Synchrotron X-ray standing wave Characterization of atomic arrangement at interface between transferred graphene and -AlO(0001)

Entani, Shiro*; Honda, Mitsunori; Naramoto, Hiroshi*; Li, S.*; Sakai, Seiji*

Surface Science, 704, p.121749_1 - 121749_6, 2021/02

https://doi.org/10.1016/j.susc.2020.121749

Graphene is expected to be one of the most promising materials for nanoelectronics and spintronics. In most graphene-based devices, the graphene channel is placed on insulating substrates. Therefore, the study of inter-facial interactions between graphene and the insulator surface is of critical importance. In this study, the vertical arrangement of graphene which is transferred on -AlO(0001) has been studied by normal incidence X-ray standing wave (NIXSW) technique. The analysis of the NIXSW profile reveals that the graphene layer is located at 3.57 () above the -AlO(0001) surface, which is larger than the interlayer distance of graphite at 3.356 (). Micro- Raman spectroscopy shows that the transferred graphene has a limited spatial distribution of hole concentration. The present study shows that transferred graphene on the sapphire substrate followed by vacuum-annealing has an atomically flat surface free from residual contaminations such as organic compounds and there occurs the hole-doping in graphene.

Electronic structure of Li@C; Photoelectron spectroscopy of the Li@C[PF] salt and STM of the single Li@C molecules on Cu(111)

Yamada, Yoichi*; Kuklin, A. V.*; Sato, Sho*; Esaka, Fumitaka; Sumi, Naoya*; Zhang, C.*; Sasaki, Masahiro*; Kwon, E.*; Kasama, Yasuhiko*; Avramov, P. V.*; et al.

Carbon, 133, p.23 - 30, 2018/07

https://doi.org/10.1016/j.carbon.2018.02.106

We report first STM observation of the Li ion endohedral C, which is of a new class of endohedral fullerenes, prepared by means of evaporation of high-purity Li@C[PF] salt in ultra-high vacuum. Prior to the STM measurements, the electronic structure of Li@C in the Li@C[PF] salt was also precisely determined. In the salt, it is shown that Li and PF have nearly single positive and negative charge, respectively, and the C cage is nearly neutral, suggesting that Li@C in the salt retains its original electronic state.

Evaluation of influence of splay fault growth on groundwater flow around geological disposal system

Takai, Shizuka; Takeda, Seiji; Sakai, Ryutaro*; Shimada, Taro; Munakata, Masahiro; Tanaka, Tadao

Nihon Genshiryoku Gakkai Wabun Rombunshi, 16(1), p.34 - 48, 2017/03

https://doi.org/10.3327/taesj.J16.003

In geological disposal, direct effect on geological repositories by active faults is avoided at a stage of site characterization; however, uncertainty remains for avoidance of faults derived from the active faults, which are concealed deep under the ground and difficult to detect in advance. In this research, the influence of growth of undetected splay faults on natural barrier in a geological disposal system, which will caused by attack of the faults in the future, was evaluated. We investigated examples of splay faults in Japan and set conditions for growth of splay faults. Furthermore, we assumed a disposal site composed of sedimentary rocks and made a hydrogeological model of growth of splay faults. We carried out groundwater flow analyses, changing parameters such as location and depth of repository and growth velocity of splay faults. The results indicate that main flow path from the repository is changed into upward flow along the splay fault due to its growth and the average velocity to the ground surface becomes one or two orders of magnitude higher than that before its growth. The results also suggest that the splay fault growth leads into the possibility of downward flow of oxidizing groundwater from ground surface area.

Evaluation for influence of new volcanic eruption on geological disposal site

Shimada, Taro; Takeda, Seiji; Sakai, Ryutaro*; Takubo, Kazuya; Tanaka, Tadao

MRS Advances (Internet), 1(61), p.4081 - 4086, 2016/00

https://doi.org/10.1557/adv.2017.193

Volcanic eruption which may affect geological disposal system directly depends on the regional location in Japan. It is required that the disposal site should be located far from existing volcanos. However, there are regions where it is impossible to exclude the possibility of appearance of new volcanic activity on the site even if the site is located far from existing volcanos. In order to identify the influence of volcanic eruption at disposal site to public if it occurs public exposure doses were evaluated based on the two scenarios considering types of eruption at new volcanic activity in Japan. One is the exposure by tephra widespread by Strombolian eruption and deposited on the ground surface, including radionuclides from vitrified waste forms after a volcanic conduit penetrated disposal galleries. The other is that by waste forms appeared at the surface by Merapi type pyroclastic flow. Exposure doses of the residents living on the tephra do not exceed 1mSv/y even when the eruption occurs at 1,000 years after closure of disposal site. Dose rate for the volcanic researchers temporarily approaching waste forms becomes less than 1mSv/h when the eruption occurs 100,000 years after. It indicated that attention should be paid to the impact by Merapi type pyroclastic flow on researchers approaching waste forms appeared rather than that by Strombolian eruption on residents living on the tephra widespread.

Spin pumping blocked by single-layer graphene

Haku, Satoshi*; Tashiro, Takaharu*; Nakayama, Hiroyasu*; Ieda, Junichi; Entani, Shiro; Sakai, Seiji; Ando, Kazuya*

Applied Physics Express, 8(7), p.073009_1 - 073009_3, 2015/07

https://doi.org/10.7567/APEX.8.073009

We found that the spin pumping in a NiFe/Pt bilayer is strongly suppressed by inserting single-layer graphene (SLG) at the interface. The spin pumping in the NiFe/Pt bilayer enhances the magnetization damping of the ferromagnetic layer, which is quantified from microwave frequency dependence of ferromagnetic resonance linewidth. We show that the enhancement of the magnetization damping due to the spin pumping disappears in a NiFe/SLG/Pt trilayer. This result indicates that the spin pumping is blocked by the atomic monolayer, demonstrating the crucial role of the interfacial short-range spin-exchange coupling in the spin pumping in metallic systems.

Contracted interlayer distance in graphene/sapphire heterostructure

Entani, Shiro; Antipina, L. Y.*; Avramov, P.*; Otomo, Manabu*; Matsumoto, Yoshihiro*; Hirao, Norie; Shimoyama, Iwao; Naramoto, Hiroshi*; Baba, Yuji; Sorokin, P. B.*; et al.

Nano Research, 8(5), p.1535 - 1545, 2015/05

https://doi.org/10.1007/s12274-014-0640-7

Atomic structure and physical properties of fused porphyrin nanoclusters

Avramov, P. V.*; Kuzubov, A. A.*; Sakai, Seiji; Otomo, Manabu*; Entani, Shiro; Matsumoto, Yoshihiro*; Eleseeva, N. S.*; Pomogaev, V. A.*; Naramoto, Hiroshi*

Journal of Porphyrins and Phthalocyanines, 18(7), p.552 - 568, 2014/07

https://doi.org/10.1142/S1088424614500291

RBS study of disordering of FeMnSi/Ge(111) heteroepitaxial interfaces

Noguchi, Masaya*; Hirata, Tomoaki*; Kawakubo, Yuki*; Narumi, Kazumasa; Sakai, Seiji; Maeda, Yoshihito

Physica Status Solidi (C), 10(12), p.1732 - 1734, 2013/12

https://doi.org/10.1002/pssc.201300380

Spin orientation transition across the single-layer graphene/nickel thin film interface

Matsumoto, Yoshihiro; Entani, Shiro; Koide, Akihiro*; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Fujikawa, Takashi*; Sakai, Seiji

Journal of Materials Chemistry C, 1(35), p.5533 - 5537, 2013/09

https://doi.org/10.1039/C3TC30872C

In-plane orientation control of 2,7-diphenyl[1]benzothieno[3,2-][1]benzothiophene monolayer on bismuth-terminated Si(111) vicinal surfaces with wettability optimization

Otomo, Manabu; Tsuchida, Yuya*; Muraya, Naoki*; Yanase, Takashi*; Sakai, Seiji; Yonezawa, Tetsu*; Nagahama, Taro*; Hasegawa, Tetsuya*; Shimada, Toshihiro*

Journal of Physical Chemistry C, 117(22), p.11555 - 11561, 2013/06

https://doi.org/10.1021/jp3117837

We report in-plane orientation control of newly developed high-mobility organic semiconductor: 2,7-diphenyl[1]benzothieno[3,2-][1]benzothiophene (DPh-BTBT). As previously reported on monolayer pentacene, it was revealed that bunched steps on vicinal Si(111) with bismuth termination break the surface symmetry and reduce three-fold symmetry of DPh-BTBT grains into quasi-single orientation. Interestingly, the critical step height necessary for the orientation control was different from that of pentacene. We examined several mechanisms of orientation control and concluded that the facet nano structure fabricated by step bunching is working as an anisotropic template. We will also show the wettability control of bismuth terminated silicon surface and show that the growth mode of DPh-BTBT is dependent on the surface nanostructure of Bi-Si.