Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a BC thin film

Norimatsu, Wataru*; Matsuda, Keita*; Terasawa, Tomoo; Takata, Nao*; Masumori, Atsushi*; Ito, Keita*; Oda, Koji*; Ito, Takahiro*; Endo, Akira*; Funahashi, Ryoji*; et al.

Nanotechnology, 31(14), p.145711_1 - 145711_7, 2020/04

https://doi.org/10.1088/1361-6528/ab62cf

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of BC on SiC and graphene on BC had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on BC acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on BC was highly boron doped, and the hole concentration could be controlled over a wide range of 210 to 210 cm. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Droplet generation during liquid jet impingement onto a horizontal plate

Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi

Experimental Thermal and Fluid Science, 98, p.86 - 94, 2018/11

https://doi.org/10.1016/j.expthermflusci.2018.05.022

Splash during liquid jet impingement onto a horizontal plate

Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro; Takata, Takashi

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 6 Pages, 2017/07

It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments are performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It is shown that the splash ratio can be correlated well as a function of the impact Weber number and dimensionless impact frequency.

Gelation process of polyacrylonitrile solutions as studied using small-angle neutron scattering techniques

Nakano, Shota*; Konno, Soken*; Tomita, Naoto*; Matsuba, Go*; Tominaga, Taiki*; Takata, Shinichi

Microsystem Technologies, 22(1), p.57 - 63, 2016/01

https://doi.org/10.1007/s00542-015-2653-x

We studied the structural formation process of polyacrylonitrile (PAN) gelation in a wide-spatial scale with the small and wide angle neutron scattering in MLF, J-PARC. In micron-scale structure, light transmittance and gelation time were evaluated. The presence of water in the mixed solvent accelerated the phase separation and gelation. In the opaque-gel case, we observed the nanometer-scaled correlation of crystalline cross-linking points and smooth boundary of two micron-scaled phases due to liquid-liquid phase separation. The correlation length is independent of the annealing time, then the cross-linking point exists locally and micro-gelation occurs during phase separation. By contrast, in the transparent-gel case, the correlation length was found to increase throughout the gelation process, and the entanglements of the polymer chains play a role similar to that of cross-linking points.

ACS cavity for J-PARC LINAC

Ao, Hiroyuki; Asano, Hiroyuki; Ouchi, Nobuo; Tsubota, Naoaki; Hasegawa, Kazuo; Hirano, Koichiro; Morishita, Takatoshi; Takata, Koji*; Naito, Fujio*; Yamazaki, Yoshishige

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.552 - 554, 2010/08

http://www.pasj.jp/web_publish/pasj7/proceedings/P_4PM/P_EH_4PM/WEPS074.pdf

The energy upgrade of the J-PARC linac was started from March 2009. In this project 20 Annular Coupled Structure (ACS) modules will be fabricated. The resonant frequency of the ACS module has to be tuned with mechanical machining before the final brazing. Therefore the test cells were fabricated to accumulate frequency tuning parameters. We fixed the final dimensions and the machining amount of the frequency tuning using these results. So far, the cell parts for the five ACS modules were tuned within 71.93 0.05 MHz. At the moment the first ACS module is being assembled and it will be completed in autumn 2010.

Status of mass production of the ACS cavity for the J-PARC linac energy upgrade

Ao, Hiroyuki; Asano, Hiroyuki; Ouchi, Nobuo; Tsubota, Naoaki; Hasegawa, Kazuo; Hirano, Koichiro; Morishita, Takatoshi; Takata, Koji*; Naito, Fujio*; Yamazaki, Yoshishige

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.618 - 620, 2010/05

http://accelconf.web.cern.ch/AccelConf/IPAC10/papers/mopec066.pdf

The mass production of the ACS (Annular-ring Coupled Structure) cavity started from March 2009 for the J-PARC linac energy upgrade from 181 MeV to 400 MeV. This upgrade project requires 18 ACS accelerating modules and two debunchers additionally within three years. The schedule is so tight that we have to optimize the fabrication process. Thus the test cells were fabricated for the all geometrical beta before the mass production to confirm the initial design and the frequency tuning procedure. This paper describes our approach for the mass production and the current status.

Pulse neutron imaging experiments in the first year of J-PARC

Kai, Tetsuya; Harada, Masahide; Oikawa, Kenichi; Sakai, Kenji; Maekawa, Fujio; Oi, Motoki; Shinohara, Takenao; Aizawa, Kazuya; Takata, Shinichi; Arai, Masatoshi; et al.

no journal, , 

Development of imaging techniques with pulse neutrons were started using the NeutrOn Beam-line for Observation and Research Use (NOBORU) of J-PARC at December 2008. The results in the first three months, future research plans and discussions on a new imaging facility in J-PARC are shown.

Neutron imaging test on NOBORU; Discrimination between water and ice by the Bragg edge method

Oikawa, Kenichi; Shinohara, Takenao; Hayashida, Hirotoshi; Aizawa, Kazuya; Takata, Shinichi; Sakai, Takuro; Harada, Masahide; Maekawa, Fujio; Suzuki, Junichi

no journal, , 

Three groups in JAEA and Hokkaido University group are developing the TOF-neutron imaging technology using NOBORU in MLF at J-PARC this year. One of the group of JAEA, imaging group of J-PARC carried out a TOF-neutron imaging of liquid and crystal phase of DO utilizing neutron energy contrast caused by the Bragg edge of the crystal.

Demonstration of magnetic field imaging with polarized neutrons and some other test experiments at J-PARC

Shinohara, Takenao; Kai, Tetsuya; Harada, Masahide; Oikawa, Kenichi; Sakai, Kenji; Oi, Motoki; Maekawa, Fujio; Takata, Shinichi; Suzuki, Junichi; Aizawa, Kazuya; et al.

no journal, , 

no abstracts in English

Development of a quadrupole magnet to polarize cold neutrons for SANS experiments

Oku, Takayuki; Suzuki, Junichi; Kira, Hiroshi; Shinohara, Takenao; Takata, Shinichi; Arai, Masatoshi; Hirota, Katsuya*; Iwashita, Yoshihisa*; Shimizu, Hirohiko*

no journal, , 

Spin selective neutron transportation and beam shaping can be realized based on the interaction between the neutron magnetic moment and magnetic field. The magnetic optics for neutrons is flexible optics since we can control its characteristics by changing the multiplicity of magnetic poles. So far, we have constructed the polarized neutron focusing system consisting of the quadrupole and sextupole magnets, and successfully introduced it into the SANS instrument. The quadrupole has a small aperture of 5 mm in diameter. Because of its small aperture, the application of the quadrupole magnet is limited in sans experiments with focusing geometry for high angular resolution. Therefore, we have developed a quadrupole magnet with a larger aperture of 15 mm in diameter and longer magnet length of 2200 mm. In this paper, we described the specifications of the new quadrupole magnet and discuss about its application in polarized neutron scattering.