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Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 59(SP), p.SPPA01_1 - SPPA01_7, 2020/11

 Times Cited Count:0 Percentile:100(Physics, Applied)

We investigate A-site cation ordering in the ferroelectric perovskite Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (BNT) by synchrotron X-ray total scattering. Although BNT has a problem of a low depolarization temperature, it is promising a lead-free piezoelectric material. Since the depolarization temperature is presumed to correspond to a relaxer like gradual order-disorder phase transition, local structure analysis is necessary to understand the structure of the diorder phase. Through this approach, the elusive connection between chemical heterogeneity and structural heterogeneity is revealed. Because of the large randomness, the Ti off-center shift is averaged out beyond the unit cell and the structure becomes very close to the average structure beyond the unit cell.

Journal Articles

Nature of structural instabilities in superconducting Sr$$_3$$Ir$$_4$$Sn$$_{13}$$

Kaneko, Koji; Cheung, Y. W.*; Hu, Y.*; Imai, Masaki*; Tanioku, Yasuaki*; Kanagawa, Hibiki*; Murakawa, Joichi*; Moriyama, Kodai*; Zhang, W.*; Lai, K. T.*; et al.

JPS Conference Proceedings (Internet), 30, p.011032_1 - 011032_6, 2020/03

Journal Articles

Synchrotron radiation-based techniques available at JAEA advanced characterization nanotechnology platform (Japan Atomic Energy Agency)

Yoneda, Yasuhiro; Yoshigoe, Akitaka; Takeda, Yukiharu; Shiwaku, Hideaki; Matsumura, Daiju; Shobu, Takahisa; Tamura, Kazuhisa

Materia, 58(12), p.763 - 769, 2019/12

This is an introduction to the equipment provided for each implementation period belonging to the structure analysis platform in the nanotechnology platform.

Journal Articles

${it In situ}$ optical microscopy of crystal growth of graphene using thermal radiation

Terasawa, Tomoo; Taira, Takanobu*; Obata, Seiji*; Saiki, Koichiro*; Yasuda, Satoshi; Asaoka, Hidehito

Vacuum and Surface Science, 62(10), p.629 - 634, 2019/10

Graphene, an atomically thin sheet composed of sp$$^{2}$$ carbon atoms, has been the most attractive material in this decade. The fascinating properties of graphene are exhibited when it is monolayer. Chemical vapor deposition (CVD) is widely used to produce monolayer graphene selectively in large-area. Here we introduce "radiation-mode optical microscopy" which we have developed in order to realize the ${it in situ}$ observation of the CVD growth of graphene. We show the method to observe graphene as bright contrast on Cu substrates in thermal radiation images. The growth mechanism, the nucleation site and rate limiting process, revealed by the ${it in situ}$ observation is presented. Finally, we show the CVD growth of graphene on Au substrates, resulting in the tuning of the emissivity of graphene by the pre-treatment procedures. Our method is not only a way to observe the graphene growth but also shed light on the thermal radiation property of graphene.

Journal Articles

Effect of hydrogen on chemical vapor deposition growth of graphene on Au substrates

Terasawa, Tomoo; Taira, Takanobu*; Yasuda, Satoshi; Obata, Seiji*; Saiki, Koichiro*; Asaoka, Hidehito

Japanese Journal of Applied Physics, 58(SI), p.SIIB17_1 - SIIB17_6, 2019/08

 Times Cited Count:0 Percentile:100(Physics, Applied)

Chemical vapor deposition (CVD) on substrates with low C solubility such as Cu and Au is promising to grow monolayer graphene selectively in a large scale. Hydrogen is often added to control the domain size of graphene on Cu, while Au does not require H$$_{2}$$ since Ar is inert against oxidation. The effect of H$$_{2}$$ should be revealed to improve the quality of graphene on Au. Here we report the effect of H$$_{2}$$ on the CVD growth of graphene on Au substrates using in situ radiation-mode optical microscopy. The in situ observation and ex situ Raman spectroscopy revealed that whether H$$_{2}$$ was supplied or not strongly affected the growth rate, thermal radiation contrast, and compressive strain of graphene on Au. We attributed these features to the surface reconstruction of Au(001) depending on H$$_{2}$$ supply. Our results are essential to achieve the graphene growth with high quality on Au for future applications.

Journal Articles

Synchrotron radiation real-time photoelectron spectroscopy study on adsorption reactions of oxygen molecule at semiconductor surfaces

Yoshigoe, Akitaka

Hoshako, 32(4), p.185 - 198, 2019/07

Synchrotron radiation photoelectron spectroscopy is a beneficial technique for precise analysis of chemical states of solid surfaces. Owing to its high luminosity, it ensures availability of termed synchrotron radiation real-time photoelectron spectroscopy which enables "${it in situ}$" observation of chemical reactions with gas molecules occurring at surfaces. In this review, oxygen adsorption reactions in the oxidation of silicon single crystal surfaces are focused. Through the demonstration of our research, the usefulness of synchrotron radiation real-time photoelectron spectroscopy to study molecular adsorption reactions at solid surfaces is briefly described and the future perspective would also be shown.

Journal Articles

Mass transport in the PdCu phase structures during hydrogen adsorption and absorption studied by XPS under hydrogen atmosphere

Tang, J.*; Yamamoto, Susumu*; Koitaya, Takanori*; Yoshigoe, Akitaka; Tokunaga, Takuma*; Mukai, Kozo*; Matsuda, Iwao*; Yoshinobu, Jun*

Applied Surface Science, 480, p.419 - 426, 2019/06

 Times Cited Count:1 Percentile:71.33(Chemistry, Physical)

Mass transports during hydrogen adsorption and absorption processes of PdCu alloys that has advantages of higher hydrogen diffusivity and economically lower-cost than the other Pd-alloys were studied. The research was made with a comparison of the well-known ordered phase of the bcc structure (the B2 phase) and a mixed phase of the fcc and B2 structures. ${it In-situ}$ ultrahigh vacuum X-ray photoelectron spectroscopy and ambient pressure X-ray photoelectron spectroscopy using synchrotron radiation were carried out to trace the chemical states of the Pd and Cu atoms as a function of temperatures. It is elucidated that the initial adsorption and absorption processes were similar in the two phases, but a hydrogen diffusion rate to the bulk was higher in the ordered phase than in the mixed one. We found the dynamics of the Pd and Cu atoms during the hydrogen adsorption/absorption processes largely depend on temperature. In the hydrogen atmosphere, the Pd atoms segregate at the surface below 373 K and Cu atoms segregate at the surface above 373 K. The present results agree well with the previous theoretical calculations and, thus, provide appropriate inputs toward developments of the hydrogen permeation materials.

Journal Articles

Simultaneous observation of Si oxidation rate and oxidation-induced strain using XPS

Ogawa, Shuichi*; Yoshigoe, Akitaka; Takakuwa, Yuji*

Vacuum and Surface Science, 62(6), p.350 - 355, 2019/06

Thermal oxidation of Si substrate is an indispensable process for the Si device fabrication. However, the influence of oxidation induced strain cannot be ignored for thin films. Synchrotron radiation real-time photoelectron spectroscopy was used as a method to measure simultaneously oxidation induced strain and oxidation rate. It was found that the acceleration of interfacial oxidation induced by thermal strain was observed for the rapid thermal oxidation. The results can be explained by the model in which point defects caused by strain become reaction sites at the SiO$$_{2}$$/Si interface.

JAEA Reports

Synchrotron radiation based XAFS analysis of the simulated nuclear waste glass samples prepared by bottom drain test in the full-scale mock-up melter (KMOC) (Contract research)

Okamoto, Yoshihiro; Nagai, Takayuki; Shiwaku, Hideaki; Kano, Shigeru; Himeno, Haruyuki*; Kobayashi, Hiroshi*; Nakatani, Mikio*

JAEA-Research 2018-013, 18 Pages, 2019/03

JAEA-Research-2018-013.pdf:1.98MB

The chemical state and local structure of some elements in the simulated nuclear waste glass samples (20 batches) prepared by bottom drain test in the full scale mock-up tests using KMOC melter were investigated by synchrotron radiation based X-ray absorption fine structure (XAFS) analysis. As a result of the analysis of cerium element, it was confirmed that the oxidation proceeds gently as the batch advanced. For manganese, iron, and zinc, there was almost no difference between batches, which seemed to be stabilized by getting into the frame structure of the borosilicate glass. There were no elements that seemed to be clearly crystalline except for platinum group elements. Remarkable precipitation was hardly observed in zirconium and molybdenum with the imaging analysis.

Journal Articles

Exploring the development of cesium removal processes via nanoscale chemical state analysis of cesium-containing clay minerals; Application of soft X-ray synchrotron radiation photoelectron microscopy to observe insulating materials

Yoshigoe, Akitaka

Hoshako Riyo No Tebiki, p.130 - 138, 2019/02

The educational book on next-generation synchrotron radiation usage is partially written. This book is being planned by several professors at Tohoku University. In this book, the contents which have already reported in our recent paper [Appl. Phys. Lett. 112 (2018) 021603.] are mainly written. The future perspective on photoemission electron microscopy using next generation synchrotron radiation and its possibility to analyze environmental samples and insulating functional materials are also described.

Journal Articles

Biodegradability of disulfide-organosilica nanoparticles evaluated by soft X-ray photoelectron spectroscopy; Cancer therapy implications

Mekaru, Harutaka*; Yoshigoe, Akitaka; Nakamura, Michihiro*; Doura, Tomohiro*; Tamanoi, Fuyuhiko*

ACS Applied Nano Materials (Internet), 2(1), p.479 - 488, 2019/01

Organosilica nanoparticles are attractive for use as drug delivery systems for cancer therapy. Ideally, the nanoparticles need to degrade in the body after drug delivery to minimize their risk. However, the biodegradation of organosilica nanoparticles has not been thoroughly investigated. In this study, we used X-ray photoelectron spectroscopy and field-emission scanning electron microscopy to investigate the degradation of organosilica nanoparticles by glutathione, a peptide found in cells. Our results indirectly indicate that glutathione is able to reduce the disulfide bonds present in the network of one type of the nanoparticles, promoting dissociation of these nanoparticles. The dissociated nanoparticles form large maple leaf-shaped structures under certain conditions. We consider the formation mechanism of these symmetrical structures.

Journal Articles

Contribution to upgrade of vitrification technology by synchrotron radiation analysis; From Chemical state analysis of waste glass to development of structural analysis to prove soundness

Okamoto, Yoshihiro; Nagai, Takayuki; Shiwaku, Hideaki

Yoyuen Oyobi Koon Kogaku, 62(1), p.11 - 17, 2019/01

The vitrified radioactive waste is a multicomponent material containing many kinds of elements. Synchrotron radiation XAFS with element selectivity is suitable for analysis of elements in the waste. From the XAFS analysis, the chemical state and the local structure of each element were clarified. Imaging XAFS technique was used as an analysis based on element distribution in the glass. The imaging XAFS is effective for analysis of elements that are less soluble in the glass like molybdenum and platinum group elements. It was clarified from the simultaneous imaging XAFS analyses of multiple elements that the chemical form of rhodium is strongly dominated by the distribution correlation with ruthenium. We proposed multi - scale structural analyses with wide angle scattering, PDF analysis, small angle scattering in order to evaluate the soundness of the vitrified waste.

Journal Articles

Application of combination between time-resolved synchrotron radiation photoelectron spectroscopy and supersonic oxygen molecular beams to surface reaction dynamics study

Yoshigoe, Akitaka

X-sen Kodenshi Bunkoho, p.271 - 282, 2018/12

Based on the series of author's studies, the author explains the time-resolved synchrotron radiation X-ray photoelectron spectroscopy and supersonic oxygen molecular beam study on the adsorption reaction dynamics of oxygen molecules at the Si single crystal surface in the section 5.10 of the new textbook "X-ray Photoelectron Spectroscopy" (Kodan-sha) edited by Yuji Takakuwa.

JAEA Reports

Investigation of simulated waste glass samples prepared from borosilicate glass frit including vanadium

Nagai, Takayuki; Okamoto, Yoshihiro; Shiwaku, Hideaki; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*; Hirono, Kazuya*; Homma, Masanobu*; Kobayashi, Hiromi*; Takahashi, Tomoe*; et al.

JAEA-Research 2018-007, 87 Pages, 2018/11

JAEA-Research-2018-007.pdf:61.21MB

To select the chemical composition of a glass frit which can increase the waste content, the simulated waste glass samples prepared from a borosilicate glass frit including vanadium (V) were investigated by using Laser Ablation (LA) ICP-AES analysis, Raman spectrometry, and synchrotron XAFS measurement in this study on foundation business of the Agency for Natural Resources and Energy.

Journal Articles

Evidence of a structural quantum critical point in (Ca$$_x$$Sr$$_{1-x}$$)$$_3$$Rh$$_4$$Sn$$_{13}$$ from a lattice dynamics study

Cheung, Y. W.*; Hu, Y. J.*; Imai, Masaki*; Tanioku, Yasuaki*; Kanagawa, Hibiki*; Murakawa, Joichi*; Moriyama, Kodai*; Zhang, W.*; Lai, K. T.*; Yoshimura, Kazuyoshi*; et al.

Physical Review B, 98(16), p.161103_1 - 161103_5, 2018/10

 Times Cited Count:4 Percentile:52.2(Materials Science, Multidisciplinary)

Journal Articles

Current status and future developments of hard X-ray photoelectron spectroscopy

Kobata, Masaaki; Okane, Tetsuo; Kobayashi, Keisuke*

Bunko Kenkyu, 67(4), p.161 - 162, 2018/08

We introduce hard X-ray photoelectron spectroscopy, which has been rapidly introduced and developed in synchrotron radiation facilities. In particular, in order to realize electronic state analysis by hard X-ray photoelectron spectroscopy of insulators, the developed charge neutralization method was described. As an example, we showed adsorption behavior of cesium to nuclear reactor structure assuming Fukushima Daiichi Nuclear Power Plant accident. Finally, future prospects of hard X-ray photoelectron spectroscopy will be described.

Journal Articles

Synchrotron radiation based X-ray absorption study for upgrade of nuclear waste vitrification technique

Okamoto, Yoshihiro; Nagai, Takayuki; Shiwaku, Hideaki

Hoshako, 31(4), p.274 - 280, 2018/07

As a method for disposal of nuclear waste, the use of vitrification technique is very promising. In this technique, many kinds of elements should be involved stably in the glass and chemical state of these elements in the glass must be confirmed in order to guarantee stability of the glass. We have used synchrotron based X-ray absorption fine structure (XAFS) technique, in which the element selectivity is utilized, to obtain the chemical state of each element in many kinds of simulated glass samples. In addition, imaging XAFS technique has been used to clarify correlation between constituent elements. We are going to contribute to research and development of the vitrification technique by using synchrotron radiation based XAFS analyses. In this article, we introduce results of the high energy XAFS of high temperature slag samples, the imaging study of high temperature borosilicate glass samples and the imaging XAFS analysis of platinum group metals in the borosilicate glass samples.

Journal Articles

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

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

Japanese Journal of Applied Physics, 57(6S3), p.06KA07_1 - 06KA07_6, 2018/06

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, in contrast to no oxide formation on GaN surface. 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. On the other hand, for the oxidation treatments above 850$$^{circ}$$C, the formation of small oxide grains was observed over the entire area of the AlGaN surface, and the growth of oxide grains significantly degraded the surface morphology. Therefore, the AlGaN/GaN MOS capacitors were fabricated on the AlGaN surface oxidized at moderate temperatures up to 800$$^{circ}$$C. While we have confirmed that relatively good interface properties are obtained for direct AlON deposition without oxidation treatment, it was found that the oxidation treatment at 400$$^{circ}$$C leads to further improvement of interface properties and reduction of C-V hysteresis.

Journal Articles

SiO$$_{2}$$/AlON stacked gate dielectrics for AlGaN/GaN MOS heterojunction field-effect transistors

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

Japanese Journal of Applied Physics, 57(6S3), p.06KA03_1 - 06KA03_6, 2018/06

 Times Cited Count:8 Percentile:29.21(Physics, Applied)

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.

Journal Articles

Implementation of atomic layer deposition-based AlON gate dielectrics in AlGaN/GaN MOS structure and its physical and electrical properties

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

Japanese Journal of Applied Physics, 57(6S3), p.06KA02_1 - 06KA02_7, 2018/06

 Times Cited Count:8 Percentile:29.21(Physics, Applied)

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.

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