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  • 1
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    Instability and associated roll structure of Marangoni convection in high Prandtl number liquid bridge with large aspect ratio (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-02-19
    Description: This paper reports the experimental results on the instability and associated roll structures (RSs) of Marangoni convection in liquid bridges formed under the microgravity environment on the International Space Station. The geometry of interest is high aspect ratio ( AR = height/diameter ≥ 1.0) liquid bridges of high Prandtl number fluids ( Pr = 67 and 207) suspended between coaxial disks heated differentially. The unsteady flow field and associated RSs were revealed with the three-dimensional particle tracking velocimetry. It is found that the flow field after the onset of instability exhibits oscillations with azimuthal mode number m = 1 and associated RSs traveling in the axial direction. The RSs travel in the same direction as the surface flow (co-flow direction) for 1.00 ≤ AR ≤ 1.25 while they travel in the opposite direction (counter-flow direction) for AR ≥ 1.50, thus showing the change of traveling directions with AR . This traveling direction for AR ≥ 1.50 is reversed to the co-flow direction when the temperature difference between the disks is increased to the condition far beyond the critical one. This change of traveling directions is accompanied by the increase of the oscillation frequency. The characteristics of the RSs for AR ≥ 1.50, such as the azimuthal mode of oscillation, the dimensionless oscillation frequency, and the traveling direction, are in reasonable agreement with those of the previous sounding rocket experiment for AR = 2.50 and those of the linear stability analysis of an infinite liquid bridge.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Carbon nanotube dispersed conductive network for microbial fuel cells (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-08-27
    Description: Microbial fuel cells (MFCs) are promising devices for capturing biomass energy. Although they have recently attracted considerable attention, their power densities are too low for practical use. Increasing their electrode surface area is a key factor for improving the performance of MFC. Carbon nanotubes (CNTs), which have excellent electrical conductivity and extremely high specific surface area, are promising materials for electrodes. However, CNTs are insoluble in aqueous solution because of their strong intertube van der Waals interactions, which make practical use of CNTs difficult. In this study, we revealed that CNTs have a strong interaction with Saccharomyces cerevisiae cells. CNTs attach to the cells and are dispersed in a mixture of water and S. cerevisiae , forming a three-dimensional CNT conductive network. Compared with a conventional two-dimensional electrode, such as carbon paper, the three-dimensional conductive network has a much larger surface area. By applying this conductive network to MFCs as an anode electrode, power density is increased to 176  μ W/cm 2 , which is approximately 25-fold higher than that in the case without CNTs addition. Maximum current density is also increased to approximately 8-fold higher. These results suggest that three-dimensional CNT conductive network contributes to improve the performance of MFC by increasing surface area.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Effect of the hexagonal phase interlayer on rectification properties of boron nitride heterojunctions to silicon (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-02-07
    Description: Rectification properties of boron nitride/silicon p-n heterojunction diodes fabricated under low-energy ion impact by plasma-enhanced chemical vapor deposition are studied in terms of the resistive sp 2 -bonded boron nitride (sp 2 BN) interlayer. A two-step biasing technique is developed to control the fraction of cubic boron nitride (cBN) phase and, hence, the thickness of the sp 2 BN interlayer in the films. The rectification ratio at room temperature is increased up to the order of 10 4 at ±10 V of biasing with increasing the sp 2 BN thickness up to around 130 nm due to suppression of the reverse leakage current. The variation of the ideality factor in the low bias region is related to the interface disorders and defects, not to the sp 2 BN thickness. The forward current follows the Frenkel-Poole emission model in the sp 2 BN interlayer at relatively high fields when the anomalous effect is assumed. The transport of the minority carriers for reverse current is strongly limited by the high bulk resistance of the thick sp 2 BN interlayer, while that of the major carriers for forward current is much less affected.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
    Electronic Resource
    Electronic Resource
    A Monte Carlo study of the pattern formation during transitions in n-alkane crystals (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 7627-7633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotator phase transition in n-alkane was recently found to show a characteristic pattern of preferred growth along the b-axis (shorter axis) of the unit cell. In order to investigate the origin of this anisotropic growth, a pattern formation in n-alkane crystal is studied during the transition between the low temperature orthorhombic (LO) phase and the rotator (R) phase by use of the Monte Carlo method. Of possible factors that will influence the growth pattern, we here concentrate on the mode of chain packing by assuming that the chains have rigid planar zigzag conformation and are placed in a regular orthohexagonal lattice. The herringbone order in the LO phase is found to develop rather quickly resulting characteristic domains with the (100) and (110) boundaries. The domain boundaries run preferentially along the b-axis at lower temperatures and are considered as a stacking fault or antiphase boundary. The transition between the LO phase and the R phase is found to exhibit a characteristic pattern, where the R phase domains grow preferentially along the b-axis. All these behaviors are shown to originate from different energies of the (100) and (110) boundaries. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481357
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  • 5
    Electronic Resource
    Electronic Resource
    Photoluminescence studies in CuAlSe2 epilayers grown by low-pressure metalorganic chemical-vapor deposition (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1225-1232 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photoluminescence (PL) spectra were investigated for CuAlSe2 epilayers grown on GaAs(001) substrates by means of low-pressure metalorganic chemical-vapor deposition. PL properties were studied with relation to metalorganic precursors used for the growth. High-quality undoped epilayers exhibited PL peaks related to a free exciton (2.739 eV) and a bound exciton (2.677 eV). The other undoped epilayers exhibited PL bands at 2.3, 2.4, and 2.5 eV originating from donor-acceptor (D-A) pair recombinations. Some of them were found to have a common activation energy for the thermal quenching of 50±10 meV. The PL spectrum changed drastically by impurity doping. Intense green emissions at 2.51 and 2.43 eV were observed in Zn and Mg-doped epilayers, respectively, which were interpreted as D-A pair recombinations based on the dependencies of the PL spectra on excitation intensity, decay time, and temperature. The donor and the acceptor activation energies (ED and EA) were estimated to be 110 and 230 meV, respectively, for the Zn-related D-A pair emission at 2.51 eV. Similarly, ED and EA for CuAlSe2:Mg were estimated to be 140±10 and 270±10 meV, respectively. Furthermore, D-A pair recombinations between 2.3 and 2.5 eV for CuAlSe2:I were studied. CuAlSe2 was proven to be a promising material for short-wavelength visible-light-emitting devices. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358990
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  • 6
    Electronic Resource
    Electronic Resource
    Heteroepitaxy and characterization of CuGaSe2 layers grown by low-pressure metalorganic chemical-vapor deposition (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3009-3015 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CuGaSe2 chalcopyrite compounds were grown heteroepitaxially on both GaAs and GaP substrates by means of the low-pressure metalorganic chemical-vapor deposition method. Optical and structural properties were characterized comprehensively by photoreflectance (PR), photoluminescence (PL), x-ray diffraction, transmission electron microscopy, transmission electron diffraction, and electron-probe microanalysis. The CuGaSe2 epilayers had c(001) surface on GaAs(001) substrates and a(100) surface on GaP(001) substrates, respectively, the results being similar to the case of CuAlSe2. Energies of A, B, and C excitons associated with uppermost valence bands were determined from analysis of PR spectra, and the energies of good-quality epilayers are close to those of the bulk crystal. The slight increase of the crystal-field splitting in the valence bands were discussed in terms of the lattice strain in the epilayer caused by the lattice mismatch. Low-temperature PL spectra exhibited an intense peak at 1.71 eV, the energy being in good agreement with the A-exciton energy. A weak peak due to a free-to-acceptor transition was also observed at 1.66 eV. A broad PL peak at 1.76 eV was observed together with the intense band-edge PL at 1.67 eV, and the peak was assigned to relate to the B-exciton transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357503
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  • 7
    Electronic Resource
    Electronic Resource
    Laser power dependence of particulate formation on pulse laser deposited films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2029-2036 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The density and the size of particulates in films laser-deposited at room temperature using various target materials were observed to depend strongly on the target material and the laser power density. However, loose universal relations between the deposition rates and the particulate density as well as the particulate size were found, where the latter corresponds approximately to the ratio of the laser power density to the ablation threshold. Furthermore, particulates consisting of only some of the target elements such as CuOx were found. Additionally, an acceptably high deposition rate was obtained by using halide and sulfide targets. These materials offer a possibility of deposition using a low power laser. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360179
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  • 8
    Electronic Resource
    Electronic Resource
    Monoenergetic positron beam study of Si-doped GaAs epilayers grown by low-pressure metalorganic chemical vapor deposition using tertiarybutylarsine (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3880-3885 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si-doped GaAs epilayers grown by low-pressure metalorganic chemical vapor deposition (MOCVD) using tertiarybutylarsine (tBAs) were investigated using a slow positron beam. The concentration of Ga vacancies, VGa, generated in GaAs epilayers was increased drastically by heavy Si doping of more than 1019 cm−3, where the deactivation of Si occurred. This result suggests that the deactivation of Si in GaAs is mainly caused by a VGa-related defect, such as a VGa-SiGa complex. The VGa concentration in the samples grown using tBAs was found to be almost the same as that grown using arsine (AsH3). On the other hand, the VGa concentration in MOCVD-grown Si-doped GaAs is lower than that in molecular-beam-epitaxy-grown material for the same Si concentrations. The generation mechanisms of VGa were found to be greatly dependent on the growth and/or doping methods, in addition to the Si doping concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352900
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  • 9
    Electronic Resource
    Electronic Resource
    Thermal conversion of semi-insulating GaAs in high-temperature annealing (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 615-618 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-temperature annealing of semi-insulating GaAs has been studied. Thermal conversion induced by annealing at 1060–1200 °C can be explained by the causes of both the reduction of EL2 concentration and the generation of deep acceptors during high-temperature annealing. Both of them can be rationalized by the supposition that the antisite defect, AsGa, breaks into AsI and VGa, and the latter is a deep acceptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353371
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  • 10
    Electronic Resource
    Electronic Resource
    Boron doping of silicon by ArF excimer laser irradiation in B2H6 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7204-7210 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Boron doping of silicon using a pulsed ArF excimer laser (λ=193 nm, FWHM=17 ns) with B2H6 has been investigated. Doping atoms are supplied mainly from both thermal and photochemical decomposition of the adsorbed layers on the surface. UV laser irradiation realizes both high surface carrier concentration (1×1021 cm−3) and a very shallow junction (0.1 μm). Diodes fabricated by laser doping show good electrical characteristics (n factor=1.10, reverse current density=1×10−7 A/cm2 at −5 V). Thermal annealing improves the reverse current density (3×10−9 A/cm2 at −5 V). A numerical calculation of boron concentration profiles has been performed by solving the diffusion equation in the melted region, which is evaluated by the heat conduction equation. From this calculation the diffusion coefficient of boron in liquid phase silicon (3×10−4 cm2/s) is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344553
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