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Journal Articles

Finding RHEED conditions sensitive to hydrogen position on Pd(100)

Kawamura, Takaaki*; Fukaya, Yuki; Fukutani, Katsuyuki

Surface Science, 722, p.122098_1 - 122098_8, 2022/08

no abstracts in English

Journal Articles

Hydrogen absorption and diffusion behaviors in cube-shaped palladium nanoparticles revealed by ambient-pressure X-ray photoelectron spectroscopy

Tang, J.*; Seo, O.*; Rivera Rocabado, D. S.*; Koitaya, Takanori*; Yamamoto, Susumu*; Namba, Yusuke*; Song, C.*; Kim, J.*; Yoshigoe, Akitaka; Koyama, Michihisa*; et al.

Applied Surface Science, 587, p.152797_1 - 152797_8, 2022/06

The hydrogen absorption and diffusion mechanisms on cube-shaped Pd nanoparticles (NPs) which are important hydrogen-storage materials were studied using X-ray photoelectron spectroscopy and DFT calculations. In the surface region, hydrogen absorption showed almost similar behavior regardless of the NPs size. It was found that the octahedral sites are more favorable than the tetrahedral sites for hydrogen occupation. We also clarified that the hydrogen atoms absorbing on the smaller-sized Pd NPs diffuse to the subsurface more actively because of the weakened Pd-H bond by the surface disordering, which plays an important role in hydrogen adsorption at a low H$$_{2}$$ pressure.

Journal Articles

Ortho-para conversion of molecularly chemisorbed H$$_{2}$$ on Pd(210)

Ueta, Hirokazu; Fukutani, Katsuyuki

Vacuum and Surface Science, 64(9), p.430 - 434, 2021/09

Journal Articles

Ultrafast surface Dirac fermion dynamics of Sb$$_2$$Te$$_3$$-based topological insulators

Sumida, Kazuki; Ishida, Yukiaki*; G$"u$dde, J.*; H$"o$fer, U.*; Shin, S.*; Kimura, Akio*

Progress in Surface Science, 96(2), p.100628_1 - 100628_15, 2021/05

 Times Cited Count:0 Percentile:0.07(Chemistry, Physical)

Journal Articles

Development of ${it spatiotemporal}$ measurement and analysis techniques in X-ray photoelectron spectroscopy; From NAP-HARPES to 4D-XPS

Toyoda, Satoshi*; Yamamoto, Tomoki*; Yoshimura, Masashi*; Sumida, Hirosuke*; Mineoi, Susumu*; Machida, Masatake*; Yoshigoe, Akitaka; Suzuki, Satoru*; Yokoyama, Kazushi*; Ohashi, Yuji*; et al.

Vacuum and Surface Science, 64(2), p.86 - 91, 2021/02

We have developed ${it spatiotemporal}$ measurement and analysis techniques in X-ray photoelectron spectroscopy. To begin with, time-division depth profiles of gate stacked film interfaces have been achieved by NAP-HARPES (Near Ambient Pressure Hard X-ray Angle-Resolved Photo Emission Spectroscopy) data. We then have promoted our methods to quickly perform peak fittings and depth profiling from time-division ARPES data, which enables us to realize 4D-XPS analysis. It is found that the traditional maximum entropy method (MEM) combined with Jackknife averaging of sparse modeling in NAP-HARPES data is effective to perform dynamic measurement of depth profiles with high precision.

Journal Articles

Precise chemical state analyses of ultrathin hafnium films deposited on clean Si(111)-7$$times$$7 surface using high-resolution core-level photoelectron spectroscopy

Kakiuchi, Takuhiro*; Matoba, Tomoki*; Koyama, Daisuke*; Yamamoto, Yuki*; Kato, Daiki*; Yoshigoe, Akitaka

Surface Science, 701, p.121691_1 - 121691_8, 2020/11

Ultrathin hafnium films on Si(111)-7$$times$$7 were studied using synchrotron radiation photoelectron spectroscopies to reveal the chemical states at interface and surface. Ultrathin Hf layers grow on clean Si(111)-7$$times$$7 surface by lever rule. Surface and interface of Hf/Si(111) contain three components (metallic Hf layers, Hf monosilicide (HfSi) and Si-rich Hf silicide). Ultrathin Hf layers changes HfSi$$_{2}$$ islands on bared Si(111)-7$$times$$7 surface after annealing at 1073 K. It was found that the long axes of the rectangle islands expand the direction connecting the corner holes in DAS model of clean Si(111)-7$$times$$7 surface.

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

The initial oxidation on silicon surfaces with (113) orientation has been investigated by high-resolution photoelectron spectroscopy with synchrotronradiation. In the present study, we investigated both the Si2p state and O1s state to evaluate the oxide thickness, composition, and to assess the strainat 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

Initial oxidation processes of ultrathin hafnium film and hafnium disilicide islands on Si(100)-2$$times$$1 surfaces studied using core-level X-ray photoelectron spectroscopy

Kakiuchi, Takuhiro*; Yamasaki, Hideki*; Tsukada, Chie*; Yoshigoe, Akitaka

Surface Science, 693, p.121551_1 - 121551_8, 2020/03

We investigated the initial oxidation of ultrathin hafnium (Hf) film on Si(100)-2$$times$$1 using photoelectron spectroscopy. Metallic Hf rapidly oxidized, transforming into hafnium dioxide (HfO$$_{2}$$) and its suboxides. The other HfSi component at the interface was nearly unreactive with O$$_{2}$$ molecules. These facts suggest that the metallic Hf component plays a vital role in the initial oxidation of the ultrathin Hf/Si(100) film. After annealing from 873 K to 973 K, the Hf suboxides in low ionic valences progressed into fully oxidized HfO$$_{2}$$. Once the annealing temperature reached c.a.1073 K, oxygen atoms were entirely removed from the ultrathin HfO$$_{2}$$/Si(100) film containing SiO$$_{2}$$ at the interface. Simultaneously, ultrathin HfO$$_{2}$$ layers changed into islands of Hf disilicide ($$i$$-HfSi$$_{2}$$) on a bare Si(100)-2$$times$$1 surface. The $$i$$-HfSi$$_{2}$$ component showed slight reactivity with O$$_{2}$$ molecules at 298 K. In contrast to the initial oxidation of clean Si(100)-2$$times$$1 surface, the dangling bonds on bare Si(100)-2$$times$$1 surface among $$i$$-HfSi$$_{2}$$ oxidized preferentially.

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

Turbomolecular pump as main pump in a high-power proton accelerator vacuum system

Kamiya, Junichiro; Kinsho, Michikazu; Ogiwara, Norio*; Sakurai, Mitsuru*; Mabuchi, Takuya*; Wada, Kaoru*

Vacuum and Surface Science, 62(8), p.476 - 485, 2019/08

J-PARC 3GeV rapid cycling synchrotron (RCS) is one of the highest beam power proton accelerators. Challenges for achieving low pressure region in ultra-high vacuum (UHV) in the beam line are the large outgassing source. We focused turbo molecular pumps (TMP) as maing pump because it can evacuate the continuous and additional outgassing with large pumping speed in wide pressure range. It is also possible to evacuate from low vacuum to UHV with only a few hours by using TMP, which ensures users' experimental time after vacuum device maintenance. During more than 10 years operation of the vacuum system, many experiences have been accumulated about the usage of TMP in RCS. In this presentation, we discussed about validity of TMP as main pump in high power proton beam accelerator by showing the performance of the beam line pressure during the beam operation. Further, in anticipation of upgrade higher beam power more than 1 MW, validity of a combination of TMP and NEG pump will be mentioned.

Journal Articles

Development of a gas distribution measuring system for 2-D beam profile monitor

Yamada, Ippei; Ogiwara, Norio*; Hikichi, Yusuke*; Kamiya, Junichiro; Kinsho, Michikazu

Vacuum and Surface Science, 62(7), p.400 - 405, 2019/07

no abstracts in English

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:2 Percentile:22.92(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.

Journal Articles

STM-induced SiO$$_{2}$$ decomposition on Si(110)

Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Asaoka, Hidehito; Tsukada, Chie*; Yoshida, Hikaru*; Yoshigoe, Akitaka

e-Journal of Surface Science and Nanotechnology (Internet), 16, p.370 - 374, 2018/08

Journal Articles

Structure analysis of two-dimensional atomic sheets by total-reflection high-energy positron diffraction

Fukaya, Yuki

e-Journal of Surface Science and Nanotechnology (Internet), 16, p.111 - 114, 2018/04

no abstracts in English

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

Localization of cesium on montmorillonite surface investigated by frequency modulation atomic force microscopy

Araki, Yuki*; Sato, Hisao*; Okumura, Masahiko; Onishi, Hiroshi*

Surface Science, 665, p.32 - 36, 2017/11

 Times Cited Count:9 Percentile:53.71(Chemistry, Physical)

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:8.15(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

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:5 Percentile:32.3(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

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

176 (Records 1-20 displayed on this page)