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Journal Articles

Gas barrier properties of chemical vapor-deposited graphene to oxygen imparted with sub-electronvolt kinetic energy

Ogawa, Shuichi*; Yamaguchi, Hisato*; Holby, E. F.*; Yamada, Takatoshi*; Yoshigoe, Akitaka; Takakuwa, Yuji*

Journal of Physical Chemistry Letters (Internet), 11(21), p.9159 - 9164, 2020/11

 Times Cited Count:2 Percentile:42.52(Chemistry, Physical)

Atomically thin layers of graphene have been proposed to protect surfaces through the direct blocking of corrosion reactants such as oxygen with low added weight. The long term efficacy of such an approach, however, is unclear due to the long-term desired protection of decades and the presence of defects in as-synthesized materials. Here, we demonstrate catalytic permeation of oxygen molecules through previously-described impermeable graphene by imparting sub-eV kinetic energy to molecules. These molecules represent a small fraction of a thermal distribution thus this exposure serves as an accelerated stress test for understanding decades-long exposures. The permeation rate of the energized molecules increased 2 orders of magnitude compared to their non-energized counterpart. Graphene maintained its relative impermeability to non-energized oxygen molecules even after the permeation of energized molecules indicating that the process is non-destructive and a fundamental property of the exposed material.

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.

Journal Articles

Review of the microdosimetric studies for high-energy charged particle beams using a tissue-equivalent proportional counter

Tsuda, Shuichi; Sato, Tatsuhiko; Ogawa, Tatsuhiko; Sasaki, Shinichi*

JPS Conference Proceedings (Internet), 11, p.060004_1 - 060004_6, 2016/11

Track structure and energy deposition around charged particle beams in microscopic site of a living cell is important information for understanding of biological effects of energetic heavy ion beams. In this work, measurements of lineal energy ($$y$$) distributions for various kinds of ion beams have been performed for the verification of the microdosimetric function that incorporated in the PHITS code. In the international symposium focused on radiation detectors, the wall-less tissue equivalent proportional counter that developed in this study to measure $$y$$ distributions will be introduced, together with a series of data.

Journal Articles

Measurement of lineal energy distributions for ion beams using a wall-less tissue equivalent proportional counter

Tsuda, Shuichi; Sato, Tatsuhiko; Ogawa, Tatsuhiko

JAEA-Review 2015-022, JAEA Takasaki Annual Report 2014, P. 141, 2016/09

Deposit energy distribution in microscopic site in a living cell is important information for understanding of biological effects of energetic heavy ion beams. In this work, a wall-less tissue equivalent proportional counter has been used for the measurement of lineal energy ($$y$$) distributions and dose-mean of $$y$$ ($$overline{y}$$$$_{D}$$) at radial direction of 30 MeV H at TIARA, for the verification of the microdosimetric function of PHITS. The measured $$yf$$ ($$y$$) summed in radial direction agree with the corresponding data from the microdosimetric calculations using the PHITS code fairly well. The $$overline{y}$$$$_{D}$$ of 30 MeV proton beam presents the smallest value at $$r$$ = 0.0 and gradually increase with radial distance, while the values of heavy ions such as iron showed rapid decrease with radial distance. This experimental result demonstrates that the stochastic deposit energy distribution of high-energy protons in microscopic region is rather constant both in the core and in the penumbra region of the track structure.

Journal Articles

Detection of molecular oxygen adsorbate during room-temperature oxidation of Si(100)2$$times$$1 surface; In situ synchrotron radiation photoemission study

Yoshigoe, Akitaka; Yamada, Yoichi*; Taga, Ryo*; Ogawa, Shuichi*; Takakuwa, Yuji*

Japanese Journal of Applied Physics, 55(10), p.100307_1 - 100307_4, 2016/09

 Times Cited Count:1 Percentile:6.36(Physics, Applied)

Synchrotron radiation photoelectron spectroscopy during the oxidation of the Si(100)2$$times$$1 surface at room temperature revealed the existence of the molecularly adsorbed oxygen, which was considered to be absent. The O 1s spectra was found to be similar to that of the oxidation of Si(111)7$$times$$7 surfaces. Also the molecular oxygen was appeared after the initial surface oxides, indicating that this was not a precursor for dissociation oxygen adsorption onto the clean surface. We have proposed presumable structural models for atomic configurations, where the molecular oxygen was resided on the oxidized silicon with two oxygen atoms at the backbonds.

Journal Articles

Enhancement of SiO$$_{2}$$/Si(001) interfacial oxidation induced by thermal strain during rapid thermal oxidation

Ogawa, Shuichi*; Tang, J.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Takakuwa, Yuji*

Journal of Chemical Physics, 145(11), p.114701_1 - 114701_7, 2016/09

 Times Cited Count:3 Percentile:14.34(Chemistry, Physical)

Enhancement of SiO$$_{2}$$/Si(001) interfacial oxidation induced by thermal strain during rapid thermal oxidation was revealed by real time photoelectron spectroscopy using high intensity and high energy-resolution synchrotron radiation. This experimental result indicates the usefulness of the unified Si oxidation reaction model mediated by point defect generation.

Journal Articles

Valence-band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

Yamaguchi, Hisato*; Ogawa, Shuichi*; Watanabe, Daiki*; Hozumi, Hideaki*; Gao, Y.*; Eda, Goki*; Mattevi, C.*; Fujita, Takeshi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; et al.

Physica Status Solidi (A), 213(9), p.2380 - 2386, 2016/09

 Times Cited Count:8 Percentile:46.1(Materials Science, Multidisciplinary)

We report valence-band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. The degree of oxygen functionalization was controlled by annealing temperature, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in the density of states around the Fermi level upon thermal annealing at $$sim$$ 600$$^{circ}$$C. The result indicates that while there is an apparent bandgap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of bandgap closure was correlated with the electrical, chemical, and structural properties to determine a set of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of 500$$^{circ}$$C leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to an as-synthesized counterpart.

Journal Articles

Measurement of the stochastic radial dose distribution for a 30-MeV proton beam using a wall-less tissue-equivalent proportional counter

Tsuda, Shuichi; Sato, Tatsuhiko; Ogawa, Tatsuhiko

Radiation Protection Dosimetry, 168(2), p.190 - 196, 2016/02

 Times Cited Count:1 Percentile:14.27(Environmental Sciences)

Deposit energy distribution in microscopic site in a living cell is important information for understanding of biological effects of energetic heavy ion beams. In this work, a wall-less tissue equivalent proportional counter has been used for the measurement of lineal energy (y) distributions and dose-mean of y (yD) at radial direction of 30 MeV H at TIARA, for the verification of the microdosimetric function of PHITS. The measured yf(y) summed in radial direction agree with the corresponding data from the microdosimetric calculations using the PHITS code fairly well. The yD of 30 MeV proton beam presents the smallest value at r = 0.0 and gradually increase with radial distance, while the values of heavy ions such as iron showed rapid decrease with radial distance. This experimental result demonstrates that the stochastic deposit energy distribution of high-energy protons in microscopic region is rather constant both in the core and in the penumbra region of the track structure.

Journal Articles

Energy-dependent fragmentation cross sections of relativistic $$^{12}$$C

Ogawa, Tatsuhiko; Sato, Tatsuhiko; Hashimoto, Shintaro; Satoh, Daiki; Tsuda, Shuichi; Niita, Koji*

Physical Review C, 92(2), p.024614_1 - 024614_14, 2015/08

AA2015-0260.pdf:2.96MB

 Times Cited Count:25 Percentile:87.68(Physics, Nuclear)

For prediction of radiological impact of heavy ions in accelerator facilities, space missions and cancer therapy, nuclear reaction models play a fundamental role. As one of such models, JAERI Quantum molecular dynamics (JQMD) has been successfully used to describe production of residue and secondary particles in nucleus-nucleus collisions. However, it has been pinpointed that JQMD underestimates projectile-like fragments produced in peripheral collisions. Moreover, no cross section data systematically measured over a wide energy range are not available, which makes it difficult to benchmark the reaction models. In this study, we develop a method to measured fragmentation cross sections using a thick target and detecting fragments produced from incident ions fragmented in the target using telescope detectors. Thus we obtained fragmentation cross sections systematically over a wide energy range. We also revise the description of reaction mechanism and ground-state nuclear structure in JQMD to take into account for peripheral collisions accurately. So far, ground-state nuclei got excited and sometimes disintegrated owing to frame transform from the laboratory system to the center-of-mass system. Fragment production cross sections calculated by the revised JQMD (JQMD2.0) are in better agreement with the literature data.

Journal Articles

Self-accelerating oxidation on Si(111)7$$times$$7 surfaces studied by real-time photoelectron spectroscopy

Tang, J.*; Nishimoto, Kiwamu*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Watanabe, Daiki*; Teraoka, Yuden; Takakuwa, Yuji*

Surface and Interface Analysis, 46(12-13), p.1147 - 1150, 2014/12

 Times Cited Count:1 Percentile:2.1(Chemistry, Physical)

Journal Articles

Graphene growth and carbon diffusion process during vacuum heating on Cu(111)/Al$$_{2}$$O$$_{3}$$ substrates

Ogawa, Shuichi*; Yamada, Takatoshi*; Ishizuka, Shinji*; Yoshigoe, Akitaka; Hasegawa, Masataka*; Teraoka, Yuden; Takakuwa, Yuji*

Japanese Journal of Applied Physics, 52(11), p.110122_1 - 110122_8, 2013/11

 Times Cited Count:17 Percentile:63.5(Physics, Applied)

Journal Articles

Relation between oxidation rate and oxidation-induced strain at SiO$$_{2}$$/Si(001) interfaces during thermal oxidation

Ogawa, Shuichi*; Tang, J.*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Teraoka, Yuden; Takakuwa, Yuji*

Japanese Journal of Applied Physics, 52(11), p.110128_1 - 110128_7, 2013/11

 Times Cited Count:10 Percentile:46(Physics, Applied)

Journal Articles

SiO desorption kinetics of Si(111) surface oxidation studied by real-time photoelectron spectroscopy

Tang, J.*; Nishimoto, Kiwamu*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Watanabe, Daiki*; Teraoka, Yuden; Takakuwa, Yuji*

e-Journal of Surface Science and Nanotechnology (Internet), 11, p.116 - 121, 2013/11

Journal Articles

Nonlinear O$$_{2}$$ pressure dependence of the initial oxide growth kinetics on Si(111) surfaces; Photoelectron spectroscopy observation and molecular orbital calculation of oxidation states

Tang, J.*; Nishimoto, Kiwamu*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Watanabe, Daiki*; Teraoka, Yuden; Takakuwa, Yuji*

Dai-18-Kai Getosutakku KenkyuKai Yokoshu, p.191 - 194, 2013/01

Journal Articles

Vacuum annealing formation of graphene on diamond C(111) surfaces studied by real-time photoelectron spectroscopy

Ogawa, Shuichi*; Yamada, Takatoshi*; Ishizuka, Shinji*; Yoshigoe, Akitaka; Hasegawa, Masataka*; Teraoka, Yuden; Takakuwa, Yuji*

Japanese Journal of Applied Physics, 51(11), p.11PF02_1 - 11PF02_7, 2012/11

 Times Cited Count:23 Percentile:70.04(Physics, Applied)

Journal Articles

Observation of graphene-on-diamond formation studied by real-time photoelectron spectroscopy

Ogawa, Shuichi*; Yamada, Takatoshi*; Ishizuka, Shinji*; Watanabe, Daiki*; Yoshigoe, Akitaka; Hasegawa, Masataka*; Teraoka, Yuden; Takakuwa, Yuji*

Hyomen Kagaku, 33(8), p.449 - 454, 2012/08

Graphene-on-insulator structures are required for fabrication of the graphene transistor. Diamond has been attracted as the substrate for graphene growth because it has a larger band gap and break down voltage compared with SiC. The detail of graphitization on a diamond surface has not been clarified yet because the nondestructive evaluation for graphene-on-diamond (GOD) structure was hard. In this study, we have developed an evaluation method of GOD based on the photoemission spectroscopy using synchrotron radiation focusing the shift of photoelectron spectra due to band bending. We can clearly determine the graphitization temperature on the diamond C(111) surface as approximately 1120 K, which is lower than that on an SiC substrate. It is also confirmed from C 1s photoelectron spectra, there is the buffer layer at the interface between the grapheme layer and the diamond substrate.

Journal Articles

Oxidation-enhanced condensation of Ge atoms on Si$$_{1-x}$$Ge$$_{x}$$ alloy layer studied by real-time photoelectron spectroscopy

Ogawa, Shuichi*; Hozumi, Hideaki*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Kaga, Toshiteru*; Teraoka, Yuden; Takakuwa, Yuji*

Oyo Butsuri Gakkai Hakumaku, Hyomen Butsuri Bunkakai, Shirikon Tekunoroji Bunkakai Kyosai Tokubetsu Kenkyukai Kenkyu Hokoku, p.67 - 70, 2011/01

The oxidation-enhanced Ge atoms condensation kinetics on an Si$$_{1-x}$$Ge$$_{x}$$ alloy layer has been investigated by the real-time photoemission spectroscopy using the synchrotron radiation. The Si$$_{1-x}$$Ge$$_{x}$$ alloy layer was formed with a thermal evaporation method on a p-type Si(001) surface, and this alloy layer was oxidized at Langmuir-type adsorption. During oxidation at 773 KC, it is found that the Ge atoms are not oxidized, only SiO$$_{2}$$ film is formed on the Si$$_{1-x}$$Ge$$_{x}$$ alloy layer. Furthermore, the desorption of GeO molecules does not occur during the oxidation of alloy layer. On the other hand, not only Si atoms but also Ge atoms are oxidized at room temperature. This difference can be explained using the unified oxidation model mediated by the point defect generation, namely it is suggested that a lot of vacancies are generated during oxidation of the Si$$_{1-x}$$Ge$$_{x}$$ alloy layer at 773K and Ge atoms diffuse through these vacancies.

Journal Articles

Oxidation-enhanced difusion of C atoms on Si$$_{1-x}$$C$$_{x}$$ alloy layer/Si(001) surface under oxide growth and etching conditions

Hozumi, Hideaki*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Harries, J.; Teraoka, Yuden; Takakuwa, Yuji*

Oyo Butsuri Gakkai Hakumaku, Hyomen Butsuri Bunkakai, Shirikon Tekunoroji Bunkakai Kyosai Tokubetsu Kenkyukai Kenkyu Hokoku, p.181 - 184, 2010/01

The oxidation kinetics on the Si$$_{1-x}$$C$$_{x}$$ alloy layer has been investigated using the real-time XPS measurement. Experiments were performed at the BL23SU of SPring-8. The Si$$_{1-x}$$C$$_{x}$$ alloy layer was formed with exposing a p-type Si(001) surface to ethylene, and the Si$$_{1-x}$$C$$_{x}$$ alloy layer was oxidized at Langmuir-type adsorption (773 K) and 2D oxide island growth (933 K), respectively. In case of Langmuir-type adsorption, it is found that no carbon atoms are oxidized and carbon concentration at the SiO$$_{2}$$/Si interface increases. These results indicate the carbon atom condensation occurs, leading to the SiO$$_{2}$$/Si$$_{1-x}$$C$$_{x}$$/Si layers formation. On the other hand, the carbon concentration decrease by 20% in spite of the etching of 38 Si layers in the 2D oxide island growth. Based on these results, it is found that the diffusion of carbon atoms is occurred due to not only oxide growth but also Si etching.

Journal Articles

Real-time photoelectron spectroscopy study of 3C-SiC nucleation and growth on Si(001) surface by carbonization with ethylene

Hozumi, Hideaki*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Ishizuka, Shinji*; Harries, J.; Teraoka, Yuden; Takakuwa, Yuji*

JSPS 141 Committee Activity Report, p.317 - 322, 2009/12

It is reported that Si$$_{1-x}$$C$$_{x}$$ alloy layer was formed on an Si(001) surface with C$$_{2}$$H$$_{4}$$ exposure at 933 K before nucleation. However information of the chemical bonding state and concentration of adsorbed carbon has not been clear. Therefore the carbonization reaction kinetics on an Si(001) surface reacted with C$$_{2}$$H$$_{4}$$ exposure was observed by real-time XPS to investigate the 3C-SiC nucleation kinetics. The experiments were performed at the BL23SU of SPring-8. It is suggested that the C1s spectra is composed of at least three chemically-shifted components, which are assigned to carbon-poor Si$$_{1-x}$$C$$_{x}$$ alloy, carbon-rich Si$$_{1-x}$$C$$_{x}$$ alloy and 3C-SiC. The 3C-SiC nuclei began to generate at 8000s. Using C1s and Si2p$$_{3/2}$$ peaks, carbon concentration of the Si$$_{1-x}$$C$$_{x}$$ alloy layer was estimated to be about 0.17 of x. Therefore it is suggested that critical carbon concentration is 17%.

Journal Articles

Temporal and spatial variations of radiocarbon in Japan Sea Bottom Water

Kumamoto, Yuichiro*; Aramaki, Takafumi*; Watanabe, Shuichi*; Yoneda, Minoru*; Shibata, Yasuyuki*; Togawa, Orihiko; Morita, Masatoshi*; Shitashima, Kiminori*

Journal of Oceanography, 64(3), p.429 - 441, 2008/06

 Times Cited Count:10 Percentile:26.24(Oceanography)

In 1995 and 2000, radiocarbon ratio ($$Delta$$$$^{14}$$C) of total dissolved inorganic carbon was measured in the Japan Sea, a semi-closed marginal sea in the western North Pacific, where deep and bottom waters are formed in itself. Compiling them with historical radiocarbon data in the Japan Sea, temporal and spatial variations of the radiocarbon in the bottom water below 2000 m depth were elucidated. $$Delta$$$$^{14}$$C in the bottom waters in the western Japan and Yamato Basins increased by about 20 ‰ between 1977/79 and 1995 and did not changed between 1995 and 1999/2000, suggesting penetration of surface bomb-produced radiocarbon into the bottom waters due to bottom ventilation in the earlier period and stagnation of the bottom ventilation in the following period, respectively. In the eastern Japan Basin, the bottom $$Delta$$$$^{14}$$C increased by about 10 ‰ between 1977/79 and 2002, suggesting less ventilation of the bottom water in the basin. The temporal changes of the radiocarbon, tritium, and dissolved oxygen suggest sporadic occurrences of the bottom ventilation between 1979 and 1984 and its stagnation between 1984 and 2004 in the eastern Japan and Yamato Basins. The former is probably due to spreading of a newly ventilated bottom water in the western Japan Basin in the severe winter of 1976-1977 along the abyssal circulation in the Japan Sea. The latter does not conflict with temporal changes of bomb-produced $$^{137}$$Cs and chlorofluorocarbon-11 in the bottom water.

163 (Records 1-20 displayed on this page)