Search

Your search keyword '"Takeuchi, Daisuke"' showing total 919 results
Start Over Author "Takeuchi, Daisuke"
919 results on '"Takeuchi, Daisuke"'

1. Atomic observation on diamond (001) surfaces with non-contact atomic force microscopy

Author

Zhang, Runnan, Yasui, Yuuki, Fukuda, Masahiro, Ozaki, Taisuke, Ogura, Masahiko, Makino, Toshiharu, Takeuchi, Daisuke, and Sugimoto, Yoshiaki

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

To achieve atomic-level characterization of the diamond (001) surface, persistent efforts have been made over the past few decades. The motivation behind the pursuit extends beyond investigating surface defects and adsorbates; it also involves unraveling the mystery of the smooth growth of diamond. However, the inherently low conductivity and the short C-C bonds render atomic resolution imaging exceptionally challenging. Here, we successfully overcame these challenges by employing non-contact atomic force microscopy with reactive Si tips. Atomic resolution imaging was achieved even at room temperature. With density-functional-theory calculations, we clarified that the critical factors for atomic resolution are in the formation of tilted C-Si bonds between scanning probes and surfaces, along with reordering of the surface C-C dimers. Implications of the findings extend beyond the realm of surface characterization. The present atomic-resolution microscopies drive future advancements in diamond technologies by providing avenues for identifying dopants and constructing artificial nanostructures.

Published
2024

2. Tight Exponential Strong Converse for Source Coding Problem with Encoded Side Information

Author

Takeuchi, Daisuke and Watanabe, Shun

Subjects
Computer Science - Information Theory
Abstract

The source coding problem with encoded side information is considered. A lower bound on the strong converse exponent has been derived by Oohama, but its tightness has not been clarified. In this paper, we derive a tight strong converse exponent. For the special case such that the side-information does not exists, we demonstrate that our tight exponent of the WAK problem reduces to the known tight expression of that special case while Oohama's lower bound is strictly loose. The converse part is proved by a judicious use of the change-of-measure argument, which was introduced by Gu-Effros and further developed by Tyagi-Watanabe. Interestingly, the soft Markov constraint, which was introduced by Oohama as a proof technique, is naturally incorporated into the characterization of the exponent. A technical innovation of this paper is recognizing that the soft Markov constraint is a part of the exponent, rather than a penalty term that should be vanished. In fact, via numerical experiment, we provide evidence that the soft Markov constraint is strictly positive. The achievability part is derived by a careful analysis of the type argument; however, unlike the conventional analysis for the achievable rate region, we need to derive the soft Markov constraint in the analysis of the correct probability. Furthermore, we present an application of our derivation of strong converse exponent to the privacy amplification., Comment: 15 pages, 5 figures; v2 adds an analysis of full-side information case; v3 adds numerical experiment and an application to the privacy amplification

Published
2022

11. Impact of water vapor annealing treatments on Al2O3/diamond interface.

Author

Zhang, Xufang, Matsumoto, Tsubasa, Sometani, Mitsuru, Ogura, Masahiko, Kato, Hiromitsu, Makino, Toshiharu, Takeuchi, Daisuke, Inokuma, Takao, Yamasaki, Satoshi, and Tokuda, Norio

Subjects
WATER vapor, DIAMONDS, DIAMOND surfaces, FIELD-effect transistors, VALENCE bands, DENSITY of states
Abstract

Our group developed the first inversion-type p-channel diamond metal–oxide–semiconductor field-effect transistor, which featured normally off properties by employing water vapor annealing treatments for the oxygen-terminated diamond surface. Despite the comprehensive device-grade characterization, the impact of water vapor annealing treatments on the Al2O3/diamond interface has not been investigated in detail. In this work, we fabricated four diamond metal–oxide–semiconductor (MOS) capacitors without and with water vapor annealing treatments for various times of 30 min, 1 h, and 2 h and conducted the cycle capacitance–voltage (C–V) and simultaneous C–V measurements. The large cycle C–V shift existed in the sample without water vapor annealing treatment, whereas it was significantly suppressed by water vapor annealing treatments, indicating the effective passivation of the traps with long time constants. The simultaneous C–V results showed a similar trend that the frequency dispersion of the simultaneous C–V was dramatically reduced with water vapor annealing treatments, and the interface quality of Al2O3/diamond had a slight dependence on the water vapor annealing times. Based on simultaneous C–V measurements, the interface state density (Dit) at an energy level of 0.2–0.6 eV from the valence band edge of diamond was extracted for the different MOS capacitors. The Dit was reduced by one order of magnitude with water vapor annealing treatments, and it almost did not change with the water vapor annealing times. Besides, the flat band voltage shift and effective fixed charge were also dramatically reduced by water vapor annealing. The possible physical reason for the interface improvement by water vapor annealing treatments was discussed. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

12. Synthesis and thermal-optical behaviors of non-conventional benzidine-based oligomers containing tetrasubstituted Schiff base arms.

Author

Salwadi, Nur Fatin Liyana, Yeap, Guan-Yeow, Yamazaki, Shohei, Kimura, Nanako, and Takeuchi, Daisuke

Subjects
POLARIZING microscopes, OPTICAL microscopes, OLIGOMERS, ALKOXY compounds, LOW temperatures, SCHIFF bases
Abstract

New benzidine-based oligomers containing four Schiff base arms with terminal alkoxy chains CnH2n+1 (n = 6–12) were characterized by elemental, spectroscopic (UV, FT-IR, and NMR) and DFT techniques. The thermal-optical behaviors were observed using differential calorimetry and polarized optical microscope. Upon heating the molecules with n = 8, 10, and 12 exhibited endothermic peaks characteristic of the crystal-soft crystal B transition in addition to crystal-crystal subphases. It can be generalized that all oligomers showed unusual curing temperature of which the compounds with odd alkoxy chain carbon numbers possess lower curing temperatures in comparison with the analogous compounds of even parity. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

24. Olefin Polymerization with Non-metallocene Catalysts (Late Transition Metals)

Author

Takeuchi, Daisuke, Landfester, Katharina, Series editor, Salzer, Reiner, Series editor, Carpenter, Barry, Series editor, Ceroni, Paola, Series editor, Mahlke, Claudia, Series editor, Leszczynski, Jerzy, Series editor, Kirchner, Barbara, Series editor, Luh, Tien-Yau, Series editor, Polfer, Nicolas C., Series editor, and Osakada, Kohtaro, editor

Published
2014
Full Text
View/download PDF

25. Oligomerization of Olefins

Author

Takeuchi, Daisuke, Osakada, Kohtaro, Landfester, Katharina, Series editor, Salzer, Reiner, Series editor, Carpenter, Barry, Series editor, Ceroni, Paola, Series editor, Mahlke, Claudia, Series editor, Leszczynski, Jerzy, Series editor, Kirchner, Barbara, Series editor, Luh, Tien-Yau, Series editor, Polfer, Nicolas C., Series editor, and Osakada, Kohtaro, editor

Published
2014
Full Text
View/download PDF

28. Ethylene polymerization using N-Heterocyclic carbene complexes of silver and aluminum

Author

Kimura, Nanako, Takeuchi, Daisuke, Ogura, Sayoko, Takazawa, Ayaka, Kakiage, Masaki, Yamanobe, Takeshi, and Uehara, Hiroki

Abstract

Various transition metal catalysts have been utilized for ethylene polymerization. Silver catalysts have attracted less attention as the catalysts, but are potential for production of high molecular weight polyethylene. Herein, we report that silver complexes with various N-heterocyclic carbene (NHC) ligands in combination with modified methylaluminoxane (MMAO) afford polyethylene with high molecular weight (melting point over 140°C). SEM observation showed that the produced polyethylene has ultra-high molecular weight. NMR investigation of the reaction between the silver complexes with organoaluminums indicate that the NHC ligands transfer from the silver complex to aluminum to produce NHC aluminum complexes. Ph3C[B(C6F5)4] abstract methyl group from the NHC aluminum complex to afford cationic aluminum complex. The NHC aluminum complex promoted ethylene polymerization in the presence of Ph3C[B(C6F5)4] and organoaluminums. NHC ligand also promoted ethylene polymerization in combination with MMAO to produce polyethylene with high melting point (140.7°C). Thus, the aluminum complexes are considered to be the actual active species in silver-catalyzed ethylene polymerization.

Published
2023
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results