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  • 2000-2004  (2)
  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Metallurgical study of Ni/GaAs contacts. I. Experimental determination of the solid portion of the Ni-Ga-As ternary-phase diagram (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2122-2128 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray diffraction on powders and single crystals has been performed to determine the limits of homogeneity and crystallographic data of metallic ternary phases which occur in the bulk Ni-Ga-As system and to draw the solid portion of the phase diagram. The samples were prepared in closed, small-volume containers to prevent the formation of gas-phase products. Five ternary phases which crystallize in hexagonal symmetry and are all structurally derived from the NiAs type were evidenced. Among them, three phases show hexagonal superlattices: a(3)1/2×3c, 2a×4c, and 3a×2c which denote ordered structures. Neither nickel nor ternary phases are in thermodynamic equilibrium with GaAs, in contrast to the binaries NiGa, Ni2 Ga3, and NiAs which are. The bulk-phase diagram determined in this study provides a framework within which most of the experimental data concerning the products of reactions at Ni/GaAs interfaces can be understood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344307
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  • 2
    Electronic Resource
    Electronic Resource
    Metallurgical study of Ni/GaAs contacts. II. Interfacial reactions of Ni thin films on (111) and (001) GaAs (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2129-2136 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The solid-state interactions at the Ni/(111) and (001) GaAs interfaces were investigated in the temperature range 25–600 °C by Rutherford backscattering spectrometry and channeling experiments, x-ray diffractometry, and four-point probe. The samples were prepared by depositing nickel films, 70 nm thick, onto clean (111) and (001) GaAs single-crystal substrates under 5×10−10 Torr vacuum. Then they were annealed for 1 h at increasing temperatures under a flow of forming gas (90% N2-10% H2). The sequence of phase formation was the following: first, a ternary phase at 200 °C, then a mixture of two ternary phases at 250 and 350 °C, and finally from 400 to 580 °C a mixture of a ternary phase and NiAs. This last structure was stable up to 600 °C on (111) GaAs, but at this temperature a further consumption of GaAs led to a mixture of (NiGa+NiAs) onto (001) GaAs. Small differences were observed versus the orientation of the GaAs samples but all the ternary and binary phases exhibited epitaxial arrangements with both the (111) and (001) GaAs substrates. The ternary-phase diagram for the bulk Ni-Ga-As system provides the basis for understanding the sequence of the above results and much of the information in the literature about Ni/GaAs interfacial reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344308
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Solutal convection during directional solidification of a binary alloy: Influence of side walls (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2086-2092 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study the effect of rigid side walls on the onset of solutal convection in the melt is investigated for upward solidification of a binary alloy. The physics is described by the Navier–Stokes equations in the Boussinesq approximation and by the balance of solute, which is coupled with the appropriate boundary conditions. By using a Tau–Chebyshev spectral method the numerical resolution of the perturbed system has been carried out for two alloys: lead–tin, which is the reference in the literature, and lead–thallium, which is currently under study. For both cases the lateral confinement has a stabilizing effect for all the aspect ratios that have been considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866661
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Relationship between thermal conductivity and water content of soils using numerical modelling (2003)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 54 (2003), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: There is no simple and general relationship between the thermal conductivity of a soil, λ, and its volumetric water content, θ, because the porosity, n, and the thermal conductivity of the solid fraction, λs, play a major part. Experimental data including measurements of all the variables are scarce. Using a numerical modelling approach, we have shown that the microscopic arrangement of water influences the relation between λ and θ. Simulated values for n ranging from 0.4 to 0.6, λs ranging from 2 to 5 W m−1 K−1 and θ from 0.1 to 0.4 can be fitted by a simple linear formula that takes into account n, λs and θ. The results given by this formula and by the quadratic parallel (QP) model widely used in physical property studies are in satisfactory agreement with published data both for saturated rocks and for unsaturated soils. Consequently, the linear formula and the QP model can be used as practical and efficient tools to investigate the effects of water content and porosity on the thermal conductivity of the soil and hence to optimize the design of thermal in situ techniques for monitoring water content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2003.00539.x
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  • 5
    Electronic Resource
    Electronic Resource
    Three-dimensional crack monitoring by electrical resistivity measurement (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    European journal of soil science 55 (2004), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Soil cracks formed by natural processes play a key role in water and gas transfer. Patterns of soil cracks are, however, difficult to characterize. Our aim here is to assess the effectiveness of three-dimensional electrical resistivity surveys in detecting soil crack networks. A three-dimensional electrical survey was carried out by a square array quadripole with Cu–CuSO4 electrodes (electrode spacing of 3 cm). The measurements were made with two orientations (0° and 90°) on a block (26 cm × 30 cm × 40 cm) of soil while it dried for 18 days under controlled conditions. Two indexes, calculated from the apparent resistivity values, were evaluated to detect the degree of soil heterogeneity: (i) an anisotropy index based on the ratio between the apparent resistivity at 0° and that at 90°; and (ii) the angle-array orientation corresponding to the preferential anisotropic orientation (maximum resistivity). The anisotropy index provided information on the presence of cracks and the orientation for crack width 〉 1 mm in the first pseudo-depth (i.e. depth of investigation), while the angle-array orientation provided information on crack extension for the whole pseudo-depth. Information about the presence, position, orientation and extension of cracks can be obtained from an analysis of apparent resistivity obtained by a three-dimensional electrical survey. Such direct analysis will help the resistivity inversion to detect the crack network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.2004.00632.x
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