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Journal Articles

Ion desorption from bulk cesium chloride at moderate temperature ($$<$$500$$^{circ}$$C) under electric field

Baba, Yuji; Shimoyama, Iwao

e-Journal of Surface Science and Nanotechnology (Internet), 16, p.53 - 59, 2018/03

Surface ionization for cesium chloride and Cs-adsorbed soil has been investigated. For cesium chloride, neutral cesium was desorbed around 645$$^{circ}$$C which is close to the melting point of cesium. While Cs$$^{+}$$ ion was desorbed from 400$$^{circ}$$C. The ratio of desorbed ions and neutrals (Cs$$^{+}$$/Cs$$^{0}$$) has a maximum around 410 $$^{circ}$$C. Temperature dependence of Cs$$^{+}$$/Cs$$^{0}$$ was analyzed using Saha-Langmuir equation, As a result, it was found that the temperature maximum is due to the changes of the surface work function induced by the phase transition of CsCl.

Journal Articles

Micro-orientation control of silicon polymer thin films on graphite surfaces modified by heteroatom doping

Shimoyama, Iwao; Baba, Yuji; Hirao, Norie*

Advances in Engineering (Internet), 1 Pages, 2018/02

The performance of organic devices largely depends on molecular orientation in organic films. Whereas micro-orientation control of organic molecules is an indispensable technology for integration of organic devices, the method has not been established. We attempted to control micro-orientation of polydimethylsilane (PDMS) thin films by deposition of PDMS on graphite substrates modified by hetero atom doping using ion beam. Polarization dependence measurements of X-ray absorption spectroscopy and molecular orbital calculations clarified that PDMS films have lying, standing, and random orientations on the non irradiated, N$$_{2}$$$$^{+}$$-irradiated, and Ar$$^{+}$$-irradiated graphite surfaces, respectively. Furthermore, photoemission microscopy observation clarified that a PDMS film showed micro-patterns on a graphite surface with a microstructure on the order of $$mu$$m by separating N$$_{2}$$$$^{+}$$-irradiated and non irradiated areas. These results demonstrate our method is promising for micro-orientation of organic molecules.

Journal Articles

Nanoscale spatial analysis of clay minerals containing cesium by synchrotron radiation photoemission electron microscopy

Yoshigoe, Akitaka; Shiwaku, Hideaki; Kobayashi, Toru; Shimoyama, Iwao; Matsumura, Daiju; Tsuji, Takuya; Nishihata, Yasuo; Kogure, Toshihiro*; Okochi, Takuo*; Yasui, Akira*; et al.

Applied Physics Letters, 112(2), p.021603_1 - 021603_5, 2018/01

 Percentile:100(Physics, Applied)

A synchrotron radiation photoemission electron microscope (SR-PEEM) was applied to demonstrate pinpoint analysis of micrometer-sized weathered biotite clay particles with artificially adsorbed cesium (Cs) atoms. Despite the insulating properties of the clay, we observed the spatial distributions of constituent elements (Si, Al, Cs, Mg, Fe) without charging issues. We found that Cs atoms were likely to be adsorbed evenly over the entire particle. Spatially-resolved X-ray absorption spectra (XAS) of the Cs M$$_{4,5}$$-edge region showed Cs to be present in a monocation state (Cs$$^{+}$$). Further pinpoint XAS measurements were also performed at the Fe L$$_{2,3}$$-edge to determine the chemical valence of the Fe atoms. Our results demonstrate the utility of SR-PEEM as a tool for spatially-resolved chemical analyses of various environmental substances, which is not limited by the poor conductivity of samples.

Journal Articles

Microstructure analysis using X-ray absorption on heat-affected zone of reactor pressure vessel steel

Iwata, Keiko; Takamizawa, Hisashi; Ha, Yoosung; Okamoto, Yoshihiro; Shimoyama, Iwao; Honda, Mitsunori; Hanawa, Satoshi; Nishiyama, Yutaka

Photon Factory Activity Report 2017, 2 Pages, 2018/00

no abstracts in English

Journal Articles

Proposed cesium-free mineralization method for soil decontamination; Demonstration of cesium removal from weathered biotite

Honda, Mitsunori; Shimoyama, Iwao; Kogure, Toshihiro*; Baba, Yuji; Suzuki, Shinichi; Yaita, Tsuyoshi

ACS Omega (Internet), 2(12), p.8678 - 8681, 2017/12

Journal Articles

Challenges for enhancing Fukushima environmental resilience, 4; Development of physical and heat treatment methods on aiming at decontamination, volume reduction and reuse of contaminated soil

Yaita, Tsuyoshi; Honda, Mitsunori; Shimoyama, Iwao; Ito, Kenichi*; Mampuku, Yuzo*; Tsuji, Takuya; Matsumura, Daiju

Nippon Genshiryoku Gakkai-Shi, 59(8), p.483 - 487, 2017/08

no abstracts in English

Journal Articles

Micro-orientation control of silicon polymer thin films on graphite surfaces modified by heteroatom doping

Shimoyama, Iwao; Baba, Yuji; Hirao, Norie*

Applied Surface Science, 405, p.255 - 266, 2017/05

 Times Cited Count:1 Percentile:81.49(Chemistry, Physical)

NEXAFS spectroscopy is applied to study orientation structures of polydimethylsilane (PDMS) films deposited on heteroatom-doped graphite substrates prepared by ion beam doping. The Si ${it K}$-edge NEXAFS spectra of PDMS show opposite trends of polarization dependence for non irradiated and N$$_{2}$$$$^{+}$$-irradiated substrates, and show no polarization dependence for an Ar$$^{+}$$-irradiated substrate. Based on a theoretical interpretation of the NEXAFS spectra via first-principles calculations, we clarify that PDMS films have lying, standing, and random orientations on the non irradiated, N$$_{2}$$$$^{+}$$-irradiated, and Ar$$^{+}$$-irradiated substrates, respectively. Furthermore, photoemission electron microscopy indicates that the orientation of a PDMS film can be controlled with microstructures on the order of $$mu$$m by separating irradiated and non irradiated areas on the graphite surface. These results suggest that surface modification of graphite using ion beam doping is useful for micro-orientation control of organic thin films.

Journal Articles

Development of cesium-free mineralization for decontamination and reuse of radioactive contaminated soil in Fukushima

Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*; Baba, Yuji; Hirao, Norie*; Okamoto, Yoshihiro; Yaita, Tsuyoshi; Suzuki, Shinichi

Photon Factory News, 35(1), p.17 - 22, 2017/05

We introduce Cs-free mineralization (CFM) for Cs removal and reuse of radioactive-contaminated soil in Fukushima and report recent work conducted in the BL27A beamline in Photon Factory. In this work, we investigated compositional and structural changes of Cs-sorbed weathered biotite (WB) before and after heating treatment with addition of NaCl-CaCl$$_{2}$$ salts under low-pressure condition, to study Cs desorption mechanism from clay minerals. X-ray fluorescence spectroscopy clarified that almost all Cs and K were removed with the salts at 700 $$^{circ}$$C. On the other hand, Ca increased with heating temperature. X-ray diffraction and transmission electron microscopy analysis clarified that phase transitions from WB to some Ca-rich silicate minerals, e.g., augite, were caused by the heating treatment with the salt. Based on these results, CFM is proposed for Cs removal utilizing the mechanism in which large monovalent cations are discharged with accompanying the phase transition. We also discuss the role of Cl in this reaction showing chemical bonding change of Cl observed using X-ray absorption spectroscopy in the early stage of the chemical reaction.

Journal Articles

Mechanism of Cs removal from Fukushima weathered biotite by heat treatment with a NaCl-CaCl$$_{2}$$ mixed salt

Honda, Mitsunori; Okamoto, Yoshihiro; Shimoyama, Iwao; Shiwaku, Hideaki; Suzuki, Shinichi; Yaita, Tsuyoshi

ACS Omega (Internet), 2(2), p.721 - 727, 2017/02

 Times Cited Count:5 Percentile:44.21(Chemistry, Multidisciplinary)

Journal Articles

Chemical states of trace-level strontium adsorbed on layered oxide by XPS and XANES under total reflection condition

Baba, Yuji; Shimoyama, Iwao

Photon Factory Activity Report 2016, 2 Pages, 2017/00

In order to elucidate the adsorption states of radioactive Sr-90 in soil, chemical bonding states of non-radioactive strontium adsorbed on layered oxide (mica) have been investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy. Since the number of atoms in radioactive Sr-90 is extremely small, the XPS and XANES were measured under total reflection condition of the incident X-rays. The detection limit in total reflection XPS was about 150 pg/cm$$^{2}$$, which corresponds to 300 Bq of Sr-90. The Sr 2p$$_{3/2}$$ core-level energy in XPS shifted to lower energy with the decrease in the thickness of Sr layer. Also, the Sr 2p$$_{3/2}$$ $$rightarrow$$ Sr 4d$$^{*}$$ resonance energy in XANES shifts to lower energy with the decrease in the thickness. On the basis of a simple point charge model, it was elucidated that the chemical bond between Sr and mica surface becomes ionic with the decrease in the adsorbed amount of strontium.

Journal Articles

Formation of carbon alloys by low-energy ion doping and its application for adsorptive desulfurization

Shimoyama, Iwao

Hoshasen To Sangyo, (141), p.7 - 11, 2016/12

Desulfurization is an indispensable process on hydrogen formation from fossil fuel. Adsorptive desulfurization, alternative to conventional hydrogenation desulfurization, requires development of stable activated carbon adsorbents with high performance. I study dopant dependence on thiophene adsorption for carbon alloys prepared by heteroatom doping using low-energy ion beam. I doped nitrogen and phosphorus as dopants of group 15 elements in graphite surfaces, and clarified that phosphorus is superior in thiophene adsorption to nitrogen, and that the effect of phosphorus is higher with room temperature doping than with high temperature doping by about 10 times. X-ray absorption spectroscopy indicated that local structures around phosphorus sites were different between them. I attribute the high adsorption property to formation of curved phosphorus sites prepared by room temperature doping. Above results suggest that the property of carbon alloy can be controlled by low-energy ion beam.

Journal Articles

Chemical state analysis of trace-level alkali metals sorbed in micaceous oxide by total reflection X-ray photoelectron spectroscopy

Baba, Yuji; Shimoyama, Iwao; Hirao, Norie*

Applied Surface Science, 384, p.511 - 516, 2016/10

AA2016-0127.pdf:0.71MB

 Times Cited Count:1 Percentile:88.02(Chemistry, Physical)

Chemical states of cesium as well as the other alkali metals (sodium and rubidium) sorbed in micaceous oxides have been investigated by total reflection X-ray photoelectron spectroscopy (TR-XPS). For cesium, it was shown that ultra-trace amount of cesium down to about 100 pg/cm$$^{-2}$$ can be detected by TR-XPS. This amount corresponds to about 200 Bq of $$^{137}$$Cs (t$$_{1/2}$$ = 30.2y). It was demonstrated that ultra-trace amount of cesium corresponding to radioactive cesium level can be measured by TR-XPS. As to the chemical states, it was found that core-level binding energy in TR-XPS for trace-level cesium shifted to lower-energy side compared with that for thicker layer. A reverse tendency is observed in sodium. Based on charge transfer within a simple point-charge model, it is concluded that chemical bond between alkali metal and micaceous oxide for ultra-thin layer is more polarized that for thick layer.

Journal Articles

Desorption behavior of Cs from clay minerals by thermal heating in a vacuum; Analyses by thermal desorption spectroscopy and synchrotron radiation X-ray photoelectron spectroscopy

Hirao, Norie; Shimoyama, Iwao; Baba, Yuji; Izumi, Toshinori; Okamoto, Yoshihiro; Yaita, Tsuyoshi; Suzuki, Shinichi

Bunseki Kagaku, 65(5), p.259 - 266, 2016/05

 Times Cited Count:3 Percentile:72.14(Chemistry, Analytical)

After the Fukushima nuclear plant accident, radiocesium was strongly fixed to clay minerals in the soil. Some dry methods with heating are being developed to remove radiocesium from the soil. In this work, we propose a new dry method that combines heat treatment in vacuum and molten salts to reduce the processing temperature in dry methods. Vermiculite saturated with non-radioactive Cs was heated in vacuum, and Cs contents in the vermiculite were compared before and after heating using X-ray photoelectron spectroscopy. Approximately 40% of cesium were removed by heating at 800$$^{circ}$$C for three minutes when only vermiculite was heated. Approximately 70% of cesium were removed by heating at 450$$^{circ}$$C for three minutes when vermiculite was heated with NaCl/CaCl$$_{2}$$ mixed salts. Based on these results, this method is expected to reduce temperature and increase efficiency on dry methods for cesium removal from clay minerals.

Journal Articles

Thiophene adsorption on phosphorus- and nitrogen-doped graphites; Control of desulfurization properties of carbon materials by heteroatom doping

Shimoyama, Iwao; Baba, Yuji

Carbon, 98, p.115 - 125, 2016/03

 Times Cited Count:20 Percentile:16.62(Chemistry, Physical)

The amounts of adsorbed thiophene were compared among phosphorus- and nitrogen-doped graphite and graphite damaged by Ar$$^{+}$$ irradiation to clarify the influence of heteroatom doping on the adsorptive desulfurization properties of $$pi$$-conjugated carbon materials. On the basis of thiophene coverages estimated from X-ray photoelectron spectroscopy, Phosphorus-doped graphite had an adsorption ability that was 10-20 times larger than that of Nitrogen-doped graphite, indicating that the adsorptive desulfurization property of carbon largely depends on dopant atoms. Polarization dependent analysis using near-edge X-ray absorption fine structure spectroscopy was used to distinguish the configurations at dopant sites, indicating that the curved structures of phosphorus sites exhibited approximately 10 times greater adsorption abilities when compared with the planar structures. Theoretical simulation using molecular orbital calculations indicated different dopant effects between phosphorus and nitrogen along with different thiophene adsorption behaviors between planar and curved structures. Finally, experimental thiophene desorption results obtained at different temperatures revealed an advantage of phosphorus doping for reactivation.

Journal Articles

Electronic structures at phosphorus sites doped in graphite; Spectral analysis of P K-edge NEXAFS with DVX$$alpha$$ calculations

Shimoyama, Iwao; Baba, Yuji

DV-X$$alpha$$ Kenkyu Kyokai Kaiho, 28(1&2), p.62 - 69, 2016/03

We studied electronic structures at phosphorus sites doped in graphite to clarify the dopant effect on catalytic activity of P-doped graphite using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A sample prepared by high-temperature doping at 700 $$^{circ}$$C showed graphite-like clear polarization dependence of P K-edge NEXAFS spectra indicating planar structure at phosphorus sites. We calculated electronic structures at phosphorus sites in carbon model clusters using the DV-X$$alpha$$ method and compare them with NEXAFS. The electronic structure at planar phosphorus site with three carbon coordination reproduced the NEXAFS spectra. On the other hand, samples prepared by room-temperature doping and post annealing at 800 $$^{circ}$$C showed deterioration of polarization dependence of NEXAFS. We clarified that an electronic structure of a curved carbon model cluster with a pentagon reproduced change of polarization dependence and spectral shape of NEXAFS. This means local structures at phosphorus sites can be controlled by substrate temperatures during ion dopings.

Journal Articles

X-ray absorption fine structure at the cesium $$L$$3 absorption edge for cesium sorbed in clay minerals

Honda, Mitsunori; Shimoyama, Iwao; Okamoto, Yoshihiro; Baba, Yuji; Suzuki, Shinichi; Yaita, Tsuyoshi

Journal of Physical Chemistry C, 120(10), p.5534 - 5538, 2016/03

 Times Cited Count:11 Percentile:32.04(Chemistry, Physical)

Journal Articles

Development of fluorescence XAFS system in soft X-ray region toward operando conditions using polycapillary X-ray lens

Honda, Mitsunori; Shimoyama, Iwao; Baba, Yuji; Suzuki, Shinichi; Okamoto, Yoshihiro; Yaita, Tsuyoshi

e-Journal of Surface Science and Nanotechnology (Internet), 14, p.35 - 38, 2016/02

Journal Articles

Interaction between ultra-trace amount of cesium and oxides studied by total-reflection X-ray photoelectron spectroscopy

Baba, Yuji; Shimoyama, Iwao; Hirao, Norie; Izumi, Toshinori

e-Journal of Surface Science and Nanotechnology (Internet), 13, p.417 - 421, 2015/09

 Times Cited Count:1

The interaction between alkali metals and oxides has attracted much attention as heterogeneous catalysis, chemical reaction promoters, and high intensity electron emitter. Also the interaction of cesium and oxides has become important subject, because radioactive cesium trapped in minerals such as clay and soil may cause health risks. In the present study, we analyzed chemical states of ultra-trace amount of cesium on oxide surfaces by total reflection X-ray photoelectron spectroscopy (TR-XPS) exited by synchrotron radiation. For the adsorbed cesium thicker than 0.01 layer, cesium is weakly bound with oxide through Van-der-Waals force. On the other hand, for ultra-thin layer about 0.002 layer, the chemical bond changes to covalent bond. It is suggested that this change in the chemical bonding state is one of the reasons why radioactive cesium is hard to be released from minerals.

Journal Articles

Contracted interlayer distance in graphene/sapphire heterostructure

Entani, Shiro; Antipina, L. Y.*; Avramov, P.*; Otomo, Manabu*; Matsumoto, Yoshihiro*; Hirao, Norie; Shimoyama, Iwao; Naramoto, Hiroshi*; Baba, Yuji; Sorokin, P. B.*; et al.

Nano Research, 8(5), p.1535 - 1545, 2015/05

 Times Cited Count:17 Percentile:20.87(Chemistry, Physical)

Journal Articles

Highly durable carbon-supported Pt catalysts prepared by hydrosilane-assisted nanoparticle deposition and surface functionalization

Saito, Akinori*; Tsuji, Hiromi*; Shimoyama, Iwao; Shimizu, Kenichi*; Nishina, Yuta*

Chemical Communications, 51(27), p.5883 - 5886, 2015/04

 Times Cited Count:10 Percentile:46.57(Chemistry, Multidisciplinary)

no abstracts in English

312 (Records 1-20 displayed on this page)