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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：0 Percentile：0(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.*; Di
o, W. A.*; Fukutani, Katsuyuki
ACS Nano, 16(9), p.14362 - 14369, 2022/09
Times Cited Count：1 Percentile：46.65(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.
C thin filmNorimatsu, Wataru*; Matsuda, Keita*; Terasawa, Tomoo; Takata, Nao*; Masumori, Atsushi*; Ito, Keita*; Oda, Koji*; Ito, Takahiro*; Endo, Akira*; Funahashi, Ryoji*; et al.
Nanotechnology, 31(14), p.145711_1 - 145711_7, 2020/04
Times Cited Count：5 Percentile：42.55(Nanoscience & Nanotechnology)We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of BC on SiC and graphene on BC had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on BC acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on BC was highly boron doped, and the hole concentration could be controlled over a wide range of 2
10
to 210
cm
. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.
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：11 Percentile：58.97(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：26.71(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.
-polarization Raman microscopySaito, Yuika*; Tokiwa, Kenshiro*; Kondo, Takahiro*; Bao, J.*; Terasawa, Tomoo; Norimatsu, Wataru*; Kusunoki, Michiko*
AIP Advances (Internet), 9(6), p.065314_1 - 065314_6, 2019/06
Times Cited Count：2 Percentile：12.68(Nanoscience & Nanotechnology)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 cm2/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.
Terasawa, Tomoo; Taira, Takanobu*; Obata, Seiji*; Yasuda, Satoshi; Saiki, Koichiro*; Asaoka, Hidehito
no journal, ,
Monolayer selective growth of graphene was achieved by chemical vapor deposition on a Cu substrate due to its low carbon solubility. In this study, we attempted the in-situ observation of chemical vapor deposition of graphene on a Au substrate with low carbon solid solubility like Cu by a radiation-mode optical microscopy. In the radiation images, the bright contrast started the growth between the trenches of the Au foil and progressed parallel to the trenches. The result of Raman mapping measurement indiceted that this contrast corresponded to graphene. In the presentation, we will also discuss the growth mechanism of graphene on the Au substrate.
2Yano, Masahiro; Terasawa, Tomoo; Yasuda, Satoshi; Machida, Shinichi*; Asaoka, Hidehito
no journal, ,
no abstracts in English
2Yano, Masahiro; Terasawa, Tomoo; Yasuda, Satoshi; Machida, Shinichi*; Asaoka, Hidehito
no journal, ,
The anisotropic diffusion coefficient ratio of the Si atoms on the Si(110)-162 reconstructed structure is determined by observing the "void" by scanning tunneling microscope (STM). The void length was measured to evaluate the anisotropic growth rate ratios for each void depth. The anisotropy of the void shape decreased as the void became deeper, indicating the reduction of the Si density ratio during the diffusion on the sidewall. Taking the migration of diffusing Si atoms to the upper and lower terraces and the adjacent sidewalls into account, we determined that the diffusion coefficient in the direction along the [1
2] or [12] parallel to the step rows of the 162 reconstructed structure is 3.0 times higher than that of the other direction.
Terasawa, Tomoo; Taira, Takanobu*; Obata, Seiji*; Yasuda, Satoshi; Saiki, Koichiro*; Asaoka, Hidehito
no journal, ,
Since the solubility of carbon in copper is very low, monolayer graphene can be selectively grown by chemical vapor deposition (CVD) on a copper substrate. Thus, CVD growth of graphene is considered the most promising technique for the next-generation electronics. Here we report the CVD growth of graphene on gold substrates which also have the low solubility of carbon. We achieved the in-situ observation of the CVD growth of graphene on a gold foil by radiation-mode optical microscopy (Rad-OM). Figure shows the Rad-OM images of a gold foil at the growth time of 15, 30, and 40 min at 900
C under Ar, H, and CH gas flow at 240, 8, and 5 sccm, respectively. The bright islands, corresponding to graphene confirmed by Raman spectroscopy, appeared between two trenches of the gold foil and grew parallel to the trenches. We will discuss the growth kinetics of graphene on gold, on the basis of the in-situ Rad-OM observation.
Terasawa, Tomoo; Obata, Seiji*; Yasuda, Satoshi; Saiki, Koichiro*; Asaoka, Hidehito
no journal, ,
no abstracts in English
2 surfaceAsaoka, Hidehito; Yano, Masahiro; Terasawa, Tomoo; Yasuda, Satoshi
no journal, ,
no abstracts in English
Terasawa, Tomoo; Yasuda, Satoshi; Hayashi, Naoki*; Norimatsu, Wataru*; Ito, Takahiro*; Machida, Shinichi*; Yano, Masahiro; Saiki, Koichiro*; Asaoka, Hidehito
no journal, ,
We report the band structure of graphene grown on hex-Au(001) using angle resolved photoemission spectroscopy (ARPES). We prepared graphene on hex-Au(001) by chemical vapor deposition and took ARPES image of the sample at AichiSR BL7U. The linear graphene band shows the intensity reduction at the binding energy of approximately 0.9 eV, indicating the modification of band structure of graphene by quasi-one dimensional potential of the hex-Au(001) reconstructed surface.
Yano, Masahiro; Terasawa, Tomoo; Machida, Shinichi*; Yasuda, Satoshi; Asaoka, Hidehito
no journal, ,
no abstracts in English
Terasawa, Tomoo; Yasuda, Satoshi; Hayashi, Naoki*; Norimatsu, Wataru*; Ito, Takahiro*; Machida, Shinichi*; Yano, Masahiro; Saiki, Koichiro*; Asaoka, Hidehito
no journal, ,
Terasawa, Tomoo; Yasuda, Satoshi; Hayashi, Naoki*; Norimatsu, Wataru*; Ito, Takahiro*; Machida, Shinichi*; Asaoka, Hidehito
no journal, ,
Graphene shows absorptivity and emissivity of 2.3% independent from the wavelength, however, the wavelength selectivity of the optical properties is required for device applications. Here we report the observation of the electronic band structure and thermal radiation of graphene grown on hex-Au(001) structure. The thermal radiation of graphene grown on hex-Au(001) was decreased in the optical microscopy which observed the light with the wavelength of 700-900 nm. The same sample showed the modified band structure observed by angle resolved photoemission spectroscopy. We will discuss the relation between the thermal radiation and band structure of graphene on Au substrates.
Terasawa, Tomoo; Yasuda, Satoshi; Hayashi, Naoki*; Norimatsu, Wataru*; Ito, Takahiro*; Machida, Shinichi*; Yano, Masahiro; Saiki, Koichiro*; Asaoka, Hidehito
no journal, ,
