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514 results on '"Morikawa, Yoshitada"'

151. Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

Author

60324977, Matsui, Fumihiko, Eguchi, Ritsuko, Nishiyama, Saki, Izumi, Masanari, Uesugi, Eri, Goto, Hidenori, 10373523, Matsushita, Tomohiro, Sugita, Kenji, 20126121, Daimon, Hiroshi, Hamamoto, Yuji, Hamada, Ikutaro, Morikawa, Yoshitada, Kubozono, Yoshihiro, 60324977, Matsui, Fumihiko, Eguchi, Ritsuko, Nishiyama, Saki, Izumi, Masanari, Uesugi, Eri, Goto, Hidenori, 10373523, Matsushita, Tomohiro, Sugita, Kenji, 20126121, Daimon, Hiroshi, Hamamoto, Yuji, Hamada, Ikutaro, Morikawa, Yoshitada, and Kubozono, Yoshihiro

Abstract

application/pdf, From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K)C8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3 Å and 5.7 Å above the photoelectron emitter C atom and the stacking structures were determined as AB- and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2 × 2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K)C8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms.

Published
2016

152. Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

Author

Matsui, Fumihiko, 322, 60324977, Eguchi, Ritsuko, Nishiyama, Saki, 27439, Izumi, Masanari, 27440, Uesugi, Eri, 27441, Goto, Hidenori, 27442, Matsushita, Tomohiro, 194, 10373523, Sugita, Kenji, 27443, Daimon, Hiroshi, 29, 20126121, Hamamoto, Yuji, 27444, Hamada, Ikutaro, 27445, Morikawa, Yoshitada, 27446, Kubozono, Yoshihiro, 27447, Matsui, Fumihiko, 322, 60324977, Eguchi, Ritsuko, Nishiyama, Saki, 27439, Izumi, Masanari, 27440, Uesugi, Eri, 27441, Goto, Hidenori, 27442, Matsushita, Tomohiro, 194, 10373523, Sugita, Kenji, 27443, Daimon, Hiroshi, 29, 20126121, Hamamoto, Yuji, 27444, Hamada, Ikutaro, 27445, Morikawa, Yoshitada, 27446, Kubozono, Yoshihiro, and 27447

Abstract

From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K)C8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3?A and 5.7?A above the photoelectron emitter C atom and the stacking structures were determined as AB- and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2?×?2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K)C8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms., journal article

Published
2016

157. Diffusion mechanism of Na ion–polaron complex in potential cathode materials NaVOPO4 and VOPO4 for rechargeable sodium-ion batteries.

Author

Luong, Huu Duc, Pham, Thi Dung, Morikawa, Yoshitada, Shibutani, Yoji, and Dinh, Van An

Abstract

Using the density functional method, we investigated the crystal and electronic structures and the electrochemical properties of NaxVOPO4 (x = 0, 1) and explored the diffusion mechanism of Na ions in these materials. The van der Waals interaction was also taken into account to include the non-local electron correlation in the calculation of structural parameters and voltage. The diffusion of Na ions is treated as a process of the Na vacancy–positive small polaron complex in NaVOPO4 and the Na ion–negative small polaron complex in VOPO4, respectively. During the charging (discharging) process, the removal (insertion) of a Na ion would result in the formation of a positive (negative) small polaron at one of the two first nearest vanadium sites to the Na vacancy. Three elementary diffusion processes, including the single, crossing and parallel diffusion processes, are explored. It is found that the [010] direction is preferable for Na ion diffusion in both the charging and discharging processes. The influence of small polaron migration on Na ion diffusion in the charging state is negligible, whereas such effect is considerably strong in the discharging process. Moreover, while three elementary diffusion processes in NaVOPO4 require the same energy, the parallel diffusion process in VOPO4 is not preferred. The diffusion of Na vacancy accompanied by a positive polaron in the full charging process requires an activation energy of 395 meV, while the diffusion of Na ion accompanied by a negative polaron in the discharging state, VOPO4, has a higher activation energy of 627 meV. With a voltage and activation barrier similar to that of the olivine phosphate LiFePO4, these sodium-based materials are expected to be promising cathode materials for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Published
2018
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158. Enhancement of CO2 adsorption on oxygen-functionalized epitaxial graphene surface under near-ambient conditions.

Author

Yamamoto, Susumu, Takeuchi, Kaori, Hamamoto, Yuji, Liu, Ro-Ya, Shiozawa, Yuichiro, KoitayaPresent address: Japan Science and Technology Agency (JST) Precursory Research for Embryonic Science and Technology (PRESTO) 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan., Takanori, Someya, Takashi, Tashima, Keiichiro, Fukidome, Hirokazu, Mukai, Kozo, Yoshimoto, Shinya, Suemitsu, Maki, Morikawa, Yoshitada, Yoshinobu, Jun, and Matsuda, Iwao

Abstract

The functionalization of graphene is important in practical applications of graphene, such as in catalysts. However, the experimental study of the interactions of adsorbed molecules with functionalized graphene is difficult under ambient conditions at which catalysts are operated. Here, the adsorption of CO2 on an oxygen-functionalized epitaxial graphene surface was studied under near-ambient conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). The oxygen-functionalization of graphene is achieved in situ by the photo-induced dissociation of CO2 with X-rays on graphene in a CO2 gas atmosphere. The oxygen species on the graphene surface is identified as the epoxy group by XPS binding energies and thermal stability. Under near-ambient conditions of 1.6 mbar CO2 gas pressure and 175 K sample temperature, CO2 molecules are not adsorbed on the pristine graphene, but are adsorbed on the oxygen-functionalized graphene surface. The increase in the adsorption energy of CO2 on the oxygen-functionalized graphene surface is supported by first-principles calculations with the van der Waals density functional (vdW-DF) method. The adsorption of CO2 on the oxygen-functionalized graphene surface is enhanced by both the electrostatic interactions between the CO2 and the epoxy group and the vdW interactions between the CO2 and graphene. The detailed understanding of the interaction between CO2 and the oxygen-functionalized graphene surface obtained in this study may assist in developing guidelines for designing novel graphene-based catalysts. [ABSTRACT FROM AUTHOR]

Published
2018
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159. Vibration-driven reaction of CO2on Cu surfaces via Eley–Rideal-type mechanism

Author

Quan, Jiamei, Muttaqien, Fahdzi, Kondo, Takahiro, Kozarashi, Taijun, Mogi, Tomoyasu, Imabayashi, Takumi, Hamamoto, Yuji, Inagaki, Kouji, Hamada, Ikutaro, Morikawa, Yoshitada, and Nakamura, Junji

Abstract

Understanding gas–surface reaction dynamics, such as the rupture and formation of bonds in vibrationally and translationally excited (‘hot’) molecules, is important to provide mechanistic insight into heterogeneous catalytic processes. Although it has been established that such excitation can affect the reactions occurring via dissociative mechanisms, for associative mechanisms—in which the gas-phase reactant collides directly with a surface-adsorbed species—only translational excitation has been observed to affect reactivity. Here we report a bond-formation reaction that is driven by the vibrational energy of reactant molecules and occurs via an (associative) Eley–Rideal-type mechanism, in which the reaction takes place in a single collision. Hot CO2in a molecular beam is found to react with pre-adsorbed hydrogen atoms directly on cold Cu(111) and Cu(100) surfaces to form formate adspecies. The vibrational energy of CO2is more effective at promoting the reaction than translational energy, the reaction rate is independent of the surface temperature and the experimental results are consistent with density functional theory calculations. Vibrational and translational energies have previously been observed to promote reactions at surfaces occurring via dissociative mechanisms. Now, it has been shown that the reaction of CO2with surface-adsorbed atomic hydrogen—which occurs via an associative (Eley–Rideal-type) mechanism—can be driven by vibrationally exciting CO2.

Published
2019
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161. Desorption dynamics of CO2 from formate decomposition on Cu(111).

Author

Muttaqien, Fahdzi, Oshima, Hiroyuki, Hamamoto, Yuji, Inagaki, Kouji, Hamada, Ikutaro, and Morikawa, Yoshitada

Subjects
AB initio quantum chemistry methods, MOLECULAR dynamics, FORMATES, CARBON dioxide, VAN der Waals forces, DENSITY functionals
Abstract

We performed ab initio molecular dynamics analysis of formate decomposition to CO2 and H on a Cu(111) surface using van der Waals density functionals. Our analysis shows that the desorbed CO2 has approximately twice larger bending vibrational energy than the translational, rotational, and stretching vibrational energies. Since formate synthesis, the reverse reaction of formate decomposition, has been suggested experimentally to occur via the Eley–Rideal mechanism, our results indicate that the formate synthesis can be enhanced if the bending vibrational mode of CO2 is excited rather than the translational and/or stretching vibrational modes. Detailed information on the energy distribution of desorbed CO2 as a formate decomposition product may provide new insights for improving the catalytic activity of formate synthesis. [ABSTRACT FROM AUTHOR]

Published
2017
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165. ZnO with engineered surface defects as a competent photocatalyst for CO2photoreduction into valuable fuels under simulated solar light irradiation

Author

Mahmud, Rabiatul Aliah, Ahmed Ali, Khozema, Putri, Lutfi Kurnianditia, Morikawa, Yoshitada, and Mohamed, Abdul Rahman

Abstract

Photocatalysis is one of the eco-friendly methods in greenhouse gases abatement by utilizing renewable resources such as sunlight. This study examined defective ZnO nanoparticles that serve as carbon dioxide (CO2) adsorption and activation sites in photocatalytic reactions. The defective ZnO nanoparticles were synthesized via a facile precipitation-hydrothermal method by only controlling the concentration of NaOH as the precipitating agent. The rough surface of ZnO were formed due to the heating treatment, where it conveniently removed the attached inorganic molecules on ZnO surfaces. The roughness surface of ZnO was observed by using Transmission Electron Microscopy (TEM) analysis, in which the pores with bright spot can be observed. Additionally, the defects originating from oxygen vacancies (VO), zinc interstitials (Zni) and carbonates groups (CO32−)was successfully optimized over variation of NaOH concentrations proven by Photoluminescence (PL) and X-Ray Photoelectron Spectroscopy (XPS) analysis. Here, 1 : 4 ZnO exhibited the highest CH4yield (1.3 ×10-1µmol) and 3-fold production than commercial ZnO (4.8 × 10-2µmol). The reusability of 1 : 4 ZnO was demonstrated by conducting 4 cycles of stability test, which revealed a robust photocatalyst of 7.7% performance reduction after 4th cycle. A schematic mechanism pertaining to the novel defective ZnO nanoparticles in CO2photoreduction to valuable fuels was proposed in this study, which undoubtedly will contribute a positive effect to industry’s long-term sustainability.

Published
2023
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169. Termination dependence of surface stacking at 4H-SiC (0001) -1×1: Density functional theory calculations

Author

Hara, Hideyuki, 1000080358184, Morikawa, Yoshitada, 1000040252598, Sano, Yasuhisa, 1000010174575, Yamauchi, Kazuto, Hara, Hideyuki, 1000080358184, Morikawa, Yoshitada, 1000040252598, Sano, Yasuhisa, 1000010174575, and Yamauchi, Kazuto

Abstract

Hideyuki Hara, Yoshitada Morikawa, Yasuhisa Sano, and Kazuto Yamauchi Phys. Rev. B 79, 153306 (2009)., We study the effect of adsorbates on the relative stability of hexagonal and cubic stacking sequences at the topmost SiC bilayers of 4H-SiC (0001) -1×1 surfaces using first-principles calculations. We investigate F-terminated, OH-terminated, H-terminated, and clean surfaces, and in all cases, the cubic structure is more stable than the hexagonal structure. The energy difference between the two structures, however, significantly depends on adsorbates and is largest on the clean surface while it is smallest on the H-terminated surface. Stabilization of the cubic structure at F-terminated and OH-terminated surfaces is in contradiction to a simple argument based on the electrostatic interaction and we attribute it to orbital hybridization between occupied states of adsorbates and unoccupied states of the substrate surface. The present results suggest a possible means of controlling step bunching and the SiC stacking sequence by surface adsorbates. © 2009 The American Physical Society.

Published
2009

182. Theoretical study of n-alkane adsorption on metal surfaces

Author

Morikawa, Yoshitada, Ishii, Hisao, Seki, Kazuhiko, Morikawa, Yoshitada, Ishii, Hisao, and Seki, Kazuhiko

Abstract

The interaction between n-alkane and metal surfaces has been studied by means of density-functional theoretical calculations within a generalized gradient approximation (GGA). We demonstrate that although the GGA cannot reproduce the physisorption energy well, our calculations can reproduce the experimentally observed work-function change and softening of the CH stretching mode reasonably well. We also show that the most significant factor determining their dependence on metal substrates is the distance between the molecule and the substrate.

Published
2004

183. Adsorption of CO2on Graphene: A Combined TPD, XPS, and vdW-DF Study

Author

Takeuchi, Kaori, Yamamoto, Susumu, Hamamoto, Yuji, Shiozawa, Yuichiro, Tashima, Keiichiro, Fukidome, Hirokazu, Koitaya, Takanori, Mukai, Kozo, Yoshimoto, Shinya, Suemitsu, Maki, Morikawa, Yoshitada, Yoshinobu, Jun, and Matsuda, Iwao

Abstract

The adsorption of CO2molecules on monolayer epitaxial graphene on a SiC(0001) surface at 30 K was investigated by temperature-programmed desorption and X-ray photoelectron spectroscopy. The desorption energy of CO2on graphene was determined to be (30.1–25.1) ± 1.5 kJ/mol at low coverages and approached the sublimation energy of dry ice (27–25 kJ/mol) with increasing the coverage. The adsorption of CO2on graphene was thus categorized into physisorption, which was further supported by the binding energies of CO2in core-level spectra. The adsorption states of CO2on graphene were theoretically examined by means of the van der Waals density functional (vdW-DF) method that includes nonlocal correlation. The experimental desorption energy was successfully reproduced with high accuracy using vdW-DF calculations; the optB86b-vdW functional was found to be most appropriate to reproduce the desorption energy in the present system.

Published
2017
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