71 results on '"Yoshitake Toda"'
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2. Hydride-ion conductivity and enhanced atmospheric stability of hydride-fluoride SrMgH4–xFx
- Author
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Nur Ayu, Naoki Matsui, Guangzhong Jiang, Takashi Hirose, Takashi Itoh, Takeya Mezaki, Yoshitake Toda, Kota Suzuki, Masaaki Hirayama, Takashi Saito, Takashi Kamiyama, and Ryoji Kanno
- Abstract
Few hydride-ion conductors exhibit chemical stability and hydride-ion conductivity, which are essential properties in developing hydride-ion-driven electrochemical devices. Herein, we successfully synthesized a novel hydride-fluoride system, SrMgH4 − xFx, possessing high atmospheric stability and relatively high hydride-ion conductivity. The correlation between anion composition, structure, hydride-ion conductive properties, and atmospheric stability in the hydride-fluoride system was elucidated. The doping of fluoride ions at hydrogen sites resulted in high atmospheric stabilities while retaining hydride-ion conductivities of SrMgH2F2 and SrMgHF3 of 3.4 × 10− 4 and 1.4 × 10− 4 S cm− 1 at 400°C, respectively. For SrMgHF3, in particular, 84% ionic conductivity was retained after exposure to the atmosphere. Hydride-fluoride systems enable the balancing of the ionic conductivity and atmospheric stability by controlling the H/F ratio. Our findings provide insight for use in effective material design to expand the use of metal hydrides in practical solid electrolytes for use in hydride-ion-driven devices.
- Published
- 2022
3. Synthesis, structure, and electrical conductivity of Sr2LiH2N nitride hydride
- Author
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Guangzhong Jiang, Naoki Matsui, Takeya Mezaki, Yoshitake Toda, Kota Suzuki, Masaaki Hirayama, Takashi Saito, Takashi Kamiyama, and Ryoji Kanno
- Subjects
Inorganic Chemistry ,Materials Chemistry ,Ceramics and Composites ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2022
4. Optical and Electrical Properties of Perovskite Variant (CH3NH3)2SnI6
- Author
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Hideo Hosono, Yoshitake Toda, and Fuji Funabiki
- Subjects
Electron mobility ,Materials science ,business.industry ,Photovoltaic system ,02 engineering and technology ,Conductivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,General Energy ,Semiconductor ,law ,Solar cell ,Optoelectronics ,Direct and indirect band gaps ,Crystallite ,Physical and Theoretical Chemistry ,0210 nano-technology ,business ,Perovskite (structure) - Abstract
In recent years, lead halide perovskites have emerged as excellent photovoltaic materials for solar power generation. However, because they are toxic and chemically unstable in air, lead-free perovskites are also being investigated. In this study, the perovskite variant (CH3NH3)2SnI6 was studied. Polycrystalline films of (CH3NH3)2SnI6 were prepared using the thermal evaporation method. The films had a direct band gap of 1.81 eV with a strong absorption coefficient of ∼7 × 104 cm–1. In addition, the films were n-type with a carrier concentration of ∼2 × 1015 cm–3 and an electron mobility of ∼3 cm2 V–1 s–1. Moreover, the conductivity was increased by a factor of 4 under simulated solar illumination (100 mW cm–2). These results indicate that (CH3NH3)2SnI6 is a lead-free optical semiconductor suitable for solar cell applications.
- Published
- 2018
5. High Electron Density on Ru in Intermetallic YRu2: The Application to Catalyst for Ammonia Synthesis
- Author
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Yasuhiro Niwa, Masaaki Kitano, Hiroshi Mizoguchi, Yoshitake Toda, Tomofumi Tada, Hideo Hosono, Takaya Ogawa, Yasukazu Kobayashi, and Hitoshi Abe
- Subjects
Electron density ,Materials science ,Hydrogen ,Inorganic chemistry ,Intermetallic ,chemistry.chemical_element ,02 engineering and technology ,Laves phase ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,Ruthenium ,Ammonia production ,Electron transfer ,General Energy ,chemistry ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Ruthenium is the most effective catalyst reported to date for ammonia synthesis under mild conditions, especially when an electron promoter is used. However, electron donation from the promoter has not been sufficient because the promoter contacts with Ru only through its surface. Here, we report a Laves phase intermetallic bulk catalyst, YRu2, which has higher electron density on Ru. This is derived from large electron transfer from Y to Ru, which is first confirmed by X-ray absorption fine structure measurements and theoretical calculations. In addition, YRu2 has high hydrogen solubilities leading to suppression of hydrogen poisoning, a common drawback of Ru-based catalysts. Consequently, YRu2 exhibits higher catalytic activity for ammonia synthesis over 300 times that with pure ruthenium. The present results suggest a simple concept for ammonia synthesis: Laves phase intermetallic compounds of Ru and more electropositive metals are more efficient catalysts than pure Ru because of the large electron pro...
- Published
- 2018
6. Multiple Roles of Hydrogen Treatments in Amorphous In-Ga-Zn-O Films
- Author
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Toshio Kamiya, Hidenori Hiramatsu, Hideo Hosono, Keisuke Ide, Haochun Tang, Naoki Ohashi, Hideya Kumomi, Yosuke Kishida, Satoru Matsuishi, Yoshitake Toda, and Shigenori Ueda
- Subjects
010302 applied physics ,Materials science ,Chemical engineering ,Hydrogen ,chemistry ,0103 physical sciences ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Amorphous solid - Published
- 2017
7. Difficulty of carrier generation in orthorhombic PbO.
- Author
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Min Liao, Seiji Takemoto, Zewen Xiao, Yoshitake Toda, Tomofumi Tada, Shigenori Ueda, Toshio Kamiya, and Hideo Hosono
- Subjects
ORTHORHOMBIC crystal system ,CRYSTAL structure ,LEAD oxides ,PULSED laser deposition ,ANNEALING of metals ,DENSITY functional theory - Abstract
Polycrystalline β-PbO films were grown by pulsed laser deposition in atmospheres ranging from oxygen-poor (the oxygen pressure of 0.01 Pa) to oxygen-rich (13 Pa) conditions, and the oxygen chemical potential was further enhanced by ozone annealing to examine hole doping. It was found that each of the as-grown β-PbO films showed poor electrical conductivity, σ?1.4?×?10
-7 S cm-1 , regardless of the oxygen pressure. The density functional calculations revealed that native defects including Pb and O vacancies have deep transition levels and extremely high formation enthalpies, which indicates difficulty of carrier generation in β-PbO and explains the experimentally observed poor electrical conductivity. The analysis of the electronic structures showed that the interaction between Pb 6s and O 2p orbitals is weak due to the deep energy level of Pb 6s and does not raise the valence band maximum (VBM) level unlike that observed in SnO, which is also supported by ultraviolet photoemission spectroscopy measurements. The deep acceptor transition levels of the native defects are attributed to the deep VBM of β-PbO. On the other hand, annealing β-PbO films in reactive oxygen-containing atmospheres (i.e., O3 ) led to a significantly enhanced electrical conductivity (i.e., σ>7.1?×?10² S cm-1 ) but it is the result of the formation of an n-type PbO2 phase because oxygen chemical potential exceeded the phase boundary limit. The striking difference in carrier generation between PbO and SnO is discussed based on the electronic structures calculated by density functional theory. [ABSTRACT FROM AUTHOR]- Published
- 2016
- Full Text
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8. Ultrawide band gap amorphous oxide semiconductor, Ga–Zn–O
- Author
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Takumi Sekiya, Junghwan Kim, Yoshitake Toda, Norihiko Miyokawa, Toshio Kamiya, Hideo Hosono, Hidenori Hiramatsu, and Keisuke Ide
- Subjects
Materials science ,Photoemission spectroscopy ,Band gap ,02 engineering and technology ,Electron ,Integrated circuit ,medicine.disease_cause ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Materials Chemistry ,medicine ,010302 applied physics ,business.industry ,Metals and Alloys ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Flexible electronics ,Semimetal ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,Ionization energy ,0210 nano-technology ,business ,Ultraviolet - Abstract
We fabricated amorphous oxide semiconductor films, a-(Ga1–xZnx)Oy, at room temperature on glass, which have widely tunable band gaps (Eg) ranging from 3.47–4.12 eV. The highest electron Hall mobility ~ 7 cm2 V− 1 s− 1 was obtained for Eg = ~ 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in Eg with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region.
- Published
- 2016
9. Water Durable Electride Y5Si3: Electronic Structure and Catalytic Activity for Ammonia Synthesis
- Author
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Yoshitake Toda, Jiang Li, Tomofumi Tada, Toshiharu Yokoyama, Yangfan Lu, Hideo Hosono, Masaaki Kitano, and Shigenori Ueda
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Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Activation energy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Nitrogen ,Catalysis ,Dissociation (chemistry) ,0104 chemical sciences ,Ammonia production ,Metal ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,visual_art ,visual_art.visual_art_medium ,Electride ,Chemical stability ,0210 nano-technology - Abstract
We report an air and water stable electride Y5Si3 and its catalytic activity for direct ammonia synthesis. It crystallizes in the Mn5Si3-type structure and confines 0.79/f.u. anionic electrons in the quasi-one-dimensional holes. These anionic electrons strongly hybridize with yttrium 4d electrons, giving rise to improved chemical stability. The ammonia synthesis rate using Ru(7.8 wt %)-loaded Y5Si3 was as high as 1.9 mmol/g/h under 0.1 MPa and at 400 °C with activation energy of ∼50 kJ/mol. Its strong electron-donating ability to Ru metal of Y5Si3 is considered to enhance nitrogen dissociation and reduce the activation energy of ammonia synthesis reaction. Catalytic activity was not suppressed even after Y5Si3, once dipped into water, was used as the catalyst promoter. These findings provide novel insights into the design of simple catalysts for ammonia synthesis.
- Published
- 2016
10. Chemical Design and Example of Transparent Bipolar Semiconductors
- Author
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Hideo Hosono, Takeshi Arai, Shigenori Ueda, Yoshitake Toda, Junghwan Kim, and Soshi Iimura
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business.industry ,Chemistry ,Doping ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Transparency (human–computer interaction) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Engineering physics ,Catalysis ,Controllability ,Tetragonal crystal system ,Colloid and Surface Chemistry ,Semiconductor ,Electrical resistivity and conductivity ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Electronic band structure ,business ,Realization (systems) - Abstract
Transparent bipolar semiconductors (TBSCs) are in demand for transparent electronics to serve as the basis for next generation optoelectronic devices. However, the poor carrier controllability in wide-bandgap materials makes the realization of a bipolar nature difficult. Only two materials, CuInO2 and SnO, have been reported as TBSCs. To satisfy demand for the coexistence of transparency and bipolarity, we propose a design concept with three strategies; choice of early transition metals (eTM) such as Y3+ and Zr4+ for improving controllability of carrier doping, design of chemical bonds to obtain an appropriate band structure for bipolar doping, and use of a forbidden band-edge transition to retain transparency. This approach is verified through a practical examination of a candidate material, tetragonal ZrOS, which is chosen by following the criteria. ZrOS exhibits an excellent controllability of the electrical conductivity (10–7–10–2 S cm–1), p- or n-type nature with ∼10–2 S cm–1 by Y or F doping, respec...
- Published
- 2017
11. Rattling of Oxygen Ions in a Sub-Nanometer-Sized Cage Converts Terahertz Radiation to Visible Light
- Author
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Eduard Khutoryan, Hideo Hosono, Ishiyama Shintaro, Peter V. Sushko, Toshitaka Idehara, Satoru Matsuishi, and Yoshitake Toda
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Photoluminescence ,Chemistry ,Terahertz radiation ,General Engineering ,General Physics and Astronomy ,02 engineering and technology ,Electron ,Radiation ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystal ,Ionization ,0103 physical sciences ,General Materials Science ,Atomic physics ,010306 general physics ,0210 nano-technology ,Excitation ,Visible spectrum - Abstract
A simple and robust approach to visualization of continuous wave terahertz (CW-THz) light would open up opportunities to couple physical phenomena that occur at fundamentally different energy scales. Here we demonstrate how nanoscale cages of Ca12Al14O33 crystal enable conversion of CW-THz radiation to visible light. These crystallographic cages are partially occupied with weakly bonded oxygen ions and give rise to a narrow conduction band that can be populated with localized, yet mobile electrons. CW-THz light excites a nearly stand-alone rattling motion of the encaged oxygen species, which promotes electron transfer from them to the neighboring vacant cages. When the power of CW-THz light reaches tens of watts, the coupling between forced rattling in the confined space, electronic excitation and ionization of oxygen species, and corresponding recombination processes result in emission of bright visible light.
- Published
- 2017
12. P-176L:Late-News Poster: Deposition and Structuring Processes of a Newly Developed Transparent Amorphous Oxide Semiconductor for the Electron Transport and Injection Layers of AM-OLEDs
- Author
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Yoshitake Toda, Satoru Fujitsu, Nobuhiro Nakamura, Eiji Matsuzaki, Hideo Hosono, Toshinari Watanabe, Junghwan Kim, Satoru Watanabe, and Naomichi Miyakawa
- Subjects
Amorphous oxide semiconductor ,Materials science ,business.industry ,OLED ,Optoelectronics ,Nanotechnology ,Electric transport ,Aperture ratio ,business ,Electron transport chain ,Structuring ,Deposition (law) - Abstract
Processes of a new transparent amorphous oxide semiconductor (TAOS) as ETL and EIL were developed. Conventional processes can be applied for the deposition and structuring of the new TAOS, which enables to fabricate inverted OLEDs. The new TAOS materials make it possible to realize thicker ETL, potentially giving impacts not only on yield, but also on higher aperture ratio and cost reduction by omitting resin banks.
- Published
- 2015
13. SnAs with the NaCl-type Structure: Type-I Superconductivity and Single Valence State of Sn
- Author
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Hikaru Sato, Yue Wang, Hideo Hosono, Hidenori Hiramatsu, Shigenori Ueda, and Yoshitake Toda
- Subjects
Superconductivity ,Valence (chemistry) ,Condensed matter physics ,Chemistry ,General Chemical Engineering ,General Chemistry ,Structure type ,Nonlinear Sciences::Chaotic Dynamics ,Condensed Matter::Materials Science ,Crystallography ,Condensed Matter::Superconductivity ,Lattice (order) ,Physics::Atomic and Molecular Clusters ,Materials Chemistry ,Condensed Matter::Strongly Correlated Electrons - Abstract
We examined the superconductivity of SnAs and the valence state of Sn in its lattice with an expectation that SnAs and related compounds with the NaCl-type structure might exhibit superconductivity...
- Published
- 2014
14. Two-Dimensional Transition-Metal Electride Y2C
- Author
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Shigenori Ueda, Hideo Hosono, Zewen Xiao, Satoru Matsuishi, Toshio Kamiya, Hechang Lei, Xiao Zhang, and Yoshitake Toda
- Subjects
chemistry.chemical_compound ,Materials science ,Transition metal ,chemistry ,General Chemical Engineering ,Inorganic chemistry ,Materials Chemistry ,Ionic crystal ,Electride ,General Chemistry ,Electron - Abstract
Electrides are ionic crystals in which the anionic electrons are confined to interstitial subnanometer-sized spaces. At present, the reported electrides only consist of main-group elements. Here, w...
- Published
- 2014
15. ARPES studies of the inverse perovskite Ca3PbO : Experimental confirmation of a candidate 3D Dirac fermion system
- Author
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Yukiko Obata, Koji Horiba, Yoshitake Toda, Ryu Yukawa, Hideo Hosono, Hiroshi Kumigashira, and Satoru Matsuishi
- Subjects
Physics ,Condensed matter physics ,Photoemission spectroscopy ,Fermi level ,Inverse ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Dirac fermion ,0103 physical sciences ,symbols ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Perovskite (structure) - Abstract
We investigate the band structure of the inverse perovskite ${\mathrm{Ca}}_{3}\mathrm{PbO}$, a candidate three-dimensional (3D) Dirac fermion material, through soft x-ray angle-resolved photoemission spectroscopy. Conelike band dispersions are observed for ${\mathrm{Ca}}_{3}\mathrm{PbO}$, in close agreement with the predictions of electronic structure calculations. We further demonstrate that chemical substitution of Bi for Pb is effective in tuning the Fermi level of ${\mathrm{Ca}}_{3}\mathrm{PbO}$ while leaving its electronic structure intact. Our study confirms that the inverse perovskite family provides a promising platform for the exploration of 3D Dirac fermion systems.
- Published
- 2017
16. Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs
- Author
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Hideo Hosono, Junghwan Kim, Yoshitake Toda, Satoru Watanabe, and Toshio Kamiya
- Subjects
010302 applied physics ,Organic electronics ,Multidisciplinary ,Materials science ,business.industry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Cathode ,Amorphous solid ,law.invention ,Anode ,chemistry.chemical_compound ,Semiconductor ,chemistry ,law ,0103 physical sciences ,Physical Sciences ,OLED ,Optoelectronics ,Electride ,0210 nano-technology ,business ,Ohmic contact - Abstract
Efficient electron transfer between a cathode and an active organic layer is one key to realizing high-performance organic devices, which require electron injection/transport materials with very low work functions. We developed two wide-bandgap amorphous (a-) oxide semiconductors, a-calcium aluminate electride (a-C12A7:e) and a-zinc silicate (a-ZSO). A-ZSO exhibits a low work function of 3.5 eV and high electron mobility of 1 cm2/(V · s); furthermore, it also forms an ohmic contact with not only conventional cathode materials but also anode materials. A-C12A7:e has an exceptionally low work function of 3.0 eV and is used to enhance the electron injection property from a-ZSO to an emission layer. The inverted electron-only and organic light-emitting diode (OLED) devices fabricated with these two materials exhibit excellent performance compared with the normal type with LiF/Al. This approach provides a solution to the problem of fabricating oxide thin-film transistor-driven OLEDs with both large size and high stability.
- Published
- 2016
17. P-177L: Late-News Poster : Highly Efficient Inverted OLEDs using A New Transparent Amorphous Oxide Semiconductor
- Author
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Junghwan Kim, Naomichi Miyakawa, Satoru Watanabe, Eiji Matsuzaki, Hideo Hosono, Toshio Kamiya, Nobuhiro Nakamura, and Yoshitake Toda
- Subjects
Transparency (projection) ,Amorphous oxide semiconductor ,Electron transport layer ,Materials science ,business.industry ,Electrode ,OLED ,Optoelectronics ,Low work function ,Chemical stability ,business ,Ohmic contact - Abstract
Highly efficient inverted OLED was fabricated by using a newly developed new transparent amorphous oxide semiconductor (TAOS) for an electron transport layer. This new TAOS has high mobility (˜1cm2/Vs), low work function (˜3.5 eV), sufficient chemical stability and high transparency, and can form Ohmic contact with conventional electrodes (ITO, Al, etc.).
- Published
- 2015
18. P.142L:Late-News Poster: Electron Injecting Material for OLEDs driven by Oxide TFTs: Amorphous C12A7 Electride
- Author
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Yoshitake Toda, Toshinari Watanabe, Setsuro Ito, Yudai Tomota, Hideo Hosono, Naomichi Miyakawa, Satoru Watanabe, Toshio Kamiya, and Kazuhiro Ito
- Subjects
Electron injection layer ,Materials science ,business.industry ,Oxide ,Electron ,Amorphous solid ,chemistry.chemical_compound ,chemistry ,OLED ,Electride ,Optoelectronics ,Work function ,Thin film ,business - Abstract
Transparent thin film of amorphous 12CaO·7Al2O3 electride, sputter-deposited at RT, having work function of 2.9 − 3.1 eV, was found to act as a good electron injection layer for OLED, and was adequate in combination with n-channel IGZO-TFTs.
- Published
- 2013
19. Dicalcium nitride as a two-dimensional electride with an anionic electron layer
- Author
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Hideo Hosono, Satoru Matsuishi, Kimoon Lee, Yoshitake Toda, and Sung Wng Kim
- Subjects
chemistry.chemical_compound ,Electron mobility ,Multidisciplinary ,Magnetoresistance ,Chemistry ,Electrical resistivity and conductivity ,Scattering ,Chemical physics ,Mean free path ,Electride ,Electron ,Nitride ,Atomic physics - Abstract
The ionic crystal Ca2N is shown to be an electride in terms of [Ca2N]+·e−, with diffusive two-dimensional transport in dense electron layers. The physical properties of electrides — ionic crystals in which electrons behave as anions — significantly depend on the topology of the confining cavity for anionic electrons. Thus, an essential step towards practical electride applications is to discover new confinement spaces with unique topologies. Confined two-dimensional electron layers have previously been achieved by artificially fabricating hetero-interface structures usually of semiconducting materials. Here the authors extend the range of materials demonstrating such behaviour to an electride, dicalcium nitride (Ca2N). This compound has ideal properties for electron confinement: a layered structure with appropriate interlayer spacing and a chemistry that allows for loosely bound electron layers without electron trapping. By providing a new material image for electrides, this work should lead to a series of two-dimensional electrides with unique physical properties. Recent studies suggest that electrides—ionic crystals in which electrons serve as anions—are not exceptional materials but rather a generalized form, particularly under high pressure1,2,3. The topology of the cavities confining anionic electrons determines their physical properties4. At present, reported confining sites consist only of zero-dimensional cavities or weakly linked channels4. Here we report a layered-structure electride of dicalcium nitride, Ca2N, which possesses two-dimensionally confined anionic electrons whose concentration agrees well with that for the chemical formula of [Ca2N]+·e−. Two-dimensional transport characteristics are demonstrated by a high electron mobility (520 cm2 V−1 s−1) and long mean scattering time (0.6 picoseconds) with a mean free path of 0.12 micrometres. The quadratic temperature dependence of the resistivity up to 120 Kelvin indicates the presence of an electron–electron interaction. A striking anisotropic magnetoresistance behaviour with respect to the direction of magnetic field (negative for the field perpendicular to the conducting plane and positive for the field parallel to it) is observed, confirming diffusive two-dimensional transport in dense electron layers. Additionally, band calculations support confinement of anionic electrons within the interlayer space, and photoemission measurements confirm anisotropic low work functions of 3.5 and 2.6 electronvolts, revealing the loosely bound nature of the anionic electrons. We conclude that Ca2N is a two-dimensional electride in terms of [Ca2N]+·e−.
- Published
- 2013
20. Photoemission study ofLaAlO3/SrTiO3andLaAlO3/Nb:SrTiO3: Insulator-insulator versus insulator-semiconductor interfaces
- Author
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Toshihiro Kobayashi, Tomofumi Susaki, Shigenori Ueda, Hideo Hosono, Kosuke Matsuzaki, and Yoshitake Toda
- Subjects
Materials science ,Semiconductor ,business.industry ,0103 physical sciences ,Optoelectronics ,02 engineering and technology ,Insulator (genetics) ,021001 nanoscience & nanotechnology ,010306 general physics ,0210 nano-technology ,business ,01 natural sciences - Published
- 2016
21. ChemInform Abstract: Water Durable Electride Y5Si3: Electronic Structure and Catalytic Activity for Ammonia Synthesis
- Author
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Jiang Li, Shigenori Ueda, Hideo Hosono, Yoshitake Toda, Toshiharu Yokoyama, Masaaki Kitano, Yangfan Lu, and Tomofumi Tada
- Subjects
Ammonia production ,chemistry.chemical_compound ,Chemical engineering ,Chemistry ,Electride ,General Medicine ,Electronic structure ,Powder xrd ,Catalysis - Abstract
The air and water stable title electride is characterized by powder XRD, transport, magnetic, and thermodynamic measurements, PES, and DFT calculations.
- Published
- 2016
22. Water Durable Electride Y₅Si₃: Electronic Structure and Catalytic Activity for Ammonia Synthesis
- Author
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Yangfan, Lu, Jiang, Li, Tomofumi, Tada, Yoshitake, Toda, Shigenori, Ueda, Toshiharu, Yokoyama, Masaaki, Kitano, and Hideo, Hosono
- Abstract
We report an air and water stable electride Y5Si3 and its catalytic activity for direct ammonia synthesis. It crystallizes in the Mn5Si3-type structure and confines 0.79/f.u. anionic electrons in the quasi-one-dimensional holes. These anionic electrons strongly hybridize with yttrium 4d electrons, giving rise to improved chemical stability. The ammonia synthesis rate using Ru(7.8 wt %)-loaded Y5Si3 was as high as 1.9 mmol/g/h under 0.1 MPa and at 400 °C with activation energy of ∼50 kJ/mol. Its strong electron-donating ability to Ru metal of Y5Si3 is considered to enhance nitrogen dissociation and reduce the activation energy of ammonia synthesis reaction. Catalytic activity was not suppressed even after Y5Si3, once dipped into water, was used as the catalyst promoter. These findings provide novel insights into the design of simple catalysts for ammonia synthesis.
- Published
- 2016
23. Difficulty of carrier generation in orthorhombic PbO
- Author
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Tomofumi Tada, Hideo Hosono, Seiji Takemoto, Zewen Xiao, Shigenori Ueda, Yoshitake Toda, Toshio Kamiya, and Min Liao
- Subjects
010302 applied physics ,Phase boundary ,Materials science ,Annealing (metallurgy) ,Doping ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Oxygen ,Pulsed laser deposition ,chemistry ,Electrical resistivity and conductivity ,0103 physical sciences ,Orthorhombic crystal system ,Crystallite ,0210 nano-technology - Abstract
Polycrystalline β-PbO films were grown by pulsed laser deposition in atmospheres ranging from oxygen-poor (the oxygen pressure of 0.01 Pa) to oxygen-rich (13 Pa) conditions, and the oxygen chemical potential was further enhanced by ozone annealing to examine hole doping. It was found that each of the as-grown β-PbO films showed poor electrical conductivity, σ 7.1 × 102 S cm−1) but it is the result of the formation of an n-type PbO2 phase because oxygen chemical potential exceeded the phase boundary limit. The striking difference in carrier generation between PbO and SnO is discussed based on the electronic structures calculated by density functional theory.
- Published
- 2016
24. Models of stoichiometric and oxygen-deficient surfaces of subnanoporous 12CaO·7Al 2 O 3
- Author
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Masahiro Hirano, Yoshitake Toda, Peter V. Sushko, Alexander L. Shluger, and Hideo Hosono
- Subjects
Band gap ,General Mathematics ,General Engineering ,Oxide ,General Physics and Astronomy ,Electronic structure ,Electron ,Metal ,chemistry.chemical_compound ,chemistry ,Chemical physics ,Lattice (order) ,visual_art ,visual_art.visual_art_medium ,Electride ,Atomic physics ,Stoichiometry - Abstract
Surface structures of stoichiometric and oxygen-deficient complex subnanoporous oxide 12CaO·7Al 2 O 3 (C12A7) are generated by simulating lattice rupture under the influence of an external strain. Extra-framework anions are found to serve as buffers, maintaining stability of the lattice cages in both elastic and inelastic stretching regimes. Modification of the local atomic structure in the near-surface region reduces the band gap in stoichiometric insulating C12A7. On the contrary, the band gap appears in the oxygen-deficient form of C12A7, which is metallic in the bulk. This is due to formation of the surface electron traps, which differ both in the type of the local atomic structure and stability of the electronic states. The implications of this electronic structure for the surface chemical and electron emission properties are discussed.
- Published
- 2011
25. Growth of 12CaO·7Al2O3 single crystal with tetragonal symmetry by Czochralski method
- Author
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Hideo Hosono, Kazuhisa Kurashige, Shunsuke Ueda, Satoru Matsuishi, Sung Wng Kim, Yoshitake Toda, Masahiro Hirano, and Masashi Miyakawa
- Subjects
Diffraction ,Metals and Alloys ,Crucible ,chemistry.chemical_element ,Surfaces and Interfaces ,Crystal structure ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ion ,Crystal ,Crystallography ,Tetragonal crystal system ,chemistry ,Materials Chemistry ,Iridium ,Single crystal - Abstract
Single crystals of 12CaO·7Al2O3 (C12A7) have been grown by the Czochralski method with three different growth directions of , , and . Employment of a 2.0% oxygen-containing nitrogen atmosphere and use of an iridium crucible were the critical factors for obtaining the single crystal. The crystal exhibited orange color resulting from the incorporation of Ir4+ ions of ∼ 5 × 1017 cm− 3, presumably occupying at Ca2+ sites. High resolution X-ray diffraction analyses indicated that the C12A7 single crystal shows the tetragonal symmetry belonging to the space group I 4 ― 2 m .
- Published
- 2008
26. n-type conversion of SnS by isovalent ion substitution: Geometrical doping as a new doping route
- Author
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Zewen Xiao, Hideo Hosono, Fan-Yong Ran, Hidenori Hiramatsu, Toshio Kamiya, and Yoshitake Toda
- Subjects
Condensed Matter - Materials Science ,Electron mobility ,Multidisciplinary ,Materials science ,business.industry ,Photoemission spectroscopy ,Doping ,Fermi level ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,chemistry.chemical_element ,Article ,Ion ,symbols.namesake ,Crystallography ,Semiconductor ,chemistry ,symbols ,Density functional theory ,business ,Tin - Abstract
Tin monosulfide (SnS) is a naturally p-type semiconductor with a layered crystal structure, but no reliable n-type SnS has been obtained by conventional aliovalent ion substitution. In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates. Substituting Pb2+ for Sn2+ converted the majority carrier from hole to electron and the free electron density ranged from 1012 to 1015 cm−3 with the largest electron mobility of 7.0 cm2/(Vs). The n-type conduction was confirmed further by the position of the Fermi level (EF) based on photoemission spectroscopy and electrical characteristics of pn heterojunctions. Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which results in the electron doping.
- Published
- 2015
27. ChemInform Abstract: Two-Dimensional Transition-Metal Electride Y2C
- Author
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Xiao Zhang, Satoru Matsuishi, Yoshitake Toda, Hechang Lei, Shigenori Ueda, Hideo Hosono, Zewen Xiao, and Toshio Kamiya
- Subjects
Crystallography ,chemistry.chemical_compound ,Transition metal ,Chemistry ,Electride ,General Medicine ,Electron ,Crystallite ,Stoichiometry - Abstract
Polycrystalline layered Y2C with quasi-2D anionic electrons confined in the interlayer is prepared by melting stoichiometric amounts of Y shots and C granules under Ar.
- Published
- 2015
28. Narrow Bandgap in beta-BaZn2As2 and Its Chemical Origins
- Author
-
Hechang Lei, Fan-Yong Ran, Toshio Kamiya, Hidenori Hiramatsu, Shigenori Ueda, Zewen Xiao, Yoshitake Toda, Hideo Hosono, Satoru Matsuishi, and Jiangang Guo
- Subjects
Chemical Physics (physics.chem-ph) ,Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Photoemission spectroscopy ,Band gap ,business.industry ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Chemistry ,Crystal structure ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Semiconductor ,Atomic orbital ,Electrical resistivity and conductivity ,Physics - Chemical Physics ,Beta (plasma physics) ,business ,Order of magnitude - Abstract
Beta-BaZn2As2 is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that beta-BaZn2As2 and LaZnAsO have similar bandgaps; however, the bandgap of beta-BaZn2As2 (previously-reported value ~0.2 eV) is one order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of beta-BaZn2As2 is determined to be 0.23 eV from the intrinsic region of the tem-perature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemi-cal bonding nature probed by 6 keV hard X-ray photoemission spectroscopy, hybrid density functional calculations, and the ligand theory. One origin is the direct As-As hybridization between adjacent [ZnAs] layers, which leads to a secondary splitting of As 4p levels and raises the valence band maximum. The other is that the non-bonding Ba 5dx2-y2 orbitals form unexpectedly deep conduction band minimum (CBM) in beta-BaZn2As2 although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between beta-BaZn2As2 and LaZnAsO.
- Published
- 2015
- Full Text
- View/download PDF
29. Czochralski Growth of 12CaO·7Al2O3 Crystals
- Author
-
Kazuhisa Kurashige, Katsuro Hayashi, Satoru Matstuishi, Masahiro Hirano, Yoshitake Toda, and Hideo Hosono
- Subjects
Diffraction ,Aluminium oxides ,Materials science ,Nanoporous ,chemistry.chemical_element ,Crucible ,General Chemistry ,Condensed Matter Physics ,Crystal ,Crystallography ,chemistry ,General Materials Science ,Iridium ,Ingot ,Single crystal - Abstract
Single crystals of nanoporous 12CaO·7Al2O3 (C12A7) as large as 27 mm in diameter, 120 mm in length, and 207 g in weight have been successfully grown by the Czochralski method. We found that a 2.0% oxygen-containing nitrogen atmosphere and an iridium crucible are the critical factors for success. The crystal ingot exhibited an orange color resulting from the incorporation of Ir4+ ions of ca. 5 × 1017 cm-3, which presumably occupy Ca2+ sites. X-ray diffraction analysis indicated that the ingot obtatined was a single crystal with few domains.
- Published
- 2006
30. Energetics of Formation and Oxidation of Microporous Calcium Aluminates: A New Class of Electrides and Ionic Conductors
- Author
-
Hideo Hosono, Alexandra Navrotsky, Yoshitake Toda, and Olga Trofymluk
- Subjects
General Chemical Engineering ,Aluminate ,Inorganic chemistry ,Ionic bonding ,General Medicine ,General Chemistry ,Microporous material ,Calorimetry ,Standard enthalpy of formation ,chemistry.chemical_compound ,chemistry ,Formula unit ,Materials Chemistry ,Physical chemistry ,Calcium aluminates ,Stoichiometry - Abstract
Microporous calcium aluminates with a common formula [Ca12Al14O33-δ]2δ+(2δe-), (0 < δ ≤ 1), represent a new family of electrides with conducting extraframework electrons encaged within the framework. Their enthalpies of oxidation to eliminate these electrons and obtain a stoichiometric Ca12Al14O33 compound, and formation enthalpies relative to the most stable annealed calcium aluminate Ca12Al14O33.46 (which contains excess oxygen probably as O- and O2- species), are studied by transposed temperature drop calorimetry and drop solution calorimetry in molten lead borate at 1080 K. The standard enthalpy of oxidation per O2 consumed is −579.4 ± 9.4 kJ/mol (or −144.8 ± 9.4 kJ per encaged electron). The enthalpies obtained for samples with variable amounts of electrons (and less than 33 oxygens per formula unit) are compared to that for oxidation of a stoichiometric Ca12Al14O33 sample to an oxygen-rich composition. The study supports the idea that the oxidation of the stoichiometric Ca12Al14O33 sample results in...
- Published
- 2005
31. Thin film fabrication of nano-porous 12CaO·7Al2O3 crystal and its conversion into transparent conductive films by light illumination
- Author
-
Masahiro Hirano, Yoshitake Toda, Hideo Hosono, Toshio Kamiya, Katsuro Hayashi, and Masashi Miyakawa
- Subjects
Fabrication ,Materials science ,Band gap ,business.industry ,Metals and Alloys ,Mineralogy ,Surfaces and Interfaces ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Crystal ,Carbon film ,Materials Chemistry ,Ultraviolet light ,Optoelectronics ,Thin film ,business ,Transparent conducting film - Abstract
Thin film fabrication of crystalline 12CaO·7Al2O3 (C12A7) with zeolitic structure was examined, and their electrical and optical properties were measured. Polycrystalline thin films were prepared by post-annealing of amorphous films in oxygen atmosphere at temperatures above 800 °C. Choice of substrates was crucial for obtaining single-phase thin films. Although various oxide substrates (single crystals of Al2O3, Y-stabilized ZrO2, MgO and silica glass) were examined, single-phase films were obtained only for MgO substrates and the other substrates reacted with the CaO component in the films during post-annealing. The optical band gap of C12A7 was evaluated to be 5.9 eV. Hydride ions were incorporated into the film by a thermal treatment in a hydrogen atmosphere at 1200 °C. The resulting transparent thin films were converted into transparent persistent electronic conductors exhibiting an electrical conductivity 6.2×10−1 S cm−1 at 300 K by ultraviolet light illumination. This is the first example of transparent conductive thin film in which conductive areas can be patterned directly by light.
- Published
- 2003
32. High-Density Electron Anions in a Nanoporous Single Crystal: [Ca_24_Al_28_O_64_]^4+^(4e^-^)
- Author
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Satoru Matsuishi, Katsuro Hayashi, Toshio Kamiya, Yoshitake Toda, Masahiro Hirano, Isao Tanaka, Masashi Miyakawa, and Hideo Hosono
- Subjects
Bipolaron ,Multidisciplinary ,Stereochemistry ,Alkalide ,General Medicine ,Electron ,Crystal structure ,Conductivity ,Ion ,Crystal ,Crystallography ,chemistry.chemical_compound ,chemistry ,Physics::Atomic and Molecular Clusters ,Electride ,Singlet state ,Single crystal - Abstract
We removed ∼100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO·7Al 2 O 3 , leading to the formation of high-density (∼2 × 10 21 cm – 3 ) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F + center and migrates throughout the crystal by hopping to a neighboring cage with conductivity ∼100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca 24 Al 28 O 64 ] 4 + (4 e – ) may be regarded as a thermally and chemically stable single crystalline “electride.”
- Published
- 2003
33. Fabrication of Highly Conductive 12CaO·7Al2O3 Thin Films Encaging Hydride Ions by Proton Implantation
- Author
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Yoshitake Toda, Toshio Kamiya, Masahiro Hirano, Masashi Miyakawa, Katsuro Hayashi, and Hideo Hosono
- Subjects
Materials science ,Fabrication ,Chemistry ,business.industry ,Hydride ,Mechanical Engineering ,Proton implantation ,Nanotechnology ,General Medicine ,Ion ,12CaO.7Al2O3 ,Ion implantation ,Chemical engineering ,Mechanics of Materials ,Optoelectronics ,General Materials Science ,Thin film ,business ,Porous medium ,Electrical conductor - Published
- 2003
34. Conversion of an ultra-wide bandgap amorphous oxide insulator to a semiconductor
- Author
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Naoto Watanabe, Takumi Sekiya, Naoki Ohashi, Toshio Kamiya, Norihiko Miyokawa, Yoshitake Toda, Hideo Hosono, Shigenori Ueda, Junghwan Kim, Hidenori Hiramatsu, Koji Kimoto, and Keisuke Ide
- Subjects
010302 applied physics ,Electron mobility ,Materials science ,Band gap ,business.industry ,Oxide ,Schottky diode ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Amorphous solid ,chemistry.chemical_compound ,Semiconductor ,chemistry ,Modeling and Simulation ,0103 physical sciences ,Optoelectronics ,General Materials Science ,Thin film ,0210 nano-technology ,business ,Diode - Abstract
The variety of semiconductor materials has been extended in various directions, for example, to very wide bandgap materials such as oxide semiconductors as well as to amorphous semiconductors. Crystalline β-Ga2O3 is known as a transparent conducting oxide with an ultra-wide bandgap of ~4.9 eV, but amorphous (a-) Ga2Ox is just an electrical insulator because the combination of an ultra-wide bandgap and an amorphous structure has serious difficulties in attaining electronic conduction. This paper reports semiconducting a-Ga2Ox thin films deposited on glass at room temperature and their applications to thin-film transistors and Schottky diodes, accomplished by suppressing the formation of charge compensation defects. The film density is the most important parameter, and the film density is increased by enhancing the film growth rate by an order of magnitude. Additionally, as opposed to the cases of conventional oxide semiconductors, an appropriately high oxygen partial pressure must be chosen for a-Ga2Ox to reduce electron traps. These considerations produce semiconducting a-Ga2Ox thin films with an electron Hall mobility of ~8 cm2V−1 s−1, a carrier density Ne of ~2 × 1014 cm−3 and an ultra-wide bandgap of ~4.12 eV. An a-Ga2Ox thin-film transistor exhibited reasonable performance such as a saturation mobility of ~1.5 cm2 V−1 s−1 and an on/off ratio >107. Reversing the usual role of oxygen during deposition of semiconducting thin films makes it easier to produce bendable electronics. Crystalline gallium oxide is a large-bandgap semiconductor that can handle the strong electric fields used to supply power components. However, it usually turns into an insulator when produced as amorphous, flexible thin films. Now, Junghwan Kim from the Tokyo Institute of Technology in Japan and colleagues have found that high partial pressures of oxygen gas during rapid laser deposition transforms amorphous gallium oxide films into semiconductors. While most oxide films are manufactured under low-oxygen conditions, the researchers discovered their procedure suppresses the formation of electron-trapping defects that diminish conductivity. Prototype thin-film transistors and diodes demonstrated the potential for using amorphous gallium oxide for high-efficiency devices. Crystalline Ga2O3 is an ultra-wide bandgap oxide semiconductor, but electron conduction in amorphous Ga2Ox has never been attained to date. Here we succeeded in converting amorphous Ga2Ox to a semiconductor with the bandgap of ~4.12 eV and the electron mobility ~8 cm2 V−1 s−1. The key is to suppress charge compensation defects by increasing the film density and suppress formation of oxygen-poor and oxygen-excess defects. It produces thin-film transistors and Schottky diodes with high on currents and on/off ratios.
- Published
- 2017
35. Narrow bandgap in β-BaZn₂As₂ and its chemical origins
- Author
-
Zewen, Xiao, Hidenori, Hiramatsu, Shigenori, Ueda, Yoshitake, Toda, Fan-Yong, Ran, Jiangang, Guo, Hechang, Lei, Satoru, Matsuishi, Hideo, Hosono, and Toshio, Kamiya
- Abstract
β-BaZn2As2 is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that β-BaZn2As2 and LaZnAsO have similar bandgaps; however, the bandgap of β-BaZn2As2 (previously reported value ~0.2 eV) is 1 order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of β-BaZn2As2 is determined to be 0.23 eV from the intrinsic region of the temperature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemical bonding nature probed by 6 keV hard X-ray photoemission spectroscopy, hybrid density functional calculations, and the ligand theory. One origin is the direct As-As hybridization between adjacent [ZnAs] layers, which leads to a secondary splitting of As 4p levels and raises the valence band maximum. The other is that the nonbonding Ba 5d(x(2)-y(2)) orbitals form an unexpectedly deep conduction band minimum (CBM) in β-BaZn2As2 although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between β-BaZn2As2 and LaZnAsO.
- Published
- 2014
36. NH(2-) dianion entrapped in a nanoporous 12CaO·7Al2O3 crystal by ammonothermal treatment: reaction pathways, dynamics, and chemical stability
- Author
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Masaaki Kitano, Hideo Hosono, Fumitaka Hayashi, Yoshitake Toda, Yudai Tomota, and Toshiharu Yokoyama
- Subjects
Ion exchange ,Chemistry ,Nanoporous ,Inorganic chemistry ,General Chemistry ,Biochemistry ,Catalysis ,Ion ,symbols.namesake ,Hydrogen storage ,Colloid and Surface Chemistry ,Nanocages ,Yield (chemistry) ,symbols ,Chemical stability ,Raman spectroscopy - Abstract
Inorganic imides are useful for hydrogen storage and base-catalyzed reactions but are extremely unstable under ambient conditions, which hinders their practical use as functional materials. Here, we demonstrate that NH2(-) and H(-), as well as NH(2-), can be incorporated into the nanocages of the mayenite crystals, [Ca24Al28O64](4+)(e(-))4 and [Ca24Al28O64](4+)(O(2-))2, by ammonothermal treatment. We evaluated the reaction conditions and found that the anion exchange reaction proceeded at higher than 500 °C. Raman spectroscopy showed that the N-H band position of encaged NH(2-) was close to that of CaNH and MgNH crystals. We also studied the reaction pathways that yield NH2(-) and NH(2-) anions and their dynamic motions by (1)H NMR spectroscopy. Successive reactions of encaged e(-) and O(2-) ions with NH3 yielded NH2(-), NH(2-), and H(-) or OH(-), in which the O(2-) ion reacted more efficiently with NH3. The maximum NH(2-) concentration and content were ∼2.7 × 10(20) cm(-3) and ∼0.25 (wt %)NH, respectively. The short spin-lattice relaxation time found in (1)H NMR suggests that the incorporated NH2(-) and NH(2-) rotate or librate in the cage near room temperature. Stability tests showed that the encaged NH(2-) ions are chemically stable under ambient conditions and in organic solvents. These results are attributed to the encapsulation of active anions within subnanometer-sized cages composed of Ca-O-Al oxide frameworks. The encaged NH(2-) desorbed as NH3 at higher than 500 °C under vacuum (Ea = 172 kJ mol(-1)). It is thus expected that C12A7:NH(2-) will function as a reactive nitrogen source for nitrogen transfer reactions by in situ cage degradation.
- Published
- 2014
37. ChemInform Abstract: Layered Compounds BaM2Ge4Ch6(M: Rh, Ir and Ch: S, Se) with Pyrite-Type Building Blocks and Ge-Ch Heteromolecule-Like Anions
- Author
-
Jun-ichi Yamaura, Hideo Hosono, Jiangang Guo, Yanpeng Qi, Hechang Lei, and Yoshitake Toda
- Subjects
chemistry.chemical_classification ,Chalcogen ,Crystallography ,Base (chemistry) ,chemistry ,engineering ,General Medicine ,Pyrite ,engineering.material - Abstract
The title compounds are prepared from mixtures of Rh or Ir, BaS or BaSe, Ge, and S or Se (h-BN capsule, 5 GPa, 1473 K, 2 h).
- Published
- 2014
38. Layered compounds BaM2Ge4Ch6 (M = Rh, Ir and Ch = S, Se) with pyrite-type building blocks and Ge-Ch heteromolecule-like anions
- Author
-
Jun-ichi Yamaura, Yanpeng Qi, Jiangang Guo, Hideo Hosono, Hechang Lei, and Yoshitake Toda
- Subjects
Condensed Matter - Materials Science ,Valence (chemistry) ,Chemistry ,Stacking ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,engineering.material ,Inorganic Chemistry ,Crystallography ,Covalent bond ,Tetrahedron ,engineering ,Orthorhombic crystal system ,Pyrite ,Physical and Theoretical Chemistry - Abstract
Structure and chemical features of layered compounds BaM2Ge4Ch6 (M = Rh, Ir; Ch = S, Se) synthesized under high-pressure and high-temperature method are systematically studied. These compounds crystallize in an orthorhombic phase with space group Pbca (No. 61). The remarkable structural feature is to have the M-Ge-Ch pyrite-type building units, stacking with Ba-Ch layers alternatively along c axis. It is very rare and novel that pyrite-type subunits as the building blocks in the layered compounds. Theoretical calculations and experimental results indicate that there are strongly polarized covalent bonds between Ge and Ch atoms, forming heteromolecule-like anions in these compounds. Moreover, Ge atoms in this structure exhibit unusual valence state (~ +1) due to the tetrahedral coordination environment of Ge atoms along with M and Ch atoms simultaneously., 24 pages, 12 figures, 5 tables
- Published
- 2014
39. ChemInform Abstract: Indium-Based Ultraviolet-Transparent Electroconductive Oxyfluoride InOF: Ambient-Pressure Synthesis and Unique Electronic Properties in Comparison with In2O3
- Author
-
Yoshitake Toda, Koichi Kajihara, Tatsuya Mori, Hideo Hosono, Kiyoshi Kanamura, and Hidenori Hiramatsu
- Subjects
Chemical engineering ,Chemistry ,Thermal decomposition ,medicine ,Organic chemistry ,chemistry.chemical_element ,General Medicine ,medicine.disease_cause ,Ultraviolet ,Indium ,Electronic properties ,Ambient pressure - Abstract
Single-phase, powdered InOF is prepared by thermal decomposition of InF3·3H2O under flowing O2 (360—440 °C, 2 h).
- Published
- 2013
40. Activation and splitting of carbon dioxide on the surface of an inorganic electride material
- Author
-
Hiroyuki Hirayama, Antonio Torrisi, Navaratnarajah Kuganathan, Hideo Hosono, Yoshitake Toda, and Peter V. Sushko
- Subjects
chemistry.chemical_compound ,Multidisciplinary ,Spitting ,Materials science ,chemistry ,Chemical engineering ,Carbon dioxide ,General Physics and Astronomy ,Electride ,General Chemistry ,Bioinformatics ,Article ,General Biochemistry, Genetics and Molecular Biology - Abstract
Activation of carbon dioxide is the most important step in its conversion into valuable chemicals. Surfaces of stable oxide with a low work function may be promising for this purpose. Here we report that the surfaces of the inorganic electride [Ca24Al28O64]4+(e−)4 activate and split carbon dioxide at room temperature. This behaviour is attributed to a high concentration of localized electrons in the near-surface region and a corrugation of the surface that can trap oxygen atoms and strained carbon monoxide and carbon dioxide molecules. The [Ca24Al28O64]4+(e−)4 surface exposed to carbon dioxide is studied using temperature-programmed desorption, and spectroscopic methods. The results of these measurements, corroborated with ab initio simulations, show that both carbon monoxide and carbon dioxide adsorb on the [Ca24Al28O64]4+(e−)4 surface at RT and above and adopt unusual configurations that result in desorption of molecular carbon monoxide and atomic oxygen upon heating., Effective activation and spitting of carbon dioxide are important steps in its conversion to valuable chemicals. Here the authors report an inorganic electride material with a high concentration of near-surface electrons that is capable of adsorbing and decomposing carbon dioxide.
- Published
- 2013
41. Indium-based ultraviolet-transparent electroconductive oxyfluoride InOF: ambient-pressure synthesis and unique electronic properties in comparison with In2O3
- Author
-
Kiyoshi Kanamura, Tatsuya Mori, Hideo Hosono, Hidenori Hiramatsu, Koichi Kajihara, and Yoshitake Toda
- Subjects
Chemistry ,Band gap ,business.industry ,Analytical chemistry ,General Chemistry ,Conductivity ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Semiconductor ,Electron affinity ,Direct and indirect band gaps ,Work function ,business ,Ultraviolet photoelectron spectroscopy ,Ambient pressure - Abstract
A method for the synthesis of single-phase powdered InOF under ambient pressure has been developed. The method involves pyrolysis of a hydrate of InF3 in an O2 atmosphere of controlled humidity. Various intermediate phases were formed during the pyrolysis, and their structures and interconversions were analyzed. Combined results of optical absorption measurements and density functional calculations indicate that InOF is a direct band gap material with a band gap energy of ∼3.7 eV. Unlike In2O3, the electrical conductivity of polycrystalline InOF pellets can be controlled over ∼8 orders of magnitude from ∼10(-8) S cm(-1) to ∼2 S cm(-1) by thermal annealing, and the sample with the highest conductivity was a nearly degenerate n-type semiconductor with a relatively small carrier concentration of ∼10(18) cm(-3). The work function of InOF measured by ultraviolet photoelectron spectroscopy is ∼3.5 eV and is smaller by ∼1.5 eV than that of In2O3. This difference comes from a decrease in the electron affinity.
- Published
- 2013
42. Surface of room-temperature-stable electride [Ca24Al28O64]4+(e-)4: preparation and its characterization by atomic-resolution scanning tunneling microscopy
- Author
-
Masahiro Hirano, Hiroyuki Hirayama, Yousuke Kubota, Hideo Hosono, and Yoshitake Toda
- Subjects
Materials science ,Nanostructure ,Macromolecular Substances ,Surface Properties ,Molecular Conformation ,General Physics and Astronomy ,Nanotechnology ,law.invention ,Crystal ,Scanning probe microscopy ,chemistry.chemical_compound ,Electrical resistivity and conductivity ,law ,Microscopy, Scanning Tunneling ,Materials Testing ,General Materials Science ,Particle Size ,Aluminum Compounds ,Ohmic contact ,General Engineering ,Electric Conductivity ,Temperature ,Calcium Compounds ,Nanostructures ,chemistry ,Chemical physics ,Surface modification ,Electride ,Scanning tunneling microscope - Abstract
The nanocage compound crystal [Ca24Al28O64]4+(e-)4 (C12A7:e-) is a room-temperature-stable electride. Although bulk C12A7:e- exhibits metallic conduction, the surface of an as-prepared sample or one prepared by mechanical fracture in ultrahigh vacuum is almost insulating and exhibits distinct non-ohmic contact. We studied whether the intrinsic surface of this electride exhibits metallic conduction or not by examining various conditions for preparing the intrinsic surface. A combination of sputtering with thermal annealing led to the emergence of metallic conductivity in a specific condition. Suitably prepared surfaces revealed ohmic contact even in an ambient atmosphere. Atomic-resolution scanning tunneling microscopy (STM) images of the surfaces were consistent with a structural model in which the cage structure in the bulk C12A7:e- electride is conserved at the surface.
- Published
- 2011
43. ChemInform Abstract: Work Function of a Room-Temperature, Stable Electride [Ca24Al28O64]4+(e-)4
- Author
-
Hiroshi Yanagi, Masaaki Kobata, Toshio Kamiya, Keisuke Kobayashi, Jung Jin Kim, Masahiro Hirano, Yoshitake Toda, Eiji Ikenaga, Sigenori Ueda, and Hideo Hosono
- Subjects
chemistry.chemical_compound ,Chemistry ,Chemical physics ,Electride ,Work function ,General Medicine - Published
- 2008
44. Room temperature-stable electride as a synthetic organic reagent: application to pinacol coupling reaction in aqueous media
- Author
-
Yoshitake Toda, Kohtaro Osakada, Masahiro Hirano, and Daisuke Takeuchi, Hideo Hosono, and Haritha Buchammagari
- Subjects
chemistry.chemical_compound ,Pinacol coupling reaction ,Aqueous medium ,Chemistry ,Reagent ,Organic Chemistry ,Electrophile ,Electride ,Crystal structure ,Physical and Theoretical Chemistry ,Photochemistry ,Biochemistry - Abstract
Room temperature-stable inorganic electride [Ca(24)Al(28)O(68)](4+)4e(-) was employed for a pinacol coupling reaction in aqueous media. Ca-Al-O gel formed by the destruction of the crystal structure of an electride by water media played a key role in transferring the electron to electrophilic aldehydes. Aromatic aldehydes reacted smoothly with moderate to high yields.
- Published
- 2007
45. Synthesis of a Room Temperature Stable 12CaO×7Al2O3 Electride from the Melt and Its Application as an Electron Field Emitter
- Author
-
Katsuro Hayashi, Hideo Hosono, Masahiro Hirano, Yoshitake Toda, and Sung Wng Kim
- Subjects
Reducing atmosphere ,Analytical chemistry ,General Medicine ,law.invention ,Annealing (glass) ,Field electron emission ,chemistry.chemical_compound ,chemistry ,law ,Phase (matter) ,Electride ,Crystallite ,Crystallization ,Single crystal - Abstract
A room temperature (RT) stable electride was realized by thermally annealing an insulating 12CaO·7Al2O3 (C12A7) single crystal in a calcium metal vapor. Here we report a simple and direct method for synthesizing polycrystalline C12A7 electride (C12A7:e-); the solidification of a “melt” in a reducing atmosphere and the crystallization of a “glass” with an oxygen-deficient composition in a vacuum. The carbon-related anion (C22-) presumably serves as the template for the formation of the C12A7 phase in the solidification process and may be spontaneously released from the lattice during the cooling process, leaving mobile electrons in the lattice. Also the C22- ions accommodated in the glass may play a significant role in the formation of C12A7:e- during the crystallization. The polycrystalline C12A7:e- exhibits an electrical conductivity up to 5 S·cm-1 at 300 K, which corresponds to an electron concentration of ∼3 × 1019 cm-3 and a nearly equal mobility of ∼0.1 cm2·V-1·s-1 to that of the single crystalline C...
- Published
- 2006
46. Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs.
- Author
-
Toshio Kamiya, Hideo Hosono, Junghwan Kim, Yoshitake Toda, and Satoru Watanabe
- Subjects
AMORPHOUS alloys ,SEMICONDUCTORS ,ORGANIC electronics ,ORGANIC light emitting diodes ,ELECTRON mobility - Abstract
Efficient electron transfer between a cathode and an active organic layer is one key to realizing high-performance organic devices, which require electron injection/transport materials with very low work functions. We developed two wide-bandgap amorphous (a-) oxide semiconductors, a-calcium aluminate electride (a-C12A7:e) and a-zinc silicate (a-ZSO). A-ZSO exhibits a low work function of 3.5 eV and high electron mobility of 1 cm
2 /(V · s); furthermore, it also forms an ohmic contact with not only conventional cathode materials but also anode materials. A-C12A7:e has an exceptionally low work function of 3.0 eV and is used to enhance the electron injection property from a-ZSO to an emission layer. The inverted electron-only and organic light-emitting diode (OLED) devices fabricated with these two materials exhibit excellent performance compared with the normal type with LiF/Al. This approach provides a solution to the problem of fabricating oxide thin-film transistor-driven OLEDs with both large size and high stability. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
47. Field Emission of Electron Anions Clathrated in Subnanometer-Sized Cages in [Ca24Al28O64]4+(4e-)
- Author
-
Satoru Matsuishi, Kazushige Ueda, Hideo Hosono, Katsuro Hayashi, Toshio Kamiya, Masahiro Hirano, and Yoshitake Toda
- Subjects
chemistry.chemical_compound ,Field electron emission ,Materials science ,Mechanics of Materials ,Chemistry ,Chemical physics ,Mechanical Engineering ,Electride ,General Materials Science ,General Medicine ,Electron ,Molecular physics - Published
- 2004
48. Persistent Electronic Conduction in 12CaO7Al2O3 Thin Films Produced by Ar Ion Implantation: Selective Kick-Out Effect Leads to Electride Thin Films
- Author
-
Yoshitake Toda, Hideo Hosono, Katsuro Hayashi, Masahiro Hirano, Toshio Kamiya, and Masashi Miyakawa
- Subjects
Crystal ,chemistry.chemical_compound ,Materials science ,Ion implantation ,chemistry ,Analytical chemistry ,Electride ,Electron ,Thin film ,Thermal conduction ,Ion ,Conductor - Abstract
A new method to convert 12CaO7Al2O3 (C12A7) thin films to electronic conductor by hot Ar+ ion implantation has been developed and its mechanism is discussed. It was found that hot Ar+ ion implantation extruded free O2- ions in C12A7 films by kick-out effects at fluences higher than 1×1017 cm−2, which left electrons in the cages embedded in C12A7 crystal and produced high concentration F+-like centers (∼1.4×1021 cm−3). The resulting films show coloration and persistent electronic conduction with conductivities up to ∼1 Scm−1. On the other hand, fluences less than 1×1017 cm−2 kept the films transparent and insulating.
- Published
- 2004
49. Water Durable Electride Y5Si3: Electronic Structure and Catalytic Activity for Ammonia Synthesis.
- Author
-
Yangfan Lu, Jiang Li, Tomofumi Tada, Yoshitake Toda, Shigenori Ueda, Toshiharu Yokoyama, Masaaki Kitano, and Hideo Hosono
- Published
- 2016
- Full Text
- View/download PDF
50. Ammonia decomposition by ruthenium nanoparticles loaded on inorganic electride C12A7:e−
- Author
-
Hideo Hosono, Toshiharu Yokoyama, Yoshitake Toda, Yoshimi Kanie, Fumitaka Hayashi, Masaaki Kitano, Michikazu Hara, and Yasunori Inoue
- Subjects
Ammonia ,chemistry.chemical_compound ,Hydrogen carrier ,chemistry ,Desorption ,Inorganic chemistry ,chemistry.chemical_element ,Electride ,General Chemistry ,Antibonding molecular orbital ,Decomposition ,Catalysis ,Ruthenium - Abstract
The use of ammonia as a hydrogen carrier has received much attention due to its high hydrogen content and liquid state under mild conditions, which could lead to fuel cell applications. This study demonstrates facile ammonia decomposition on ruthenium nanoparticles loaded on inorganic electride, C12A7:e−. A high turnover frequency (∼12 s−1 at 400 °C) and low activation energy (64 kJ mol−1) for recombinative N2 desorption were obtained for Ru/C12A7:e−. N2-temperature programmed desorption (N2-TPD) and kinetic analyses indicate that the high catalytic performance is due to the low work function of chemically stable C12A7:e−, which enables electron injection to the antibonding orbital of the Ru–N bond formed transiently through the reaction by raising the Fermi level of Ru metal.
- Published
- 2013
Catalog
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