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Terasawa, Tomoo; Matsunaga, Kazuya*; Hayashi, Naoki*; Ito, Takahiro*; Tanaka, Shinichiro*; Yasuda, Satoshi; Asaoka, Hidehito
Vacuum and Surface Science, 66(9), p.525 - 530, 2023/09
As Au (001) surfaces exhibit a quasi-one-dimensional corrugated structure, Hex-Au(001), its periodicity was predicted to change the electronic structure of graphene when graphene was grown on this surface. Furthermore, the hybridization between graphene and Au is known to introduce bandgap and spin polarization into graphene. Here, we report angle-resolved photoemission spectroscopy and density functional theory calculation of graphene on a Hex-Au(001) surface. A bandgap of 0.2 eV in the graphene Dirac cone was observed at the crossing point of the graphene Dirac cone and Au 6sp bands, indicating that the origin of the bandgap formation was the hybridization between the graphene Dirac cone and Au 6sp band. We discussed the hybridization mechanism and anticipated spin injection into the graphene Dirac cone.
Yasuda, Satoshi; Di
o, W. A.*; Fukutani, Katsuyuki
Vacuum and Surface Science, 66(9), p.514 - 519, 2023/09
Monolayer graphene, representative of atomically thin crystals, has recently shown unexpectedly high proton and deuteron permeability under ambient conditions. It also permeates (filters) hydrogen (deuterium) isotope ion with high selectivity. These results suggest possible ways of developing novel and efficient hydrogen isotope gas enrichment techniques for manufacturing silicon semiconductors, optical fibers, drug development, nuclear fusion, and other related applications. And yet, despite its importance, experimental studies remain scarce and the separation mechanism contentious. Here, we introduce our recent findings on how quantum tunneling of hydrons through graphene could account for the high hydron selectivity of graphene.
Yano, Masahiro; Yasuda, Satoshi; Fukutani, Katsuyuki; Asaoka, Hidehito
RSC Advances (Internet), 13(21), p.14089 - 14096, 2023/05
Times Cited Count：0 Percentile：0(Chemistry, Multidisciplinary)Bottom-up synthesis on metal surfaces has attracted attention for the fabrication of graphene nanoribbons (GNRs) with atomically-precise chemical structures to realize novel electronic devices. However, control of length and orientation on surfaces during GNR synthesis is difficult, thus, achieving longer and aligned GNR growth is a significant challenge. Herein, we report GNR synthesis from a well-ordered dense monolayer on Au crystalline surfaces for long and oriented GNR growth. Scanning tunneling microscopy showed that 10,10'-dibromo-9,9'-bianthracene (DBBA) precursors deposited on Au(111) at room temperature self-assembled into a well-ordered dense monolayer, and the straight molecular wire structure was formed where Br atoms in each precursor were adjacent along the wire axis. The DBBAs in the monolayer were found to be hardly desorbed from the surface under subsequent heating and efficiently polymerize along with the molecular arrangement, resulting in more long and oriented GNR growth compared to the conventional growth method. The result is attributed to be suppression of random diffusion and desorption of the DBBAs on the Au surface during polymerization due to the densely-packed DBBA structure. Additionally, an investigation of the effect of the Au crystalline plane on the GNR growth revealed further anisotropic GNR growth on Au(100) compared to Au(111) due to the stronger interactions of DBBA with Au(100). These findings provide fundamental knowledge for controlling GNR growth from a well-ordered precursor monolayer to achieve more long and oriented GNRs.
Balois-Oguchi, M. V.*; Hayazawa, Norihiko*; Yasuda, Satoshi; Ikeda, Katsuyoshi*; Nguyen, T. Q.*; Escao, M. C.*; Tanaka, Takuo*
Journal of Physical Chemistry C, 127(12), p.5982 - 5990, 2023/03
Times Cited Count：2 Percentile：52.07(Chemistry, Physical)Micrometer-sized wrinkles in graphene are known to affect the electronic properties of graphene due to their shape and the strain variations they create. Here, we analyze the strain distribution and doping of a graphene wrinkle having 1.9 nm width using tip-enhanced Raman spectroscopy (TERS) in ambient conditions. We found a strong correlation between the TERS images of the graphene wrinkle and the electronic Raman scattering (eRS) of the Au(111) substrate. Our work demonstrates that the as-fabricated physical and electronic properties of nanometer-sized features, such as wrinkles, can be probed and studied in detail with TERS which is essential for nanodevice characterization.
Terasawa, Tomoo; Matsunaga, Kazuya*; Hayashi, Naoki*; Ito, Takahiro*; Tanaka, Shinichiro*; Yasuda, Satoshi; Asaoka, Hidehito
Physical Review Materials (Internet), 7(1), p.014002_1 - 014002_10, 2023/01
Times Cited Count：3 Percentile：72.03(Materials Science, Multidisciplinary)Au(001) surfaces exhibit a complex reconstructed structure [Hex-Au(001)] comprising a hexagonal surface and square bulk lattices, yielding a quasi-one-dimensional corrugated surface. When graphene was grown on this surface, the periodicity of the corrugated surface was predicted to change the electronic structure of graphene, forming bandgaps and new Dirac points. Furthermore, the graphene-Au interface is promising for bandgap generation and spin injection due to band hybridization. Here, we report the angle-resolved photoemission spectroscopy and density functional calculation of graphene on a Hex-Au(001) surface. The crossing point of the original and replica graphene 
bands showed no bandgap, suggesting that the one-dimensional potential was too small to modify the electronic structure. A bandgap of 0.2 eV was observed at the crossing point of the graphene and Au 
bands, indicating that the bandgap is generated using hybridization of the graphene and Au bands. We discussed the hybridization mechanism and concluded that the R30 configuration between graphene and Au and an isolated electronic structure of Au are essential for effective hybridization between graphene and Au. We anticipate that hybridization between graphene and Au would result in spin injection into graphene.
Yasuda, Satoshi; Matsushima, Hisayoshi*; Harada, Kenji*; Tanii, Risako*; Terasawa, Tomoo; Yano, Masahiro; Asaoka, Hidehito; Gueriba, J. S.*; Dio, W. A.*; Fukutani, Katsuyuki
ACS Nano, 16(9), p.14362 - 14369, 2022/09
Times Cited Count：12 Percentile：85.62(Chemistry, Multidisciplinary)The fabrication of hydrogen isotope enrichment system is essential for the development of industrial, medical, life science, and nuclear fusion fields, therefore alternative enrichment techniques with high separation factor and economic feasibility have been still explored. Herein, we report the fabrication of heterogeneous electrode with layered structures consisting of palladium and graphene layers for polymer electrolyte membrane electrochemical hydrogen pumping for the hydrogen isotope enrichment. We demonstrated significant bias voltage dependence of hydrogen/deuterium (H/D) separation ability and its high H/D at lower bias voltage. Theoretical analysis also demonstrated that the observed high H/D at low bias voltage stems from hydrogen isotopes tunneling through atomically-thick graphene during the electrochemical reaction, and the bias dependent H/D results in a transition from the quantum tunneling regime to classical over- barrier regime for hydrogen isotopes transfer via the graphene. These findings provide new insight for a novel economical methodology of efficient hydrogen isotope enrichment.
Terasawa, Tomoo; Fukutani, Katsuyuki; Yasuda, Satoshi; Asaoka, Hidehito
e-Journal of Surface Science and Nanotechnology (Internet), 20(4), p.196 - 201, 2022/07
Graphene is a perfect impermeable membrane for gases but permeable to hydrogen ions. Hydrogen ion permeation shows the isotope effect, i.e., deuteron is slower than proton when permeating graphene. However, the permeation mechanism and the origin of the isotope effect are still unclear. Here, we propose a strategy to discuss the hydrogen ion permeation mechanism of graphene by developing an ion source with ultraslow, monochromatic, and mass-selected hydrogen ion beam. We employed a hemispherical monochromator and a Wien filter for the ion source to achieve the energy and mass resolutions of 0.39 eV and 1 atomic mass unit, respectively. The energetically sharp ion beam is expected to allow us to directly measure the permeability of graphene with high accuracy.
Yasuda, Satoshi; Tamura, Kazuhisa; Kato, Masaru*; Asaoka, Hidehito; Yagi, Ichizo*
Journal of Physical Chemistry C, 125(40), p.22154 - 22162, 2021/10
Times Cited Count：10 Percentile：57.69(Chemistry, Physical)Understanding electrochemical behavior of the alkaline metal cation-graphene interface in electrolyte is essential for understanding the fundamental electrochemical interface and development of graphene-based technologies. We report comprehensive analysis of the electrochemical behavior of both alkaline metal cations and graphene using electrochemical surface X-ray diffraction (EC-SXRD) and Raman (EC-Raman) spectroscopic techniques in which the interfacial structure of cations and the charging state and mechanical strain of the graphene can be elucidated. EC-SXRD and cyclic voltammetry demonstrated electrochemically driven specific adsorption and desorption of cations on the graphene surface involved in the dehydration and hydration process. This study provides new insight for understanding fundamental electrochemical behavior of the alkaline metal cation-graphene interface and contributes to the development of carbon-based novel applications.
Yasuda, Satoshi
Denki Kagaku, 89(3), p.256 - 261, 2021/09
We introduce our recent study on confinement of Hydrogen Molecules at graphene-metal interface by electrochemical hydrogen evolution reaction.
Shamoto, Shinichi; Lee, M. K.*; Fujimura, Yuki; Kondo, Keietsu; Ito, Takashi; Ikeuchi, Kazuhiko*; Yasuda, Satoshi; Chang, L.-J.*
Materials Research Express (Internet), 8(7), p.076303_1 - 076303_6, 2021/07
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)Pb, Ga, and Ga doped lead free Sn-Ag-Cu solders are used to study the gallium effect for the low joint resistivity with silver sheathed DI BISCCO type H tapes. The results are reported.
Kato, Masaru*; Fujibayashi, Natsuki*; Abe, Daiki*; Matsubara, Naohiro*; Yasuda, Satoshi; Yagi, Ichizo*
ACS Catalysis, 11(4), p.2356 - 2365, 2021/02
Times Cited Count：36 Percentile：88.11(Chemistry, Physical)Fe-N-C oxygen reduction reaction catalyst is a key materials in polymer electrolyte fuel cell. However, the many Fe-N-C electrocatalysts still suffer from product selectivity due to the production of H
O as the byproduct. In this work, we synthesized an ORR electrocatalyst of Cu
, Fe, and N-doped carbon nanotubes. This heterobimetallic catalyst showed the selective four electron reduction of O to HO. Kinetic analysis of the electrocatalytic ORR and hydrogen peroxide reduction reaction in acidic media revealed that Cu, Fe-N-doped catalyst showed two orders of magnitude higher rate constants for the direct four electron reduction of O to HO than those for the two electron reduction of O to HO, whereas a monometallic Fe-N-doped catalyst showed the same order of magnitude, indicating that the heterometallic cooperativity had a drastic impact on the ORR kinetics.
Kato, Masaru*; Nakahoshiba, Ryota*; Ogura, Kazuya*; Tokuda, Shoichi*; Yasuda, Satoshi; Higashi, Kotaro*; Uruga, Tomoya*; Uemura, Yohei*; Yagi, Ichizo*
ACS Applied Energy Materials (Internet), 3(7), p.6768 - 6774, 2020/07
Times Cited Count：15 Percentile：62.59(Chemistry, Physical)To understand electronic effects of nitrogen-doped and polymer-coated carbon supports on the catalytic activity of Pt-based nanostructured catalysts, we prepared Pt
Ni nanoframes (NFs) supported on polybenzimidazole (PBI)-coated and uncoated carbon nanotubes for the oxygen reduction reaction (ORR), and then compared their catalytic activities and electronic properties with those of NFs immobilized on nitrogen-doped and undoped carbon supports. Although both PBI-coating and nitrogen-doping approaches improved the catalytic activity of NFs, 
X-ray photoelectron spectroscopy and 
X-ray absorption spectroscopy revealed that nitrogen doping showed electronic effects on NFs, whereas PBI-coating showed almost no impact on the electronic state of NFs but stabilized Pt(OH)
species under electrochemical conditions. Our studies demonstrate that difference in microscopic environments of nitrogen atoms at the catalyst/support interface is highly sensitive to the electronic effects of supports on Pt-based electrocatalysts.
Yasuda, Satoshi; Tamura, Kazuhisa; Terasawa, Tomoo; Yano, Masahiro; Nakajima, Hideaki*; Morimoto, Takahiro*; Okazaki, Toshiya*; Agari, Ryushi*; Takahashi, Yasufumi*; Kato, Masaru*; et al.
Journal of Physical Chemistry C, 124(9), p.5300 - 5307, 2020/03
Times Cited Count：14 Percentile：60.14(Chemistry, Physical)Confinement of hydrogen molecules at graphene-substrate interface has presented significant importance from the viewpoints of development of fundamental understanding of two-dimensional material interface and energy storage system. In this study, we investigate H confinement at a graphene-Au interface by combining selective proton permeability of graphene and the electrochemical hydrogen evolution reaction (electrochemical HER) method. After HER on a graphene/Au electrode in protonic acidic solution, scanning tunneling microscopy finds that H nanobubble structures can be produced between graphene and the Au surface. Strain analysis by Raman spectroscopy also shows that atomic size roughness on the graphene/Au surface originating from the HER-induced strain relaxation of graphene plays significant role in formation of the nucleation site and H storage capacity.
optical microscopy of crystal growth of graphene using thermal radiationTerasawa, 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
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 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 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.
Terasawa, Tomoo; Taira, Takanobu*; Yasuda, Satoshi; Obata, Seiji*; Saiki, Koichiro*; Asaoka, Hidehito
Japanese Journal of Applied Physics, 58(SI), p.SIIB17_1 - SIIB17_6, 2019/08
Times Cited Count：4 Percentile：21.91(Physics, Applied)Chemical vapor deposition (CVD) on substrates with low C solubility such as Cu and Au is promising to grow monolayer graphene selectively in a large scale. Hydrogen is often added to control the domain size of graphene on Cu, while Au does not require H since Ar is inert against oxidation. The effect of H should be revealed to improve the quality of graphene on Au. Here we report the effect of H on the CVD growth of graphene on Au substrates using in situ radiation-mode optical microscopy. The in situ observation and ex situ Raman spectroscopy revealed that whether H was supplied or not strongly affected the growth rate, thermal radiation contrast, and compressive strain of graphene on Au. We attributed these features to the surface reconstruction of Au(001) depending on H supply. Our results are essential to achieve the graphene growth with high quality on Au for future applications.
Terasawa, Tomoo; Saiki, Koichiro*; Yasuda, Satoshi; Asaoka, Hidehito
Dai-39-Kai Nihon Netsu Bussei Shimpojiumu Koen Rombunshu (CD-ROM), p.262 - 264, 2018/11
Graphene, monolayer graphite, has been expected as one of the new materials targeting the next generation electronics since its first isolation in 2004, due to the ultrahigh carrier mobility up to 100,000 cm/Vs and high transparency of 97.7%. The high transparency of graphene make it invisible on various substrates. Particularly, graphene on Cu, one of the common growth substrates for high-quality graphene, cannot be observed by optical microscopes. Here, we report the optical microscopic method to visualize graphene using thermal radiation. We observed a Cu surface by a zoom-lens and a CMOS camera during the growth of graphene by chemical vapor deposition. When graphene was grown on Cu substrates, the thermal radiation intensity increased at the area covered with graphene. The thermal radiation contrast between Cu surfaces with and without graphene showed that the thermal radiation intensity increased as the number of graphene layers in a layer-by-layer manner. We quantitatively analyzed the thermal radiation contrasts at various temperatures. We found the thermal radiation contrast was independent from the sample temperature. This result suggests that the emissivity of graphene is independent from the temperature, which is consistent with the theory of the optical properties of graphene. Our findings are essential for the discussion of the thermal radiation from the atomically thin materials including graphene.
Yasuda, Satoshi; Uchibori, Yosuke*; Wakeshima, Makoto*; Hinatsu, Yukio*; Ogawa, Hiroaki; Yano, Masahiro; Asaoka, Hidehito
RSC Advances (Internet), 8(66), p.37600 - 37605, 2018/11
Times Cited Count：12 Percentile：42.69(Chemistry, Multidisciplinary)We present a quantitative study on the effect of a newly obtained thermal history on the formation of Fe-N-C catalytic sites. A short and repeated heating process is employed as the new thermal history, where short heating (1 min) followed by quenching is applied to a sample with arbitrary repetition. Through electrochemical quantitative analysis, it is found that the new process effectively increases the Fe-N-C mass-based site density (MSD) to almost twice that achieved using a conventional continuous heating process, while the turn-over frequency (TOF) is independent of the process. Elemental analysis shows that the new process effectively suppresses the thermal desorption of Fe and N atoms during the initial formation stage and consequently contributes to an increase in the Fe-N-C site density. The resultant catalytic activity (gravimetric kinetic current density (0.8 V vs. RHE)) is 1.8 times higher than that achieved with the continuous heating process.
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
reduction reaction region at void periphery on Si(110)Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Tsukada, Chie*; Yoshida, Hikaru*; Yoshigoe, Akitaka; Asaoka, Hidehito
Japanese Journal of Applied Physics, 57(8S1), p.08NB13_1 - 08NB13_4, 2018/07
Times Cited Count：2 Percentile：9.42(Physics, Applied)Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Asaoka, Hidehito
Japanese Journal of Applied Physics, 57(6S1), p.06HD04_1 - 06HD04_4, 2018/06
Times Cited Count：4 Percentile：20.17(Physics, Applied)