H. Tatsuoka

Shizuoka University, Sizuoka, Shizuoka, Japan

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Publications (121)177.03 Total impact

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    ABSTRACT: Si and silicide nanowires/microrods were synthesized using metal-chloride-based sources by the CVD technique. In the case of Si nanowire synthesis, the morphological structures of the products depended on the distance from the source material. The distance dependence of the morphological and structural properties of the nanostructures was investigated to systemically clarify the shape modification phenomena in Si nanowire synthesis. The modification of the cross-sectional shape of the Si nanowires/microrods was successfully demonstrated. The triangular nanowire has a sawtooth faceting structure on its sidewall. In addition, the synthesis of Mn-silicide phases over the entire range of the Mn-Si system was examined. The effect of adding an impurity to the source materials on the structural modifications of the resulting nanowires/microrods was also investigated. It is expected that the morphological and structural control of the nanowires/microrods will be improved by a simple thermal treatment using a metal chloride as the source material.
    No preview · Article · Jul 2015 · Japanese Journal of Applied Physics
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    ABSTRACT: We report the point contact visible luminescence from Ga-doped ZnO layers. The Ga-doped ZnO layers were grown by the thermal oxidation of ZnS substrates with gallium in the air. The injected light emission was observed around the point-contact surface of ZnO layers when a forward DC voltage in the range of 2.5-9.8 V was applied (point contact was positive). Typically, we illustrated the luminescent spectrum for 6.7 V which showed a wide emission band centering at 680 nm. [DOI: 10.1380/ejssnt.2015.201]
    Preview · Article · Apr 2015 · e-Journal of Surface Science and Nanotechnology
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    ABSTRACT: Compositionally homogeneous Ga-doped Si0.68Ge0.32 bulk crystals were grown with two different doping concentrations, i.e., 1 × 1018 cm−3 (GSG1) and 1 × 1019 cm−3 (GSG2), using a vertical gradient freezing method. The growth was carried out under a mild temperature gradient of 0.57 °C/mm using a sandwich structured sample, i.e., Si(seed)/Ga-doped Ge/Si(feed). The grown crystals were cut along the growth direction to study the compositional variations, etch pit densities (EPDs), and thermoelectric characteristics. Electron backscatter diffraction analysis indicated that the (111) orientation has larger area compared with other orientations in the grown crystal. The electrical resistivity decreased along the growth direction although the carrier concentrations and mobility of the crystals were unchanged, possibly because of the variation in EPDs. Moreover, the electrical resistivity was found to be large at the high EPD region of the crystal. The electrical resistivity of all the samples gradually increased with temperature. The maximum values of Seebeck coefficients in GSG1 and GSG2 samples were 466 µV/K at 818 K and 459 µV/K at 892 K, respectively. The calculated power factors of GSG1 and GSG2 were higher than previously reported values (1416 µW m−1 K−2) for Si0.81Ge0.19.
    No preview · Article · Jan 2015 · Crystal Growth & Design
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    ABSTRACT: The ZnO layer with thickness of 1.6 μm in ZnO/ZnGa2O4 composite structure was grown by the thermal oxidation of ZnS substrate with gallium. The optical property of the ZnO thick layer was investigated by time-resolved photoluminescence. A single UV emission around 375 nm with short lifetime was observed at room temperature while the visible emission was absolutely quenched. The UV emission band was composed of the neutral donor bound exciton (D0X) and donor-acceptor pair (DAP) emission peaks with large full-width at half-maximums (FWHMs) at 3.367 and 3.318 eV, respectively, at 10 K. However, the intensity of the D0X emission was stronger than that of the DAP emission at measuring temperatures of 10–300 K.
    No preview · Article · Dec 2014 · Science China Technological Sciences
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    Preview · Article · Aug 2014
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    ABSTRACT: It was demonstrated that flake-like structures containing Si-based nanosheets were successfully synthesized on Si(111) substrates. By exposure of CaSi2/Si substrates to CrCl2 vapor, Ca atoms were extracted from CaSi2, then, the Si-based nanosheets were formed. The structural properties of the Si-based nanosheets formed at the edge of the flakes were examined. It is noted that the flake-like structures were rooted to the substrates, and that the Si-based nanosheets were easily exfoliated from the flake-like structures, to expose the surfaces corresponding to the Si{111} planes of the nanosheet, originated from the corrugated Si(111) layers linked by Ca in CaSi2.
    No preview · Article · Aug 2014 · Journal- Ceramic Society Japan
  • Hirokazu Tatsuoka · Wen Li · Er Chao Meng · Daisuke Ishikawa · Kaito Nakane
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    ABSTRACT: The structural control and morphological modification of a series of silicide, oxide and Ag metal nanostructures have been further discussed with reviews of nanostructure syntheses, such as CrSi2 nanowire bundles - dendrites, MoSi2 nanosheets, α-Fe2O3 nanowires - nanobelts, CuO/Cu2O nanowire axial heterostructures, ZrO2/SiOx and CrSi2/SiOx core/shell nanowires. In addition, the syntheses of Ag - three-dimensional dendrites, two-dimensional dendrites, two-dimensional fractal structures, particles and nanowires also were discussed. Moreover, the structural and morphological properties of the nanostructures were examined. The structural control and morphological modifications of the nanostructures have been successfully demonstrated by the appropriate thermal treatments with specific starting materials. A large volume of silicide nanowire bundles, large area of oxide nanowire arrays and large area Ag nanostructure coatings were successfully fabricated.
    No preview · Article · Mar 2014 · Solid State Phenomena
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    ABSTRACT: Si dissolution into Ge melt, solute transport in the Si-Ge solution and crystal growth of SiGe alloys were in situ observed by X-ray penetration method. The rectangular shaped sandwich sample of Si (seed)/Ge/Si (feed) was used for the experiment. X-ray intensities penetrated through the sample, which was heated up to the growth temperature of 1200 degrees C, were recorded by rectangular shaped CdTe line sensor as a function of time and temperature. The experimental results demonstrated that the dissolution of Si seed was larger compared to Si feed crystal although Si feed temperature was relatively higher than that of seed. Crystal growth of SiGe was observed at the feed interface as the growth interface was observed clearly by an abrupt change of penetrated X-ray intensity near the growth interface. Since the crystal grew with Si rich composition (at high temperature 1200 degrees C), solution becomes Ge richer which causes penetrated X-ray intensity variation at the growth interface. The growth mechanism for the observed SiGe growth process was discussed based on the penetrated X-ray intensity profile and a growth model. The composition of the grown sample was measured by FE-EPMA analysis.
    Full-text · Article · Mar 2014 · Journal of Alloys and Compounds
  • Q. Yang · X. Zhou · T. Nukui · Y. Saeki · S. Izumi · A. Tackeuchi · H. Tatsuoka · S. Liang
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    ABSTRACT: The ultraviolet photoluminescence of ZnO/ZnGa2O4 composite layer grown by the thermal oxidation of ZnS with gallium was investigated by the time-resolved photoluminescence as a function of measuring temperature and excitation power. With increase of excitation power, the D 0X emission is easily saturated than the DAP emission from ZnO/ZnGa2O4 composite layer, and which is dramatically enhanced as compared with that from pure ZnO layer grown without gallium. The radiative recombination process with ultra-long lifetime controlled the carrier recombination of ZnO/ZnGa2O4 composite layer.
    No preview · Article · Feb 2014 · AIP Advances
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    ABSTRACT: Si dissolution into Ge melt, solute transport in the Si-Ge solution and crystal growth of SiGe alloys were in-situ observed by X-ray penetration method. The rectangular shaped sandwich sample of Si (seed)/Ge/Si (feed) was used for the experiment. X-ray intensities penetrated through the sample, which was heated up to the growth temperature of 1,200 °C, were recorded by rectangular shaped CdTe line sensor as a function of time and temperature. The experimental results demonstrated that the dissolution of Si seed was larger compared to Si feed crystal although Si feed temperature was relatively higher than that of seed. Crystal growth of SiGe was observed at the feed interface as the growth interface was observed clearly by an abrupt change of penetrated X-ray intensity near the growth interface. Since the crystal grew with Si rich composition (at high temperature 1,200 °C), solution becomes Ge richer which causes penetrated X-ray intensity variation at the growth interface. The growth mechanism for the observed SiGe growth process was discussed based on the penetrated X-ray intensity profile and a growth model. The composition of the grown sample was measured by FE-EPMA analysis.
    Full-text · Article · Dec 2013 · Journal of Alloys and Compounds
  • Wen Li · Kaito Nakane · Hirokazu Tatsuoka
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    ABSTRACT: Polycrystalline Mg2Si and MnSi1.7 nanowire bundles were synthesized by the heat treatment of Si nanowire arrays under a Mg vapor and MnCl2 vapor, respectively. The structural properties of Mg2Si and MnSi1.7 nanowires and the fabrication phenomenon of them were in-vestigated. The syntheses of Mg2Si and MnSi1.7 nano-wires were carried out at 500 °C and 600 °C for 5 h, respectively, and the morphology of the Si nanowires was preserved after reaction. The density of Mg2Si nanowire bundles was increased compared to that of the Si nanowire arrays, and the density of MnSi1.7 nanowire bundles was decreased. These reactions provided the low-cost and controllable synthetic techniques to synthesize large scale and one-dimensional semi-conducting metal silicides for thermoelectric applications. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    No preview · Article · Dec 2013 · physica status solidi (c)
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    ABSTRACT: Si nanowires were grown on Si(111) substrates, and the shape modification of the nanowires was demonstrated. With the Au catalyst, the highly symmetric faceted silicide solid particle in the Au-Si eutectic solution was formed on the top of the nanowires, and the solid catalyst defined the shape of the Si nanowire. Namely, the VLS growth mechanism was followed by the VSS growth mechanism, and the modified shaped faceted Si nanowire was formed during the VSS growth. This result makes us to expect to control the shape of the nanowires by the formation of facetted silicide particles grown during the Au catalytic growth. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    No preview · Article · Dec 2013 · physica status solidi (c)
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    Wen Li · Kaito Nakane · Motofumi Suzuki · Hirokazu Tatsuoka
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    ABSTRACT: Periodic Mg2Si nanorod arrays were synthesized by the heat treatment of Si nanorod arrays with porous structure under Mg vapor. The structural properties of the Si and Mg2Si nanorods were investigated. The morphology of the Si nanorod arrays is preserved in the Mg2Si nanorod arrays. The diameter and height of the Mg2Si nanorods were significantly increased to 420 nm and 600 nm compared to those of the Si nanorods. The volumetric expansion from Si nanorods to Mg2Si nanorods is about V/VSi = 1.55 and the density of Si nanorods with porous structure is about 48.3%. Periodic Mg2Si nanorod arrays will be useful to control thermal and/or solar radiation. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Full-text · Article · Dec 2013 · physica status solidi (c)
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    Wen Li · Daisuke Ishikawa · Hirokazu Tatsuoka
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    ABSTRACT: A variety of nanostructure bundles and arrays based on semiconducting metal silicides have been synthesized using abundant and non-toxic starting materials. Three types of fabrication techniques of the nanostructure bundles or arrays, including direct growth, template synthesis using natural nanostructured materials and template synthesis using artificially fabricated nanostructured materials are demonstrated. CrSi2 nanowire bundles were directly grown by the exposure of Si substrates to CrCl2 vapor at atmospheric pressure. A hexagonal MoSi2 nanosheet, Mg2Si/MgO composite nanowire and Mg2Si nanowire bundles and MnSi1.7 nanowire array were synthesized using a MoS2 layered material, a SiOx nanofiber bundle, a Si nanowire array, and a Si nanowire array as the templates, respectively. Additionally, the fabrication phenomenon and structural properties of the nanostructured semiconducting metal silicides were investigated. These reactions provided the low-cost and controllable synthetic techniques to synthesize large scale and one-dimensional semiconducting metal silicides for thermoelectric applications.
    Preview · Article · Oct 2013 · Functional Materials Letters

  • No preview · Article · Sep 2013
  • Wen Li · Daisuke Ishikawa · Junhua Hu · Hirokazu Tatsuoka
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    ABSTRACT: MnSi1.7 layers have been successfully grown using a molten salt method. It was found that homogeneous MnSi1.7 layers with columnar domain structure can be grown on MnSi substrates. The dependence of the thickness and domain structure of the layers on the growth conditions was investigated. It was found that the deposited atoms, namely Si, were the dominant diffusion species, and the formation of Kirkendall voids was avoided for the silicidation reaction based on interdiffusion. The layer thickness could be controlled by the growth temperature and time, and was diffusion controlled. The interdiffusion coefficient was approximately 5 × 10-10 cm2/s for growth temperature of 900°C. The activation energy of interdiffusion was deduced to be approximately 1.1 eV for growth of the MnSi1.7 layers. This growth technique provides a simple and controllable method to grow large-area, high-quality MnSi1.7 layers.
    No preview · Article · Sep 2013 · Journal of Electronic Materials
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    ABSTRACT: The shape modification of Si nanowires is demonstrated using faceted solid silicide catalysts. The Si nanowires were grown on Si(111) substrates covered with Au as a catalyst using MnCl2 and Si powders as source materials. The solid silicide catalysts were nucleated and formed in the Au-Si catalyst solution at the top of the nanowires during the growth. The faceted solid silicides grew larger with increased growth time and played a role as a solid catalyst. The faceted shape of the catalyst defines the shape of the faceted Si nanowire. The squared Si nanowires were grown with the growth direction of Si[111] and the sidewalls of {110} and {211} planes. The growth evolution of the faceted Si nanowires occurs by a vapor-liquid-solid mechanism followed by the silicide vapor-solid-solid mechanism. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
    No preview · Article · Sep 2013 · AIP Advances
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    Full-text · Article · Apr 2013 · Journal of Crystal Growth
  • H. Tatsuoka · W. Li · E. Meng · D. Ishikawa
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    ABSTRACT: A variety of nanostructured silicide bundles using abundant, nontoxic materials have been prepared. The CrSi2 nanowire, Mg2Si/MgO composite nanowire and Mg2Si nanowire bundles were synthesized using a Si substrate, a SiOx nanofiber bundle, and a Si nanowire array, respectively. The hexagonal MoSi2 nanosheet bundles were also synthesized using a MoS2 layered material as the template. The growth phenomena and the structural properties of the nanostructured materials have been investigated. In addition, the preparation of the CrSi2/SiOx radial nanowire structures is examined.
    No preview · Article · Mar 2013 · ECS Transactions
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    ABSTRACT: Chromium disilicide (CrSi2) nanostructures were grown by the exposure of Si substrates to CrCl2 vapor at atmospheric pressure, and the growth condition dependence on the morphological and structural properties of CrSi2 was systemically investigated. The various structures of CrSi2, such as microrods, nanowire bundles along with microrods and dendritic nanowire structures, have been grown. It was found that the Si substrate temperature and the quantity of the CrCl2 source materials significantly affect the morphological and structural properties of the CrSi2 structures. The structural evolution of CrSi2 has been discussed on the basis of thermodynamic reactions, vapor deposition growth and dendritic growth phenomena. This growth process provides a simple and controllable method to grow novel nano-scaled structures of transition metal silicides for technological use.
    No preview · Article · Feb 2013 · Journal of Crystal Growth