Researcher Database

Researcher Profile and Settings


Affiliation (Master)

  • Faculty of Information Science and Technology Electronics for Informatics Integrated Systems Engineering

Affiliation (Master)

  • Faculty of Information Science and Technology Electronics for Informatics Integrated Systems Engineering


Profile and Settings


  • Doctor of Engineering (Electrical Engineering), Hokkaido University(1997/06 Hokkaido University)
  • Master of Engineering (Electrical Engineering), Hokkaido University(1992/03 Hokkaido University)

Profile and Settings

  • Name (Japanese)

  • Name (Kana)

  • Name


Alternate Names


Research Interests

  • electron swarm   Boltzmann equation   magnetized plasma   electron transport   Monte Carlo simulation   プラズマエレクトロニクス   Electric Discharges   Plasma Electronics   

Research Areas

  • Energy / Basic plasma science
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electric/electronic material engineering

Research Experience

  • 2004 - 2007 Hokkaido University Graduate School of Information Science and Technology, Division of Electronics for Informatics
  • 2004 - 2007 Associate Professor
  • 2007 - 北海道大学大学院情報科学研究科情報エレクトロニクス専攻集積システム講座集積プロセス学研究室 准教授
  • 2007 - Associate Professor
  • 1998 - 2004 北海道大学大学院工学研究科電子情報工学専攻集積材料デバイス工学講座集積電子材料工学分野 助教授
  • 1998 - 2004 Associate Professor,Associate Professor, Hokkaido University
  • 1997 - 1998 北海道大学大学院工学研究科電子情報工学専攻集積材料デバイス工学講座集積電子材料工学分野 助手
  • 1997 - 1998 Research Associate
  • 1995 - 1997 北海道大学工学部電子情報工学専攻集積材料デバイス工学講座集積電子材料工学分野 助手
  • 1995 - 1997 Research Associate
  • 1992 - 1995 北海道大学工学部電気工学科電気応用工学講座 助手
  • 1992 - 1995 Research Associate


  •        - 1992  Hokkaido University
  •        - 1992  Hokkaido University  Graduate School, Division of Engineering  Division of Electrical Engineering
  •        - 1990  Hokkaido University  School of Engineering
  •        - 1990  Hokkaido University  Faculty of Engineering  Department of Electrical Engineering


  • 2016/07 日本学術振興会 平成27年度特別研究員等審査会専門委員(書面担当)表彰
    受賞者: 菅原 広剛書面審査における有意義な審査意見
  • 2000 電気学会 電気学会優秀論文発表賞
    平成11年電気学会基礎・材料・共通部門大会 No. 59 (1999)菅原広剛、八幡貴志、酒井洋輔:「一定衝突周波数モデルにおける電磁界下電子群ドリフト速度のベクトル軌跡について」
  • 1997 電気学会 電気学会優秀論文発表賞
    平成8年度電気学会基礎・材料・共通部門総合研究会 ED-96-218 (1996)菅原広剛、田頭博昭、酒井洋輔:「気体中の電子群重心移動速度-速度空間モーメント方程式による導出-」
  • 1995/03 電気学会 電気学会論文発表賞(賞B)
    平成6年度電気関係学会北海道支部連合大会講演 No. 50 (1994)菅原広剛、酒井洋輔、田頭博昭:「気体の電離係数(CCXXXV)-完全吸収陽極近傍の電子後方拡散の効果-」
  • 1992/04 電気学会論文発表賞(賞A)
    電気学会放電研究会講演 ED-91-69 (1991)菅原広剛、酒井洋輔、田頭博昭:「ボルツマン方程式の直接数値解法(Convective Scheme)によるArガス中電子スオームのシミュレーション」
  • 1990/08 電気学会 電気学会論文発表賞(賞B)
    受賞者: 菅原 広剛平成2年電気学会全国大会講演 No. 155 (1990)菅原広剛、酒井洋輔、田頭博昭:「気体の電離係数(CLXXXVIII)-ボルツマン方程式の直接数値解法-」

Published Papers

  • Luca Vialetto, Hirotake Sugawara, Savino Longo
    Plasma 7 (1) 121 - 145 2024/02/16 [Refereed][Not invited]
    In this review, we detail the commonality of mathematical intuitions that underlie three numerical methods used for the quantitative description of electron swarms propagating in a gas under the effect of externally applied electric and/or magnetic fields. These methods can be linked to the integral transport equation, following a common thread much better known in the theory of neutron transport than in the theory of electron transport. First, we discuss the exact solution of the electron transport problem using Monte Carlo (MC) simulations. In reality we will go even further, showing the interpretative role that the diagrams used in quantum theory and quantum field theory can play in the development of MC. Then, we present two methods, the Monte Carlo Flux and the Propagator method, which have been developed at this moment. The first one is based on a modified MC method, while the second shows the advantage of explicitly applying the mathematical idea of propagator to the transport problem.
  • Tsukasa Kobayashi, Hirotake Sugawara, Kei Ikeda
    Japanese Journal of Applied Physics 62 (SL) SL1020-1 - SL1020-10 0021-4922 2023/05/11 [Refereed][Not invited]
    Abstract In order to accurately evaluate the electron acceleration process in the time evolution calculation of electron velocity distribution function (EVDF) based on the Boltzmann equation, an improved scheme blending upwind and central differences is introduced into the propagator method (PM). While the previous PM based on the upwind scheme needs fine cells to obtain an accurate EVDF at low electric fields, the improved PM is robust against coarse cells, which allows the reduction of the cell resolution. Calculations of the EVDF in Ar under RF electric fields demonstrated that the blending scheme can provide satisfactorily accurate results even with cells about tenfold larger than the upwind case at low reduced electric fields below 1 Td, which leads to much shorter computational time because the reduction of number of cells satisfactorily compensates the complexity of the blending scheme. This technique has been built into a new user-friendly PM software named BOSPROM.
  • Ryota Okazaki, Hirotake Sugawara
    Japanese Journal of Applied Physics 62 (SL) SL1003-1 - SL1003-8 0021-4922 2023/04/12 [Refereed][Not invited]
    Abstract We investigate the partial resonance as one of the mechanisms of the electron heating to sustain inductively coupled plasmas driven under confronting divergent magnetic fields having an electron confinement function. Dependence of the partial resonance on operating conditions are observed. The electron energy gain (EEG), defined as a measure for evaluation of the partial resonance, was calculated by a Monte Carlo method under various magnetic field strengths and the RF antenna positions. It is confirmed that the partial resonance is observed in the resonant region even in low electric field and strong magnetic field. As an attempt to utilize the partial resonance, we demonstrate enhancement of the EEG and resulting ionization in the resonant region by placing the RF antenna near a region where the magnetic field lines running through the resonant region reach. 
  • Yui Okuyama, Yuka Yasuzawa, Hirotake Sugawara
    Electrical Engineering in Japan 216 (1) 0424-7760 2023/02/07 [Refereed][Not invited]
  • Yui Okuyama, Yuka Yasuzawa, Hirotake Sugawara
    IEEJ Transactions on Fundamentals and Materials 142 (10) 397 - 405 0385-4205 2022/10/01 [Refereed][Not invited]
  • Naoto Nohara, Hirotake Sugawara
    IEEJ Transactions on Fundamentals and Materials 142 (6) 288 - 289 0385-4205 2022/06/01 [Refereed][Not invited]
  • Hirotake Sugawara, Yuya Nakata
    The European Physical Journal D 76 (2) 32-1 - 32-11 1434-6060 2022/02 [Refereed][Not invited]
  • Hirotake Sugawara, Hikaru Iwamoto
    Japanese Journal of Applied Physics 60 (4) 046001 - 046001 0021-4922 2021/04/01 [Refereed][Not invited]
  • H. Takahashi, H. Sugawara
    Japanese Journal of Applied Physics 59 (3) 036001-1 - 036001-6 2020/02/17 [Refereed][Not invited]
  • Yuya Nakata, Takeshi Sato, Hirotake Sugawara
    IEEE Transactions on Plasma Science 49 (1) 83 - 90 0093-3813 2020 [Refereed][Not invited]
  • NAKASHIMA Katsuhiro, TAKAHASHI Hironori, SUGAWARA Hirotake
    Japanese Journal of Applied Physics 58 (11) 116001-1 - 116001-7 2019/11 [Refereed][Not invited]
  • Hirotake SUGAWARA
    Japanese Journal of Applied Physics 58 (10) 108002-1 - 108002-4 2019/10 [Refereed][Not invited]
  • SUGAWARA Hirotake
    Plasma Science and Technology 21 (9) 094001-1 - 094001-18 2019 [Refereed][Not invited]
  • H. Takahashi, K. Nakashima, T. Yamamoto, H. Sugawara
    Japanese Journal of Applied Physics 57 (12) 126101-1 - 126101-7 2018/12 [Refereed][Not invited]
  • Hirotake Sugawara
    Japanese Journal of Applied Physics 57 (3) 038001-1 - 038001-3 1347-4065 2018/03/01 [Refereed][Not invited]
    In Monte Carlo simulations of electron swarms, sample electrons were copied periodically so that a sufficient number of samples are obtained in equilibrium after relaxation even under a severe attachment-dominated condition where most electrons vanish during the relaxation. The final sampling results were equivalent to those sampled by a conventional method, and the computational time conventionally wasted for the tracking of vanishing electrons was reduced drastically. The time saved can be utilized for tracking more samples to reduce statistical fluctuation. The efficiency of this technique and its limitation are discussed quantitatively together with details on its implementation.
  • Hirotake Sugawara
    PLASMA SOURCES SCIENCE & TECHNOLOGY 26 (4) 044002-1 - 044002-16 0963-0252 2017/04 [Refereed][Not invited]
    A propagator method (PM), a numerical technique to solve the Boltzmann equation (BE) for the electron velocity or energy distribution function (EVDF/EEDF) of electron swarms in gases, was customized to obtain the equilibrium solution quickly. The PM calculates the number of electrons in cells defined in velocity space using an operator called the propagator or Green's function. The propagator represents the intercellular transfer of electrons corresponding to the electron velocity change due to the acceleration by the electric field and the collisional events with gas molecules. The relaxation of the EVDF to its drift equilibrium solution proceeds with iterative propagator operations for the EVDF. Merits of the PM are that the series expansion of the EVDF as done in the BE analyses is not required and that time evolution of the electron swarm can be observed if necessary. On the other hand, in case only the equilibrium solution of the EVDF is wanted, the relaxation can be accelerated numerically. A demonstration achieved a shortening of the computational time by about three orders of magnitude. Furthermore, this scheme was applied to calculations of a set of electron transport parameters required in fluid-model simulations, i.e. the effective ionization frequency, the centroid drift velocity and the longitudinal diffusion coefficient, using the zeroth-, first- and second-order moment equations derived from the BE. A detailed description on the PM calculation was presented.
  • Tappei Yamamoto, Hirotake Sugawara
    IEEJ Transactions on Fundamentals and Materials 137 (6) 363 - 364 1347-5533 2017 [Refereed][Not invited]
    Confronting divergent magnetic fields (CDMFs) applied to an inductively coupled plasma have a function to confine electrons within the source region. We discussed judgement criteria for electron escape from the source region to the diffusion region across the separatrix of the CDMFs. Passage of electron gyration center across the separatrix and collisional events in the diffusion region were newly introduced as effective criteria.
  • Hirotake Sugawara, So Ogino
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 (7) 07LD05-1 - 07LD05-6 0021-4922 2016/07 [Refereed][Not invited]
    The electron motion under confronting divergent magnetic fields (CDMFs) applied to inductively coupled plasmas was simulated using a Monte Carlo method. The CDMFs induced by two coaxial dc coils confined electrons in one side of the separatrix of the CDMFs. However, electrons diffused across the separatrix mainly in two ways. One was the displacement of their gyrocenters due to scattering near the outer part of the separatrix. This process tended to occur for high-energy electrons with correspondingly large gyroradii. The other was passage through the weak magnetic field around the center. This process was allowed for low-energy electrons. The position-dependent selectivity about the electron energy was pointed out as a seed property for applications of the separatrix as a magnetic filter or shutter. The mechanism by which the functions of the separatrix emerge was explained from a viewpoint of electron motion under the CDMFs. (C) 2016 The Japan Society of Applied Physics
  • Yudai Minami, Yusuke Asami, Hirotake Sugawara
    IEEE TRANSACTIONS ON PLASMA SCIENCE 42 (10) 2550 - 2551 0093-3813 2014/10 [Refereed][Not invited]
    We simulated electron motion in confronting divergent magnetic fields (CDMFs) using a Monte Carlo method. Fundamental plasma structure under a filtering effect of the separatrix of CDMFs was depicted. Hot spots of energy deposition into electrons were observed not only near the RF antenna but also near the equistrength surface of 2B(ECR), where B-ECR is the RF-resonant magnetic field strength.
  • Yusuke Asami, Hirotake Sugawara
    IEEE TRANSACTIONS ON PLASMA SCIENCE 42 (10) 2540 - 2541 0093-3813 2014/10 [Refereed][Not invited]
    Production and transport of etchant ions in an RF (13.56 MHz) magnetic neutral loop (NL) discharge plasma in the presence and the absence of an ac (1.695 MHz) substrate bias were simulated using a Monte Carlo method. Under the bias, electrons accelerated near the NL were attracted to the substrate and produced more etchant ions near the substrate than in the absence of the bias. Effect of bias leading to enhancement of the ion inflow to the substrate was discussed.
  • Takuhei Yoshida, Yohei Sakurai, Hirotake Sugawara, Akihiro Murayama
    ELECTRICAL ENGINEERING IN JAPAN 185 (1) 9 - 16 0424-7760 2013/10 [Refereed][Not invited]
    We simulated electron and ion motions in a neutral loop discharge plasma under the control of the foot of the separatrix sweeping over the substrate and the neutral loop moving within a short distance from the RF antenna by a Monte Carlo method. We analyzed the distributions of ion production and ion flux to the substrate. We found that ion production is sensitive to the magnetic field gradient rather than to the electric field strength. Moreover, by superposing the flux distributions weighted by the residence time of the foot of the separatrix on the substrate, we obtained a uniform time-averaged distribution of the ion flux to the substrate in a radius range of r = 4.0 to 14.0 cm with sigma/m = 0.25% (m: mean, sigma: standard deviation). (c) 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(1): 9-16, 2013; Published online in Wiley Online Library ( DOI 10.1002/eej.22417
  • Hirotake Sugawara
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 (6) 064501-1 - 064501-6 0031-9015 2013/06 [Refereed][Not invited]
    Electron gyration and scattering in a gas under antiparallel gradient magnetic fields (APGMFs) and rf electric field were simulated using a Monte Carlo method to identify the factors of the electron confinement effect of the APGMFs. The inward shift of the gyrocenter at electron scattering worked as an additional factor to electron meandering, which has been regarded as the primary factor of the electron confinement. This scattering-based inward electron attraction occurs by a simple principle that the gyroradius and residence time of electrons become greater under weaker magnetic fields in the inner region of the APGMFs.
  • Hirotake Sugawara
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (5) 056101-1 - 056101-5 0021-4922 2013/05 [Refereed][Not invited]
    Electron conduction in CF4 under a simplified model quadrupole magnetic field (QMF) and rf electric fields at f = 13.56, 27.12, and 40.68 MHz was analyzed using a Monte Carlo method, following the manner of electron swarm analyses. This field configuration simulated current paths of magnetic neutral loop discharge plasmas used for dry etching. The electron conduction therein was focused on as an elemental process of plasma power deposition. The electrons formed a star-shaped distribution with four rays along the separatrices of the QMF. The effective electron conductivity quantified as the amplitude of mean electron velocity was high around the central axis. The time-averaged mean electron velocities in the four regions of the QMF were biased under a rectification effect of the magnetic field. With increasing f, the high-conductivity region expanded and ionization was promoted. An enhancement of plasma power deposition under high driving frequencies was indicated. (C) 2013 The Japan Society of Applied Physics
  • Takuhei Yoshida, Yohei Sakurai, Hirotake Sugawara, Akihiro Murayama
    IEEJ Transactions on Fundamentals and Materials 132 (4) 278 - 283 0385-4205 2012 [Refereed][Not invited]
    We simulated the electron and ion motions in a neutral loop discharge plasma under the control of the foot of separatrix sweeping over a substrate and the neutral loop moving within a short distance from the RF antenna by a Monte Carlo method. We analyzed the distributions of ion production and ion flux to the substrate. We revealed that ion production is sensitive to the gradient of magnetic field rather than the electric field strength. Moreover, by superposing the flux distributions weighted by the passage time of the foot of separatrix on the substrate, we obtained a uniform time-averaged distribution of ion flux to the substrate in a radius range of r = 4.0-14.0 cm with σ/m = 0.25% (m: the average, s: the standard deviation). © 2012 The Institute of Electrical Engineers of Japan.
  • Tsuyoshi Osaga, Hirotake Sugawara, Yohei Sakurai
    PLASMA SOURCES SCIENCE & TECHNOLOGY 20 (6) 065003-1 - 065003-7 0963-0252 2011/12 [Refereed][Not invited]
    Electron motion in a CF(4) magnetic neutral loop discharge (NLD) plasma was simulated using a Monte Carlo method. The spatial distribution of electrons illustrated the fundamental structure of the NLD plasma, and its dynamics were depicted from the distributions of the mean electron energy, the electron energy gain and the azimuthal electron flux. The peak of mean electron energy appeared at the neutral loop (NL), which confirmed that electrons gain energy near this loop. High mean electron energy was observed not only near the NL but also along the separatrices of the quadrupole magnetic field. Energetic electrons were transported along the separatrices and induced ionization at those locations. However, the electron distribution had valleys along the separatrices, because electrons accelerated near the NL were likely to leave this region where the binding of the magnetic field is weak. The azimuthal electron flux representing the loop plasma current showed that the electron conduction path around the NL, which has conventionally been modelled as a ring conductor, has a particular directionality due to the rectification effect of antiparallel magnetic fields composing the quadrupole magnetic field. The directionality in the upper and lower regions of the quadrupole magnetic field was opposite to that in the inner and outer regions.
  • Yushi Fukuda, Junichi Takayama, Norichika Asaoka, Yoshiyuki Suda, Hirotake Sugawara, Akihiro Murayama
    IEEE TRANSACTIONS ON PLASMA SCIENCE 39 (11) 3133 - 3139 0093-3813 2011/11 [Refereed][Not invited]
    Remote plasma is an efficient method to synthesize carbon nanomaterials because it can avoid the damage due to ion bombardment and can supply active precursor species for their growth. We introduced dc plasma to the CH(4) thermal chemical vapor deposition (CVD) of carbon nanotubes (CNTs) in order to decompose CH(4) efficiently. The effect of the plasma was investigated through the gas contents observed by a quadrupole mass spectrometer and the quality of CNTs evaluated by Raman spectroscopy. High-quality single-walled CNTs grew on Al(2)O(3)/Fe/Al(2)O(3) substrates, on which CNTs did not grow in conventional thermal CVD. The intensity ratio of the G peak to D peak in Raman spectra (G/D ratio) was 41.8. Since the CNT yield increased with the discharge voltage, the activation of precursors by the plasma seemed to promote the CNT growth significantly. At this time, C(2)H(x) and C(3)H(x), produced in the plasma, also increased. Thus, they seemed to contribute to the CNT growth. The diameter of CNTs, as well as the CNT yield, increased with increasing discharge voltage. This indicated the presence of the optimum precursor supply rate depending on the size of catalyst particles to keep them active.
  • Tsuyoshi Osaga, Yohei Sakurai, Hirotake Sugawara
    IEEE TRANSACTIONS ON PLASMA SCIENCE 39 (11) 2546 - 2547 0093-3813 2011/11 [Refereed][Not invited]
    We simulated the electron motion in a quadrupole magnetic field that drives a neutral loop discharge (NLD) plasma using a Monte Carlo method. The structure of the electron distribution in the NLD plasma was observed. Electrons underwent reciprocating motion between reflecting boundaries as they gyrated along magnetic field lines. During this motion, they deviated from the neutral loop and concentrated beside the separatrices of the quadrupole magnetic field.
  • Yohei Sakurai, Tsuyoshi Osaga, Hirotake Sugawara
    IEEE TRANSACTIONS ON PLASMA SCIENCE 39 (11) 2550 - 2551 0093-3813 2011/11 [Refereed][Not invited]
    The production and transport of ions in a neutral loop (NL) discharge plasma under a quadrupole magnetic field are investigated using a Monte Carlo method. The ion production occurred around the separatrices of the quadrupole magnetic field and decreased as the NL shrunk. The ion flux on the substrate had its peak near the foot of a separatrix. It was demonstrated that the time-averaged ion flux on the substrate can be distributed uniformly by controlling the magnetic field so that the foot of the separatrix sweeps over the substrate.
  • Hirotake Sugawara, Tsuyoshi Osaga, Hiromori Yamamoto
    PLASMA SOURCES SCIENCE & TECHNOLOGY 20 (5) 055002-1 - 055002-7 0963-0252 2011/10 [Refereed][Not invited]
    Electron transport in CF4 under linearly gradient antiparallel magnetic fields was analysed in order to investigate the fundamental properties of magnetic neutral loop discharge plasmas used for material processing. The electron motion was simulated by a Monte Carlo method under a radio-frequency (rf) electric field applied perpendicularly to the directions of both the magnetic field and its gradient. Two typical electron motions, meandering in a weak magnetic field and gyration in a strong magnetic field, were observed with particular directionalities. The meandering electrons drifted forward on average similarly to those under a dc electric field. The gyration induced an electron drift towards the inverse direction. The direction of electron flux was dependent not only on the rf phase but also on the distance from the magnetically neutral midplane between the antiparallel magnetic fields. The electron conduction path formed along the midplane had a structure consisting of forward and inverse lanes. A peculiar result was that the direction of local electron flux was always forward in the strong magnetic field whereas the drift of gyrating electrons was towards the inverse direction. This seemingly paradoxical result can appear in the presence of the density gradient of the electron distribution.
  • Hirotake Sugawara, Tsuyoshi Osaga, Hideo Tsuboi, Kiyoshi Kuwahara, Seiji Ogata
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 (8) 086001-1 - 086001-5 0021-4922 2010/08 [Refereed][Not invited]
    A Monte Carlo simulation of electron transport in electric and magnetic fields was performed to analyze experimental data of the electron temperature T(e) and electron number density n(e) measured in a magnetic neutral loop discharge (NLD) plasma driven in Ar at 0 13 Pa T(e) and n(e) in the vicinity of the substrate holder were measured with a triple probe, and their radial profiles had peaks at different radial positions The simulation reproduced these peak positions well under the chosen boundary condition that the electron reflectivity of the side wall was lower than that of the reactor ceiling and the substrate holder It was explained that the T(e) peak was formed by high-energy electrons transported from the, neutral loop along a separatrix of the quadrupole magnetic field and that the n(e) peak consisted of electrons undergoing reciprocating motion between the reactor ceiling and the substrate (C) 2010 The Japan Society of Applied Physics
  • Kouichiro Mizuno, Hirotake Sugawara, Akihiro Murayama
    IEEJ Transactions on Fundamentals and Materials 130 (4) 319 - 324 1347-5533 2010 [Refereed][Not invited]
    We have composed amorphous fluorocarbon (a-C:F) polymer films, which are low-k insulators, by plasma-enhanced chemical vapor deposition using C8F18 as the feedstock. In our previous attempts to form multi-layered a-C:F films under various combinations of plasma power density P and deposition time T, it was found that a-C:F films deposited at a high P (typically 2.0 W/cm3) in a short T (∼1 min) became wavy when they are deposited on other a-C:F films deposited at a low P (0.2 W/cm3). A heating experiment for the films showed that their thermal tolerance was dependent on P films deposited at 0.2 W/cm3 started to melt at 250-270°C, while those deposited at 2.0 W/cm3 did at 350-370°C. It is considered that species of the precursors for the a-C:F film deposition are determined by P through the degree of C8F18 decomposition. The waving is induced by heating the lower layer during the deposition of the upper layer. The following conditions are necessary for the waving the lower layer is deposited at a low P, the upper layer is deposited at a temperature at which the lower layer expands but does not melt, and the upper layer is not thickened excessively to keep its flexibility. © 2010, The Institute of Electrical Engineers of Japan. All rights reserved.
  • Yoshiyuki Suda, Atsushi Okita, Junichi Takayama, Akinori Oda, Hirotake Sugawara, Yosuke Sakai, Shinichiro Oke, Hirofumi Takikawa
    IEEE TRANSACTIONS ON PLASMA SCIENCE 37 (7) 1150 - 1155 0093-3813 2009/07 [Refereed][Not invited]
    We have successfully grown carbon nanotubes (CNTs) by plasma-enhanced chemical vapor deposition (PECVD) using alcohol. When 0.01-wt% ferrocene was added to the alcohol, vertically aligned CNTs grew at 650 degrees C. By contrast, a few CNTs and mostly carbon nanoparticles; were obtained by pure alcohol PECVD even though the Fe catalyst was coated on Si substrates. Comparing this PECVD experiment with thermal alcohol CVD showed that only the PECVD method can be used to grow CNTs under the reported experimental conditions. To understand the plasma properties for CNT growth, particularly plasma species contained in a gas phase of alcohol plasma, the plasma was analyzed using optical-emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). From the OES measurement, emission peaks from the excitation states Of C(2), CH, CHO, CH(2)O, CO, H, O(2), C(+), and CO(+) were identified, while the QMS measurement also showed the existence of H(2), O, and CO. These results indicate that, in alcohol plasma, oxidants and reductants exist together and potentially promote/suppress CNT growth depending on the process conditions. The contribution of C(x)H(y) (x >= 1, y >= 3) radicals, which were produced by decomposition reactions in alcohol plasma as a CNT precursor, is discussed.
  • Krishnendu Bhattacharyya, Yoshiyuki Suda, Atsushi Okita, Takeshi Saito, Atsushi Ozeki, Masayuki Maekawa, Junichi Takayama, Hirotake Sugawara, Yosuke Sakai
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (3) 1897 - 1903 1533-4880 2009/03 [Refereed][Not invited]
    Based on recent theoretical photoluminescence intensity calculations, the population densities of sixteen semiconducting single-walled carbon nanotubes grown by alcohol catalytic chemical vapor deposition were estimated for two different temperatures. The profiles of population density merely as functions of tube-diameter or chiral angle are found to be widely scattered. However, systematic profiles are detectable when separately split into (2n+m), (n+2m) and (n-m) family arrays. Apart from these well-knit family behaviors, the population densities of the group of nanotubes forming another three possible series [viz. constant-n, constant-m and constant-(n+m)] also show evidence of good correlations. Hence, a two-dimensional chiral-zone selective growth principle is hypothesized.
  • Hirotake Sugawara, Yosuke Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 41 (13) 135208-1 - 135208-7 0022-3727 2008/07 [Refereed][Not invited]
    Electron motion in CF(4) at 0.67 Pa under crossed electric (E) and magnetic (B) fields was simulated by a Monte Carlo method to investigate fundamental properties of electron transport in neutral loop discharge plasmas for dry etching. As a simplified model of the electron path in the plasma, a magnetically neutral plane was assumed between linearly gradient antiparallel B fields, and a uniform E field was applied along the neutral plane perpendicularly to the B fields. The electron behaviour showed two contrasting modes depending on the direction of the B fields relative to the E field. In the field configuration which confines the electrons near the neutral plane, values of the mean electron energy, the drift velocity and the effective ionization frequency were close to those under the dc E field without B field. On the other hand, in the opposite B field configuration, the electrons hardly drifted along the E field, but instead, they showed a constant lateral diffusion driven by the E x B drift. A reverse-blocking effect of the gradient antiparallel B fields is reported.
  • Youhei Hizume, Atsushi Okita, Akinori Oda, Hirotake Sugawara, Yoshiyuki Suda, Yosuke Sakai
    IEEJ Transactions on Fundamentals and Materials 128 (10) 5 - 628 0385-4205 2008 [Refereed][Not invited]
    A CH4/H2 radio frequency capacitively coupled plasma used for synthesis of carbon nanotubes (CNTs) was simulated with a 1-dimensional fluid model. The pressure of CH4 was fixed at 1 Torr and that of H2 varied from 0 to 9 Torr. When the H2 mixture ratio was 0.1, the fluxes of H2 + and H3 + to the substrate were respectively about 5 and 10 times those for the case without H2 mixing. In our previous experiment, a slight mixture of H 2 promoted CNT growth. We inferred that this was because H 2 maintained the activity of the catalyst particle from which CNT grew. The present numerical result supports our hypothesis. In addition, C xHy(x, y≥2) accumulated with time. This accumulation is not negligible because it lowers the electron temperature. We estimated the H2 ionization rate in CH4/CxHy is about 2/3 of that in CH4. It is pointed out that we need to consider the accumulation of CxHy to improve the accuracy of the estimation of CNT growth. © 2008 The Institute of Electrical Engineers of Japan.
  • Dual distributions for the metallic and semiconducting single-walled carbon nanotubes observed by Raman spectroscopy
    K. Bhattacharyya, Y. Suda, A. Okita, T. Saito, A. Ozeki, M. Maekawa, J. Takayama, H. Sugawara, Y. Sakai
    Carbon - Sci. Tech. 1 4 - 8 2008 [Refereed][Not invited]
  • Atsushi Okita, Yoshiyuki Suda, Akinori Oda, Junji Nakamura, Atsushi Ozeki, Krishnendu Bhattacharyya, Hirotake Sugawara, Yosuke Sakai
    CARBON 45 (7) 1518 - 1526 0008-6223 2007/06 [Refereed][Not invited]
    Carbon nanotubes (CNTs) were synthesized using CH4/H-2 plasmas and plasmas simulated using a one-dimensional fluid model. The thinnest and longest CNTs with the highest number density were obtained using CH4/H-2 = 27/3 sccm at 10 Torr. These conditions allowed CNTs to grow for 90 min without any meaningful loss of catalyst activity. However, an excess H-2 Supply to the CH4/H-2 mixture plasma made the diameter distribution of the CNTs wider and the yield lower. Hydrogen concentration is considered to affect catalyst particle size and activity during the time interval before starting CNT growth (=incubation period). With CH4/H-2 = 27/3 sccm for a growth time of 10 min efficient CNT growth was achieved because the amount of carbon atoms in the CNTs and that calculated from simulation showed good agreement. The effect of hydrogen etching on CNTs was analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy by observing CNTs treated by H-2 plasma after CNT growth. It was confirmed that (a) multi-walled CNTs were not etched by the H-2 plasma, (b) the C 1s XPS spectra of the CNTs showed no chemical shift after the treatment, and (c) C-H bonds were produced in CNTs during their growth. (c) 2007 Elsevier Ltd. All rights reserved.
  • Hirotake Sugawara, Naoki Mori, Yosuke Sakai, Yoshiyuki Suda
    JOURNAL OF COMPUTATIONAL PHYSICS 223 (1) 298 - 304 0021-9991 2007/04 [Refereed][Not invited]
    Techniques to reduce the computational load for determination of electron-molecule collisions in Monte Carlo simulations of electrical discharges have been presented. By enhancing the detection efficiency of the no-collision case in the decision scheme of the collisional events, we can decrease the frequency of access to time-consuming subroutines to calculate the electron collision cross sections of the gas molecules for obtaining the collision probability. A benchmark test and an estimation to evaluate the present techniques have shown a practical timesaving efficiency. (c) 2006 Elsevier Inc. All rights reserved.
  • Yuki Hayakawa, Yoshiyuki Suda, Tamotsu Hashizume, Hirotake Sugawara, Yosuke Sakai
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 (12-16) L362 - L364 0021-4922 2007/04 [Refereed][Not invited]
    Hydrogen gas sensors based on single-walled carbon nanotube (SWCNT) films were fabricated with Pd comb-like electrodes. The SWCNT films were deposited by Mo/Co catalyst-assisted chemical vapor deposition using alcohol. The film included a high-density network of SWCNTs. The SWCNT film sensor showed a large conductance change and a fast response (20s) upon exposure to 1% H-2 gas in air at room temperature, while the conductance change was negligible for devices using Au electrodes.
  • Atsushi Okita, Atsushi Ozeki, Yoshiyuki Suda, Junji Nakamura, Akinori Oda, Krishnendu Bhattacharyya, Hirotake Sugawara, Yosuke Sakai
    We synthesized vertically aligned carbon nanotubes (CNTs) using multilayered catalyst thin films (Fe/Al2O3 and Al2O3/Fe/Al2O3) by RF (13.56 MHz) CH4/H-2/Ar plasma-enhanced chemical vapor deposition. Pretreatment of the catalyst is crucial for CNT growth. In this paper, we analyzed the effect of catalyst reduction on CNT growth. Catalyst thin films on substrates were reduced by H-2 plasma pretreatment at 550 degrees C to form nanometer-sized catalyst particles. The multilayered thin films were analyzed; the chemical composition and oxidation state by X-ray photoelectron spectroscopy (XPS) and the surface morphology by scanning electron microscopy (SEM). The Fe 2p peak of the XPS spectra showed that FexOy in the as-deposited catalyst was effectively reduced to Fe by a pretreatment of duration 4 min. Using this catalyst, we obtained CNTs with an average diameter of 10.7 nm and an average length of 5.3 mu m. However, pretreatment longer than 4 min resulted in shorter CNTs and the Fe peak was shifted from Fe to Fe3O4. These transitions (Fe2O3 -> Fe3O4 -> Fe -> Fe3O4) can be explained by the enthalpy of the oxides. This result indicates the presence of an optimum ratio between Fe and FexOy to maximize the CNT lengths.
  • H Sugawara, Y Sakai
    When an electron swarm in gas is composed of component electron swarms individually in drift equilibrium, the higher-order diffusion coefficients (HDCs) of the composite electron swarms are equal to those. of the component electron swarms. We have derived this equality theoretically and have examined it by numerical simulation. The HDCs are the time derivatives of higher-order cumulants, which are quantities characterizing the shape of a spatial electron distribution. This fact seemingly indicates the dependence of the HDCs of the composite electron swarms on the arrangement of the component electron swarms. However, the equality holds irrespective of the relative positions and electron populations of the component electron swarms. We have given a consistent explanation to these facts. We have also discussed electron swarm development from dispersed or multiple electron sources that may appear in practical experiments.
  • MA Bratescu, Y Yoshizaki, Y Suda, Y Sakai, H Sugawara, O Takai
    THIN SOLID FILMS 506 145 - 149 0040-6090 2006/05 [Refereed][Not invited]
    A dielectric barrier discharge (DBD) in Ar/CH4 gas mixtures used for amorphous hydrogenated carbon (a-C:H) film deposition was investigated. It was found that the a-C:H film properties (the ratios of sp(3)/Isp(2) and CH3/CH2, the number density of hydrogen atoms in the film and the energy band gap) correlate with the number densities of Ar(I-S5) atom and CH(chi(2) Pi) radical. A high value of the energy band gap, which corresponds to a high content of sp(3) fraction in the film was obtained, when the CH radical number density in the plasma was relatively small (similar to 10(8) cm(-3)). The DBD breakdown voltage decreased when the a-C:H film was deposited on the dielectric surface of the electrode. (c) 2005 Published by Elsevier B.V.
  • A Okita, Y Suda, A Ozeki, H Sugawara, Y Sakai, A Oda, J Nakamura
    JOURNAL OF APPLIED PHYSICS 99 (1) 014302-1 - 014302-7 0021-8979 2006/01 [Refereed][Not invited]
    Carbon nanotubes (CNTs) were grown on Si substrates by rf CH4 plasma-enhanced chemical vapor deposition in a pressure range of 1-10 Torr, and then characterized by scanning electron microscopy. At 1 Torr, the CNTs continued growing up to 60 min, while their height at 4 Torr had leveled off at 20 min. CNTs hardly grew at 10 Torr and amorphous carbon was deposited instead. CH4 plasma was simulated using a one-dimensional fluid model to evaluate the production and transport of radicals, ions, and nonradical neutrals. The amount of simulated carbon supplied to the electrode surface via the flux of radicals and ions such as CH3, C2H5, and C2H5+ was consistent with estimations from experimental results.
  • Analysis of CH4 rf plasmas for carbon naotube growth: Comparison between computer modeling and experimental results
    A.Okita, Y.Suda, A.Ozeki, H.Sugawara, Y.Sakai, A.Oda, J.Nakamura, 中村, 潤児
    J.Appl.Phys 99 014302  2006/01 [Refereed][Not invited]
  • H Sugawara, A Oda, Y Sakai
    IEEE TRANSACTIONS ON PLASMA SCIENCE 33 (2) 548 - 549 0093-3813 2005/04 [Refereed][Not invited]
    Monte Carlo simulation shows that the electron velocity distribution function (EVDF) in CF4 in crossed electric and magnetic fields (E x B fields) has two peaks at low E/B values. The EVDF peaks are formed around a pair of points in velocity space at which electrons are stationary against the acceleration under the E x B fields and scattering by collisions with CF4 molecules. The stationary points appear when the E/B value is lower than the electron speed at which the total electron collision frequency in CF4 takes its minimum.
  • Investigation of excited species in a carbon ablation plume in nitrogen gas environment
    M. A. Bratescu, Y. Sakai, N. Sakura, D. Yamaoka, Y. Suda, H. Sugawara
    Plasma Processes and Polymers 489 - 498 2005 [Refereed][Not invited]
  • H Sugawara, T Ishigaki, Y Hirochi, Y Sakai
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 43 (11A) 7705 - 7706 0021-4922 2004/11 [Refereed][Not invited]
    It has been predicted that near-threshold ionization (NTI) in a gaseous dielectric inhibits the development of electron avalanche when the gaseous dielectric has a sufficient capability for low-energy electron attachment. The NTI leaves little energy for the primary and secondary electrons involved in the ionization; thus, both electrons can be captured by dielectric gas molecules without further ionization. A computational estimation indicates that this process can occur in SF6.
  • MA Bratescu, N Sakura, D Yamaoka, Y Sakai, H Sugawara, Y Suda
    APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 79 (4-6) 1083 - 1088 0947-8396 2004/09 [Refereed][Not invited]
    In this work, we investigated a carbon plasma plume produced by laser ablation of a graphite target in a nitrogen gas environment. The spatial distributions of C and N atoms were measured by time-resolved absorption spectroscopy. The spatial distributions of the relative densities of CN radicals, C-2, and C-3 molecules were measured using time-resolved emission spectroscopy. We determined that nitrogen gas produced an increase in carbon atom and molecule densities in the ablation plume. It was observed that the addition of RF plasma to the plume increased the CN radicals and C atom densities, and decreased the C-2 and C-3 molecule densities. The RF plasma changed the evolution of various fractional species of C, N, CN, C-2, and C-3 in the ablation plume. The chemical reactions with and without RF plasma were explained using the evolution and density of the fractional species of C, N, CN, C-2, and C(3)in the plume.
  • C Biloiu, IA Biloiu, Y Sakai, H Sugawara, A Ohta
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 22 (4) 1158 - 1165 0734-2101 2004/07 [Refereed][Not invited]
    Amorphous fluorocarbon polymer films (a-C:F) have been grown by plasma enhanced chemical vapor deposition from a new precursor, namely perfluoro-octane (C8F18) vapor. The dielectric and insulating properties of the films have been assessed by means of capacitance-voltage and current-voltage characteristics, breakdown voltage measurements, scanning electron microscopy, and ellipsometric analyses. In the investigated frequency range, 120 Hz-1 MHz, the films have a low dielectric constant (approximate to2.4) and a low dielectric loss (less than or equal to3 x 10(-2)). The electrical conduction mechanism is ohmic in the weak electric field regime, with a bulk resistivity of 4 x 10(15) Omega cm, and a trap modulated space charge limited conduction in the strong electric field regime. For a film thickness between 1 and 12 mum, the dielectric strength varies with film thickness according to E(B)similar toh(-0.53). For a film thickness of 1 mum the film dielectric strength was 2.7 MV/cm while for 12 mum it decreased to 0.9 MV/cm. Measurements of the breakdown voltage in nitrogen gas in the low pressure regime between a-C:F coated cathode and copper anode showed an enhancement of the breakdown voltage by a factor of 2.5 with respect to the case of copper-copper electrodes. (C) 2004 American Vacuum Society.
  • Takuya Ishigaki, Yuuki Hirochi, Hirotake Sugawara, Yosuke Sakai
    IEEJ Transactions on Fundamentals and Materials 124 (2) 126 - 131 1347-5533 2004 [Refereed][Not invited]
    In a recent trend that reduction of SF6 used for electric power equipment is required to avoid global warming, dilution of SF6 by other gases of less environmental load is considered as a practical solution. Gas mixtures such as SF6/N2 and SF6/c-C4F8 have a desirable feature called synergy effect that the critical values of reduced electric field (E/N)lim are higher than the partial-pressure-weighted values obtained from (E/N)lim of their components. In order to obtain a guide to seek for new insulating gas mixtures with the synergy effect, we have investigated the synergy mechanism from a viewpoint of collaboration between electron energy loss by collisions and electron attachment. The following mechanisms have been indicated as primary factors of the synergy effect (i) a large attachment cross section of SF6 lying in a low electron energy region plays the main role of the electron capture (ii) in order to feed electrons into the low energy region of (i) efficiently, a steep rise of an inelastic collision cross section at its onset energy is required. We have evaluated these factors by a Boltzmann equation analysis, and have synthesized the synergy effect using model gases for demonstration. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.
  • Yasunao Yoshizaki, Maria-Antoaneta Bratescu, Yosuke Sakai, Yoshiyuki Suda, Hirotake Sugawara
    IEEJ Transactions on Fundamentals and Materials 124 (2) 158 - 163 1347-5533 2004 [Refereed][Not invited]
    A dielectric barrier discharge in Ar and CH4 gas mixtures used for a-C:H film deposition was investigated. The number densities of Ar(1s2: resonant level) and Ar(1s5: metastable levels) atoms were measured using a high sensitive detection method based on plasma modulation and laser absorption spectroscopy. The CH(X2П) radical number density was measured by an actinometry method. The excitation transfer process from the Ar(1s5) atom to the CH(A2Δ) radical was detected by a laser collisionally induced fluorescence method. The a-C:H film properties (the content of sp3 and sp2 hybridization and the content of the CH3 and CH2 hydrocarbon groups) were correlated with the number densities of the Ar(1s5) atom and the CH(X2П) radical. In the a-C:H film, maximum value of the sp3/sp2 was obtained, when the CH(X2П) number density in DBD plasma was minimum. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.
  • H Sugawara, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 36 (16) 1994 - 2000 0022-3727 2003/08 [Refereed][Not invited]
    We have simulated electron acceleration under short intense impulse electric fields of 0.1-1 kV cm(-1) strength and similar to1 ns duration in N-2 at 65.5 Pa. The electron acceleration is completed in a practically collisionless condition when the impulse duration is comparable with or shorter than the electron mean free time. On the basis of this feature, we have proposed a way to produce a group of monoenergetic electrons. The electron energy after acceleration is controllable by the impulse strength and duration, and we have demonstrated selective promotion of the excitation producing N-2(A(3)E(u)(+)) metastable excited molecules. The selectivity has been quantified as the efficiency of the electron energy utilized for the target reaction, and efficiencies of 20-30% have been achieved in this simulation. These values are higher than those of electron swarms in DC equilibrium, in which the efficiency is at most 10%. The electron behaviour under impulse electric fields and the dependence of the energy efficiency on the impulse profile have been investigated.
  • SY So, A Oda, H Sugawara, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 35 (22) 2978 - 2987 0022-3727 2002/11 [Refereed][Not invited]
    CF4 radio frequency (rf) (13.56 MHz) capacitively coupled plasmas were simulated using a two-dimensional fluid model of cylindrical symmetry. We investigated their periodic steady state and transient behaviour after step changes of the amplitude of a power source voltage. The results were compared with those obtained by a one-dimensional model. The two-dimensional model showed that the plasmas in a harmonic steady state have asymmetric profiles due to generation of a dc self-bias through an asymmetric electrode system with grounded wall. The transient response of the plasmas in the two-dimensional model was qualitatively similar to those of the one-dimensional model except in the powered electrode edge region where the radial component of the electric field was significant.
  • MA Bratescu, Y Sakai, D Yamaoka, Y Suda, H Sugawara
    APPLIED SURFACE SCIENCE 197 257 - 262 0169-4332 2002/09 [Refereed][Not invited]
    In a plume produced by excimer ArF laser, the number densities of excited atoms and electrons, and the expansion velocity of ablated carbon atoms in an Ar gas were measured and compared with those obtained in vacuum. A saturation in C(3(1)P(1)(0)) density was observed as the laser fluence increased. This saturation was shown to be closely related to the electron density saturation. The excitation of Ar(4s'[1/2](1)(0)) and C(3(1)P(1)(0)) was interpreted by electron collisions and was dependent on gas pressure and excimer laser fluence. (C) 2002 Elsevier Science B.V All rights reserved.
  • プラズマディスプレイ用混合希ガス中の励起移行効果
    内田諭, 菅原広剛, 酒井洋輔, 渡辺恒雄
    電気学会論文誌A 122-A (8) 729 - 735 2002 [Refereed][Not invited]
  • H Sugawara, K Satoh, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 34 (21) 3191 - 3196 0022-3727 2001/11 [Refereed][Not invited]
    The electron velocity distribution function (EVDF) of electron swarms in N-2 has a constricted part at an electron energy of around 2-3 eV. This feature has been explained by considering the barrier effect of vibrational excitation collisions that prevents the gain of energy by slow electrons. In order to investigate the barrier effect in detail further, we simulated the electron behaviour around the energy range of the barrier. We found that momentum transfer collisions also contribute to the barrier effect in collaboration with vibrational excitation. In addition, an evaluation of the electron flow in velocity space is thought to indicate a factor by which the presence of the barrier effect in N-2 is revealed in the EVDF; the depression of the electron interchange across the barrier is not only due to the barrier effect itself but also due to the small electron transfer associated with the energy loss by electronic excitation.
  • SY So, A Oda, H Sugawara, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 34 (12) 1919 - 1927 0022-3727 2001/06 [Refereed][Not invited]
    CF4 radio-frequency (rf) plasmas are often driven in time-modulation modes to obtain higher etching performance. For dynamic and stable control of CF4 plasmas, we investigated the transient behaviour of the plasmas after step up or down of the amplitude of the power source voltage V-s (t). Using a one-dimensional fluid model, we simulated a CF4 capacitively coupled plasma that transfers from a periodic steady state to another at 0.2 Torr in a 20 mm parallel-plate gap. In addition, we compared such plasma responses to the step down to 0 V at the phases at which V-s(t) takes zero and peak values. Fundamental properties of transient CF4 plasmas were discussed.
  • S Uchida, H Sugawara, Y Sakai, T Watanabe, BH Hong
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 34 (6) 947 - 953 0022-3727 2001/03 [Not refereed][Not invited]
    The influence of Ar addition to conventional Plasma Display Panel gases, Xe/Ne and Xe/He mixtures, on the radiation characteristics and the discharge onset voltage is studied using a Boltzmann equation method coupled with rate equations for electrons and excited species. When Ar is added to Xe/Ne mixtures, the efficiency of ultraviolet light radiation from Xe (1S(2,4)) and Xe-2* increases 7-17% for E / p(0) between 3 and 100 V cm(-1) Torr(-1). In Xe/He mixtures, the efficiency increases over 20% for E / p(0) < 10 V cm(-1) Torr(-1) In addition, the visible light radiation of the 600 nm band from excited Ne, which makes the contrast worse, is effectively reduced. On the other hand, the discharge onset voltage increases with Ar addition because of a decrease in the effective secondary electron emission coefficient.
  • CxFy polymer film deposition in rf and dc C7F16 vapor plasmas
    Y. Sakai, M. Akazawa, Y. Sakai, H. Sugawara, M. Tabata, C. P. Lungu, A. M. Lungu
    Transactions of Korean Institute of Electrical and Electronic Material Engineers 2 (1) 1 - 6 2001/03 [Refereed][Not invited]
  • CP Lungu, AM Lungu, Y Sakai, H Sugawara, M Tabata, M Akazawa, M Miyamoto
    VACUUM 59 (1) 210 - 219 0042-207X 2000/10 [Refereed][Not invited]
    Polymer films containing CxFy have been deposited in Fluorinert vapor (C7F16) plasmas. The spatial and temporal evolution of optical emission of CF2 and C-2 radicals was monitored and kinetics of the C7F16 decomposition process was discussed. The films were deposited on stainless steel, glass, molybdenum and silicon wafers at room temperature with the vapor pressures, 40 and 100 Pa. Electrical properties such as the breakdown voltage and dielectric constant as well as the structure of the films were analyzed. The composition and characteristics of the films were determined by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques, scanning electron microscopy and electron spin resonance spectroscopy. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • A Oda, H Sugawara, Y Sakai, H Akashi
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 33 (12) 1507 - 1513 0022-3727 2000/06 [Refereed][Not invited]
    Xe dielectric barrier discharges at different gap lengths under applied pulse voltages with trapezoidal and sinusoidal waveforms were simulated using a self-consistent one-dimensional fluid model. In both waveforms, the light output power depended not only on the amplitude of voltage waveforms but also on the discharge gap length. At the narrower discharge gap, the light output efficiency was improved by increasing the time gradient of the applied voltage when the trapezoidal pulse is applied, and by decreasing the duty ratio in the sinusoidal case. In the present simulation, we adopted a fast numerical method for calculation of electric field introducing an exact expression of the discharge current.
  • H Sugawara, T Yahata, A Oda, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 33 (10) 1191 - 1196 0022-3727 2000/05 [Refereed][Not invited]
    We calculated the drift velocity vector W Of electron swarms in crossed electric and magnetic fields using a Monte Carlo method. Values of W in F-2, CF4 and constant-collision-frequency (CCF) model gases at various values of the reduced electric and magnetic fields, E/N and B/N (N is the gas molecule number density), were illustrated as vector loci in velocity space. Under a CCF condition, W draws right semicircular loci with varying B and N at a constant E when the number of electrons is conservative. These semicircular loci can be a reference to characterize the W behaviour in real gases. We presented an analytical derivation of W in the CCF condition, extending its expression to that in the presence of ionization and attachment. Features of thr vector loci in F-2 and CF4 were discussed.
  • E Suetomi, M Tanaka, S Kamiya, S Hayashi, S Ikeda, H Sugawara, Y Sakai
    COMPUTER PHYSICS COMMUNICATIONS 125 (1-3) 60 - 74 0010-4655 2000/03 [Refereed][Not invited]
    Direct current glow discharge plasma sources are being developed as reactors for immobilization of radioactive krypton gas recovered from the off-gas stream of a nuclear fuel reprocessing plant. In order to design these reactors, two-dimensional simulations have been performed using a fluid model coupled with Poisson's equation. Nonlinear governing equations were expressed by a fully implicit scheme and the equations were solved using the Newton-Krylov method. Mr, investigated algorithm performance of two methods from the Krylov projection techniques, namely the Bi-CGSTAB method and the transpose-free quasi-minimal residual (TFQMR) method. The results showed that the Bi-CGSTAB method converged considerably faster than the TFQMR method. Direct current glow discharge plasmas in three types of krypton immobilization apparatus were simulated to study the differences in electrode geometry. Simulation results agreed qualitatively with measurements of electron density. (C) 2000 Elsevier Science B.V. All rights reserved.
  • S Uchida, H Sugawara, Y Sakai, T Watanabe, BH Hong
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 33 (1) 62 - 71 0022-3727 2000/01 [Refereed][Not invited]
    The electron swarm parameters of Xe/He and Xe/Ne mixtures are analysed with a Boltzmann equation method in which secondary generations of electrons through excited atoms are properly considered. The swarm parameters are examined for a wide range of the electron concentrations from the Townsend discharge region to thr: working condition of plasma display panels (PDPs). Using ionization coefficients obtained in this work and referred values of secondary electron emission coefficients from MgO film, the discharge onset voltage V-b is discussed. The Paschen curves around (p(0)d)(min) at which V-b has a minimum are compared for Xe/He and Xe/Ne mixtures. Under the working conditions for PDP discharges, the radiation rates of ultraviolet light (lambda = 130, 147 and 173 nm) from the Xe resonance levels and Xe excimer are calculated. A suitable discharge condition for designing PDP is discussed with respect to various values of the gas mixture ratio, gas pressure and reduced electric field.
  • CP Lungu, AM Lungu, M Akazawa, Y Sakai, H Sugawara, M Tabata
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 38 (12B) L1544 - L1546 0021-4922 1999/12 [Refereed][Not invited]
    An attempt to fabricate fluorinated carbon (fluoropolymer) films by rf (13.56 MHz) plasma enhanced chemical vapor deposition was made using novel fluorocarbon sourer materials of C7F16, (C3F7)(3)N/(C4F9)(3)N and C8F18/C8F16O. The deposited films were transparent and displayed excellent electrical properties as interlayer dielectrics for LSI using deep-submicron technology, namely, a dielectric constant as low as 2.0 and a dielectric strength higher than 2 MV/cm. The refractive index of these films was 1.38.
  • A Oda, Y Sakai, H Akashi, H Sugawara
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 32 (21) 2726 - 2736 0022-3727 1999/11 [Refereed][Not invited]
    A self-consistent one-dimensional modelling of a Xe gas discharge between electrodes covered with dielectric barrier is presented for power frequencies from 50 kHz to 1 MHz and gas pressures from 10 to 400 Tan Spatiotemporal profiles of the concentration of electrons, ions, excited atoms and excimers are obtained. Excimers are mainly produced in the sheath regions. The efficiencies of spontaneous emission from excimers and resonance-state atoms increase with an increase in the input powers for gas pressures higher than 50 Torr. A characteristic period during which the barrier wall charge significantly influences the electric field in bulk region was found, and discharge properties in the period are discussed.
  • H Sugawara, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 32 (14) 1671 - 1680 0022-3727 1999/07 [Refereed][Not invited]
    A simulation technique for the analysis of the transverse evolution of electron swarms in gases was developed based on moment equations derived from the Boltzmann equation. A numerical calculation of the moment equations for an electron swarm was performed using a propagator method and it was demonstrated that the propagator method can be used to calculate the higher-order transverse diffusion coefficients stably. Applying a Hermite expansion technique, the electron distribution in real space and other electron swarm parameters were derived as functions of the transverse position. The calculation result was verified by comparisons with those by a Monte Carlo simulation and other methods. Features of the transverse electron swarm evolution were presented.
  • H Sugawara, Y Sakai, H Tagashira, K Kitamori
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 31 (3) 319 - 327 0022-3727 1998/02 [Refereed][Not invited]
    Spatio-temporal development of electron swarms in gases is simulated using a propagator method based on a series of one-dimensional spatial moment equations. When the moments up to a sufficient order are calculated, the spatial distribution function of electrons, p(x), can be constructed by an expansion technique using Hermite polynomials and the weights of the Hermite components are represented in terms of the electron diffusion coefficients. ii is found that the higher order Hermite components tend to zero with time; that is, the normalized form of p(x) tends to a Gaussian distribution. A time constant of the relaxation is obtained as the ratio of the second-and third-order diffusion coefficients, D-3(2)/D-L(3). The validity of an empirical approximation in time-of-flight experiments that treats p(x) as a Gaussian distribution is indicated theoretically. It is also found tl-lat the diffusion coefficient is defined as the derivative of a quantity called the cumulant which quantifies the degree of deviation of a statistical distribution from a Gaussian distribution.
  • J Yang, PLG Ventzek, H Sugawara, Y Sakai, K Kitamori, H Tagashira
    JOURNAL OF APPLIED PHYSICS 82 (5) 2093 - 2105 0021-8979 1997/09 [Refereed][Not invited]
    Models capturing the periodic steady-state behavior of rf capacitively coupled discharges are now commonplace. New plasma sources have been motivated by selectivity, charge-damage mitigation, and general process control needs in plasma processing of electronic materials. These new sources require models that can accurately capture the transient behavior of the plasma source. Such models are not commonplace because the behavior of transport parameters in transients is still not well understood and because the problem is inherently stiff, i.e., widely disparate time scales are important. In this paper, we present the results of an investigation of the simplest type of transient, known as a step disturbance, in a 2 cm gap parallel-plate argon discharge at 1 Torr. As examples, two classes of step transients are considered: step increases in the peak-to-peak (pp) applied voltage (300 to up to 450 V pp) and step decreases (300 to as low as 150 V pp). The resulting transients are interpreted in terms of time scales representative of electron and ion motion in the sheath, ionization dynamics, and neutral transport processes. The possibility of using these transients as a means of process identification is discussed. (C) 1997 American Institute of Physics.
  • H. Sugawara, H. Tagashira, Y. Sakai
    電気学会論文誌A 117-A (7) 749 - 753 1997/06 [Refereed][Not invited]
  • H Sugawara, H Tagashira, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 30 (3) 368 - 373 0022-3727 1997/02 [Refereed][Not invited]
    The centroid drift velocity W-r and the mean electron velocity W-v of electron swarms in gases have different values even under the same electric field when electron-impact ionization and/or electron attachment processes are present. A new evaluation technique for W-r is proposed based on moment equations, in which the quantitative difference between W-r and W-v is described as a function defined in velocity space. W-r values are derived from calculations using a propagator method performed in velocity space without the electron distribution in real space. The effects of ionization and attachment on W-r are quantitatively analysed for F-2 and SF6, and the mechanism producing the difference between W-r and W-v is illustrated.
  • H Sugawara, H Tagashira, Y Sakai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 29 (5) 1168 - 1174 0022-3727 1996/05 [Refereed][Not invited]
    An explicit expression for the velocity distribution of ion swarms in warm gas is deduced for a constant-collision-frequency symmetric charge exchange model. The ion velocity distribution, the drift velocity and the diffusion coefficient are calculated under DC and AC electric fields. It is found that the ion velocity distribution normalized with respect to the thermal velocity is a function only of dimensionless parameters fixed by physical quantities given as analysis conditions. These dimensionless parameters are potentially good scaling parameters by which different experimental conditions may be compared.
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 28 (1) 61 - 67 0022-3727 1995/01 [Refereed][Not invited]
    Exponential spatial growth of electron swarms in gases under steady-state Townsend conditions may be observed not only in the downstream region of an electron source but also in the upstream region due to backward diffusion. Relations among swarm parameters in the upstream region were deduced and found to have peculiar characteristics. For example, the sign of the average electron velocity V-d for steady-state Townsend conditions depends on whether the gas is electropositive or electronegative. This property is confirmed quantitatively by calculating the electron energy distribution using a propagator method modified for analysis in the upstream region. As an example of the effect of backward diffusion, the decay in the electron number density in front of the anode in a steady-state Townsend experiment between parallel plane electrodes was studied. The decay is caused by the missing electrons absorbed at the anode. The energy distribution of the missing electrons has a non-equilibrium relaxation region and the equilibrium region lies towards the cathode direction. The number density of the missing electrons showed an exponential spatial dependence in the equilibrium region. The relative gradient of the decrease agreed well with the relative density gradient alpha obtained in the upstream region. It was also found that the electron energy distribution in the decaying region tends to that in the upstream equilibrium region.
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 27 (1) 90 - 94 0022-3727 1994/01 [Refereed][Not invited]
    A new simulation technique for obtaining the equilibrium electron energy distributions of electron swarms in gases under steady-state Townsend conditions is proposed based on a propagator method. The electron energy distribution function could be obtained from calculations in only one slab in real space, assuming exponential spatial growth of an electron swarm and similarity of the electron energy distribution at any position. The electron energy distributions were analysed in argon at E/N = 1414 Td for a case of a positive large value of the effective ionization coefficient alpha and in an argon (90%)/fluorine (10%) mixture at E/N = 56.6, 84.8, 113.1 and 141.1 Td for a case of values of alphaBAR crossing zero. The results agreed excellently with those of a Monte Carlo simulation and a Boltzmann equation analysis. This propagator method was found to deduce stably proper solutions for both positive and negative values of alphaBAR. A relation between the present method for a steady-state Townsend condition and a similar method for a pulsed Townsend condition is discussed.
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 25 (10) 1483 - 1487 0022-3727 1992/10 [Refereed][Not invited]
    The position-dependent swarm parameters and the energy distribution F(epsilon, x) of electrons in argon gas have been analysed using a propagator method in which a proper relation between the trajectories of electrons and the cells in an energy epsilon and position x space were considered. The results showed fine structures of damped fluctuation in the swarm parameters, which had been seen from the results of a Monte Carlo method. When initial electrons with zero energy were ejected from the cathode, F(epsilon, x) at E/N = 283 Td could not reach the equilibrium condition even at the distance at which the equilibrium values of mean energy, drift velocity, etc of electrons seemed to have already been obtained.


Books etc

  • 放電基礎パラメータと放電応用技術の最前線
    菅原 広剛 (Contributor2.2.1節「プロパゲータ法による電子スオーム解析」、2.2.2節「モンテカルロ法における電子衝突判定の高速化」)
    社団法人電気学会 2010/04
  • 窒素の放電プラズマが見せる多様性と最新応用
    菅原 広剛 (Contributor5章1節「N2およびSF6/N2混合ガス中の電子衝突過程と電子エネルギー分布」)
    社団法人電気学会 2006/08


  • SUGAWARA Hirotake
    The 19th Asian Conf. on Electrical Discharge  2018/11  Xianyang, Shaanxi, China
  • 菅原 広剛
    XXIV Europhysics Conf. on Atomic and Molecular Physics of Ionized Gases  2018/07  Glasgow, Scotland, UK
  • 菅原 広剛
    20th Gaseous Electronics Meeting  2018/06  Magnetic Island, Townsville, Australia
  • 菅原 広剛
    10th Asia-Pacific Int. Symp. on the Basics and Applications of Plasma Technol.  2017/12  Chung Yuan Christian University, Taoyuan, Taiwan
  • 菅原 広剛
    XXXIII Int. Conf. Phenomena in Ionized Gases  2017/07  Estoril/Lisboa, Portugal
  • Fundamental study on filter effect of confronting divergent magnetic fields applied to a low-pressure inductively coupled plasma  [Invited]
    SUGAWARA Hirotake
    9th Int. Conf. Reactive Plasmas/68th Ann. Gaseous Electronics Conf./33rd Symp. Plasma Processing  2015/10
  • Electron conduction under the rectification effect of antiparallel magnetic fields  [Invited]
    SUGAWARA Hirotake
    XVI Int. Workshop on Low-Energy Positron and Positronium Physics & XVII Int. Symp. on Electron-Molecule Collisions and Swarms  2015/07  Maynooth, Ireland
  • Monte Carlo simulation of electron motion in confronting divergent magnetic fields  [Not invited]
    SUGAWARA Hirotake
    XXXI Int. Conf. Phenomena in Ionized Gases  2013/07
  • Stochastic scattering process to induce inward electron flow in electron conduction path between antiparallel gradient magnetic fields  [Not invited]
    SUGAWARA Hirotake
    XXI Europhysics Conf. on Atomic and Molecular Physics of Ionized Gases  2012/07
  • 不平等磁界下の電子輸送  [Invited]
    菅原 広剛
    原子分子データ応用フォーラムセミナー・核融合科学研究所原子分子データと原子分子過程モデルの活用・普及研究会  2011/12
  • Monte Carlo simulation of electron transport under quadrupole magnetic field and radio-frequency electric field  [Not invited]
    SUGAWARA Hirotake
    30th Int. Conf. Phenomena in Ionized Gases  2011/08
  • Electron drift along magnetically neutral channels between gradient magnetic fields  [Invited]
    SUGAWARA Hirotake
    15th Gaseous Electronics Meeting  2008/02  Murramarang Resort, Australia
  • Electron acceleration under short intense impulse electric fields  [Invited]
    SUGAWARA Hirotake
    XVth Int. Conf. on Gas Discharges and their Applications  2004/09  Toulouse, France
  • Control of selectivity in electron-molecule reactions by impulse field electron acceleration  [Invited]
    SUGAWARA Hirotake
    Int. Symp. on Electron-Molecule Collisions and Swarms  1999/07  The Waterfront Town, Tokyo, Japan
  • Electron behavior under characteristic magnetic fields applied to inductively coupled plasmas for control of charged particle transport  [Invited]
    SUGAWARA Hirotake
    XVIII Int. Workshop on Low-Energy Positron and Positronium Physics (POS) & XIX Int. Symp. on Electron-Molecule Collisions and Swarms (EMS)

Association Memberships

  • THE JAPAN SOCIETY OF APPLIED PHYSICS   日本工学教育協会   社団法人電気学会   The Institute of Electrical Engineers of Japan   

Research Projects

  • 日本学術振興会:年度科学研究費助成金
    Date (from‐to) : 2019/04 -2022/03 
    Author : 菅原 広剛
  • 日本学術振興会:科学研究費助成金
    Date (from‐to) : 2016/04 -2019/03 
    Author : 菅原 広剛
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010/04 -2015/03 
    Author : MURAYAMA Akihiro, SUEOKA Kazuhisa, SUGAWARA Hirotake
    We have studied spin-polarized lasing, which can transform electron-spin information into circular polarization properties in stimulated emission, by employing III-V compound semiconductor quantum dots (QDs) exhibiting strong suppression of spin relaxation. Spin-injection dynamics and spin relaxation in QDs in addition to fabrication processes of QDs have been studied for the purpose of temporal spin storage during the emission. We show that Pauli spin blocking is a major factor of spin loss during the spin injection into QDs. To resolve this issue, we conclude that high density QDs and tunneling of spins from two-dimensional electron systems realize highly efficient and ultrafast spin injection into QDs. QD light emitting diodes with active layers composed of QDs and metallic ferromagnetic spin electrodes have been fabricated, which indicates circularly polarized electroluminescence reflecting efficient electron-spin injection.
  • 対向発散磁界を印加した誘導結合型プロセスプラズマ中の反応性粒子流の計算機解析
    Japan Society for the Promotion of Science:Grant-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : Hirotake SUGAWARA
  • 低気圧高密度磁気中性線環状放電プロセスプラズマのモデリングと動的制御特性解析
    Japan Society for the Promotion of Science:Grant-in-Aid for Scientific Research
    Date (from‐to) : 2010/04 -2013/03 
    Author : 菅原 広剛
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2007 -2009 
    Author : SUGAWARA Hirotake, SUDA Yoshiyuki
    Amorphous fluorocarbon (a-C:F) films, which are applicable to insulation of electrical power equipment and integrated circuits, were deposited by plasma-enhanced chemical vapor deposition using a C_8F_<18> feedstock. When the a-C:F films were composed at a low plasma power, the thermal tolerance of the films was weak for less bondings between molecular chains in the a-C:F films (loose films). The dielectric constant of these a-C:F films had a tendency to be lower than that of conventional a-C:F films with dense bondings between molecular chains (firm films). This feature is desirable for reduction of the dielectric energy loss in power equipment and the delay of the signal transmission in the integrated circuits. In addition, we found a waving phenomenon of the firm film due to the heat given during the deposition of the firm film on a loose film. The voids made under the wavy film are also expected to contribute to the reduction of the dielectric constant of the a-C:F films.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2005 -2007 
    Author : SAKAI Yosuke, SUGAWARA Hirotake, SUDA Yoshiyuki
    SF_6 gas shows excellent properties as an electric insulating material, however as it's global warming factor is extremely big, the gas is now forbidden to be exhausted outdoors. The present research is, in place of SF_6 gas usage, to propose an alternative technique that conductor parts, which are coated by amorphous carbon-fluoride (a-C:F) film processed in plasma, are introduced in a gas insulation system. Then, the air breakdown voltage between the coated electrodes was shown to be the same level or even higher than that of SF_6 gas between the conventional electrodes. The main results are summarized as follow, 1) a-C:F film with a few hundred nanometers thickness was coated, in a chemically and physically stable condition, on the surface of spherical metal electrodes, 2) the present film was shown to be a tetrafluoroethylene (PTFE) like film with a low dielectric constant and high breakdown strength as a result of the analyses by SEM, XPS, FTIR and others, 3) the gas breakdown voltage in the Paschen curve, in which the breakdown voltage is given as a function of pd (p: gas pressure and d: gap length), in the present electrodes was the same level as the case of SF_6 in the conventional electrode system, 4) the surface condition of a-C:F film depended on the amount of buffer gases (Ar, He) in the RF plasma. In addition, assuming breakdown of a part of the film, re-deposition of a-C:F film was tried on the original surface, then, 4) double layers and triple layers, in the case of second and third times deposition, were clearly obtained. And in the case of the third times deposition, on the surface an interesting regularly patterned figures appeared.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2004 -2006 
    Author : 菅原 広剛
    本研究は、集積回路製造工程で排出されるフルオロカーボンであるCF_4地球温暖化ガスを非平衡プラズマにより効率的に分解する方法として選択的分解反応促進が期待されるプラズマへの衝撃電界重畳を提案し解析するものである。衝撃電界により電子した電子の衝突過程の計算機解析による定量的評価を中心として、以下1〜3の結果を得た。 1.衝撃電界下の電子の挙動解析とエネルギー効率の評価: 衝撃電界で与える電子加速量を変化させ、共にCF_4分解に寄与する中性解離と電離性解離のエネルギー消費割合をモンテカルロ法で計算・比較した。加速量増加に伴い閾値の大きな電離性解離に費やされるエネルギー割合が単調増加し、中性解離の割合は飽和傾向を示した。プラズマ維持と解離促進を同時に図るためには電離性解離の閾値を超える高エネルギー領域にまで電子を加速することが必要で、この点で衝撃電界電子加速が有効と考えられる。 2.CF_4ラジオ周波数プラズマ解析系構築と新高速衝突判定法の提案: 電極を含む系でCF_4プラズマ中の解離生成種の生成頻度と空間分布とを統計的に安定に扱う手法を提案した。また計算負荷となっていたCF_4分子と電子との衝突判定において、無衝突となる場合を効率よく検出し電子衝突断面積計算を省く新高速判定法を提案した。これにより電子追跡に要する計算負荷を著しく軽減させ、追跡電子数増や長時間計算、また混合ガスへの対応を容易にした。 3.CF_4中電子輸送過程: CF_4中の電子加速時初期緩和過程に見られる空間分布の複数ピーク形状と電子輸送係数の緩和過程を解析した。研究者間で想定が異なる電子衝突断面積構成により空間分布、電子輸送係数とも差異が生じた。衝撃電界電子加速の制御性評価の際は特に、加速途中で電子の集団性を失わせる低・中エネルギー部の電子衝突断面積構成への依存性が大きいと考えられる。 主な結果は研究発表欄の論文として公表した。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2002 -2003 
    Author : 菅原 広剛
    地球温暖化防止のためのSF_6絶縁ガス使用量低減に向け、SF_6をN_2他で希釈した際に現われる絶縁特性相乗効果発生機構を混合ガス中の電子エネルギー損失過程と電子捕獲機構の面から解析した。 平成15年度は、電子のエネルギー損失過程および衝突間の電子挙動に関する14年度の解析結果を踏まえ、既に構築済みの計算機プログラムを用いて、電子衝突断面積の組み合わせの効果を主にSF_6/N_2、SF_6/CO_2、SF_6/c-C_4F_8の3つの混合ガスの比較を通じて解析した。解析結果は次のようにまとめられる。 SF_6/N_2混合ガス中では、電子はN_2との衝突によりエネルギーを失って低エネルギーとなり、2〜3eV付辺に存在するN_2の弾性衝突および振動励起衝突の断面積ピークに起因するバリア効果(電子エネルギー上昇を妨げる)によって低エネルギー状態に保たれその間にSF_6により捕獲されることが電子衝突履歴の追跡により確認できた。 SF_6/CO_2でもCO_2のバリア効果が見られるが、CO_2はN_2に比べバリアが低く高エネルギー寄りに位置することから電子を低エネルギー域に閉じ込め付着を促す働きはSF_6/N_2ほど強くない。N_2とCO_2についてはバリア効果の強弱とSF_6との相乗効果の程度は大小関係が一致しており、この種の混合ガスの相乗効果はバリア効果によるものと推測された。 SF_6/c-C_4F_8混合ガスにおいては、c-C_4F_8の電子励起衝突断面積の立ち上がりが急なことが励起の閾値付近での衝突を起こり易くし、励起衝突直後の電子エネルギーを低くする結果をもたらす。SF_6の電子付着は低エネルギーほど起こり易いため、閾値近くの励起衝突が直接電子付着に結びつくためと考えられる。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2001 -2003 
    Author : SAKAI Yosuke, SUDA Yoshiyuki, AKAZAWA Masamichi, SUGAWARA Hirotake, NAKAJIMA Masatoshi, BRATESCU A. maria
    In order to reduce the usage of SFs insulation gas, which has high GWP (global warming potential), the present project proposed to use a-C:F film coated conductor prepared by RF plasma CVD method for insulation of electric power systems as alternatives of SF_6. This project was motivated because we had experienced very high deposition rates in RF plasma if per-fluorocarbon vapors were used. The main results are listed as follows. l. The deposition rate on Si and A1 substrates was > 100-200nm/min, which is a few tens times higher than those obtained by conventional CF_4 and C_2F_6 gases. 2. The a-C:F film, which is composed of C-C and C-F bonds, was excellent insulation properties (dielectric constant 【approximately equal】 2) with high density and good thermal strength. 3. The breakdown voltage V_s of N_2, Ar and He between the a-C:F film coated Al electrodes were 3 times larger than that between Al ones in low p(pressure)d(gap length) region. For pd<20 Torr/cm the V_s was rather higher than that of SFs. 4. Reason of the enhancement of V_s was explained by the fact that secondary electron emission rate was reduced significantly by this film coating. 5. Effect of decomposed species in the plasma on the a-C:F film properties was tried to examine, but in this project term it was not really cleared.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2000 -2001 
    Author : 菅原 広剛
    C_7F_<16>を材料としたプラズマCVD法でアモルファスフルオロカーボン(CF)膜を堆積した。XPSでF/C組成比を、静電容量測定とエリプソメータによる膜厚測定から比誘電率ε_rを、正極性針対平板電極系絶縁破壊試験で絶縁耐力をそれぞれ測定し、熱処理(100〜300℃)後の膜厚減少分から耐熱性を評価した。これらの結果から(1)材料のガス圧依存性(30〜80Pa)、(2)He混合(0〜30Pa)の影響、(3)酸素混合(2〜4Pa)の影響を検討した。 (1)では低圧ほどF/C比が上昇しε_rは2.1程度まで下がったが、同時に堆積率も低下し耐熱性試験時の膜厚減少幅も大きくなった。絶縁耐力は2MV/cm以上であった。材料ガス圧による膜質制御では耐熱性向上と誘電率低減の両立は難しかった。類似の巨大分子材料C_8F_<18>を用いて堆積したCF膜でも比誘電率は2.5以下、絶縁耐力は1MV/cm以上であった。 (2)ではHe増加に伴いε_rが低下し(1)同様の傾向が見られた。加えて、堆積中のプラズマ状態が安定して膜質のばらつきが減り再現性が向上した。 (3)ではCF膜からのC原子引き抜きによるF/C比増加即ちε_r低下を期待したが、酸素活性種のエッチング効果が強く数Paの混合で堆積率が著しく低下し、6Pa以上では膜堆積できなくなった。2〜4Paにおける堆積膜の膜質はばらつきが大きいものの、中には低いε_rが得られた例もあり、多孔質構造のような空疎なCF膜が得られた可能性が示唆される。 続いて、絶縁破壊部再生を模擬し、CF膜で被覆済みの面と基板が露出した面が接する個所へのCF膜再堆積を試みた。膜厚の時間変化から、再堆積開始時は露出面への堆積の方が速やかに進む傾向が見られたが、再堆積が進行した後は、被覆面と露出面に堆積したCF膜の厚さは同程度になった。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1998 -1999 
    Author : 菅原 広剛
    RF(13.56MHz)非平衡放電プラズマに衝撃電界を重畳することによりプラズマ中の電子を短時間のうちに揃って加速し、単一エネルギー的な電子群を生成してフロン12の分解反応の選択性、効率の向上とバルク領域での大体積分解反応の促進を図る技法を流体コードを用いて計算機解析した。 衝撃電界を印加するとプラズマシースの厚さが変化してこれを吸収してしまうため、衝撃電界がバルク領域に到達する時間は限られるが、誘電緩和時間の見積りや数値解析の結果、数ns程度の間は衝撃電界を維持でき、電子エネルギーをフロン12解離のしきい値(中性解離7.2eV、解離性電離12.2eV以上)まで高めることができた。フロン12は高エネルギー領域で中性解離・解離性電離、低エネルギー領域で解離性付着の衝突断面面積を持ち、これらは共に分解反応に寄与する。しかし低エネルギー領域での電子付着が大きいと放電維持が困難になることから、解離性電離を選択的に促進し分解処理と放電維持を同時に図るのが効果的である。 バルク領域へ到達する衝撃電界の大きさは衝撃電界の立ち上がり時間に対して敏感に変化し、衝撃電界の立ち上がりが急峻な程バルクに到達する電界も大きいことが確認された。強度500V/cm、印加時間5nsの衝撃電界について立ち上がり時間を2nsから0.25nsに縮めると、分解処理量は35%程度増加した。この程度の立ち上がり時間は数kV規模の高電圧パルス発生装置で実現しているが、実際の回路では容量と抵抗を小さくしてプラズマ中に大きな変位電流が流れるようにする必要がある。衝撃電界を逆極性で印加しても同程度の電子加速効果が得られたことから考えると、衝撃電界印加は任意の方向で構わないものと思われる。したがって衝撃電界印加のための電極をRF放電駆動用電極とは別に設けて回路定数設定の自由度を高めることも可能と考えられる。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1997 -1999 
    Author : SAKAI Yosuke, HOUNO Hitoshi, IGARASHI Tatsushi, SUGAWARA Hirotake
    Investigation on decomposition of air pollutants, such as nitrogen dioxides, fluorocarbons (CィイD27ィエD2FィイD216ィエD2, (CィイD23ィエD2FィイD27ィエD2)ィイD23ィエD2N/(CィイD24ィエD2FィイD24ィエD2)ィイD23ィエD2N or CィイD28ィエD2FィイD28ィエD2/ CィイD28ィエD2FィイD216ィエD2O), volatile chemical compounds, etc. and change them into non-harmful substances has been carried out using a hybrid method of electrical discharge and VUV light (172nm) irradiation. The discharge characteristics between barrier and corona type has been simulated in order to design an efficient decomposing system and VUV light source. The results are shown as follows, 1) NOィイD22ィエD2 with gas pressures between 1 and 3 Torr was decomposed into NィイD22ィエD2 and OィイD22ィエD2 by dc discharge, in addition, by irradiation of VUV light the decomposition speed was accelerated. The synergetic effect for the decomposition level and speed were confirmed by observation of the decomposed species by a gas chromatography, emission spectra from plasma and a quadrupole mass analysis. 2) Fluorocarbons, CィイD27ィエD2FィイD216ィエD2, (CィイD23ィエD2FィイD27ィエD2)ィイD23ィエD2N/(CィイD24ィエD2FィイD24ィエD2)ィイD23ィエD2N and CィイD28ィエD2FィイD28ィエD2/CィイD28ィエD2FィイD216ィエD2O, were decomposed by dc and rf discharge plasma. In this case no synergetic effect by VUV irradiation was seen. In a plasma phase a various kind of species, such as CF, CFィイD22ィエD2, CFィイD23ィエD2, CィイD22ィエD2FィイD23ィエD2, CィイD22ィエD2FィイD25ィエD2, CィイD23ィエD2FィイD23ィエD2, CィイD23ィエD2FィイD25ィエD2, CィイD23ィエD2FィイD26ィエD2, were observed by a mass analysis method. Some of the fragments among them were found to be captured on the electrode surface as a film. 3) On the electrode surface it was seen by XPS spectra that thin film was composed of CF, CFィイD22ィエD2, CFィイD23ィエD2 and -C-CFィイD2xィエD2. The electrical properties of this film were fine, namely high electric strength and low dielectric constant. 4) This result suggested that this film was applicable to interlayer insulation of integrated circuits and insulation of power apparatus. 5) The barrier discharge for application of VUV and decomposition of pollutants was analyzed by a computer simulation method.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1995 -1996 
    Author : SAKAI Yosuke, IGARASHI Tatsusi, SUGAWARA Hirotake, VENTZEK Peter
    In order to improve the capability of of Xe gas excimer lamps from which vacuum ultra-violet light is obtained, the characteristics and filamentation of barrier discharge plasma, and the factors which determine the light intensity and efficiency have been investigated. The main results obtained in this work are as follows. 1) In aXe gas barrier plasma, the magnitude of charge concentration accumulated on the surface of barriers increased with decreasing the frequencies of power source, and the production rate of excimers increased with decreasing the rise-time of the pulse voltage applied to plasma. Filamentation which might occur by non-uniformity in a uniform volume discharges was found to be initiated by a local gas temperature rise in excimer laser discharges. 2) In order to understand a relation between the laser spectroscopic signals and the plasma properties in non-equilibrium plasmas, the photon concentrations which are used for the laser diagnostics did not appreciably disturb the electron energy distribution but significantly changes the concentration of local excited levels. 3) In Xe/Ne mixtures, the laser absorption and opt-galvanic signals showed that the concentration of the metastable Xe was largest in the vicinity of the cathode under DC discharge. In the case of LF (10kHz-500kHz) discharges, the concentration had two peaks in the vicinity of the ground and powered electrodes. As a conclusion it was suggested that an optimum design of excimer lamps was to utilize the sheath regions where the electron temperature was high enough to obtain a high value of excimer production rate.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1995 -1995 
    Author : 田頭 博昭, 中神 芳武, 菅原 広剛, 下妻 光夫, 酒井 洋輔
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1994 -1994 
    Author : 田頭 博昭, 横澤 亜由美, 菅原 広剛, ヴェンシェック ピーター, 酒井 洋輔
    本研究は当初Si_3N_4薄膜を形成するためのラジカルを発生するRFプラズマのシミュレーション解析とその薄膜形成過程のシミュレーションに主としてあてられる予定であったが、Si_3N_4ならびにそのプリカーサラジカルに関する研究が不十分のため、急遽方針を転換して、次のような研究を行ない、成果を発表した。 1)アモルファスシリコン膜堆積についてダイヤモンド格子も用いたモデリングを行い、これによってスピン密度の研究を行なった。その結果、スピン密度を与えるもととなるダングリングボンドはボイド中にあるという結論を得たが、これはおそらく相当に堆積速度が大きく十分密な膜となっていないときの結果であろうと思われる。最近のきわめて良質な膜では、ボイドとダングリングボンドは相関が薄いと報告されており、この点の検討が、今後必要であることを明らかにした。 2)電荷転移と弾性衝突がある気体中のイオンの速度分布、スオームパラメータのモンテカルロ法による研究を行ない、電荷転移によるピークをもつ速度分布の特異な形状が弾性衝突により緩和されることを明らかにした。M.Kushnerが与えた周波数をもとにモノシランガス中のシリルイオンの拡散係数を求めた。 3)RF非平衡プラズマの制御を目的として、トランスジェント特性をもとめ、制御を行なうときの基礎的データを得た。また、比例オンオフ制御による制御性をシミュレーション研究し、制御可能性を見いだした。 4)来年度研究予定のTEOS中の電離係数を、北見工大吉田研究室と協力して測定し、初めてその値を与えた。これは、TEOSガス中のプラズマのシミュレーションの基礎を与えるものである。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1993 -1994 
    Author : 田頭 博昭, ピーター ヴェンツェック, 菅原 広剛, 下妻 光夫, 酒井 洋輔
    本研究はミクロンオーダーの直径を持つファインパウダを絶縁空間に浮遊させることにより気体の電気的絶縁破壊電圧を向上し、かつその種類を選ぶことにより、無公害的にこれを行ない、高電圧機器の電気的絶縁をハロゲンフリーな気体絶縁とする可能性を実験的に見いだすことを目的としている。以下に研究成果を報告する。 使用したパウダはSiO_2、TiO_2及びSi_3N_4で、電極間に印加した電圧は直流(DC)、50Hz交流(AC)及び標準雷インパルス(LI)である。LI印加時は、50%フラッシ-オーバ電圧V_<50>を昇降法により求めている。紫外線照射は行なっていない。 まず、SiO_2パウダで半球電極間にLIを印加した時、V_<50>はギャップ長1mmで空気の約1.6倍に上昇した。DC、AC電圧印加時にあったパウダの電極への付着はなかった。 TiO_2パウダではLI印加時で、SiO_2パウダ使用時とほぼ同程度で、ギャップ長1mmで空気での値の約1.5倍となった。しかし、DC及びAC電圧印加時では、絶縁破壊電圧の大幅な上昇はなかった。ACでは、約1.1〜1.2倍の上昇が見られたが、DCでは空気の絶縁破壊電圧とほぼ同じであった。いづれの電圧でも、SiO_2パウダの実験で見られたパウダの電極への付着は観察されなかった。 Si_3N_4パウダを用いて同様に実験を行なった。LI電圧印加時では、そのV_<50>はギャップ長1mmで空気の約1.6倍となった。AC及びDCでは、絶縁破壊電圧の大きな上昇は見られない。また、パウダの電極への付着も観察されていない。 LI電圧印加時では、いずれのパウダでも絶縁破壊電圧は空気より上昇した。しかし、AC及びDC電圧を印加した場合、SiO_2パウダを使用したときが最もパウダの効果が現れている。これは、パウダが帯電し電極に付着するということに関係しているものと思われる。各パウダでの、帯電の状況及び電極に付着した場合の付着量を調べ、絶縁破壊電圧の上昇の要因の検討を行なっている。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1993 -1993 
    Author : 菅原 広剛
    本研究は大気汚染の原因の1つとして考えられている窒素酸化物のコロナ放電による分解をコンピュータシミュレーションにより解析し、分解反応機構の解明ならびに分解反応の高効率化を図ることを目的とする。 コロナ放電のシミュレーションに必要な窒素酸化物分子の衝突断面積の推定は、定常タウンゼント法による電離係数の測定結果に、ボルツマン方程式解析による結果を合わせるよう断面積修正を繰返して行なう計画であったが、実際にボルツマン方程式解析を試みたところ、窒素酸化物のような電子付着性のガスの場合には計算が不安定となる場合があることがわかった。そこで、より安定な解析手法として、研究代表者らが開発しコロナ放電の解析に用いる計画であったプロパゲ-タ法を衝突断面積の推定にも導入することとした。 プロパゲ-タ法を定常タウンゼント法に適用する場合、従来の適用方法では電子の実空間における位置およびエネルギーの両方について空間分割を行なう必要があり、膨大な計算機容量を必要としていた。本研究ではこの点を踏まえ、エネルギーに関する空間分割のみで定常タウンゼント状態の解を求めることができる手法を新たに開発した。新手法の確立に伴って解析に必要な計算機容量が大幅に軽減されたため、従来は大型計算機で行なっていたシミュレーションが本年度購入備品の超高速アクセラレータボードをパーソナルコンピュータに搭載した計算機系で実行可能となった。 本研究で開発した手法は、解析に必要な計算機容量が従来の手法に比較して格段に小さい。また、本研究の対象である窒素酸化物のように、従来の手法では解析困難な場合があるとされている電子付着を含む条件にも対応可能な手法である。その成果は、研究発表覧に示すように英国物理学会誌に論文として掲載された。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1993 -1993 
    Author : 田頭 博昭, 横澤 亜由美, 菅原 広剛, 酒井 洋輔
    1.平成5年度の研究目的は、モノシラン中の非平衡rfプラズマによる水素化アモルファスシリコン堆積時のラジカル発生、輸送、表面反応と膜堆積過程におけるラジカルの挙動を明らかにすることである。 2.平成5年度の研究成果は、以下の(1)〜(3)に要約される。(1)ラジカル発生のシミュレーション;比較的小規模な計算でラジカル発生量を求めることができる連続の式に基づくモデルをつくり、電極間のラジカル発生レート分布を求めた。モンテカルロモデルから得たラジカル発生レートとよい一致が得られた。(2)イオンの拡散係数と移動度の導出;上記のシミュレーション支援のため文献値がないモノシランイオンのドリフト速度および拡散係数、平均エネルギーをモンテカルロ法で求めた。衝突断面積は文献値を用いている。拡散係数は1Torr、E/N=1414Tdで約2500cm^2/sであった。(3)ラジカルによる膜堆積過程のシミュレーション;シリルラジカル等による膜堆積過程を解明するため、堆積サイトがダイヤモンド構造をなしているモデルを用いてモンテカルロ法で、堆積率、水素含有量、スピン密度、膜密度を求めた。従来用いていた立方格子モデルと比較して、膜密度および堆積率に関しては実験的に得られた値(2.1gcm^<-3>)あるいは傾向(基板温度にほとんど依存しない)とほぼ一致した。また水素含有量に関しては、基板温度200〜400°Cにおいて実験値と一致した値が得られたが、基板温度を500°C以上に加熱した場合、水素含有量がほぼ10%一定となり、実験値から得られる傾向より大きな値となった。これは隣接するH終端ボンドとダングリングボンドの結合に必要な活性化エネルギーを大きく見積りすぎたためと思われる。スピン密度に関しては、ラジカルとサイトの反応式の多くがダングリングボンドをつくり出すため、膜中にこれが残る可能性が高く、このため実験値とは大きく異なった値が得られたものと思われる。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1992 -1993 
    Author : SAKAI Yosuke, SUGAWARA Hirotake, TABATA Masayoshi, TAGASHIRA Hiroaki
    The ovjective of this work is to investigate a possibility of concentrating a very small amount of nitrogen-dioxide molecules in a flue gas and decomposing them by discharge and ultra-violet light. Light-induced-Drift(LID) technique is used for the comcentration. In this project the decomposition experiment and LID concentration experiment go side by side. The main results are as follows. 1)NO_2 molecules of 80%-90% were decomposed into N_2 and O_2 molecules in a NO_2 glow discharge with pressures between 1 and 7 Torr. It was shown that decomposed species, N_2 and O_<2'> were generated through NO. 2)In order to know the effect of ultre-violet light generated in the discharge on the NO_2 decomposition and a possibility of NO_2 decomposition by ultra-violent light, a trial of irradiation of UV light to NO_2 has been carried out. NO_2 was shown to be decomposed into N_2 and O_<2'> however the decomposing porcess was suggested to be different from the discharge process. 3) Values of the electron impace ionization coefficient and secondary coefficient for NO_2 gas are a few tens of percentage smaller than those for air, while the electron attachment coefficient for NO_2 is larger than that for O_2. 4)Using the results mentioned in 3) and the electron collision cross sections of N_2O which have been reported, the cross sections of NO_2 were estimated by Boltzman equation analysis method. These data play a very important role in analyzing the NO_2 decomposition process in discharges. 5)LID experiment system is now constructed, with a dye laser and a laser diode, and an improved type of drift tube. An experiment starts in SF_6 and He buffer gases. The results mentioned above have been obtained, however investigation of NO_2 decomposition by UV light and its mechanism, detailed anallysis of scientific problem of LID concentration, development of NO_2 removal technology in a flue gas are not still finised. Further investifgation have to be carried on.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1992 -1992 
    Author : 田頭 博昭, 菅原 広剛, 下妻 光夫, 酒井 洋輔
    本研究では、粒径の異なる4種類のSiO_2ファインパウダ(12μm、36μm50μm、150μm)ならびに異なる材質のパウダとしてSi_3N_4ファインパウダを空気中に浮遊させ、絶縁破壊電圧の測定を行いその諸特性について検訂した。また実験の際、質量の大きいパウダはファンによる浮遊が困難のため、電極間にパウダを散布する装置を作成し、2つの装置を用いて測定を行なった。結果を以下に示す。 (1) 12μmパウダを使用し、ファンを作動させた状態の交流絶縁破壊において、電極間にパウダのブリッジが形成されなくても絶縁破壊電圧は上昇した。この時、両電極に付着したパウダが電極間に流れこむのがみられ、これが絶縁破壊電圧の上昇に寄与しているものと思われる。 36μmパウダで同様の実験を行なったが、12μmパウダで確認されたほどの大きな絶縁破壊電圧の上昇はみられていない。 (2) 散布装置を用いた4種類の粒径の異なるSiO_2パウダに対する測定では、どの粒径のパウダも絶縁破壊電圧の大きな上昇は見られなかったが、粒径の大きいパウダと、小さいパウダではわずかであるが差があると思われる。また、同じ粒径でありながらファンによる結果(12μm、36μm)と差があるのは、電極付近にあるパウダの量の違いが影響しているものと考えられる。 (3) Si_3N_4パウダによる絶縁破壊実験ではパウダが重いため浮遊している量が少なく、絶縁破壊電圧の上昇はあまり見られない。散布の装置に替えて同様に測定を行なっても大きな上昇はみられていない。 (4) 直流での測定において、パウダが陽極側に多量に付着しており、パウダ自身は負に帯電しているものと考えられる。
  • Modelling and Simulation of Weakly Ionized Plasmas

Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.