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JAEA Reports

Annual report of Nuclear Emergency Assistance and Training Center (April 1, 2012 - March 31, 2013)

Sato, Takeshi; Muto, Shigeo; Okuno, Hiroshi; Katagiri, Hiromi; Akiyama, Kiyomitsu; Okamoto, Akiko; Koie, Masahiro; Ikeda, Takeshi; Nemotochi, Toshimasa; Saito, Toru; et al.

JAEA-Review 2013-046, 65 Pages, 2014/02

JAEA-Review-2013-046.pdf:11.18MB

When a nuclear emergency occurs in Japan, the Japan Atomic Energy Agency (JAEA) has the responsibility of providing technical support to the National government, local governments, police, fire stations and nuclear operators etc., because the JAEA has been designated as the Designated Public Institution under the Basic Act on Disaster Control Measures and the Act on Response to Armed Attack Situations, etc.. The Nuclear Emergency Assistance and Training Center (NEAT) of JAEA provides a comprehensive range of technical support activities to an Off-Site Center in case of a nuclear emergency. Specifically, NEAT gives technical advice and information, dispatches specialists as required, and supplies the National Government and local governments with emergency equipments and materials. NEAT provides various exercise and training courses concerning nuclear disaster prevention to those personnel taking an active part in emergency response organizations at normal times. The tasks of NEAT, with its past experiences as a designated public institution including the responses to TEPCO's Fukushima Accident, have been shifted to technical supports to the national government for strengthening its abilities to emergency responses; the NEAT therefore focused on maintenance and operation of its functions, and strengthening its response abilities in cooperation with the national government. This annual report summarized these activities of JAEA/NEAT in the fiscal year 2012.

JAEA Reports

Annual report of Nuclear Emergency Assistance and Training Center (April 1, 2011 - March 31, 2012)

Katagiri, Hiromi; Okuno, Hiroshi; Okamoto, Akiko; Ikeda, Takeshi; Tamura, Kenichi; Nagakura, Tomohiro; Nakanishi, Chika; Yamamoto, Kazuya; Abe, Minako; Sato, Sohei; et al.

JAEA-Review 2012-033, 70 Pages, 2012/08

JAEA-Review-2012-033.pdf:6.38MB

When a nuclear emergency occurs in Japan, JAEA has the responsibility of providing technical support to the National government, local governments, etc., by the Basic Law on Emergency Preparedness and the Basic Plan for Disaster Countermeasures. NEAT of JAEA gives technical advice and information, dispatch specialists as required, supplies with the National Government and local governments emergency equipment and materials. NEAT provides various lectures and training courses concerning nuclear disaster prevention for emergency response organizations at normal time. Concerning the assistance to the Accident of Fukushima No.1 Nuclear Power Station caused by the Great East Japan Earthquake on 11 March, 2011, JAEA assisted activities including environmental radiation monitoring, environmental radioactivity analyses, resident public consulting etc., with its the utmost effort. This annual report summarized these activities of NEAT in the fiscal year 2011.

Journal Articles

Synchrotron radiation photoemission study of Ge$$_{3}$$N$$_{4}$$/Ge structures formed by plasma nitridation

Hosoi, Takuji*; Kutsuki, Katsuhiro*; Okamoto, Gaku*; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

Japanese Journal of Applied Physics, 50(10), p.10PE03_1 - 10PE03_5, 2011/10

 Times Cited Count:11 Percentile:47.47(Physics, Applied)

Journal Articles

Magnetization plateau of the quantum spin nanotube

Okamoto, Kiyomi*; Sato, Masahiro*; Okunishi, Koichi*; Sakai, Toru; Itoi, Chigaku*

Physica E, 43(3), p.769 - 772, 2011/01

 Times Cited Count:3 Percentile:17.85(Nanoscience & Nanotechnology)

The magnetization process of the 3-leg quantum spin nanotube is investigated by the numerical diagonalization of finite-size clusters and the density matrix renormalization group method. It is found that the magnetization plateau appears at 1/3 of the saturation magnetization for sufficiently large interchain coupling. In addition we find that in the presence of asymmetric lattice distortion, there are two different mechanisms of the magnetization plateau formation. We also successfully present a phase diagram of the magnetization plateau.

Journal Articles

Quantum spin nanotubes; Frustration, competing orders and criticalities

Sakai, Toru; Sato, Masahiro*; Okamoto, Kiyomi*; Okunishi, Koichi*; Itoi, Chigaku*

Journal of Physics; Condensed Matter, 22(40), p.403201_1 - 403201_13, 2010/10

 Times Cited Count:33 Percentile:40.7(Physics, Condensed Matter)

Recent developments of theoretical studies on spin nanotubes are reviewed, especially focusing on the S=1/2 three-leg spin tube. In contrast to the three-leg spin ladder, the tube has a spin gap in case of the regular-triangle unit cell when the rung interaction is sufficiently large. The effective theory based on the Hubbard Hamiltonian indicates a quantum phase transition to the gapless spin liquid due to the lattice distortion to an isosceles triangle. This is also supported by the numerical diagonalization and the density matrix renormalization group analyses. Furthermore, combining analytical and numerical approaches, we reveal several novel magnetic-field-induced phenomena: N$'e$el, dimer, chiral and/or inhomogeneous orders, new mechanism for the magnetization plateau formation, and others. The recently synthesized spin tube materials are also briefly introduced.

Journal Articles

Field induced exotic phenomena of the S=1/2 three-leg quantum spin nanotube

Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Sato, Masahiro*

Journal of Low Temperature Physics, 159(1-2), p.55 - 59, 2010/04

 Times Cited Count:8 Percentile:40.08(Physics, Applied)

The numerical study on the S=1/2 three-leg spin nanotube using the exact diagonalization and the density matrix renormalization group method indicated that the 1/3 magnetization plateau appears for sufficently large rung interaction caused by two different mechanisms, depending on the asymmetry.

Journal Articles

Interface engineering of Ge MOS devices with Zr0$$_{2}$$ gate dielectrics

Hosoi, Takuji*; Okamoto, Gaku*; Kutsuki, Katsuhiro*; Kagei, Yusuke*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

Oyo Butsuri Gakkai Hakumaku, Hyomen Butsuri Bunkakai, Shirikon Tekunoroji Bunkakai Kyosai Tokubetsu Kenkyukai Kenkyu Hokoku, p.145 - 148, 2010/01

We developed high quality high-$$k$$/Ge gate stacks with reduced leakage current and superior interface quality, which was fabricated by direct deposition of ZrO$$_{2}$$ on Ge substrate and thermal oxidation. Synchrotron radiation photoelectron spectroscopy revealed that thermal oxidation at 823 K caused not only an intermixing between ZrO$$_{2}$$ and Ge but also the formation of GeO$$_{2}$$ at the interlayer. We obtained an equivalent oxide thickness (EOT) of 1.9 nm, and an interface state density of 10$$^{11}$$ cm$$^{-2}$$eV$$^{-1}$$ for Au/ZrO$$_{2}$$/Ge capacitors. Furthermore, we found that the A1$$_{2}$$0$$_{3}$$ capping on the Zr0$$_{2}$$ 1ayer is effective for decreasing EOT. The interface state density as low as 5.3$$times$$10$$^{10}$$ cm$$^{-2}$$eV$$^{-1}$$ was obtained for the Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/Ge stack with 30 min oxidation. The EOT could be reduced to l.6 nm by 10 min oxidation. The leakage current was two orders of magnitude lower than the conventional poly-Si/SiO$$_{2}$$/Si stack.

Journal Articles

Quantum phase transitions of the asymmetric three-leg spin tube

Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Itoi, Chigaku*

Physical Review B, 78(18), p.184415_1 - 184415_11, 2008/11

 Times Cited Count:45 Percentile:84.16(Materials Science, Multidisciplinary)

We investigate quantum phase transitions of the S = $$frac{1}{2}$$ three-leg antiferromagnetic spin tube with asymmetric inter-chain (rung) exchange interactions. On the basis of the electron tube system, we propose a useful effective theory to give the global phase diagram of the asymmetric spin tube. In addition, using other effective theories we raise the reliability of the phase diagram. The density-matrix renormalization-group and the numerical diagonalization analyses show that the finite spin gap appears in a narrow region around the rung-symmetric line.

Oral presentation

In-situ characterization of chemical bonding states and thermal decomposition of Ge$$_{3}$$N$$_{4}$$ film by SR-XPS

Hosoi, Takuji*; Kutsuki, Katsuhiro*; Okamoto, Gaku*; Harada, Makoto*; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

After wet cleaning of p-Ge(001) by HF solution, the surface was anealed in an ultra-high vacuum and was nitrided using a large area nitrogen plasma apparatus in the conditions of surface temperature: 623 K, RF power: 50 W, nitrogen pressure:10.5 Torr, and reaction period: 30 min. The chemical bonding states and thermal decomposition processes of the nitide film was in-situ analyzed by synchrotron radiation photoemission spectroscopy. XPS spectra of clean Ge surface showed binding energies of Ge3d5/2 and 3/2 levels were 29.2 eV and 29.8 eV, respectively. The Ge surface nitrided by the high density plasma was oxidized by exposure to the air so that both components of nitride and oxide were observed by the SR-XPS before thermal anealing. GeO$$_{2}$$ component was selectively removed by thermal anealing up to 773 K in the UHV condition. After that XPS spectra of pure Ge$$_{3}$$N$$_{4}$$ film could be observed. We concluded chemical shift of the nitrided Ge was 2.2 eV.

Oral presentation

Quantum phase transition of spin nanotube

Sakai, Toru; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Sato, Masahiro*; Itoi, Chigaku*

no journal, , 

The spin nanotube was theoretically investigated by the numerical exact diagonalization and the density matrix renormalization group method. It was found that the three-leg spin tube exhibits a quantum phase transition between the spin gap and gapless phases, as a lattice distortion occurs. The superconductivity induced by the spin gap is also discussed.

Oral presentation

Quantum phase transition of the asymmetric three-leg spin tube

Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Otsuka, Yuichi*; Okamoto, Kiyomi*; Itoi, Chigaku*

no journal, , 

We investigate quantum phase transitions of the S=1/2 three-leg antiferromagnetic spin tube with asymmetric inter-chain (rung) exchange interactions. On the basis of the electron tube system, we propose a useful effective theory to give the global phase diagram of the asymmetric spin tube. In addition, using other effective theories we raise the reliability of the phase diagram. The density-matrix renormalization-group and the numerical diagonalization analyses show that the finite spin gap appears in a narrow region around the rung-symmetric line.

Oral presentation

Fabrication and characterization of high quality Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/GeO$$_{2}$$ layered gate dielectrics

Okamoto, Gaku*; Kutsuki, Katsuhiro*; Kagei, Yusuke*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

Structure analyses and electrical characteristic tests have been conducted for a high-k/Ge stuck of Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/GeO$$_{2}$$/Ge structure. A ZrGeO layer and intermediate oxidation number states for Ge have been confirmed in photoemission spectra in addition to a chemically-shifted Ge$$^{4+}$$ component suggesting the growth of GeO$$_{2}$$ interface layer. An Au electrode was capped on this dielectic substrate to make an Au/Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/GeO$$_{2}$$/Ge capacitor. C-V measurements were conducted for the capacitor. Hysteresis was so small of 21 mV and frequency dispersion was also small. Interface state density near a mid gap, estimated by a low temperature conductance method, was 5.3$$times$$10$$^{10}$$ cm$$^{-2}$$eV$$^{-1}$$. As a conclusion, we succeeded to make a high-k/Ge stuck which has excellent interface characteristics.

Oral presentation

SR-XPS analysis of SiO$$_{2}$$/SiC interfaces formed by thermal oxidation of 4H-SiC(000$$bar{1}$$) surfaces

Kirino, Takashi*; Kagei, Yusuke*; Okamoto, Gaku*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

no journal, , 

In order to study the origin of degradation for interface chracteristics and reliability of SiC(0001)C surfaces, chemical bonding states at SiO$$_{2}$$/SiC interfaces made on (000$$bar{1}$$)$$_{Si}$$ and (000$$bar{1}$$)$$_{C}$$ surfaces have been analyzed by using a synchrotron radiation XPS method. Si2p$$_{3/2}$$ components were extracted from Si2p photoemission peaks. Sub-oxidea components were observed in addition to the SiC substrate and the oxide layer. In the interface of the oxide layer formed on the (000$$bar{1}$$)$$_{C}$$ surface, Si$$^{1+}$$ component was small, higher oxidation number components were larger, and total amount od sub-oxides was larger comparing to that of the (000$$bar{1}$$)$$_{Si}$$ surface. A binding energy for oxide formed on the (000$$bar{1}$$)$$_{C}$$ surface was shifted to 0.22 eV higher side comparing to that of the (000$$bar{1}$$)$$_{Si}$$ surface. It indicates that band off-set of conduction band is small in the SiO$$_{2}$$/SiC interface.

Oral presentation

1/3 magnetization plateau of the 3-leg spin tube

Sakai, Toru; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*; Sato, Masahiro*

no journal, , 

no abstracts in English

Oral presentation

SR-XPS study on energy band structure of thermally grown SiO$$_{2}$$/4H-SiC interface

Kirino, Takashi*; Kagei, Yusuke*; Okamoto, Gaku*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

no journal, , 

Device ability of SiC-MOSFET's expected from physical data has not been achieved because channel resistance increases by mobility degradation due to Si0$$_{2}$$/SiC interface defects. Although high channel mobility is obtained in the MOSFET's made on a 4H-SiC(000-1)c face compared to them on a 4H-SiC(0001)Si face, reliability of an oxide film is preferential in the MOSFET's on a 4H-SiC(000-1)c face. Conduction band off-set of SiO$$_{2}$$/SiC interface and energy distribution of the interface level density are known to be different between MOSFET's on a 4H-SiC(000-1)c face and a 4H-SiC(0001)Si face. Physical origins for them are not known yet. In order to make clear the reasons for degradation of interface characteristics and reliability in the MOSFET's made on an SiC(000-1)c face, we evaluated chemical bonding states and energy band structures of Si0$$_{2}$$/SiC interfaces formed on an SiC(0001)Si face and an SiC(000-1)c face using synchrotron radiation photoemission spectroscopy.

Oral presentation

Field-induced quantum phase transitions of the asymmetric three-leg spin tube

Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*

no journal, , 

The S=1/2 three-leg spin tube has a spin gap due to the strong frustration. Using the numerical dyagonalization and the density matrix renormalization group (DMRG) calculation, we revealed new quantum phase transitions between the spin-gap and gapless phases induced by an asymmetric interchain interactions. Under high magnetic field this system also exhibits some interesting phenomena. The same numerical analysis on the magnetization process indicates that the 1/3 magnetization plateau appears for sufficiently large rung interaction caused by two different mechanisms, depending on the asymmetry.

Oral presentation

Coexistence of the staggered magnetization, dimerization, and chiral order in the magnetization plateau of the spin tube

Sakai, Toru; Sato, Masahiro*; Okunishi, Koichi*; Okamoto, Kiyomi*; Itoi, Chigaku*

no journal, , 

no abstracts in English

Oral presentation

Impact of Ge$$_{3}$$N$$_{4}$$ interface layer on EOT scaling in high-k/Ge gate stacks

Kutsuki, Katsuhiro*; Okamoto, Gaku*; Hideshima, Iori*; Uenishi, Yusuke*; Kirino, Takashi*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

no journal, , 

Direct deposition of ZrO$$_{2}$$ films on Ge substrates and subsequent thermal oxidation results in an equivalent oxide thickness (EOT) of above 2 nm while obtaining good interface quality due to interfacial GeO$$_{2}$$ formation. In this work, we proposed the use of Ge$$_{3}$$N$$_{4}$$ interlayer formed by high-density plasma nitridation for further EOT scaling because of its high resistance to oxidation and superior thermal stability. The structural modification of ZrO$$_{2}$$/Ge$$_{3}$$N$$_{4}$$/Ge after oxidation was characterized by synchrotron-radiation X-ray photoelectron spectroscopy at BL23SU in SPring-8. Ge 3d core-level spectra revealed that the Ge$$_{3}$$N$$_{4}$$ interlayer was slightly oxidized after thermal oxidation at 823 K, but N 1s spectra remained almost unchanged. This indicates that the Ge$$_{3}$$N$$_{4}$$ interlayer is effective in suppressing interfacial oxidation, thus obtaining an EOT of 1.8 nm.

Oral presentation

Determination of SiO$$_{2}$$/4H-SiC conduction band offset by SR-XPS

Kirino, Takashi*; Kagei, Yusuke*; Okamoto, Gaku*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

no journal, , 

It has been reported that hydrogen incorporation into thermally grown SiO$$_{2}$$/4H-SiC structures not only improves the interface quality, but also degrades the gate oxide reliability depending on SiC surface orientation. In this study, energy band diagrams of thermally grown SiO$$_{2}$$/4H-SiC(0001) and SiO$$_{2}$$/4H-SiC(000-1) structures with and without high-temperature hydrogen annealing were evaluated by synchrotron radiation X-ray photoelectron spectroscopy. The SiO$$_{2}$$ band gap and valence band offset at SiO$$_{2}$$/SiC interface were extracted from O 1s energy loss spectra and valence band spectra, respectively. The obtained energy band diagrams revealed that conduction band offsets at SiO$$_{2}$$/SiC interfaces were decreased after the hydrogen annealing especially for 4H-SiC(000-1) substrates. This is one possible reason for the reliability degradation of 4H-SiC metal-oxide-semiconductor devices by hydrogen incorporation.

Oral presentation

Interface engineering of ZrO$$_{2}$$/Ge gate stacks by post-deposition annealing and Al$$_{2}$$O$$_{3}$$ capping layers

Watanabe, Heiji*; Okamoto, Gaku*; Kutsuki, Katsuhiro*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*

no journal, , 

We fabricated high-quality high-k/Ge gate stacks by direct deposition of ZrO$$_{2}$$ layers on Ge substrates and subsequent post-deposition annealing. Synchrotron-radiation X-ray photoelectron spectroscopy revealed that thermally oxidizing a ZrO$$_{2}$$/Ge structure at 823 K caused not only ZrO$$_{2}$$ and Ge to intermix but also a pure GeO$$_{2}$$ interlayer to form. By optimizing subsequent oxidation conditions, we obtained a minimum EOT of 1.9 nm, negligible C-V hysteresis, and an interface state density (Dit) of a few 10$$^{11}$$ cm$$^{-2}$$eV$$^{-1}$$ for Au/ZrO$$_{2}$$/Ge capacitors. We also developed Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$ stacked gate dielectrics to control interface reaction during the post treatment. The Al$$_{2}$$O$$_{3}$$ capping on the ZrO$$_{2}$$ layer was found to be beneficial for further EOT scaling because it suppressed excess interface reaction. Scaled EOT value down to 1.6 nm and leakage current reduction were achieved.

25 (Records 1-20 displayed on this page)