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論文

Technical basis of accident tolerant fuel updated under a Japanese R&D project

山下 真一郎; 永瀬 文久; 倉田 正輝; 野澤 貴史; 渡部 清一*; 桐村 一生*; 垣内 一雄*; 近藤 貴夫*; 坂本 寛*; 草ヶ谷 和幸*; et al.

Proceedings of 2017 Water Reactor Fuel Performance Meeting (WRFPM 2017) (USB Flash Drive), 10 Pages, 2017/09

我が国では、事故耐性燃料の技術基盤を整備するために2015年に軽水炉の事故耐性燃料等(ATFs)に関する研究開発プロジェクトが立ち上がった。日本原子力研究開発機構は、国内のプラントメーカ, 燃料メーカ, 大学等が有する国内軽水炉においてジルカロイを商用利用した際の経験、知識を最大限活用するために、これらの機関と協力して本プロジェクトを実施するとともに取りまとめを行っている。プロジェクトの中で検討されているATF候補材料は、微細な酸化物粒子を分散することで強化されたFeCrAl鋼(FeCrAl-ODS鋼)と炭化ケイ素(SiC)複合材料であり、通常運転時の燃料性能は同等かそれ以上で、事故時にはジルカロイよりも長い時間原子炉炉心においてシビアアクシデント条件に耐えることが期待されている。本論文では、日本のプロジェクトで実施中の研究開発の進捗について報告する。

論文

Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

Lohrmann, A.*; Castelletto, S.*; Klein, J. R.*; 大島 武; Bosi, M.*; Negri, M.*; Lau, D. W. M.*; Gibson, B. C.*; Prawer, S.*; McCallum, J. C.*; et al.

Applied Physics Letters, 108(2), p.021107_1 - 021107_4, 2016/01

 被引用回数:17 パーセンタイル:14.47(Physics, Applied)

Creation and characterisation of single photon emitters near the surface of 4H- and 6H-silicon carbide bulk substrates and 3C-SiC epitaxially grown on silicon substrates were investigated. These single photon emitters can be created and stabilized by thermal annealing in an oxygen atmosphere at temperatures above 550 $$^{circ}$$C. Hydrofluoric acid (HF) treatment is shown to effectively annihilate the emission from defects and to restore an optically clean surface. However, the emission from the defects can be obtained after re-oxidation above 550 $$^{circ}$$C. By measuring using standard confocal microscopy techniques, the excited state lifetimes for the emitters are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice.

論文

Swelling of radiation-cured polymer precursor powder for silicon carbide by pyrolysis

武山 昭憲; 出崎 亮; 杉本 雅樹; 吉川 正人

Journal of Asian Ceramic Societies, 3(4), p.402 - 406, 2015/12

Ceramic yield, density, volume change and pore size distribution were measured for radiation- and thermally cured (poly carbo silan) PCS powder when they were pyrolyzed in the temperature ranges between 673 and 973 K. Higher ceramic yield was obtained for radiation-cured powder due to smaller amount of evolved gas. Temperature dependence of volume change and the total pore volume show the formation and disappearance of pores in the powders were determined by the volume shrinkage and evolution of decomposed gases. Volume shrinkage narrowed the pore size distribution for radiation-cured powder. For thermally cured powder, the narrowing of size distribution was disturbed by aggregated pores. Smaller amount of evolved gas from radiation-cured powder relative to thermally cured powder prevented the aggregation of pores and provided the narrow size distribution.

論文

Defect engineering in silicon carbide; Single photon sources, quantum sensors and RF emitters

Kraus, H.; Simin, D.*; Fuchs, F.*; 小野田 忍; 牧野 高紘; Dyakonov, V.*; 大島 武

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.176 - 179, 2015/11

Quantum centers in silicon carbide (SiC) have already transcended their former reputation as mere performance-hampering defects. Especially the silicon vacancies, but also other point defects offer a variety of quantum applications, completing and complementing the successful NV centers in diamond. We aim to provide an overview over the research activities on quantum centers in silicon carbide, from fundamental knowledge on the 3/2 spin multiplicity, over microwave emission and single photon sources, to axis-aware magnetic field sensing and temperature sensing. Finally, we discussed creating tailored defects in SiC using different radiation parameters.

論文

A Development of super radiation-hardened power electronics using silicon carbide semiconductors; Toward MGy-class radiation resistivity

土方 泰斗*; 三友 啓*; 松田 拓磨*; 村田 航一*; 横関 貴史*; 牧野 高紘; 武山 昭憲; 小野田 忍; 大久保 秀一*; 田中 雄季*; et al.

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.130 - 133, 2015/11

In order to develop semiconductor devices with MGy radiation resistivity, we are developing power metal-oxide-semiconductor field-effect-transistors (MOSFETs) based on silicon carbide (SiC) semiconductors. The $$gamma$$-ray irradiation responses of power SiC-MOSFETs were studied under various irradiation temperatures and humidity with various gate-bias conditions. Making comparisons between these responses, the optimum device operating condition and a better device structure were derived and MGy resistivity was achieved. Besides, $$gamma$$-ray irradiation tests for a motor-driver circuits consisting of SiC-MOSFETs were carried out, and as a result, their continuous operation up to 2 MGy was confirmed.

論文

In-situ monitoring of ion-beam luminescence of Si-O-C(-H) ceramics under proton-beam irradiation

成澤 雅紀*; 江夏 昌志; 武山 昭憲; 杉本 雅樹; 出崎 亮; 佐藤 隆博; 外薗 洋樹*; 河相 武利*; 岩瀬 彰宏*

Journal of the Ceramic Society of Japan, 123(9), p.805 - 808, 2015/09

Two kinds of Si-O-C(-H) ceramics particles having intrinsic photoluminescence (PL) spectra were prepared from silicone resin microspheres by heat treatment in a hydrogen atmosphere at 800 or 1100$$^{circ}$$C. The obtained particles were painted on a Si substrate using a binder, and ion-beam-luminescence spectra were observed under proton beam irradiation with an acceleration energy in the ranges of 1-3 MeV. Observed spectra had peaks at wavelength of 520-540 nm. These peak wavelengths were larger than those observed under UV light irradiation. The luminescence of H$$_{2}$$ 1100 (sample decarbonized at 1100$$^{circ}$$C) was bright, and that of H$$_{2}$$ 800 (sample decarbonized at 800$$^{circ}$$C) was faint. However, the intensity of luminescence decreased rapidly at an early stage of the beam irradiation. In air, a sharp luminescence band with a peak at 300 nm appeared together with the main emission with a peak in the range of 520-540 nm. The existence of the sharp band at 300 nm was apparent in the H$$_{2}$$ 800 spectra, whereas it appeared as a minor peak in the H$$_{2}$$ 1100 spectra in air.

論文

Isolated electron spins in silicon carbide with millisecond coherence times

Christle, D.*; Falk, A.*; Andrich, A.*; Klimov, P.*; Hassan, J.*; Son, N. T.*; Janz$'e$n, E.*; 大島 武; Awschalom, D.*

Nature Materials, 14(2), p.160 - 163, 2015/02

 被引用回数:128 パーセンタイル:0.92(Chemistry, Physical)

Carbon vacancy - silicon vacancy pair (V$$_{C}$$-V$$_{Si}$$) in silicon carbide (SiC) is regarded as a promising candidate for a qubit for quantum computing since V$$_{C}$$-V$$_{Si}$$ is thought to have electronic states with sharp optical and spin transitions. However, single spin operation using V$$_{C}$$-V$$_{Si}$$ has not yet been succeeded although it was revealed that V$$_{C}$$-V$$_{Si}$$ shows the characteristics as a single photon source (SPS). In this study, we studied spin properties of V$$_{C}$$-V$$_{Si}$$ created in SiC by 2 MeV-electron irradiation. First, we found V$$_{C}$$-V$$_{Si}$$ in SiC using a confocal microscope (CFM) and measured their optical detected magnet resonance (ODMR) at 20 K. Then, their spin coherence was measured from the standard two-pulse Hahn-echo sequence using ODMR. As a result, the spin coherence time exceeding 1 ms was obtained.

論文

Coherent control of single spins in silicon carbide at room temperature

Widmann, M.*; Lee, S.-Y.*; Rendler, T.*; Son, N. T.*; Fedder, H.*; Paik, S.*; Yang, L.-P.*; Zhao, N.*; Yang, S.*; Booker, I.*; et al.

Nature Materials, 14(2), p.164 - 168, 2015/02

 被引用回数:166 パーセンタイル:0.53(Chemistry, Physical)

Single silicon vacancy (V$$_{Si}$$) in silicon carbide (SiC) was studied from the point of view of single photon source for quantum computing. The V$$_{Si}$$ centers were created in high purity semi-insulating hexagonal (4H)-SiC by 2 MeV electron irradiation with fluences up to 5$$times$$10$$^{15}$$ /cm$$^{2}$$. No subsequent annealing was carried out. A couple of solid immersion lens (SIL) with 20 $$mu$$m diameter were created on samples by ion milling using 40 keV Ga focused ion beam. A typical home-built confocal setup was used after optimizing for emission in the wavelength range around 900 nm. As a result, optically detected electron spin resonance (ODMR) for V$$_{Si}$$ was observed at room temperature (RT). Using ODMR, Rabi oscillations were also observed, and the Rabi frequency increased with increasing applied-magnetic field. In addition, spin relaxation time T$$_{1}$$ and T$$_{2}$$ were detected to be 500 $$mu$$s and 160 $$mu$$s, respectively.

論文

Room temperature quantum emission from cubic silicon carbide nanoparticles

Castelletto, S.*; Johnson, B. C.*; Zachreson, C.*; Beke, D.*; Balogh, I.*; 大島 武; Aharonovich, I.*; Gali, A.*

ACS Nano, 8(8), p.7938 - 7947, 2014/08

Single Photon Sources (SPSs) in cubic (3C) Silicon Carbide (SiC) Nano Particles (NPs) were investigated. As a result, photo luminescence (PL) with broad emission at wavelength ranges between 600 and 800 nm was observed from 3C-SiC NPs at room temperature. The second order photon auto-correlation measurements revealed that defect with the PL characteristic is SPSs. The intensity and stability of the PL increased when samples were irradiated with electrons and subsequently annealed at 500 $$^{circ}$$C. From PL measurements at low temperature and theoretical analysis using spin-polarized density functional theory, the defect can be identified as carbon-antisite carbon-vacancy pair (C$$_{Si}$$V$$_{C}$$).

論文

Investigation of single-event damages on silicon carbide (SiC) power MOSFETs

水田 栄一*; 久保山 智司*; 阿部 浩之; 岩田 佳之*; 田村 貴志*

IEEE Transactions on Nuclear Science, 61(4), p.1924 - 1928, 2014/08

 被引用回数:23 パーセンタイル:3.93(Engineering, Electrical & Electronic)

Radiation effects in silicon carbide power MOSFETs caused by heavy ion and proton irradiation were investigated. In the case of ions with high LET, permanent damage (increase in both drain and gate leakage current with increasing LET) was observed and the behavior is similar to the permanent damage observed for SiC Schottky Barrier diodes in our previous study. In the case of ions with low LET, including protons, Single Event Burnouts (SEBs) were observed suddenly although there was no increase in leakage current just before SEBs. The behavior has not been observed for Si devices and thus, the behavior is unique for SiC devices.

論文

Observation of deep levels and their hole capture behavior in p-type 4H-SiC epilayers with and without electron irradiation

加藤 正史*; 吉原 一輝*; 市村 正也*; 畑山 智亮*; 大島 武

Japanese Journal of Applied Physics, 53(4S), p.04EP09_1 - 04EP09_5, 2014/04

 被引用回数:2 パーセンタイル:92.85(Physics, Applied)

Deep levels in p-type hexagonal (4H) silicon carbide (SiC) epilayers irradiated with and without electrons at 160 keV and subsequent annealing at 1000 $$^{circ}$$C were investigated. Current deep level transient spectroscopy (I-DLTS) was applied to investigate deep levels. As a result, Deep levels with activation energies less than 0.35 eV which are located near the valence band were detected. Also, two deep levels (AP1 and AP2) existed in all samples. Other deep levels appeared after the electron irradiation. Since electrons with an energy of 160 keV can knock-on only carbon atoms from the lattice site of SiC, it was concluded that the deep levels observed after irradiation were related to carbon vacancy V$$_{C}$$.

論文

Annealing of electron irradiated, thick, ultrapure 4H SiC between 1100$$^{circ}$$C and 1500$$^{circ}$$C and measurements of lifetime and photoluminescence

Klahold, W. M.*; Devaty, R. P.*; Choyke, W. J.*; 河原 洸太朗*; 木本 恒暢*; 大島 武

Materials Science Forum, 778-780, p.273 - 276, 2014/02

Ultra-pure n-type (8$$times$$10$$^{13}$$ cm$$^{-3}$$), 99 $$mu$$m thick epitaxial layers of hexagonal (4H) silicon carbide (SiC) were irradiated with electrons either at 170 keV with a fluence of 5$$times$$10$$^{16}$$ cm$$^{-2}$$ or at 1 MeV with a fluence of 1$$times$$10$$^{15}$$ cm$$^{-2}$$ in various geometries. Low temperature photoluminescence (LTPL) spectra and microwave photoconductance ($$mu$$PCD) lifetime measurements were carried out for all samples before and after annealing in argon in free standing mode or on a POCO carbon (Poco Graphite, Inc.) platform, every 50 $$^{circ}$$C from 1100 $$^{circ}$$C to 1500 $$^{circ}$$C. However, no improvement in carrier lifetime was observed although previous studies reported that carbon diffused into SiC during high temperature treatment improves carrier lifetime. The result obtained in this study suggests that simple carbon diffusion model cannot be applied and more study is required to understand the injection of carbon interstitials into the SiC lattice.

論文

Impact of carrier lifetime on efficiency of photolytic hydrogen generation by p-type SiC

三宅 景子*; 安田 智成*; 加藤 正史*; 市村 正也*; 畑山 智亮*; 大島 武

Materials Science Forum, 778-780, p.503 - 506, 2014/02

Photolytic hydrogen generation using sunlight is regarded as energy production technology for the next generation. One of the key of issues for this technology is a selection of materials for the photolysis. Silicon carbide (SiC) is expected as one of the candidate materials for this application. In this study, we measured carrier lifetimes in SiC by the microwave photoconductivity decay ($$mu$$PCD) method. In order to control carrier lifetime in SiC, some samples were irradiated with 160 keV-electrons with fluences between 1$$times$$10$$^{16}$$ and 1$$times$$10$$^{17}$$ /cm$$^{2}$$. The values of carrier lifetime in SiC were compared to photocurrents in electrolytes which directly relate to the conversion efficiency of photolytic hydrogen generation. As a result, photocurrents depend on the sum of the depletion layer width and the diffusion length which was estimated from carrier lifetimes.

論文

Identification of structures of the deep levels in 4H-SiC

中根 浩貴*; 加藤 正史*; 市村 正也*; 大島 武

Materials Science Forum, 778-780, p.277 - 280, 2014/02

Annealing behavior of the carrier lifetime and the deep levels in electron irradiated n-type and semi-insulating hexagonal (4H) silicon carbide (SiC) was studied. As a result of photo induced current transient spectroscopy (PICTS) measurements, two peaks were observed for each sample. The height of those peaks depended on annealing temperature. Comparing the annealing behavior of the peak height with temperature dependence of concentrations of various defects reported previously, we speculated that the observed peaks originate from either divacancy of silicon vacancy and carbon vacancy (V$$_{Si}$$V$$_{C}$$) or pair of carbon antisite and carbon vacancy (C$$_{Si}$$V$$_{C}$$).

論文

Synthesis of a minute SiC product from polyvinylsilane with radiation curing, 2; Ceramization process of radiation cured polyvinylsilane

出崎 亮; 杉本 雅樹; 吉川 正人; 田中 茂; 成澤 雅紀*; 岡村 清人*; 伊藤 正義*

Journal of Materials Science, 42(1), p.130 - 135, 2007/01

 被引用回数:2 パーセンタイル:87.84(Materials Science, Multidisciplinary)

われわれは、液体のケイ素系ポリマーであるポリビニルシラン(PVS)から$$gamma$$線架橋を利用してSiC微小成型体を作製している。得られるSiC微小成型体の特性と焼成条件の間には密接な関係があるので、PVSのセラミックス化過程を調べ、最適な焼成条件を見いだすことが重要である。本報では、室温で$$gamma$$線架橋されたPVSのセラミックス化過程をガス分析,熱重量分析,密度変化等の面から調べた。$$gamma$$線架橋PVSのセラミックス化は500K以上の温度で始まり、700-1100Kの温度域で急激な有機-無機変成が起こることが明らかになった。質量変化と密度変化の結果から、放射線架橋、及びその後の焼成過程におけるPVSの体積収縮率が80%であることを明らかにした。1573Kでの焼成によって得られたSiCについて、密度が2.50g/cm$$^{3}$$、微小ビッカース硬さが31.6GPaであった。

論文

Structure of sub-monolayered silicon carbide films

馬場 祐治; 関口 哲弘; 下山 巖; Nath, K. G.

Applied Surface Science, 237(1-4), p.176 - 180, 2004/10

 被引用回数:6 パーセンタイル:62.8(Chemistry, Physical)

炭化ケイ素(SiC)はシリコンに代わる次世代の半導体物質として期待されている。SiC薄膜の製造法の一つに、有機ケイ素化合物を用いた蒸着法が知られており、ミクロンオーダーの厚みを持つSiC薄膜が合成されている。本研究では、ナノメートルオーダーの厚みを持つ極薄SiCの構造を調べるため、テトラメチルシランを放電気体として用いたイオンビーム蒸着法により1原子層以下のSiCをグラファイト上に堆積させ、その電子構造を放射光光電子分光法,X線吸収微細構造法により調べた。その結果、0.1ナノメーターの厚みの蒸着層を850$$^{circ}$$Cまで加熱すると、バルクのSiCと異なった二次元構造を持つSiCが生成することがわかった。この物質のX線吸収微細構造スペクトルの偏光依存性を測定したところ、Si原子周辺に$$pi$$*軌道的な性質を持つ軌道が存在し、この$$pi$$*軌道が表面に垂直であることがわかった。このことから、得られたSiC膜は、グラファイトと同様な二次元状の構造をとることが明らかとなった。

論文

Synthesis of a minute SiC product from polyvinylsilane with radiation curing, 1; Radiation curing of polyvinylsilane

出崎 亮; 杉本 雅樹; 田中 茂; 成澤 雅紀*; 岡村 清人*; 伊藤 正義*

Journal of Materials Science, 39(18), p.5689 - 5694, 2004/09

 被引用回数:6 パーセンタイル:68.61(Materials Science, Multidisciplinary)

液体のケイ素系ポリマーであるポリビニルシラン(PVS)について$$gamma$$線照射効果を調べ、放射線架橋を利用してSiC微小成型体を作製するための最適な架橋条件を検討した。照射温度として室温と液体窒素温度(77K)を検討した。両者の場合において、真空中、$$gamma$$線を3-4MGy以上照射することにより、室温で固体状であり、かつ成型された形状を維持したままPVSを架橋させることが可能であることを明らかにした。室温での照射の方がPVSの架橋効率が高いことを明らかにした。型枠に注入したPVSに真空中、室温で$$gamma$$線を3.6MGy照射し、その後Ar中1273Kで焼成することにより、型枠と相似形であり、30-60$$mu$$mの大きさのSiC微小成型体を得ることができた。

論文

Electronic structures of ultra-thin silicon carbides deposited on graphite

馬場 祐治; 関口 哲弘; 下山 巖; Nath, K. G.

Applied Surface Science, 234(1-4), p.246 - 250, 2004/07

 被引用回数:7 パーセンタイル:58.76(Chemistry, Physical)

炭化ケイ素(SiC)は耐熱性,化学的安定性を持つワイドギャップ半導体としての応用が期待されている材料である。しかしSiC結晶はsp$$^{3}$$結合でできており固体表面では3次元的に成長するため、数原子層以下の薄膜化は難しい。しかし最近、sp$$^{2}$$結合でできたグラファイト状の構造を持つSiC単原子層が安定に存在するという理論計算が報告された。本研究はこれを実験的に確かめるため、グラファイト単結晶表面にイオンビーム蒸着法で作成した単原子層以下のSiCの構造をX線光電子分光法(XPS),X線吸収微細構造法(XANES)などの放射光を用いた内殻分光法で調べた。その結果、XPSの化学シフト及びXANESのピークエネルギーなどから、バルクのSiCと異なる構造を持つ二次元状SiCの存在を示唆する結果が得られた。また、XANESスペクトルの偏光依存性から、この二次元相がグラファイトと類似の構造を持つことが明らかとなった。

論文

Development of silicon carbide micro-tube from precursor polymer by radiation oxidation

杉本 雅樹; 出崎 亮; 田中 茂; 岡村 清人*

Key Engineering Materials, 247, p.133 - 136, 2003/00

SiC繊維の前駆体高分子であるポリカルボシラン繊維を電子線により表層のみ酸化架橋し、未架橋の内部を溶出した後セラミック化することでSiCチューブを合成可能である。ポリカルボシランの放射線酸化機構を元に繊維中空化のメカニズムについて考察した。

論文

グラファイト単結晶中に注入したシリコンの局所構造

馬場 祐治; 下山 巖; 関口 哲弘

表面科学, 23(7), p.417 - 422, 2002/07

固体炭素は二種類の局所構造、すなわちダイヤモンド構造と二次元グラファイト構造をとるのに対し、炭化ケイ素はsp3結合でできたダイヤモンド構造のみをとることが知られている。グラファイト状の構造をした二次元SixC層が存在し得るかどうかを明らかにするため、グラファイト単結晶(HOPG)にSi$$^{+}$$イオンを注入して作成したSixC膜の局所構造をX線吸収端微細構造法(NEXAFS)により調べた。Si$$^{+}$$イオンを注入した試料のSi K-吸収端のNEXAFSスペクトルに現れる共鳴吸収ピークは、他のどんなシリコン化合物の場合より低いエネルギーに観測された。また、このピーク強度の偏光依存性から、励起先の非占有軌道が$$pi$$*軌道的性質を持つこと、またその軌道の方向がグラファイト面に垂直に近いことがわかった。このことから、Si$$^{+}$$イオン注入によって生成したSi-C結合はグラファイト面にほぼ平行であり、SixC層はsp2結合でできたグラファイト状の二次元構造をしていることが明らかとなった。

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