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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2410-2413 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-chamber in situ laser processing of high-Tc YBa2Cu3O7−δ film on stainless steel (302) substrates with yttria-stabilized zirconia (YSZ) buffer layers, has been carried out using a multitarget deposition system. YSZ and YBa2Cu3O7−δ films were deposited sequentially by KrF excimer laser (λ=248 nm) at substrate temperature of 650 °C. The films were characterized by x-ray diffraction, four point probe ac electrical resistivity, scanning electron microscopy and Auger electron spectroscopy (AES) techniques. Due to the matching of the thermal expansion coefficient of YSZ with stainless steel and its diffusion barrier characteristics, good quality high-Tc films have been grown on stainless steel substrates with superconducting transition temperature, Tc (onset), of 92 K and Tco (zero resistivity temperature) of 84 K. AES depth profiling indicated little interdiffusion of Fe across the interface of YSZ and stainless steel. A laser evaporation method was used for patterning the YBa2Cu3O7−δ films and critical current density, Jc, was measured to be ∼5×104 Acm−2 at 40 K. It was observed that the zero resistivity temperature significantly changed with the variation of buffer layer thickness, buffer layer processing temperature, and ambient oxygen partial pressure during the deposition of YBa2Cu3O7−δ.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5668-5678 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics and Monte Carlo simulations are used to examine the effect on the structural properties of heterogeneous SF6–(Ar)n and SF6–(Kr)n clusters, and on the melting behavior of heterogeneous SF6–(Ar)n and homogeneous (Ar)13 and (Kr)13 clusters, of including the three-body Axilrod–Teller–Muto triple–dipole dispersion energies in the total potential energy surface governing the dynamics of the system. The behavior of these systems is governed by potentials constructed from the best available two-body interactions, and from accurate constrained dipole oscillator strength values for the triple–dipole dispersion energy coefficients reported here for the first time. The structural studies show that (virtually) all isomers are destablized by inclusion of the three-body terms, with the "stacked'' or "nonwetting'' structures being destablized relatively more than isomeric "monolayer'' or "wetting'' structures. However, the qualitative trends in relative stability are unchanged; in particular, the preference for the SF6 to be fully solvated in larger clusters formed with Ar, but to lie on the surface of larger clusters formed with Kr, remains unchanged. In contrast, the melting temperatures of the stacked and monolayer isomers of the heterogeneous SF6–(Ar)12 cluster undergo substantial change on inclusion of the three-body terms, the former dropping from ca. 30 to 22 K and the latter from 10 to 6 K. The melting temperatures of the homogeneous (Ar)13 and (Kr)13 icosahedral isomers also decreased on inclusion of the three-body interactions, and the resulting values are quite different than those obtained using the commonly accepted "effective'' two-body LJ(12,6) pair potentials for these systems.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2594-2596 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Good quality superconducting YBa2Cu3O7−δ thin films have been grown on nickel-based superalloy, viz., Hastelloy with yttria-stabilized zirconia buffer layers employing a single chamber in situ pulsed laser deposition process. YBa2Cu3O7−δ films were found to be textured with c axis perpendicular to the substrate. A plot of normalized resistance against temperature exhibited a smooth metallic behavior followed by an onset superconducting transition at 92 K with the zero resistance temperature (Tc0) of 86 K. Critical current density for these films at 77 K was ∼7000 A cm−2 and critical current (Ic) was observed to be proportional to (1 − T/Tc0)1.4.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2034-2036 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have prepared highly oriented bismuth cuprate thin films (c-axis textured) on yttria-stabilized zirconia (100) YS-ZrO2 substrates at 650 °C by pulsed excimer laser ablation in a 200 mTorr oxygen ambient. The films were annealed in oxygen and nitrogen atmospheres to study the effect on zero-resistance transition temperature (Tc0). Thin films deposited at 650 °C exhibited a Tc0 of 68 K with onset at 110 K. Post-annealing for 1 h at 400 °C in oxygen improved the Tc0 to 82 K, while the onset remained the same. X-ray diffraction, scanning electron microscopy, and Rutherford backscattering channeling studies were performed on these films for correlations between crystal structure, microstructure, and superconducting properties. X-ray diffraction patterns indicated a 2212 type phase with a=5.39 A(ring) and c=30.76 A(ring); preferential orientation of the c axis perpendicular to the substrate was observed. The lattice parameters and x-ray diffraction patterns were found to be invariant with annealing treatments that improved Tc0 from 68 to 82 K.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1460-1462 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have systematically investigated resistance of a bismuth cuprate Bi1.5Pb0.5Ca2Sr2Cu3Ox as a function of different annealing treatments. X-ray diffraction and transmission electron microscopy studies were performed on concomitant specimens for correlations between structure and superconducting properties. A sharp 110 K superconducting transition was observed in the sample which was isostructural with the n=2 member of the (Bi,Pb)2(Ca,Sr)n+1CunO2n+4+δ family. The zero resistance transition temperature Tc0 was found to be sensitive to annealing at 673 K with a best result of 100 K for 30 min annealing. It is proposed that Tc0 and transition width in bismuth cuprates are sensitive to oxygen stoichiometry.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 976-978 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have prepared high quality superconducting Y1Ba2Cu3O7−δ (YBCO) thin films on hastelloy (C) with titanium nitride (TiN) buffer layers. The hastelloy (C) is a nickel based superalloy with excellent high-temperature properties and corrosion resistance. The superconducting and TiN buffer layers were deposited sequentially at 600 °C using pulsed excimer laser irradiation of the respective targets. TiN has been suitably chosen owing to matching of thermal expansion coefficient (∼8.0–9.0×10−6/K) with hastelloy (∼9.0×10−6/K) and YBCO (∼12–13×10−6/K). X-ray diffraction, four point ac electrical resistivity and scanning electron microscope studies were performed on these films for correlations between crystal structure, microstructure, and superconducting properties. Auger electron spectroscopy (AES) was used to determine the extent of interdiffusion in metal-TiN and TiN-Y1Ba2Cu3O7−δ interfaces. These films exhibited a characteristic metallic conductivity followed by an onset of superconductivity at 91 K with a zero resistance temperature (Tco) of 85 K. Critical current density (Jc) for these films (77 K and zero magnetic field) was determined to be ∼9.0×104 A/cm2 for thin films on metallic substrates.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1785-1787 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have prepared high-quality c-axis oriented superconducting YBa2Cu3O7−δ thin films on Si (100) substrates with CoSi2 buffer layers by in situ pulsed laser ablation processing. The films were characterized by x-ray diffraction, four-point ac electrical resistivity, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. YBa2Cu3O7−δ films were found to be textured with c axis perpendicular to the substrate. A plot of normalized resistance against temperature exhibited a metallic behavior followed by an onset superconducting transition at 91 K with zero resistance temperature (Tc0) of 83 K. Cross-sectioned TEM results showed quite smooth interface between CoSi2 and Si with little interdiffusion; however, a reacted zone was observed between CoSi2 and YBa2Cu3O7−δ layers.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4927-4937 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Constrained anisotropic dipole oscillator strength techniques are used to obtain reliable values for a wide range of anisotropic and isotropic dipole properties of O2, including the dipole–dipole dispersion energy coefficients for the interaction of O2 with O2, H2, N2, CO, He, Ne, Ar, Kr, and Xe. Some of the anisotropic constraints required for our calculations are obtained via dipole sum rules from ab initio, multireference configuration interaction (CI) wave functions for the ground state of O2. The individual dipole properties of O2 considered include the dipole oscillator strength sums Sk, k=2,1,0(−1/2)−2,−3,−4,..., the logarithmic dipole sums Lk and mean excitation energies Ik, k=2(−1)−2, and, as a function of wavelength, the dynamic polarizability and its anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. Our constrained dipole oscillator strength results are often the only reliable, and sometimes the only available, ones for many of the properties and dispersion energies considered. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5935-5939 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting properties and microstructures of the YBa2Cu3AgxO7−δ composites have been studied as a function of silver content, 0〈x〈6, using a variety of techniques. The superconducting transition temperature Tc of these composites was found to be the same, ∼90 K, for the above range of composites. For values of x〉3, small quantities of 211 phase were detected along the grain boundaries. Alloy formation between Ag and Cu is proposed to take place which makes the residual composition poor in copper, resulting in the formation of nonsuperconducting 211 phase. The silver is observed in the form of precipitates at very low concentrations of silver, indicating that silver does not substitute for copper in YBa2Cu3O7. Lattice parameters of the composites were found to be invariant throughout the above composition range. The addition of Ag2O in the starting composition seems to stabilize the stoichiometric YBa2Cu3O7 by way of decomposition to Ag and O. As a result, the incorporation of oxygen and recovery of superconducting properties is enhanced in the silver composites.
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  • 10
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used the method of coherent phase modulation, first proposed by Brumer and Shapiro for controlling the rates of chemical reactions, to measure the refractive index of a gas in the vacuum ultraviolet. In these experiments we populated a Rydberg state of HCl or CO by simultaneous absorption of one VUV photon and three UV photons. Molecular ions were generated by absorption of an additional UV photon and detected with a time-of-flight mass spectrometer. The phase difference for the UV and VUV beams was altered by passing them through a cell containing either H2 or Ar. By varying the pressure in the cell we could control this phase difference and thereby modulate the ion signal. From the modulation frequency of the signal it was possible to determine the difference between the refractive indices of the gas at the UV and VUV wavelengths. Using reliable refractive indices in the UV, we extracted from our data values for the VUV indices. These values are in quantitative agreement with a calculation that uses dipole oscillator strengths constructed using constrained oscillator strength methods, taking into account the dispersion resulting from individual rotational transitions. The experimental method can be used very close to an optical transition of the refractive medium, provided that the refractive index does not vary appreciably across the bandwidth of the VUV laser.
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