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Journal Articles

Two-phase flow structure in a particle bed packed in a confined channel

Ito, Daisuke*; Kurisaki, Tatsuya*; Ito, Kei*; Saito, Yasushi*; Imaizumi, Yuya; Matsuba, Kenichi; Kamiyama, Kenji

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.6430 - 6439, 2019/08

In core disruptive accident of sodium-cooled fast reactor, cooling of residual fuel debris formed in the reactor core is one of important factors to achieve in-vessel retention of the fuel. To clarify the feasibility of the cooling which is called "in-place cooling", characteristics of gas-liquid two-phase flow in the debris bed must be well understood. Since the debris bed can be formed in a confined flow channel in the core, effect of the channel wall cannot be neglected. Thus, this study aims to clarify the effect of the wall on two-phase flow characteristics in the debris bed, which was simulated as a particle bed packed in a pipe. The pressure drop was measured and compared with results by previous models, and porosity and void fraction distributions were measured by X-ray radiography. Then, the pressure drop evaluation model was modified considering the wall effect, and the applicability of the models was discussed.

Journal Articles

Effect of porosity distribution on two-phase pressure drop in a packed bed

Kurisaki, Tatsuya*; Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Imaizumi, Yuya; Matsuba, Kenichi; Kamiyama, Kenji

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 3 Pages, 2018/11

In the evaluation of the in-place cooling which is for the residual core materials in the severe accident of sodium-cooled fast reactors, pressure loss of two-phase flow in debris bed is one of the important factors. Although Lipinski model is already proposed for the pressure loss evaluation, the accuracy would decrease when the porosity is not homogeneous. Thus, experiment to measure the pressure loss in a packed bed of non-homogeneous porosity distribution was conducted, and the Lipinski model was modified dividing the cross section to evaluate the pressure loss in it. As a result, it was confirmed that agreement of the experimental values with the values by modified Lipinski model was better than that with the original Lipinski model.

JAEA Reports

Conceptual design of multipurpose compact research reactor; Annual report FY2010 (Joint research)

Imaizumi, Tomomi; Miyauchi, Masaru; Ito, Masayasu; Watahiki, Shunsuke; Nagata, Hiroshi; Hanakawa, Hiroki; Naka, Michihiro; Kawamata, Kazuo; Yamaura, Takayuki; Ide, Hiroshi; et al.

JAEA-Technology 2011-031, 123 Pages, 2012/01

JAEA-Technology-2011-031.pdf:16.08MB

The number of research reactors in the world is decreasing because of their aging. However, the planning to introduce the nuclear power plants is increasing in Asian countries. In these Asian countries, the key issue is the human resource development for operation and management of nuclear power plants after constructed them, and also the necessity of research reactor, which is used for lifetime extension of LWRs, progress of the science and technology, expansion of industry use, human resources training and so on, is increasing. From above backgrounds, the Neutron Irradiation and Testing Reactor Center began to discuss basic concept of a multipurpose low-power research reactor for education and training, etc. This design study is expected to contribute not only to design tool improvement and human resources development in the Neutron Irradiation and Testing Reactor Center but also to maintain and upgrade the technology on research reactors in nuclear power-related companies. This report treats the activities of the working group from July 2010 to June 2011 on the multipurpose low-power research reactor in the Neutron Irradiation and Testing Reactor Center and nuclear power-related companies.

Journal Articles

Controls over structural and electronic properties of epitaxial graphene on silicon using surface termination of 3C-SiC(111)/Si

Fukidome, Hirokazu*; Abe, Shunsuke*; Takahashi, Ryota*; Imaizumi, Kei*; Inomata, Shuya*; Handa, Hiroyuki*; Saito, Eiji*; Enta, Yoshiharu*; Yoshigoe, Akitaka; Teraoka, Yuden; et al.

Applied Physics Express, 4(11), p.115104_1 - 115104_3, 2011/11

 Times Cited Count:34 Percentile:80.78(Physics, Applied)

Journal Articles

Control of epitaxy of graphene by crystallographic orientation of a Si substrate toward device applications

Fukidome, Hirokazu*; Takahashi, Ryota*; Abe, Shunsuke*; Imaizumi, Kei*; Handa, Hiroyuki*; Kang, H. C.*; Karasawa, Hiromi*; Suemitsu, Tetsuya*; Otsuji, Taiichi*; Enta, Yoshiharu*; et al.

Journal of Materials Chemistry, 21(43), p.17242 - 17248, 2011/11

 Times Cited Count:28 Percentile:67.71(Chemistry, Physical)

Journal Articles

First flight demonstration of film-laminated InGaP/GaAs and CIGS thin-film solar cells by JAXA's small satellite in LEO

Morioka, Chiharu*; Shimazaki, Kazunori*; Kawakita, Shiro*; Imaizumi, Mitsuru*; Yamaguchi, Hiroshi*; Takamoto, Tatsuya*; Sato, Shinichiro; Oshima, Takeshi; Nakamura, Yosuke*; Hirako, Keiichi*; et al.

Progress in Photovoltaics; Research and Applications, 19(7), p.825 - 833, 2011/11

 Times Cited Count:19 Percentile:65.05(Energy & Fuels)

Journal Articles

Low-energy-electron-diffraction and X-ray-phototelectron-spectroscopy studies of graphitization of 3C-SiC(111) thin film on Si(111) substrate

Takahashi, Ryota*; Handa, Hiroyuki*; Abe, Shunsuke*; Imaizumi, Kei*; Fukidome, Hirokazu*; Yoshigoe, Akitaka; Teraoka, Yuden; Suemitsu, Maki*

Japanese Journal of Applied Physics, 50(7), p.070103_1 - 070103_6, 2011/07

 Times Cited Count:31 Percentile:78.66(Physics, Applied)

Journal Articles

Oxygen-induced reduction of the graphitization temperature of SiC surface

Imaizumi, Kei*; Handa, Hiroyuki*; Takahashi, Ryota*; Saito, Eiji*; Fukidome, Hirokazu*; Enta, Yoshiharu*; Teraoka, Yuden; Yoshigoe, Akitaka; Suemitsu, Maki*

Japanese Journal of Applied Physics, 50(7), p.070105_1 - 070105_6, 2011/07

 Times Cited Count:4 Percentile:20.9(Physics, Applied)

Oral presentation

Evaluation method of radiation irradiation to space solar cell for international standardization

Imaizumi, Mitsuru*; Saito, Masashi*; Sato, Shinichiro; Yasuda, Keisuke*

no journal, , 

no abstracts in English

Oral presentation

Epitaxy of graphene on Si substrates toward three-dimensional graphene devices

Fukidome, Hirokazu*; Miyamoto, Yu*; Handa, Hiroyuki*; Takahashi, Ryota*; Imaizumi, Kei*; Suemitsu, Maki*; Yoshigoe, Akitaka; Teraoka, Yuden

no journal, , 

Graphene, two-dimensional network of sp$$^{2}$$ carbon, is one of promising materials beyond CMOS, as described in the semiconductor roadmap. The major issue is a lack of reasonable process for epitaxial growth on substrates. In fact, current production methods, such as exfoliation from graphite and epitaxy on SiC single crystals, are not mass-productive. We are seeking the ways to develop graphene-on-silicon (3D-GOS) process to match recent trends of silicon technologies. One of key issues toward 3D-GOS is the formation of epitaxial graphene on main plane directions of silicon, such as (100), (110) and (111). In this article, large area epitaxy of graphene on Si(110), Si(100) and Si(111) is presented. The result must be a good news because it can open new and realistic ways to three-dimensionally fabricate graphene-based devices beyond CMOS.

Oral presentation

LEED observation for surface structure of graphene on silicon

Takahashi, Ryota*; Miyamoto, Yu*; Handa, Hiroyuki*; Saito, Eiji*; Imaizumi, Kei*; Fukidome, Hirokazu*; Suemitsu, Maki*; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

We have succeeded to form graphene films from 3C-SiC layer on Si substrate by thermal annealing in vacuum (graphene on silicon technique:GOS). In this study, surface structures were observed by LEED and XPS methods to make clear the GOS formation mechanisms. SiC-1$$times$$1 LEED pattern was observed at 3C-SiC(111) surface on the Si substrate showing periodicity of bulk SiC. After graphene formation treatments of 1523 K thermal annealing for 30 min, graphene 1$$times$$1 pattern was observed showing periodicity of graphene. The graphene (1$$times$$1) spots were tilted by 30 deg comparing to the bulk SiC (1$$times$$1) spots. C1s-XPS observation revealed that a peak corresponding to sp$$^{2}$$ bonding increased with decreasing SiC bulk peak. Consequently, graphene formation from 3C-SiC on Si substrate is same as that on 6H-SiC(0001) substrate.

Oral presentation

Refurbishment and restart of JMTR, 11; Technology development for attractive irradiation tests, 5; Re-evaluation of thermal scattering law for neutron dosimetry

Imaizumi, Tomomi; Kadotani, Hiroyuki*; Okumura, Keisuke; Katakura, Junichi; Nagao, Yoshiharu

no journal, , 

no abstracts in English

Oral presentation

Reduction of graphitization temperature of SiC surface by addition of oxygen

Imaizumi, Kei*; Takahashi, Ryota*; Miyamoto, Yu*; Handa, Hiroyuki*; Saito, Eiji*; Fukidome, Hirokazu*; Suemitsu, Maki*; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

As the graphene, 2D-crystal of a carbon atomic layer, has a large mobility of 300000 cm$$^{2}$$/V/s, it is expected as a candidate for the next generation electronic device material. As to the practical use of graphene, a graphene-on-silicon (GOS) technique in which graphene is formed by thermal annealling on an silicon substrate covered by an SiC thin film. Since the anneal temperature is high as 1523-1573 K for the graphene formation in the former techniques including the GOS technique, such a high temperature technique is not introduced indeed in silicon device fabrication processes. We noticed a temperature-pressure phase diagram reported by Yongwei Song et al.. We have succeeded to form a graphene film on the SiC surface at a lower temperature of 1273 K by adding a bit of oxygen gas in the anneal atmosphere.

Oral presentation

LEED and XPS observations of graphene-on-Si process

Takahashi, Ryota*; Miyamoto, Yu*; Handa, Hiroyuki*; Saito, Eiji*; Imaizumi, Kei*; Fukidome, Hirokazu*; Suemitsu, Maki*; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

In this study, a graphene-on-silicon process was observed by LEED and XPS to make clear mechanisms. LEED patterns of SiC(1$$times$$1) and Si(RT3$$times$$RT3)R30$$^{circ}$$ were observed on the 3C-SiC(111) surface formed on the Si(111) surface. After the thermal annealing process at 1523 K for 30 min, a LEED pattern of graphene(1$$times$$1) was also observed. The graphene(1$$times$$1) pattern was tilted to the SiC(1$$times$$1) pattern by 30 deg as expected. The graphene formation process of 3C-SiC(111) on the Si(111) is the same as that of a 6H-SiC(0001) substrate. Comparing a C1s photoemission peak before and after the annealling process, a Cis peak corresponding to an sp$$^{2}$$ hybrid orbital appeared and a peak due to SiC bulk decreased. These facts reveal that a surface state transformation from SiC(1$$times$$1)(bulk state) to graphene(1$$times$$1)(graphene state) takes place even in the graphene-on-silicon process on Si(111) surface as well as the graphene formation process on the 6H-SiC(0001) substrate.

Oral presentation

SR-PES study on the formation of epitaxial graphene on Si substrates

Suemitsu, Maki*; Takahashi, Ryota*; Handa, Hiroyuki*; Saito, Eiji*; Imaizumi, Kei*; Fukidome, Hirokazu*; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

The up-to-date industrial fabrication method of graphene is a epitaxial graphene method, in which graphene layers are formed on the SiC substrate after thermal annealing in the vacuum condition. This method, however, has a large disadvantage, that is, an SiC bulk substrate with a large size diameter is not available with low prices. We have succeeded to make graphene on the Si substrate by thermal annealing of a 3C-SiC ultra-thin layer (80-100 nm) formed epitaxially on the Si substrate in the vacuum conditions (Graphene-On-Silicon;GOS). In this study, in order to make clear mechanisms of the GOS formation processes, low energy electron diffraction (LEED) and X-ray photoemission spectroscopy (XPS) have been applied to observe surface structures. Consequently, graphene formation processes from the 3C-SiC(111) layer on the Si(111) substrate has been found to be same as those on the 6H-SiC(0001) substrate.

Oral presentation

Controlling the interface between graphene and SiC by use of graphene-on-silicon technology

Fukidome, Hirokazu*; Takahashi, Ryota*; Imaizumi, Kei*; Handa, Hiroyuki*; Suemitsu, Maki*; Yoshigoe, Akitaka; Teraoka, Yuden

no journal, , 

Graphene layers could be formed firstly on an SiC thin film, which is fabricated on an Si substrate by a gas-source MBE method, by thermal annealing in vacuum (GOS structure). It should be controlled the interface between the SiC film and the graphene layers. In this study, relationships between chrystallographic symmetries of the Si substrate and the interface in the GOS structure were investigated. After an SiC(110), SiC(100), and SiC(111) surface is formed on the Si(110), Si(100), and Si(111) substrate, respectively, graphene layers were formed by thermal annealing of these SiC thin films up to 1523 K in vacuum. Photoemission spectroscopy of C1s core level with synchrotron radiation revealed that no interfacial layers are formed between the graphene and the SiC(110) and SiC(100) films while an interfacial layer is formed on the SiC(111) film.

Oral presentation

Real-time SR photoelectron-spectroscopy measurement of low-temperature graphitization of a SiC thin film on Si substrates under ULP oxygen ambient

Imaizumi, Kei*; Takahashi, Ryota*; Handa, Hiroyuki*; Saito, Eiji*; Fukidome, Hirokazu*; Suemitsu, Maki*; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

We found that an SiC surface changed to a graphene film even at 1273 K in the oxygen gas ambient. As subsequent experiments, real-time photoelectron spectroscopy using synchrotron radiation was applied to observe the graphene formation process in the ultra low pressure oxygen ambient. The 3C-SiC(111) surface, formed on the Si(111) surface using monomethylsilane, was used as a substrate. The real-time photoelectron spectroscopy was performed at BL23SU in the SPring-8. With increasing reaction time, a C1s photoelectron peak originated from sp$$^{2}$$ carbon increased. It reveals that a graphene film is formed on the SiC surface.

Oral presentation

LEED observation of formation of epitaxial graphene on 3C-SiC(111) ultrathin film

Takahashi, Ryota*; Miyamoto, Yu*; Handa, Hiroyuki*; Saito, Eiji*; Imaizumi, Kei*; Fukidome, Hirokazu*; Suemitsu, Maki*; Teraoka, Yuden; Yoshigoe, Akitaka

no journal, , 

New technologies beyond Si-CMOS technologies are neccessary in the Si electronic device developments. Now, graphene is attracted as it has a large mobility. It is well known that a 6H-SiC substrate surface changes to graphene by thermal annealing in vacuum as Si atoms sublimate. On the other hand, we developed the graphene-on-silicon (GOS) method in which graphene is formed from 3C-SiC thin film on an Si substrate by thermal annealing in vacuum. In this report, graphene formation processes were observed by LEED for a 6H-SiC(0001) substrate and a 3C-SiC(111) surface. It was found that the graphene formation process on a 3C-SiC(111) surface proceeded through the same surface reconstruction structure with that of 6H-SiC(0001) substrate.

Oral presentation

Orientation-mediated control of interfacial structure in epitaxial graphene on silicon substrates

Suemitsu, Maki*; Fukidome, Hirokazu*; Takahashi, Ryota*; Imaizumi, Kei*; Handa, Hiroyuki*; Yoshigoe, Akitaka; Teraoka, Yuden

no journal, , 

Formation of SiC thin layers on Si substrates followed by annealing converts the top surface into graphene (graphene on silicon;GOS). Normally, 3C-SiC(111), (110) and (100)-oriented layers are grown on Si(111), (110) and (100) substrates, respectively. Not only 3C-SiC(111) but also 3C-SiC(100) and (110) surfaces, epitaxial graphene layers were produced. The Raman spectra showed the same bands for the three orientations. Synchrotron-radiation X-ray photoelectron spectrum of C1s presented sp$$^{2}$$ carbon atoms for the three orientations. While no interfacial layers are formed on the SiC(100) and SiC(110), the interfacial layer does exist between the graphene and the SiC(111) film. The observation of the equally successful growth of graphene on these low-index SiC surfaces makes the GOS technology aviable in the post-Si device developments.

Oral presentation

LEED and SR-XPS observations of graphitization on orientationally rotated epitaxial film of 3C-SiC(111)/Si(110)

Takahashi, Ryota*; Handa, Hiroyuki*; Abe, Shunsuke*; Inomata, Shuya*; Imaizumi, Kei*; Fukidome, Hirokazu*; Teraoka, Yuden; Yoshigoe, Akitaka; Kotsugi, Masato*; Okochi, Takuo*; et al.

no journal, , 

no abstracts in English

32 (Records 1-20 displayed on this page)