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Hokkaido University Collection of Scholarly and Academic Papers (135.521 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 20 de 20

  1. Superconductivity in the ternary antimonide LaZnSb

    Wakeshima, Makoto; Sakai, Chiho; Hinatsu, Yukio
    We discovered superconductivity in the ternary antimonide La6ZnSb15, and its superconducting properties are discussed through measurements of the resistivity, specific heat and magnetization. The crystal structure of La6ZnSb15 is an orthorhombic La6MnSb15-type structure consisting of Sb sheets. Its electronic structure indicates that the conduction bands mainly originate from Sb 5p orbitals in these Sb sheets. The electrical resistivity and magnetization measurements reveal that this compound is a type-II superconductor below 3.7 K. The upper critical field at zero temperature, μ0Hc2(0), is determined to be 851(8) mT. In the normal state, the electronic specific heat coefficient, γ, and the Debye temperature,...

  2. Synthesis and properties of SMAPs 1-phospha-4-silabicyclo[2.2.2]octane derivatives

    Ochida, Atsuko; Sawamura, Masaya
    Synthesis and properties of a new class of trialkylphosphine ligands SMAPs (1-phospha-4-silabicyclo[2.2.2]octane derivatives, named after silicon-constrained monodentate alkylphosphine) with Me3P-like steric demand around the phosphorus center are described. A new feature of this class of ligands is the presence of a site for functionalization at the backside of the P-lone pair, which is not the case for Me3P. The SMAP ligands contain phosphorus and silicon atoms at each bridgehead of the bicyclo[2.2.2]octane framework. The molecular constraint of the bicyclic framework makes the steric demand around the phosphorus center as small as that of Me3P and projects the P-lone pair and...

  3. Conductance of a single molecule anchored by an isocyanide substituent to gold electrodes

    Kiguchi, Manabu; Miura, Shinichi; Hara, Kenji; Sawamura, Masaya; Murakoshi, Kei
    The effect of anchoring group on the electrical conductance of a single molecule bridging two Au electrodes was studied using disubstituted [isocyanide (CN–), thiol (S–), or cyanide (NC–)] benzene. The conductance of a single Au/1,4-diisocyanobenzene/Au junction anchored by isocyanide via a C atom (junction with the Au–CN bond) was 3×10−3G0(=2e2/h). The value was comparable to 4×10−3G0 of a single Au/1,4-benzenedithiol/Au junction with the Au–S bond. The Au/1,4-dicyanobenzene/Au molecular junction with the Au–NC bond did not show well-defined conductance values. The metal-molecule bond strength was estimated by the distance over which the molecular junction was stretched before breakdown. The stretched length...

  4. Fabrication of sustainable Au mono-atomic wire showing conductance quantization in solution

    Kiguchi, Manabu; Konishi, Tatsuya; Miura, Shin-ichi; Murakoshi, Kei
    Electric conductance of the Au nano constrictions was investigated in 0.1M Na2SO4 solution under electrochemical potential control. Point contact of Au showing the unit of the quantum conductance, G0 (2e^2/h), can be stretched as long as 1 nm when the electrochemical potential of the contact was kept at 0.5 V vs. Ag/AgCl. The result proves superior stability of Au mono atomic wire fabricated in solution. As the electrochemical potential changed to negative, the stretch length of the mono atomic wire decreased. The change of the stability was recovered as the potential became positive, indicating that the stability of the wire...

  5. Fabrication of stable Pd nanowire assisted by hydrogen in solution

    Kiguchi, M; Murakoshi, K
    We have mechanically fabricated a Pd nanowire in solution under electrochemical potential control. A clear feature appeared in the conductance histogram when the electrochemical potential of the Pd wire was kept at the hydrogen evolution potential. Conductance traces showed the Pd wire was stretched 0.4 nm in length just before breaking, suggesting that at least two Pd atoms might contribute to the formation of the Pd wire. The results indicate that a certain atomic configuration of the Pd nanowire is stabilized by hydrogen. We discuss the stabilization mechanism due to changes in bond strengths caused by hydrogen adsorption or incorporation.

  6. Electrochemical Potential Control of Stretched Length of Au Nano-wire in Solution

    Kiguchi, Manabu; Konishi, Tatsuya; Murakoshi, Kei
    Gold nano wire was mechanically fabricated in 0.1 M Na2SO4 solution under electrochemical potential control. Stretched length of the gold nano-wire was evaluated from the length of the last conductance plateau showing a unit conductance quantum, 1 G0 = 2e^2/h. Estimated wire length changed reversibly with the electrochemical potential. We have shown that the stability of the gold atomic wire could be controlled by the electrochemical potential.

  7. 電気化学電位による金単原子ワイヤーの構造制御

    木口, 学; 小西, 達也; 三浦, 進一; 村越, 敬
    Gold nano wire was mechanically fabricated in solution to study their quantized conductance behavior under the electrochemical potential control. A 1 nm length mono atomic wire showing a unit value of the quantized conductance (G0 = 2e^2/h) was fabricated in solution at room temperature by choosing appropriate electrochemical potential and electrolyte. As well as a unit value, several fractional values were also recognized at the quantization. Intensity of the fractional conductance peak at 0.6 G0 in the histogram increased as the electrochemical potential of the wire became negative. Conductance trace proves that the fractional peak in the histogram is due...

  8. Mechanical fabrication of metal nano contacts showing conductance quantization under electrochemical potential control

    Kiguchi, Manabu; Konishi, Tatsuya; Miura, Shinichi; Murakoshi, Kei
    We have mechanically fabricated Ni and Cu nano constrictions in solution, and studied their electrical conductance under the electrochemical potential control. Conductance quantization can be observed with both metals. This is the first observation of the conductance quantization behavior for non-gold metal nano constrictions, which are mechanically fabricated in solution at room temperature. The conductance of Cu was quantized in units of G0 (=2e2/h), and a sharp 1 G0 peak is observed in the conductance histogram. For Ni, a conductance plateau showed a slightly negative slope, and a broad peak at 1~1.5 G0 was observed in the histogram. The conductance...

  9. Conductance bistability of gold nanowires at room temperature

    Kiguchi, Manabu; Konishi, Tatsuya; Murakoshi, Kei
    Quantized conductance behavior of gold nanowires was studied under electrochemical potential control. We fabricated 1-nm-long monoatomic wires in solution at room temperature. Electrochemical potential significantly affected the stability of the monoatomic wire and fractional conductance peak occurrence in the conductance histogram. We revealed that the hydrogen adsorption on gold monoatomic wires was a decisive factor of the fractional peak, which was originated from the dynamic structural transition between two bistable states of the monoatomic wire showing the unit and the fractional values of the conductance. We could tune the stability of these bistable states to make the fractional conductance state...

  10. Magnetic Interactions of (μ-Pyrazolato)-Bridged Copper(II) Complexes Determined by Solid-State MAS NMR

    Oomomo, Takayuki; Maruta, Goro; Takeda, Sadamu
    We investigated electron spin densities of pyrazolato-bridged complexes [Cu(pz)2]n 1 and [Cu2(pz)2(NO3)(H2O)(phen)2]NO3 2 (Hpz = pyrazole, phen = 1, 10-phenanthroline) using solid-state high-resolution NMR to elucidate the magnetic interaction paths with the help of molecular orbital theory. We prepared deuterated analogue of these complexes, 1-d6 and 2-d6, to measure temperature dependence of 2H- and 13C-NMR shifts between 190 K and 350 K. The hyperfine coupling constants (HFCCs) and electron spin densities were determined from the slopes of the shifts as a function of the magnetic susceptibilities. The derived spin densities were all positive, which indicates the dominant magnetic interaction paths...

  11. Solid-state high-resolution NMR studies on spin density distribution of a ferromagnetic coordination polymer: Ni(NCS)2(Him)2

    Maruta, Goro; Takeda, Sadamu
    We determined hyperfine coupling constants (hfcc) of the imidazole ligand in a ferromagnetic coordination polymer, di-μ-thiocyanatobis(imidazole)nickel(II), using 1H-, 2H-, and 13C-MAS-NMR. Partially or fully deuterated sample was prepared to measure temperature dependence of the isotropic shifts of NMR signals. We obtained hfcc of AC = +0.57, +0.69, +1.88 MHz for 2-, 4-, 5-carbon and AH = +0.66, +0.37, +0.48, +0.53 MHz for 1-, 2-, 4-, 5-proton in the imidazole ligand, respectively, which indicates that unpaired electron in dx2*y2 orbital of Ni(II) ion delocalizes over the imidazole ligand. On the basis of the NMR and DFT results, we proposed an interchain...

  12. Hydrogen-assisted stabilization of Ni nanowires in solution

    Kiguchi, Manabu; Konishi, Tatsuya; Murakoshi, Kei
    We have studied conductance characteristics of mechanically fabricated Ni nanoconstrictions under controlling electrochemical potential and pH of the electrolyte. The conductance histogram showed a clear feature peaked at 1–1.5 G0 (G0=2e2 /h) when the potential of the constriction was kept at more negative potential than −900 mV versus Ag/AgCl at pH=3.7. A comparable feature also appeared at a more positive potential when a lower pH solution was used. We have revealed that Ni monoatomic contact or monoatomic wire can be stabilized in solution at room temperature under the hydrogen evolution.

  13. Biosynthetic study of FR-900848: unusual observation on polyketide biosynthesis that did not accept acetate as origin of acetyl-CoA

    Watanabe, Hiroaki; Tokiwano, Tetsuo; Oikawa, Hideaki
    The biosynthetic pathway of a potent antifungal agent, FR-900848, has been examined by administration of several 13C-labeled precursors to Streptoverticillium fervens HP-891. Although none of the 13C-labeled acetate was incorporated into FR-900848, the labeling pattern of FR-900848 derived from d-[U-13C6]glucose revealed that the fatty acid backbone of FR-900848 has been biosynthesized via a polyketide pathway. These unusual results strongly show that the major pathway to provide acetyl-CoA in this microorganism is glycolysis. Feeding experiments with d-[U-13C6]glucose, [1,3-13C2]glycerol, and l-[Me-13C]methionine provided information on the biosynthetic origin of structurally unusual parts (polycyclopropane and aminonucleoside) in this antibiotic.

  14. Dielectric properties of organic monolayers directly bonded on silicon probed by current sensing atomic force microscope

    Zhao, Jianwei; Uosaki, Kohei
    The dielectric properties of alkyl monolayers with various chain lengths [CH3(CH2)n–1- (n = 12, 14, 16, and 18)] covalently bonded to a hydrogen terminated n-type silicon (111) surface in a nanoscale region were evaluated using current sensing atomic force microscopy (AFM). A reliable electrical contact between the alkyl monolayers and the metal-coated AFM tip was achieved under slight stress. At a force less than 2 nN, current sharply increased as the bias was scanned over a critical value, showing that breakdown took place. The breakdown voltage linearly depended on the chain length of the alkyl monolayers and the dielectric strength...

  15. Infrared study of anomalous volume behavior of water–benzene mixtures in the vicinity of the critical region

    Furutaka, Seiya; Ikawa, Shun-ichi
    Volume behavior of water–benzene mixtures at temperatures and pressures in the 473–623 K and 100–350 bar ranges, respectively, has been studied by infrared in situ measurements. The densities of the benzene-rich phase were estimated from the spectroscopically determined concentrations of water and benzene and compared with the average densities before mixing, which were calculated using literature densities of neat water and neat benzene at the same temperature and pressure. Anomalously large volume change for mixing has been found in the vicinity of the critical region of the water–benzene mixtures.

  16. Near-infrared spectroscopic study of water at high temperatures and pressures

    Jin, Yusuke; Ikawa, Shun-ichi
    Near-infrared absorption of the OH stretching overtone transition of water has been measured at temperatures and pressures in the ranges of 373–673 K and 20–400 bar, respectively. The absorption profile at 673 K and 400 bar retains a mark of rotational structure, indicating that an appreciable proportion of water molecules can rotate quite freely. The molar absorption intensity decreases linearly with increasing pressure in the low-pressure region. Enthalpy for dimerization has been estimated to be 15±3 kJ/mol from the temperature dependence of the slopes. Plots of the molar absorption intensity against molar concentration are observed to be located on a...

  17. Spectroscopic study of mutual solubilities of water and benzene at high temperatures and pressures

    Jin, Yusuke; Ikawa, Shun-ichi
    Near-infrared and ultraviolet absorption of water–benzene mixtures has been measured at temperatures and pressures in the ranges of 323–673 K and 50–400 bar, respectively. Concentrations of water and benzene in both the water-rich phase and the benzene-rich phase of the mixtures were obtained from absorption intensities of near-infrared bands of water and benzene and ultraviolet bands of benzene. Mutual solubilities in molar fractions increase remarkably with increasing temperature at pressures in the two-liquid-phase coexistence region, and are consistent with previously reported values. It proves that the solubility of benzene in water is an order of magnitude smaller than that of...

  18. Anomalous volumetric behavior of water-hexane and water-decane mixtures in the vicinity of the critical region as studied by infrared spectroscopy

    Ishikawa, Yuki; Arai, Sigenori; Furutaka, Seiya; Ikawa, Shun-ichi
    Infrared spectra of binary mixtures of water with hexane and decane were measured at temperatures and pressures in the 473–648 K and 70–350 bar ranges, respectively. Volumetric concentrations of water and the hydrocarbons in the mixtures were obtained from absorption intensities of the fundamental OH stretching band of HDO and combination transitions of the hydrocarbons. Using both the concentrations, densities of the aqueous mixtures were estimated and compared with densities before mixing, which were calculated using literature densities of the neat liquids. It is found that anomalously large volume expansion on mixing occurs in the vicinity of the critical region...

  19. Spectroscopic study of water-NaCl-benzene mixtures at high temperatures and pressures

    Ohya, Tomoyuki; Kitagawa, Masaaki; Jin, Yusuke; Ikawa, Shun-ichi
    Near-infrared and ultraviolet spectra of water-NaCl-benzene mixtures have been measured in the 473–573 K and 100–400 bar range and 373–498 K and 50–300 bar range, respectively. Concentrations of water in the benzene-rich phase and benzene in the water-rich phase were estimated from integrated intensities of the absorption bands. It is found that addition of NaCl in the aqueous phase suppresses transfer of water into the benzene-rich phase, and the relative decrease in water solubility in benzene exhibits good correlation with an increase in density of the aqueous NaCl solution relative to that of neat water. The salting-out constant for the...

  20. Molecular-dynamics study of anomalous volumetric behavior of water-benzene mixtures in the vicinity of the critical region

    Ikawa, Shun-ichi
    Molecular-dynamics simulations of water-benzene mixtures at 573 K and pressures in the 85–140 bars range have been performed to examine local structure and dynamics of the mixtures, which exhibit anomalously large volume expansion on mixing as recently found by in situ near-infrared measurements. Fractional charges for a simple-point-charge-type potential of water were adjusted so as to reproduce liquid densities and the gas-to-liquid transition pressure of neat water at 573 K. A Lennard-Jones-type potential for benzene was used and the Lorentz-Berthelot combination rule was applied to the water-benzene interaction. Simulations with a N-P-T ensemble of 800-molecule system have been performed and...

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