Mitsuru Matsuura

Yamaguchi University, Yamaguti, Yamaguchi, Japan

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Publications (104)61.36 Total impact

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    ABSTRACT: We investigated photoluminescence properties of the exciton and the biexciton in CuCl quantum dots embedded in an SiO2 matrix on (λ/4)TiO2/(λ/4)SiO2 dielectric multilayers of the distributed Bragg reflector. The intensities of the free exciton luminescence band and the biexciton luminescence bands are enhanced by factors 2 and 6 times in comparison with those in only CuCl quantum dots embedded in an SiO2 matrix. The origin of this luminescence behavior is partly reflection effects of the luminescence and excitation laser lights but additional effects need to be considered. One possible candidate is the strong exciton-photon interaction due to the confinement effect of the photons in the active layer with CuCl quantum dots.
    International Journal of Modern Physics B 01/2012; 15(28n30). DOI:10.1142/S0217979201008809 · 0.46 Impact Factor
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    ABSTRACT: We calculated electronic structures of Ba8Al16Ge30 in some Al-Ge framework configurations without nearest-neighbor Al-Al bonds by using a first-principles method. The calculated band structures are similar in outline but different in detail. We also calculated thermoelectric properties by using the electronic structures to analyze the experimental results on a sintered Ba8Al16Ge30 sample. The calculated properties nearly agree with the experimental results; however, the calculated temperature dependences of electrical conductivity are slightly different from one another, because of differences in electronic structure. In this paper, we discuss the temperature dependence from the viewpoints of nonparabolic band effects.
    Journal of Electronic Materials 07/2009; 38(7). DOI:10.1007/s11664-009-0727-1 · 1.68 Impact Factor
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    Materials transactions 01/2009; 50(3):631-639. DOI:10.2320/matertrans.E-MRA2008846 · 0.80 Impact Factor
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    ABSTRACT: Thermoelectric properties of Al-substituted Ge clathrate compounds Ba <sub>8</sub> Al <sub>x</sub> Ge <sub>46-x</sub> were investigated experimentally and theoretically. Polycrystalline Ba <sub>8</sub> Al <sub>x</sub> Ge <sub>46-x</sub> (x=12–18) was synthesized by using an arc melting and a spark plasma sintering technique. The obtained samples show the n -type behavior and the carrier concentration decreases with increasing amount of Al composition from x=12 to 16. The reasonably large power factors was obtained: 900–1000 μ W / cm   K <sup>2</sup> around 900 K. Theoretically electronic structure of Ba <sub>8</sub> Al <sub>16</sub> Ge <sub>30</sub> was calculated by means of a first-principles method and then thermoelectric properties were analyzed on the basis of the result of the calculated electronic structure. The calculated thermoelectric properties agree with the experimental results very well in the wide range of temperature between room temperature and 900 K.
    Journal of Applied Physics 08/2008; 104(1-104):013702 - 013702-8. DOI:10.1063/1.2947593 · 2.19 Impact Factor
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    ABSTRACT: The electronic structure and thermoelectric properties of guest substituted clathrate compounds Ba6R2Au6Ge40 (R = Eu, Yb) are calculated using the full-potential linearized augmented plane wave method based on the density functional theory. The bottom of conduction band for Ba8Au6Ge40 is formed by one relativity dispersive band close to the M point. When the Ba 2a site is replaced by Eu and Yb, the lowest conduction bands at X point shift to lower energy side. The coupling between gusest atom at 2a sites and the host framework becomes weaker with decreasing ionic radii. This multivalley effect in M and X points yields the increase in the density of states near the conduction band edge, resulting in the increase in the Seebeck coefficient for n-type doping. On the other hand, the valence band edge is almost independent of the guests; the f-bands of Eu and Yb are narrow and distant from the band edge. The effect of Eu and Yb substitution on the Seebeck coefficient is small for p-type doping at higher temperature.
    Materials transactions 08/2007; 48(8):2108-2113. DOI:10.2320/matertrans.E-MRA2007865 · 0.80 Impact Factor
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    ABSTRACT: Tellurium-containing cationic clathrates Si46-xPxTe8 (x = 11--17) were synthesized using powder metallurgy. This study crystallized the Pm\bar{3}n (No. 223) structure and showed a p-type conductivity; their band gap energy is estimated to be 1.24 eV. Although the Si46-xPxTe8 samples with x = 16 and 17 were intrinsic, the samples with x = 11--15 were degenerated semiconductors; their electrical conductivity σ increased and their Seebeck coefficient S almost decreased with decreasing x. A power factor S2σ of 12 μW cm-1 K-2 at 1000 K and a dimensionless figure of merit \mathit{ZT} of 0.45 at 900 K were achieved for a p-type silicon clathrate Si33P13Te8.
    Japanese Journal of Applied Physics 07/2007; 46(29-32):L746-L748. DOI:10.1143/JJAP.46.L746 · 1.06 Impact Factor
  • Koji Akai, Kenji Koga, Mitsuru Matsuura
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    ABSTRACT: Electronic structure and thermoelectric properties of noble metal clathrates Ba8M6Ge40(M = Cu, Ag, An) were calculated by using a first principle based method to discuss prospect of high performance thermoelectric materials. The calculated band structures show that these clathrate compounds are degenerate semiconductors with 1) type carrier. The band gaps become narrow by noble metal doping. The band gap narrowing is caused by the valence band lifting due to anti-bonding nature between Ge and M, and conduction band widening due to frameworkguest atom coupling via Ba orbitals at 6d sites. The thermoelectric power of Ba8M6Ge40 increases with temperatures monotonically and the magnitude is smaller than 100 mu V/K under 1000K. The carrier concentration of Ba(8)M(6)GC(40) is a little larger for the high performance thermoelectric materials. The carrier concentration is controlled by varying the composition of Ba8AuxGe46-x. The optimized carrier concentration in Ba8AuxGe46-x was obtained as 4.4 x 10(26) m(-3) (p type) and 6.4 x 10(26) m(-3) (n type), respectively.
    Materials transactions 04/2007; 48(4):684-688. DOI:10.2320/matertrans.48.684 · 0.80 Impact Factor
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    ABSTRACT: The surface oxide layer of a titanium alloy treated by mechanochemical polishing (MCP) was characterized using a scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), X-ray photoelectoron spectoroscopy (XPS), auger electoron spectoroscopy (AES) and secondary ion mass spectrometry (SIMS). The results showed that surface oxide layer was amorphous titanium oxide and had about 5 nm thickness. At the interface between surface oxide layer and substrate, there was a region of high hydrogen concentration. In the same region, the Ti-F chemical component was found. It seems that this interface layer acts as a barrier for the bulk hydrogen diffusion, and gives low hydrogen concentration at the surface layer resulting in the low outgassing property in the titanium materials.
    Shinku 01/2007; 50(1):53-56. DOI:10.3131/jvsj.50.53
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    ABSTRACT: A reactive sputtering apparatus utilizing electron cyclotron resonance (ECR) was developed for the deposition of thick oxide or nitride films usable in electric devices. A high deposition rate of 44 nm/min. was achieved using a conic alloy target and the deposited soft ferrite thin films were successfully crystallized without heat treatment during film deposition. Magnetic and physical properties for the film were analyzed in terms of saturation magnetization, coercivity, uniformity of film thickness, and inner stress. Obtained properties were consistent with soft magnetic films. The result confirms the oxygen partial pressure ratio to deposition rate strongly affected the magnetic properties. Well crystallized, ultra thin 3-nm-thick Ni-Zn ferrite (100) films, were also successfully deposited on MgO (100) underlayers. These results imply the ECR sputtering method is one of the most effective deposition methods for highly crystallized polycrystalline thick and thin films. Crystal orientation was improved by low target voltage sputtering as well as a relatively low deposition rate. Further improvement is considered to be possible by deposition at lower base pressures.
    Shinku 01/2007; 49(7):424-429. DOI:10.3131/jvsj.49.424
  • Materials Science Forum 01/2007; DOI:10.4028/
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    ABSTRACT: This paper reviewed the vacuum characteristic of titanium materials and applications to an UHV system of the current research and development. It has been found that the outgassing rate of the titanium material is very low compared with an existing material such as a stainless steel or an aluminum alloy, and the UHV system made of the titanium material has very high vacuum performance, e.g., very quick pumping and the achievement of UHV/XHV pressure under the simple pre-baking condition.
    Journal of the Vacuum Society of Japan 01/2007; 50:41-46. DOI:10.3131/jvsj.50.41
  • Journal of the Japan Society of Powder and Powder Metallurgy 01/2007; 54(8):576-583. DOI:10.2497/jjspm.54.576
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    ABSTRACT: We developed a chemical polishing (CP) for titanium materials applicable to ultrahigh vacuum (UHV) and extremely high vacuum (XHV) systems. The surface roughness, Ra, of the chemically polished titanium is obtained to be 25 nm by the atomic force microscopy measurement. This value is smaller than those of the base metal (BM) and the buff-polished (BP) samples. The thickness of the surface oxide layer of CP sample is estimated to be 7 nm by the cross section of transmission electron micrograph. Amount of desorption gas of CP sample obtained by the thermal desorption measurement is smaller than those of BM and BP sample, and is the same as that of the mechanochemically polished (MCP) sample. The outgassing rate of CP sample after baking at 150°C×20 h is obtained to be 7×10-13 Pa•m•s-1. This value is lower than that of standard vacuum materials by two orders of magnitude after the ordinary baking.
    Shinku 01/2007; 49(4):254-258. DOI:10.3131/jvsj.49.254
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    ABSTRACT: The tellurium-containing cationic type-I clathrate Ge <sub>30</sub> P <sub>16</sub> Te <sub>8</sub> was synthesized and its thermoelectric properties were investigated. This clathrate showed a p -type conductivity, while most of the clathrates are n type. The Ge <sub>30</sub> P <sub>16</sub> Te <sub>8</sub> clathrate had a band gap energy of 0.62 eV and a room temperature thermal conductivity of 9 mW cm <sup>-1</sup> K <sup>-1</sup> , which is as low as those of germanium clathrates such as anionic Sr <sub>8</sub> Ga <sub>16</sub> Ge <sub>30</sub> and cationic Ge <sub>38</sub> Sb <sub>8</sub> I <sub>8</sub> . The electronic structure of the Ge <sub>30</sub> P <sub>16</sub> Te <sub>8</sub> clathrate was also calculated using an ab initio method.
    Applied Physics Letters 11/2006; 89(17-89):172106 - 172106-3. DOI:10.1063/1.2364473 · 3.52 Impact Factor
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    ABSTRACT: Outgassing properties and surface profiles of titanium materials have been investigated in this paper. Titanium materials showed excellent outgassing rates below 10<sup>-12</sup> Pams<sup>-1</sup> after baking process. These values are two orders of magnitude smaller than that for standard vacuum materials under the same pre-baking condition. Outgassing rates of the pure titanium of JIS grade 2, titanium alloy, KS100, are about 1/4 of that for a stainless steel without baking process. Titanium materials are applicable for the vacuum chamber and vacuum components. The vacuum equipment made of the titanium material has excellent vacuum performance, e.g., very quick evacuation and UHV/XHV pressures are easily obtainable
    Discharges and Electrical Insulation in Vacuum, 2006. ISDEIV '06. International Symposium on; 10/2006
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    ABSTRACT: We study optical spectra of cavity modes of exciton–polaritons in an organic crystal. The cavity is composed of distributed Bragg reflectors and anthracene crystals occupy the gap of the cavity. Many transmittance peaks corresponding to the cavity modes appear in the photonic band gap region of the transmittance spectra. The spectral positions of the cavity modes converge to the exciton resonance in anthracene. Dispersion of the cavity modes is obtained from the spectral peaks. It looks like a dispersion of the exciton–polariton in anthracene; however it differs slightly from the dispersion curve of the polariton. This discrepancy between the dispersion of the modes and the polariton curve is ascribed to the effective cavity length varying with the refractive index of anthracene.
    Journal of Luminescence 07/2006; 119:137-141. DOI:10.1016/j.jlumin.2005.12.021 · 2.37 Impact Factor
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    ABSTRACT: Well-crystallized Ni-Zn ferrite (Ni0.4Zn0.6Fe2O4) highly oriented ultrathin films were obtained at a substrate temperature of 200 °C by a reactive sputtering method utilizing electron cyclotron resonance microwave plasma, which is very effective to crystallize oxide or nitride materials without heat treatment. Thin films of Ni-Zn ferrite deposited on a MgO (100) underlayer showed an intense X-ray-diffraction peak of (400) from the Ni-Zn ferrite as compared to similar films deposited directly onto thermally oxidized Si substrates. A 1.5-nm-thick Ni-Zn ferrite film, which corresponds to twice the lattice constant for bulk Ni-Zn ferrite, crystallized on a MgO (100) underlayer.
    Journal of Applied Physics 04/2006; 99(8):507-08. DOI:10.1063/1.2169538 · 2.19 Impact Factor
  • Journal of the Magnetics Society of Japan 01/2006; 30(4):468-471. DOI:10.3379/jmsjmag.30.468
  • G. J. Zhao, K. Akai, M. Matsuura
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    ABSTRACT: The electronic structure and thermoelectric properties of Nax CoO2 ware calculated by using a full-potential linearized augmented plane-wave (FLAPW) method with a generalized gradient approximation (GGA). The partial occupancy of Na ion was taken account by the virtual-crystal like approximation. The calculated density of states is good agreement with the XPS data. The thermoelectric power was calculated by using the results of the band structure calculation within the linearized Boltzmann equation. Energy dependence of a relaxation time was neglected. The calculated thermoelectric power of Na0.85CoO2 reproduced experimental results very well for the wide temperature range without any adjustable parameter
    01/2006; DOI:10.1109/ICT.2006.331388
  • K. Akai, K. Koga, M. Matsuura
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    ABSTRACT: The electronic structure of type-III Ba clathrates was calculated by using a full-potential linearized augmented plane-wave (FLAPW) method. In the calculation of Ba6Al4Si21 a virtual crystal approximation was used. The calculated band structure shows that Ba6Al4Si21 is an intrinsic semiconductor with an indirect gap. The top of the valence band is at the Gamma point and the bottom of the conduction band is on the Lambda axis. The thermoelectric properties are calculated by using the calculated electronic states
    01/2006; DOI:10.1109/ICT.2006.331389

Publication Stats

293 Citations
61.36 Total Impact Points


  • 1997–2012
    • Yamaguchi University
      • • Department of Science and Engineering
      • • Faculty of Engineering
      Yamaguti, Yamaguchi, Japan
  • 2008–2009
    • The Open University of Japan
      Edo, Tōkyō, Japan
  • 2006
    • Air University
      Maxwell, California, United States