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Oral presentation

Physical and electrical characterization of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Shih, H.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

no journal, p.0 - 0, 2018/01

Thermal oxidation of AlGaN surface and its impact on the electrical properties of AlGaN/GaN MOS capacitors were investigated by means of synchrotron radiation photoelectron spectroscopy (SR-PES), atomic force microscopy (AFM) and C-V measurements. SR-PES analysis revealed that the AlGaN surface is oxidized even at low temperature of 400$$^{circ}$$C. However, since no noticeable change in the surface morphology was observed at temperatures up to 800$$^{circ}$$C, it can be concluded that an ultrathin oxide overlayer is formed on the AlGaN surface. The AlGaN/GaN MOS capacitors were fabricated on the AlGaN surface oxidized at moderate temperatures up to 800$$^{circ}$$C. It was found that the oxidation treatment at 400$$^{circ}$$C leads to further improvement of interface properties and reduction of C-V hysteresis.

Oral presentation

Oral presentation

Studies for construction of J-PARC transmutation experimental facility

Futakawa, Masatoshi

no journal, p.0 - 0, 2017/04

Japan Atomic Energy Agency (JAEA) proposes a transmutation of minor actinides (MA) by accelerator-driven systems (ADS). A lead-bismuth eutectic alloy (LBE) is used as a spallation target and a coolant of subcritical core because LBE has a good spallation neutron production performance and a chemically inert characteristic. However, the compatibility with steels is unfavourable especially for the typical structural materials such as a 316 stainless steel. To obtain the data for ADS design, JAEA plans to construct the Transmutation Experimental Facility (TEF) within the framework of the J-PARC project, which consists of two buildings, an ADS Target Test Facility (TEF-T) and a Transmutation Physics Experimental Facility (TEF-P). The activities to realize the TEF, a roadmap to establish the ADS transmutor and latest elemental test results for TEF construction will be introduced.

Oral presentation

SiO$$_{2}$$/AlON stacked gate dielectrics for AlGaN/GaN MOS-HFET

Watanabe, Kenta*; Terashima, Daiki*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Ishida, Masahiro*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; et al.

no journal, p.0 - 0, 2017/01

The advantage of SiO$$_{2}$$/AlON stacked gate dielectrics over SiO$$_{2}$$, AlON and Al$$_{2}$$O$$_{3}$$ single dielectric layers was demonstrated. Our systematic research revealed that the optimized stacked structure with 3.3-nm-thick AlON interlayer is beneficial in terms of superior interface quality, reduced gate leakage current and C-V hysteresis for next-generation high frequency and high power AlGaN/GaN MOS-HFETs.

Oral presentation

AlON gate dielectrics formed by repeating ALD-based thin AlN deposition and in situ oxidation for AlGaN/GaN MOS-HFETs

Nozaki, Mikito*; Watanabe, Kenta*; Yamada, Takahiro*; Shih, H.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

no journal, p.0 - 0, 2017/01

We fabricated AlON dielectric films by repeating thin AlN deposition and in situ O$$_{3}$$ oxidation for AlGaN/GaN MOS-HFETs. Uniform nitrogen distribution is achievable by the proposed ALD-based process and that nitrogen concentration can be precisely controlled by changing AlN thickness (ALD cycle number) in each step. It was found that AlON films grown by ALD system offers significant advantages in terms of practical application while keeping superior Vth stability and electrical properties at the insulator/AlGaN interface in AlGaN/GaN MOS-HFETs.

Oral presentation

The Effects of irradiation defect distribution and the steel compositions on void denuded zone formations during neutron irradiation and electron irradiation

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro*

no journal, - Pages, 2012/00

The irradiation-induced void denuded zone (VDZ) formation behaviors near grain boundaries were studied in order to clarify the effects of irradiation defect distribution and chemical compositions of steels which were developed to retard their swelling because of the decrease in mobility of point defects during irradiation. The test materials were Fe-15Cr-15Ni model alloy and PNC316 stainless steel which was developed in order to improve the void swelling resistance. These steels were neutron-irradiated in the experimental fast reactor JOYO and electron-irradiated separately using the 1 MeV high voltage electron microscopy (HVEM). The VDZ widths of each steel were evaluated by the TEM microstructural observations after irradiation. From the results in this research, it is considered that VDZ formation would be affected by chemical compositions and that the decrease of VDZ width would be related to increase of the void swelling resistance.

Oral presentation

Void denuded zone formations under electron irradiation in austenitic stainless steels modified with oversized elements

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro

no journal, - Pages, 2012/00

To predict the changes of vacancy diffusivity and concentration in alloys with additional elements to those in the based alloy from the experimentally obtained widths of void denuded zone (VDZ) formations induced during irradiations near grain boundaries, the effects of oversized additional elements of V and Zr on VDZ widths were evaluated in the electron-irradiated SUS316L and the modified type SUS316L steels with V and Zr. These steels were electron-irradiated at the temperature of 450$$^{circ}$$C. The results showed that the VDZ widths were 116nm, 95nm and almost zero in the SUS316L, the SUS316L-V and SUS316L-Zr steels respectively. The addition of V and Zr elements would have a role to decreasing the VDZ widths as results of the decrease of vacancy diffusivity in matrix under irradiations. In particular, the lesser VDZ width induced in the SUS316L-Zr would be also affected by the effective vacancy concentration.

Oral presentation

Observation of metastable O$$_{2}$$ adsorption structure on Si(111)-7$$times$$7 at room temperature by real-time O1s and Si2p XPS using synchrotron radiation

Yoshigoe, Akitaka; Teraoka, Yuden

no journal, p.0 - 0, 2007/01

Since the numbers of oxygen atoms at the backbond sites have been ambiguous only from O1s XPS, the mechanism of initial oxidation processes has been under debate. In this talk, we report the initial O$$_{2}$$ adsorption processes investigated by real-time Si2p XPS using high resolution synchrotron radiation in addition to O1s one. All experiments were performed at SUREAC2000, BL23SU, in SPring-8. After the thermal process, the oxygen gas was exposed to the clean surface at 300K and the oxidation process was in-situ monitored by real-time XPS for O1s and Si2p alternate measurement using SR. Comparing the chemical shifts of O1s with those of Si2p in photoelectron spectra, we found that the oxidation states corresponding to Si$$^{1+}$$ and Si$$^{2+}$$ were formed at the observable dosage for the metastable O$$_{2}$$ adsorbate. Thus, it is found that the metastable O$$_{2}$$ species adsorb at the on-top site of Si adatom bonding to an oxygen atom at that backbond, i.e. ins-paul structure.

Oral presentation

Development of LLRF control system for J-PARC RCS

Tamura, Fumihiko; Schnase, A.; Yamamoto, Masanobu; Nomura, Masahiro; Yoshii, Masahito*; Omori, Chihiro*; Takagi, Akira*; Hara, Keigo*; Anami, Shozo*; Ezura, Eiji*

no journal, , 

The J-PARC Rapid cycling synchrotron(RCS) requires a verystable and precise low level RF(LLRF) control system to handle theultra-high proton beam currents. The MA-loaded low-Q cavities for theRCS are driven by the superposition of the dual-harmonic RF signal forboth the acceleration and the longitudinal bunch shaping. We employ afull-digital system based on direct digital synthesis(DDS). Themulti-harmonic RF signals generated by the DDS are easily synchronizedwithout PLLs. We describe the design and the structure of the LLRFblocks. The common feedback loops are used for the stabilizing thebeam orbit and phase as well as the RF voltages of the cavity. Theheavy beam loading effect is compensated by using the beam feedforwardmethod. We also present the test results of the recently manufacturedmodules.

Oral presentation

Effect of stress history on creep behavior of rock

Hashiba, Kimihiro; Matsui, Hiroya; Sato, Toshinori; Seno, Yasuhiro

no journal, , 

In this study, multi-stage creep tests were conducted with tuff and siliceous rock. The creep stresses of each stage and the duration of the first stage were variable, and the effect of the stress history on creep behavior was examined. It was found that the primary creep strain rate might be decreased by the stress history. In particular, the effect of the stress history was notable after the first stage with the large creep stress and the long duration. It was also found that the effect of the stress history of siliceous rock was larger than that of tuff.

Oral presentation

Radiation processing of polymer

Tamada, Masao

no journal, , 

In the radiation processing of polymer, graft polymerization and crosslinking induced by high energy radiation can lead the modification of polymer materials. Metal adsorbent synthesized by graft polymerization was applied to the removal of cadmium from scallop processing and the recovery of uranium from seawater. Crosslinking was available to improve the thermal properties of biodegradable polymer such as poly-lactic acid.

Oral presentation

Application of positron imaging method for plant breeding

Matsuhashi, Shimpei

no journal, , 

no abstracts in English

Oral presentation

Study of cellular radiation response using heavy-ion microbeams

Kobayashi, Yasuhiko

no journal, , 

no abstracts in English

Oral presentation

Effect of the thermomechanical treatment conditions onto characteristics of chromium-zirconium copper after the solution treatment

Hada, Kazuhiko; Nishi, Hiroshi; Hirose, Takanori; Mori, Kensuke; Aoki, Shoji*; Wada, Masahiko*; Yamamichi, Tetsuo*

no journal, , 

Chromium-zirconium copper as precipitation hardened copper alloy is examined as one of the structural materials used for the ITER in vacuum vessel components. The process that consists of a thermomechanical treatments series of the solution treatment with rapid cooling to obtain the supersaturated solid solution and the aging treatment etc., is adopted in order to obtain the demanded high strength in manufacturing of this alloy material. However, as this alloy is precipitation hardened copper alloy, it is concerned that the great change in the strength characteristic is caused by the thermomechanical treatments conditions, especially the difference of the quenching cooling rate after the solution treatment in manufacturing. In this research, the influence of the quenching cooling rate condition after the solution treatment and the other conditions on this copper alloy was investigated by measuring the tensile test properties of the specimens that are prepared by treatments with some quenching cooling rate conditions after the solution treatment and aging treatment. One of the typical results from this study is that, for the quenching cooling rate after the solution treatment, it was understood that the cooling rate change from 1 to 10$$^{circ}$$C/s causes the great growth in the tensile strength. Therefore, when this alloy component is manufactured by heat history process like HIP process and needed to be treated solution treatment to be use for the structural component, it is important to guarantee the strength of the product by checking the quenching cooling rate after the solution treatment.

Oral presentation

Study on redox equilibrium of U$$^{4+}$$/U$$^{3+}$$ in molten NaCl-2CsCl

Nagai, Takayuki; Uehara, Akihiro*; Shirai, Osamu*; Yamana, Hajimu*

no journal, , 

no abstracts in English

Oral presentation

Analyses of DNA complex and crystallization of the DNA repair promoting protein PprA derived from Deinococcus Radiodurance

Adachi, Motoyasu; Tamada, Taro; Sato, Katsuya*; Narumi, Issei; Kuroki, Ryota

no journal, , 

The resistance of Deinococcus radiodurans to $$gamma$$-ray is 1000 times higher than that of human cells. PprA is the novel protein which promotes repairing DNA, and play a key role in the ability to resist to the radiation. The characterization of PprA have showed: (1) that the expression of PprA is controlled under another novel protein of PprI (2) that PprA promotes ligase reaction: (3) that pprA exhibits the ability to bind on DNA. In this study, our objective is the crystal structure analysis of PprA to reveal its structure-function relationships and for application as genetic and clinical tools. Here, we constructed the E. coli expression and purification system of PprA. Using the purified PprA, some small crystals in size were obtained after screening of conditions for crystalization. Beased on the analyses of DNA-PprA interaction, we showed that 280 molecules of PprA at least can bind on a DNA molecule of pUC19 plasmid (2686bp). In addition, we indicated that several DNA-PprA complexes may form higher complex, when DNA includes terminal end or nick (the cleaved part on a DNA strand). These results are important knowledge in molecular assembly and function of PprA.

Oral presentation

Positronium formation in SiO$$_{2}$$

Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*

no journal, , 

The annihilation $$gamma$$ rays from the para-pojitoronium (p-Ps) state gives narrower Doppler broadening. The broader Doppler broadening was observed at very young age region that is mainly from the annihilation process of p-Ps. It was explained by the delayed Ps slowing down and the delayed Ps formation. We have successfully obtained the experimental evidence of the delayed Ps formation.

Oral presentation

Temporal variation in performance of iodine-129 collecting media for a long-term and large-volume sampling

Miyauchi, Toru; Koarashi, Jun; Mikami, Satoshi; Kozawa, Tomoyasu*; Yokota, Tomokazu*; Isaka, Keisuke*; Akiyama, Kiyomitsu

no journal, , 

no abstracts in English

Oral presentation

Direct observation of superoxide radicals produced in water by 70MeV/u Kr ion irradiations

Taguchi, Mitsumasa; Baldacchino, G.*; Pin, S.*; Vigneron, G.*; Hichel, B.*; Kojima, Takuji

no journal, , 

no abstracts in English

Oral presentation

Airborne radioiodine monitoring technique without interference of Krypton-85 in nuclear fuel reprocessing operation

Mikami, Satoshi; Miyauchi, Toru; Koarashi, Jun; Kozawa, Tomoyasu*; Yokota, Tomokazu*; Isaka, Keisuke*; Akiyama, Kiyomitsu

no journal, , 

no abstracts in English

32603 (Records 1-20 displayed on this page)