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Journal Articles

Work function lowering of LaB$$_{6}$$ by monolayer hexagonal boron nitride coating for improved photo- and thermionic-cathodes

Yamaguchi, Hisato*; Yusa, Ryunosuke*; Wang, G.*; Pettes, M. T.*; Liu, F.*; Tsuda, Yasutaka; Yoshigoe, Akitaka; Abukawa, Tadashi*; Moody, N. A.*; Ogawa, Shuichi*

Applied Physics Letters, 122(14), p.141901_1 - 141901_7, 2023/04

https://doi.org/10.1063/5.0142591
 Times Cited Count：3 Percentile：81.68(Physics, Applied)

A lowering of work function for LaB$$_{6}$$ by monolayer hexagonal BN coating is reported. Photoemission electron microcopy (PEEM) and thermionic emission electron microscopy (TEEM) both revealed that the hBN coated region of a LaB$$_{6}$$(100) single crystal has lower work function compared to the bare (i.e., non-coated) and graphene coated regions. A larger decrease of work function for the hBN coated LaB$$_{6}$$(100) compared to graphene coated LaB$$_{6}$$(100) was qualitatively supported by our density functional theory (DFT) calculations. Adding an oxide layer in the calculations improved consistency between the calculation and experimental results. We followed up our calculations with synchrotron-radiation X-ray photoelectron spectroscopy (SR-XPS) and confirmed the presence of an oxide layer on our LaB$$_{6}$$.

Journal Articles

Oxidation reaction kinetics on transition metal surfaces observed by real-time photoelectron spectroscopy

Ogawa, Shuichi*; Zhang, B.*; Yoshigoe, Akitaka; Takakuwa, Yuji*

Vacuum and Surface Science, 64(5), p.218 - 223, 2021/05

https://doi.org/10.1380/vss.64.218

The oxidation reaction kinetics on Ti(0001) and Ni(111) surfaces were observed by real-time photoelectron spectroscopy using synchrotron radiation to measure the oxidation state and oxide thickness. After the Ti(0001) surface was wholly covered by TiO with a thickness of 1.2 nm, the rapid growth of n-type TiO$$_{2}$$ proceeded through the diffusion of Ti$$^{4+}$$ ions to the TiO$$_{2}$$ surface at 400$$^{circ}$$C. A saturation of oxygen uptake on the TiO surface indicates that the O$$_{2}$$ sticking coefficient on the TiO surface is negligibly small and the segregation of Ti to the TiO surface is a trigger to initiate the TiO$$_{2}$$ growth. On the Ni(111) surface at 350$$^{circ}$$C, a thermally stable NiO$$_{x}$$ proceeded preferentially and then the growth of p-type NiO was initiated. The time evolution of NiO thickness was represented by a logarithmic growth model, where the NiO growth is governed by the electron tunneling to the NiO surface.

Journal Articles

Dynamic observation and theoretical analysis of initial O$$_{2}$$ molecule adsorption on polar and $$m$$-plane surfaces of GaN

Sumiya, Masatomo*; Sumita, Masato*; Asai, Yuya*; Tamura, Ryo*; Uedono, Akira*; Yoshigoe, Akitaka

Journal of Physical Chemistry C, 124(46), p.25282 - 25290, 2020/11

https://doi.org/10.1021/acs.jpcc.0c07151
 Times Cited Count：11 Percentile：47.05(Chemistry, Physical)

The initial oxidation of different GaN surfaces [the polar Ga-face (+c) and N-face (-c) and the nonpolar (10$$bar{1}$$0) ($$m$$)plane] under O$$_{2}$$ molecular beam irradiation was studied by real-time synchrotron radiation X-ray photoelectron spectroscopy and DFT molecular dynamics calculation. The results predict that triplet O$$_{2}$$ either dissociates or chemisorbs at the bridge position on the +c-surface, while on N-terminated -c-surface the O$$_{0}$$2 molecule only undergoes dissociative chemisorption. On the $$m$$-GaN surface, although the dissociation of O$$_{2}$$ is dominant, the bond length and angle were found to fluctuate from those of O$$_{2}$$ molecules adsorbed on the polar surfaces. The computational model including both the surface spin and polarity of GaN is useful for understanding the interface between GaN and oxide layers in metal-oxide electronic.

Journal Articles

Roles of strain and carrier in silicon oxidation

Ogawa, Shuichi*; Yoshigoe, Akitaka; Tang, J.*; Sekihata, Yuki*; Takakuwa, Yuji*

Japanese Journal of Applied Physics, 59(SM), p.SM0801_1 - SM0801_42, 2020/07

https://doi.org/10.35848/1347-4065/ab82a9
 Times Cited Count：5 Percentile：32.24(Physics, Applied)

In this paper, we review the study of the unified Si oxidation reaction model mediated by point defect generation, in which O$$_{2}$$ dissociative adsorption occurs at dangling bonds of point defects (emitted Si atoms and vacancies) at the SiO$$_{2}$$/Si interface, and the point defect generation rate is given by a combination of oxidation-induced strain, thermal strain due to the difference in thermal expansion coefficient between Si and SiO$$_{2}$$, thermal excitation of Si emission rate, and heat of adsorption.

Journal Articles

Initial oxidation kinetics of Si(113)-(3$$times$$2) investigated using supersonic seeded molecular beams

Ono, Shinya*; Tanaka, Kazuma*; Kodama, Hiraku*; Tanaka, Masatoshi*; Yoshigoe, Akitaka; Teraoka, Yuden*

Surface Science, 697, p.121600_1 - 121600_6, 2020/07

https://doi.org/10.1016/j.susc.2020.121600
 Times Cited Count：1 Percentile：5.82(Chemistry, Physical)

The initial oxidation on silicon surfaces with (113) orientation has been investigated by high-resolution photoelectron spectroscopy with synchrotron radiation. In the present study, we investigated both the Si2p state and O1s state to evaluate the oxide thickness, composition, and to assess the strain at the SiO$$_{2}$$/Si interface. In the Si2p state, the oxidized components (Si$$^{1+}$$, Si$$^{2+}$$, Si$$^{3+}$$, Si$$^{4+}$$) were analyzed. In the O1s state, a low-binding-energy component (LBC) and a high-binding-energy component (HBC) were analyzed. To investigate the non-thermal oxidation process, we utilized the supersonic seeded molecular beam (SSMB) to enhance the translational kinetic energies ($$E_{rm t}$$) of oxygen molecules. We demonstrate that the oxide quality and oxidation kinetics are largely altered by changing $$E_{rm t}$$.

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

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

https://doi.org/10.7567/APEX.8.025701
 Times Cited Count：7 Percentile：30.78(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

${it In situ}$ 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

https://doi.org/10.1063/1.4900633
 Times Cited Count：8 Percentile：29.6(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

Characterization of air-exposed surface $$beta$$-FeSi$$_{2}$$ fabricated by ion beam sputter deposition method

Saito, Takeru; Yamamoto, Hiroyuki; Yamaguchi, Kenji; Nakanoya, Takamitsu; Hojo, Kiichi; Haraguchi, Masaharu*; Imamura, Motoyasu*; Matsubayashi, Nobuyuki*; Tanaka, Tomoaki*; Shimada, Hiromichi*

Nuclear Instruments and Methods in Physics Research B, 206, p.321 - 325, 2003/05

https://doi.org/10.1016/S0168-583X(03)00754-7
 Times Cited Count：7 Percentile：46.82(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Study on the sputter-cleaning processes of Ni by means of Kelvin probe

Luo, G.-N.*; Yamaguchi, Kenji; Terai, Takayuki*; Yamawaki, Michio*

Surface Science, 505, p.14 - 24, 2002/05

https://doi.org/10.1016/S0039-6028(02)01394-8
 Times Cited Count：3 Percentile：20.59(Chemistry, Physical)

no abstracts in English

Journal Articles

Change in tritium-sorption property of stainless steel by thermal surface oxidation

Hirabayashi, Takakuni; K.W.Sung*; Sasaki, Teikichi; Saeki, Masakatsu

Journal of Nuclear Materials, 175, p.78 - 83, 1990/00

https://doi.org/10.1016/0022-3115(90)90272-O
 Times Cited Count：9 Percentile：67.09(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Synchrotron radiation real time photoelectron spectroscopy study on oxidation dynamics of Si surface

Yoshigoe, Akitaka

no journal, , 

In this seminor recent study on oxidation dynamics of Si surfaces using synchrotron radiation real time photoelectron spectroscopy is presented and the importance and future perspective of surface chemistry in nanotechnology researches is discussed.

Oral presentation

Strain-induced reaction kinetics of O$$_{2}$$ molecule at SiO$$_{2}$$/Si interfaces studied by real-time X-ray photoelectron spectroscopy

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

no journal, , 

The reaction kinetics of O$$_{2}$$ molecule at SiO$$_{2}$$/Si interfaces were investigated as a function of O$$_{2}$$ pressure (PO$$_{2}$$) by real-time X-ray photoelectron spectroscopy at BL23SU, SPring-8, to monitor the interfacial oxide growth rate (Rint), the oxidation states (Si$$^{1+}$$, Si$$^{2+}$$, Si$$^{3+}$$ and Si$$^{4+}$$, and the magnitude of oxidation-induced strain (Si$$^{alpha}$$ and Si$$^{beta}$$) at the same time during oxidation. When increasing PO$$_{2}$$ after the surface oxidation, Rint showed a nonlinear power-low function of (PO$$_{2}$$)$$^{n}$$, where n was almost the same as 0.5 for both Si(111) and Si(001) substrates. The results are interpreted by a Si oxidation model, in which the defect generated by the oxidation-induced strain is an active site for dissociative adsorption of O$$_{2}$$ at SiO$$_{2}$$/Si interface. Furthermore, when increasing PO$$_{2}$$ during the surface oxidation, Si$$^{alpha}$$ and Si$$^{beta}$$ showed significant changes at the start of interfacial oxidation.

Oral presentation

Investigation of oxide formation process in thermally oxidized GaN surface

Yamada, Takahiro*; Yoshigoe, Akitaka; Ito, Joyo*; Asahara, Ryohei*; Nozaki, Mikito*; Nakazawa, Satoshi*; Ishida, Masahiro*; Ueda, Tetsuzo*; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

no journal, , 

To achieve high performance of GaN MOS devices, high quality interfaces between insulator and GaN are essentially needed. The precise control of native surface oxide and/or interfacial oxide layer is important. In this study, oxide formation process in thermally oxidized GaN surface is analyzed by using synchrotron radiation photoelectron spectroscopy.

Oral presentation

Initial oxidation of Cu$$_{3}$$Pd(111) surface

Tsuda, Yasutaka*; Makino, Takamasa*; Tsukada, Chie; Yoshigoe, Akitaka; Fukuyama, Tetsuya*; Okada, Michio*

no journal, , 

It is well-known that oxidation is an important chemical reactions in corrosion processes. Cu$$_{3}$$Pd has an attracting material due to its catalytic property and its oxidation is the important subject. In this presentation, initial oxidation processes at the Cu$$_{3}$$Pd(111) surface was studied by using molecular beams. In situ photoemission measurements were conducted using surface chemistry apparatus at BL23SU at SPring-8. Single crystal Cu$$_{3}$$Pd was used after cleaning by means of Ar ion sputtering and annealing. It was found that molecular beams facilitate oxidation compared to that for backfilling condition. Furthermore, diffusion of surface atoms seems to be driven with increasing surface temperature.

Oral presentation

Oxidation of Cu$$_{3}$$Pt(111) surface with hyperthermal oxygen molecule

Tsuda, Yasutaka*; Makino, Takamasa*; Tsukada, Chie; Yoshigoe, Akitaka; Fukuyama, Tetsuya*; Okada, Michio*

no journal, , 

Oxidation is a main reaction in corrosion processes and its understabding is important to develop anticorrosion materials. In this study, initial oxidation at Cu$$_{3}$$Pt(111) surface was investigated by using surface analysis apparatus at BL23SU of SPring-8. The surface oxidized by 2.3 eV molecular beams was analzyed by synchrotron radiation photoelectron spectroscopy. We confirmed that Cu L$$_{3}$$M$$_{4.5}$$M$$_{4.5}$$ AES spectrum and Cu-2p XPS spectrum show the only growth of Cu oxide whereas Pt oxide was not formed from the results of Pt-4f XPS. It was also found that the reactivity of Cu$$_{3}$$Pd(111) surface is lower than that of Cu$$_{3}$$Au(111) surface.

Oral presentation

Real-time observation of oxidation process on GaN surfaces by X-ray photoelectron spectroscopy

Sumiya, Masatomo*; Tsuda, Yasutaka; Sumita, Masato*; Yoshigoe, Akitaka

no journal, , 

Synchrotron radiation X-ray photoelectron spectroscopy (XPS) was employed to clarify the oxidized states on the polar and m-plane GaN surfaces under exposure of various oxidation gases of H$$_{2}$$O, O$$_{2}$$, N$$_{2}$$O, and NO. It was found that H$$_{2}$$O vapor has the higher reactivity. The oxygen was hardly adsorbed on the surface by irradiating N$$_{2}$$O and NO gases. Apparently, two oxidation states for O$$_{2}$$ and H$$_{2}$$O irradiation were detected on +c GaN surface. Physisorption of O$$_{2}$$ molecule was dominate. The dissociation and adsorption of H$$_{2}$$O molecules co-existed on the +c surface. The chemisorption on the m-plane of GaN was dominant, and a stable Ga-O bond was formed on the surface. These chemical oxygen states were simulated by density functional molecular dynamics calculation using a theoretical model including both electronic spins on the surfaces and the polarity of GaN.

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