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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:44.74(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

Investigation of segregation during oxidation of Ni-Cu alloy by ${{it in situ}}$ photoelectron spectroscopy

Doi, Takashi*; Nishiyama, Yoshitaka*; Yoshigoe, Akitaka; Teraoka, Yuden

Surface and Interface Analysis, 48(7), p.685 - 688, 2016/07

 Times Cited Count:2 Percentile:92.25(Chemistry, Physical)

Ni-based alloys has been widely used for plant application because of their high strength and excellent oxidation resistance. In particular, the addition of Cu in Ni-based alloys significantly improves the metal dusting resistance. It is indicated that Cu is segregated on the alloy surface in the metal dusting environment; however, the details have not been clarified yet. The behavior of Ni-2Cu alloy under a high temperature oxidation environment was investigated using ${{it in situ}}$ X-ray photoelectron spectroscopy. It was confirmed that Cu have been segregated at the surface of Ni-2Cu alloy during oxidation. These results propose that the Cu segregation improves the metal dusting resistance.

Journal Articles

Surface temperature dependence of oxidation of Cu$$_{3}$$Au(111) by an energetic oxygen molecule

Tsuda, Yasutaka*; Yoshigoe, Akitaka; Teraoka, Yuden; Okada, Michio*

Materials Research Express (Internet), 3(3), p.035014_1 - 035014_8, 2016/03

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We report a study on the surface-temperature ($$T_{s}$$) dependence of oxidation process at Cu$$_{3}$$Au(111) by using a hyperthermal oxygen molecular beam and synchrotron-radiation X-ray photoemission spectroscopy. The O-1s spectra and the corresponding O-uptake curves demonstrate that Cu$$_{2}$$O domains grow effectively at high $$T_{s}$$ of 400 and 500 K. The simple analysis of the O distribution suggests that the temperature-induced atomic diffusion causes the Cu$$_{2}$$O domains growing thicker at 500 K. The oxidation of Cu$$_{3}$$Au(111) is less efficient at $$T_{s}$$ = 300-500 K than that of Cu(111), demonstrating that the protective nature of Cu$$_{3}$$Au against oxidation, in comparison to Cu, remains even at high $$T_{s}$$.

Journal Articles

Spontaneous activation behavior of Ni$$_{3}$$Sn, an intermetallic catalyst, for hydrogen production via methanol decomposition

Fan, M.*; Xu, Y.*; Sakurai, Junya*; Demura, Masahiko*; Hirano, Toshiyuki*; Teraoka, Yuden; Yoshigoe, Akitaka

International Journal of Hydrogen Energy, 40(37), p.12663 - 12673, 2015/10

 Times Cited Count:6 Percentile:77.02(Chemistry, Physical)

The catalytic properties of single-phase Ni$$_{3}$$Sn powder in the production of hydrogen via the decomposition of methanol were investigated in isothermal tests at 713, 793, and 873 K. The catalytic activity of Ni$$_{3}$$Sn significantly increased with time at 793 and 873 K, but not at 713 K, suggesting that Ni$$_{3}$$Sn is spontaneously activated at temperatures above 793 K. At these temperatures, Ni$$_{3}$$Sn showed high selectivity for H$$_{2}$$ and CO production and low selectivity for CH$$_{4}$$, CO$$_{2}$$, and H$$_{2}$$O production, indicating that methanol decomposition was the main reaction, and that side reactions such as methanation and water-gas shift reaction were suppressed. Surface analysis revealed that fine Ni$$_{3}$$Sn particles were formed during the reaction, accompanied by a small amount of deposited carbon. The formation of these particles was suggested to be the cause for the spontaneous activation of Ni$$_{3}$$Sn.

Journal Articles

In situ SR-XPS observation of Ni-assisted low-temperature formation of epitaxial graphene on 3C-SiC/Si

Hasegawa, Mika*; Sugawara, Kenta*; Suto, Ryota*; Sambonsuge, Shota*; Teraoka, Yuden; Yoshigoe, Akitaka; Filimonov, S.*; Fukidome, Hirokazu*; Suemitsu, Maki*

Nanoscale Research Letters, 10, p.421_1 - 421_6, 2015/10

 Times Cited Count:9 Percentile:48.21(Nanoscience & Nanotechnology)

Graphene has attracted much attention as a promising material in electronics and photonics. The graphitization temperature of 1473 K or higher of graphene-on-silicon(GOS), however, is still too high to be fully compatible with the Si technology. Here, the first application of Ni-assisted formation of graphene to the GOS method was reported. We demonstrate that the graphene formation temperature can be reduced by more than 200 K by this method. Moreover, solid-phase reactions during heating/annealing/cooling procedures have been investigated in detail by using ${{it in-situ}}$ synchrotron-radiation X-ray photoelectron spectroscopy. As a result, we clarify the role of Ni/SiC reactions, in which not only Ni silicidation and but also Ni carbonization is suggested as a key process in the formation of graphene.

Journal Articles

Corrigendum to "Real time observation of oxygen chemisorption states on Si(001)-2$$times$$1 during supersonic oxygen molecular beam irradiation"

Teraoka, Yuden; Yoshigoe, Akitaka

Applied Surface Science, 346, P. 580, 2015/08

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

Journal Articles

Corrigendum to "Si 2p and O 1s photoemission from oxidized Si(001) surfaces depending on translational kinetic energy of incident O$$_{2}$$ molecules"

Teraoka, Yuden; Yoshigoe, Akitaka

Applied Surface Science, 343, P. 212, 2015/07

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

Journal Articles

Corrigendum to "Coexistence of passive and active oxidation for O$$_{2}$$/Si(001) system observed by SiO mass spectrometry and synchrotron radiation photoemission spectroscopy"

Teraoka, Yuden; Moritani, Kosuke*; Yoshigoe, Akitaka

Applied Surface Science, 343, P. 213, 2015/07

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

Journal Articles

Comprehensive study and design of scaled metal/high-$$k$$/Ge gate stacks with ultrathin aluminum oxide interlayers

Asahara, Ryohei*; Hideshima, Iori*; Oka, Hiroshi*; Minoura, Yuya*; Ogawa, Shingo*; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Letters, 106(23), p.233503_1 - 233503_4, 2015/06

 Times Cited Count:14 Percentile:35.67(Physics, Applied)

Advanced metal/high-$$k$$/Ge gate stacks with a sub-nm equivalent oxide thickness and improved interface properties were demonstrated by controlling interface reactions using ultrathin aluminum oxide (AlOx) interlayers. Comprehensive study by means of physical and electrical characterizations revealed distinct impacts of AlOx interlayers, plasma oxidation.

Journal Articles

Corrigendum to "Commissioning of surface chemistry end-station in BL23SU of SPring-8"

Teraoka, Yuden; Yoshigoe, Akitaka

Applied Surface Science, 339, P. 158, 2015/06

Journal Articles

Erratum; Precise control of Si(001) initial oxidation by translational kinetic energy of O$$_{2}$$ molecules

Teraoka, Yuden; Yoshigoe, Akitaka

Japanese Journal of Applied Physics, 54(3), P. 039204_1, 2015/03

 Times Cited Count:3 Percentile:18.62(Physics, Applied)

Journal Articles

Erratum; Oxidation of aqueous HF-treated Si(001) surface induced by translational kinetic energy of O$$_{2}$$ at room temperature

Yoshigoe, Akitaka; Teraoka, Yuden

Japanese Journal of Applied Physics, 54(3), P. 039201_1, 2015/03

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

Journal Articles

Erratum; SiO mass spectrometry and Si-2p photoemission spectroscopy for the study of oxidation reaction dynamics of Si(001) surface by supersonic O$$_{2}$$ molecular beams under 1000 K

Teraoka, Yuden; Yoshigoe, Akitaka; Moritani, Kosuke*

Japanese Journal of Applied Physics, 54(3), P. 039202_1, 2015/03

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

Journal Articles

Erratum; Initial oxidation of Si(001) induced by translational kinetic energy of O$$_{2}$$ supersonic molecular beams

Yoshigoe, Akitaka; Sano, Mutsumi*; Teraoka, Yuden

Japanese Journal of Applied Physics, 54(3), P. 039203_1, 2015/03

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

Journal Articles

In situ synchrotron radiation photoemission study of ultrathin surface oxides of Ge(111)-c(2$$times$$8) induced by supersonic O$$_{2}$$ beams

Okada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Yamada, Yoichi*; Sasaki, Masahiro*

Applied Physics Express, 8(2), p.025701_1 - 025701_4, 2015/02

 Times Cited Count:6 Percentile:67.07(Physics, Applied)

We studied the surface oxidation on a Ge(111)-c(2$$times$$8) surface at room temperature using supersonic oxygen beams as a function of the translational energy of the incident oxygen molecules ranging from 26 meV to 2.3 eV. In situ synchrotron photoemission spectroscopy performed during the oxidation revealed that the surface oxidation terminated with the formation of a sub-monolayer oxide of at most 0.52 ML, for all the beam energies examined. In addition, the oxidation state of the surface oxides was found to depend on the translational energy. These results demonstrate the precise chemical control of the ultrathin surface oxides of Ge(111)-c(2$$times$$8).

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:100(Chemistry, Physical)

Journal Articles

${{it In situ}}$ synchrotron radiation photoelectron spectroscopy study of the oxidation of the Ge(100)-2$$times$$1 surface by supersonic molecular oxygen beams

Yoshigoe, Akitaka; Teraoka, Yuden; Okada, Ryuta; Yamada, Yoichi*; Sasaki, Masahiro*

Journal of Chemical Physics, 141(17), p.174708_1 - 174708_7, 2014/11

 Times Cited Count:6 Percentile:74.16(Chemistry, Physical)

${{it In situ}}$ synchrotron radiation photoelectron spectroscopy was performed during the oxidation of the Ge(100)-2$$times$$1 surface induced by a molecular oxygen beam with various incident energies up to 2.2 eV from the initial to saturation coverage of surface oxides. The saturation coverage of oxygen on the clean Ge(100) surface was much lower than one monolayer and the oxidation state of Ge was +2 at most. This indicates that the Ge(100) surface is in strong contrast to Si surfaces. The direct adsorption process can be activated by increasing the translational energy, resulting in an increased population of Ge$$^{2+}$$ and a higher final oxygen coverage. Our findings will contribute to the fundamental understanding of oxygen adsorption processes at 300 K from the initial stages to saturated oxidation.

Journal Articles

Effect of water vapor and hydrogen treatments on the surface structure of Ni$$_{3}$$Al foil

Xu, Y.*; Ma, Y.*; Sakurai, Junya*; Teraoka, Yuden; Yoshigoe, Akitaka; Demura, Masahiko*; Hirano, Toshiyuki*

Applied Surface Science, 315, p.475 - 480, 2014/10

 Times Cited Count:7 Percentile:58.98(Chemistry, Physical)

Journal Articles

The Effects of alloying and segregation for the reactivity and diffusion of oxygen on Cu$$_{3}$$Au(111)

Oka, Kohei*; Tsuda, Yasutaka*; Makino, Takamasa*; Okada, Michio*; Hashinokuchi, Michihiro*; Yoshigoe, Akitaka; Teraoka, Yuden; Kasai, Hideaki*

Physical Chemistry Chemical Physics, 16(36), p.19702 - 19711, 2014/08

 Times Cited Count:5 Percentile:74.16(Chemistry, Physical)

707 (Records 1-20 displayed on this page)