17656012
サイクロトロン周波数を制御した熱電素子
日本学術振興会, 科学研究費助成事業, 若手研究(B), 2004年 - 2006年
長谷川 靖洋, 埼玉大学
配分額（総額）：2000000, 配分額（直接経費）：2000000
磁場中で熱電素子の性能を向上すべく、本年度は直径1〜100μm,長さ1mm程度のBi製ワイヤーをガラスで束ねたマイクロワイヤー素子を用いて、熱電性能(ゼーベック係数,抵抗率)の測定を行った。磁場中では素子のアスペクト比が大きいほどゼーベック係数の改善率が高く、また抵抗率の上昇率が低いことが報告されていた。しかしながら、これらの報告はバルク素子を用いての結果であり、アスペクト比が10以上を持ったマイクロワイヤー素子では、その挙動は不明であった。先に述べた電極接続技術を用いて磁場中でのゼーベック係数を測定したところ、期待通り、アスペクト比の大きな素子では同じ磁場強度でもその改善率が高く、また磁場中での抵抗率の上昇率も抑制することができることが確認された。磁場中のゼーベック係数と抵抗率で記述できるパワーファクターを用いて磁場中での性能評価を行った。アスペクト比が大きい素子であるほど、パワーファクターの改善率は高く、また最適磁場は高磁場側にシフトし、広い磁場範囲でパワーファクターの改善が見られた。抵抗率の逆数で表される伝導率とゼーベック係数の関係で、磁場中のパワーファクター上昇についての解析を行った。これによって、固体中のキャリアの移動度が大きいことに由来しゼーベック係数が無磁場で大きいほど、その改善率が顕著であることを示した。これはサンプル中の結晶方位に大きく依存すると考えられ、今後の素子作製の方針となる。また、磁場中でのゼーベック係数ならびにネルンスト係数を測定し、その温度依存性を明らかにした。
課題番号：16760562
マイクロプラズマによるシリコン・炭素系ナノ構造形成過程のその場観察
日本学術振興会, 科学研究費助成事業, 特定領域研究, 2004年 - 2005年
白井 肇; 長谷川 靖洋, 埼玉大学
配分額（総額）：4300000, 配分額（直接経費）：4300000
本研究は、大気圧マイクロ熱プラズマジェットを局所領域に生成、集積化し、これらのプラズマ源を用いてアモルファスシリコン(a-Si)薄膜の短時間結晶化およびシリコン・炭素系ナノ構造形成への応用を通じて、その機構解明を行った。マイクロプラズマによるシリコン、炭素系材料形成に関する研究は、これまでに微粒子の合成、エッチングが主体であった。しかし高温プラズマジェットによる表面改質に基づいた物質設計についての検討はほとんど報告がない。本研究では、短時間局所加熱による溶融状態からの冷却過程を利用した物質構造制御を目的に、針状シリコンナノ結晶(SNC : Silicon nanocones)、ナノチューブ(CNT)等シリコン・炭素系ナノ構造の形成とa-Si再結晶化機構の解明および新規物性の発現を目的とした。これらの成長機構を分光エリプソメトリー(SE)、反射率・コンダクタンスの実時間その場計測を通して明らかにすることを目的とする。
大気圧マイクロ熱プラズマジェットを生成し、プラズマ診断を通して(1)a-Si膜の短時間結晶化および(2)シリコン・炭素系ナノ構造の形成に応用した。RF、VHF電力、ガス流速を変数としてプラズマパラメータ、で(電子密度、電子温度、ガス温度、励起温度)を発光分光法により評価した。その結果電子密度:10^<15>cm^<-3>、励起温度:4000-8000K、ガス温度1100-1400℃に及ぶ超高密度プラズマであることがわかった。特にガス温度の上昇にともない、電極直下領域の温度は1400℃まで数ミリ秒の時定数で上昇し、SNC形成、アモルファスSi膜の短時間結晶化が可能であることがわかった。(1)では、基板ステージ速度およびArガス流量の制御により高結晶化度を有するSi膜の形成を実現し、TFT移動度30-55cm^2/Vsを得た。また太陽電池素子へ適用し、FF:0.45、変換効率:5.5%を得た。a-Siレーザー再結晶化に替わる技術としての展開が期待される。一方(2)では、CH_4/Ar系からFe/c-Si基板上にシリコンナノコーン(SNC)の高密度形成に成功した。外部からのCH_4供給はガス温度を上げ、基板表面温度は1400℃に達し、局所加熱効果を促進する。その結果FeSi_xナノクラスター形成、体積膨張および粘性流がSNC形成、a-Si膜の再結晶化を促進する。
課題番号：16040203
-
マイクロワイヤーアレイ構造熱電変換素子の開発を進め、現在は量子効果を取り入れたナノワイヤー構造熱電変換素子の開発を進めている。
-
