Long and oriented graphene nanoribbon synthesis from well-ordered 10,10'-dibromo-9,9'-bianthracene monolayer on crystalline Au surfaces

Yano, Masahiro; Yasuda, Satoshi; Fukutani, Katsuyuki; Asaoka, Hidehito

RSC Advances (Internet), 13(21), p.14089 - 14096, 2023/05

https://doi.org/10.1039/D2RA07570A

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.

Efficient hydrogen isotope separation by tunneling effect using graphene-based heterogeneous electrocatalysts in electrochemical hydrogen isotope pumping

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

https://doi.org/10.1021/acsnano.2c04655

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.

Electrochemically driven specific alkaline metal cation adsorption on a graphene interface

Yasuda, Satoshi; Tamura, Kazuhisa; Kato, Masaru*; Asaoka, Hidehito; Yagi, Ichizo*

Journal of Physical Chemistry C, 125(40), p.22154 - 22162, 2021/10

https://doi.org/10.1021/acs.jpcc.1c03322

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.

Confinement of hydrogen molecules at graphene-metal interface by electrochemical hydrogen evolution reaction

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

https://doi.org/10.1021/acs.jpcc.0c00995

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 radiation

Terasawa, Tomoo; Taira, Takanobu*; Obata, Seiji*; Saiki, Koichiro*; Yasuda, Satoshi; Asaoka, Hidehito

Vacuum and Surface Science, 62(10), p.629 - 634, 2019/10

https://doi.org/10.1380/vss.62.629

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.

Effect of hydrogen on chemical vapor deposition growth of graphene on Au substrates

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

https://doi.org/10.7567/1347-4065/ab19ae

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.

Absorbent property of fullerene for cesium isotope separation investigated using X-ray photoelectron spectroscopy

Sekiguchi, Tetsuhiro; Yokoyama, Keiichi; Uozumi, Yuki*; Yano, Masahiro; Asaoka, Hidehito; Suzuki, Shinichi; Yaita, Tsuyoshi

Progress in Nuclear Science and Technology (Internet), 5, p.161 - 164, 2018/11

https://doi.org/10.15669/pnst.5.161

For nuclear transmutation of cesium-135 (Cs), which is long-lived fission product, we are developing selective absorbent which takes only Cs atom in, but does not CsI. In this study, absorbing property of Cs atom onto the surface of fullerene (C) film has been investigated using synchrotron-based angle-dependent X-ray photoelectron spectroscopy (XPS). The results were compared with those of CsI. It was found that Cs penetrates into C deep bulk. In contrast, CsI deposits on shallow surface. Furthermore, XPS spectra were measured as a function of Ar-sputtering time in order to know Cs concentration profiles in deep region. Results showed that Cs penetrates into deep region of several hundreds .

STM-induced SiO 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

https://doi.org/10.1380/ejssnt.2018.370

Uniform Si nano-dot fabrication using reconstructed structure of Si(110)

Yano, Masahiro; Uozumi, Yuki*; Yasuda, Satoshi; Asaoka, Hidehito

Japanese Journal of Applied Physics, 57(6S1), p.06HD04_1 - 06HD04_4, 2018/06

https://doi.org/10.7567/JJAP.57.06HD04

Silver photodiffusion into Ge-rich amorphous germanium sulfide; Neutron reflectivity study

Sakaguchi, Yoshifumi*; Asaoka, Hidehito; Mitkova, M.*

Journal of Applied Physics, 122(23), p.235105_1 - 235105_12, 2017/12

https://doi.org/10.1063/1.5000858