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  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Microwave properties of YBa2Cu3O7−x thin films studied with coplanar transmission line resonators (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1866-1872 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microwave properties of epitaxial YBa2Cu3O7−x thin films with critical temperatures Tc up to 91.5 K and critical current densities Jc up to 6×106 A/cm2 at 77 K have been investigated between 5 and 20 GHz using coplanar transmission line resonators. Information about the surface resistance Rs and the magnetic penetration depth λL has been obtained from temperature- and power-dependent measurements of the quality factors and resonance frequencies of the resonators. The lowest surface resistance was 105 μΩ at 77 K and 38 μΩ at 9 K measured at 6.2 GHz, respectively. The dependence of Rs on the surface magnetic field Brf showed that with decreasing film quality the films exhibit a granular behavior. At high critical current densities Jc(approximately-greater-than)4×106 A/cm2, the intrinsic properties of the material show up. The magnetic penetration depth was in the range between 160 and 270 nm. Both Rs and λL turned out to be sensitive to the film quality represented by the transition width ΔTc and the critical current density Jc at 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353173
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Scattering mechanisms in inverted AlGaAs-GaAs heterostructures studied by magnetotransport measurements (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6860-6863 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We determined the single particle relaxation time τs and the classical transport scattering time τt out of Shubnikov-de Haas (SdH) measurements at a GaAs-AlGaAs-GaAs double heterostructure consisting of a normal and an inverted interface. As a result we find that even in inverted heterostructures the classical scattering time τt is an order of magnitude larger than the single particle relaxation time τs. From a comparison with theoretical calculations including scattering from remote impurities, interface charges, and interface roughness, we conclude that the mobility in inverted heterostructures at low temperatures is dominated by Coulomb scattering from remote dopants and interface charges in the barrier, rather than interface roughness scattering. Nevertheless, the mobility of the inverted interface turns out to be significantly lower than that of a normal interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349809
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The determination of excited-state geometries by analyzing resonance Raman spectra. Example—1(π−π*) state of o-chloranil (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1564-1574 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonance Raman spectra of o-chloranil were obtained by exciting the energetically lowest π–π* transition. Raman signals of three totally symmetric stretching modes (C=C, C=O, and C–C) showed pronounced intensity alterations. The intensity changes of these modes were analyzed using a dispersion formula which is based on the Kramers–Heisenberg–Dirac equation. Three-dimensional Franck–Condon integrals were calculated with the algorithm of Kupka and Cribb. The mathematical fitting of the experimentally derived spectra yielded the displacements of the potential curves along the considered normal coordinates and data of the Duschinsky mode mixing. The geometrical shifts along directions of ground-state normal coordinates were transformed to bond-length changes with the use of the eigenvector matrix L of the ground-state vibrations. L was obtained by a complete force field analysis. The excited-state geometry of o-chloranil is characterized by the contraction of the di-keto system accompanied by a weakening of the acrolein unit. The largest changes appear in the butadiene subsystem, where a conversion of bond order occurs between the double bonds and the single bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465325
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of the critical current density in HTSC thin-film multilayers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4373-4376 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this paper the limitations and perspectives of a simple remanent field technique for the determination of the critical current density (jc) in high-temperature superconductor (HTSC) thin films and in HTSC thin-film multilayers at 77 K were examined. As the comparison with resistive jc measurements on microbridges shows, jc values down to 104 A/cm2 can easily be measured with high accuracy. The method is nondestructive, fast, and inexpensive. It is especially suitable for jc measurements of double-sided coated substrates, where the determination of the individual jc values of both thin-film layers is possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143737
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of superstructures on the surfaces of sputtered YBa2Cu3O7−x thin films by low-energy electron diffraction (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1465-1467 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface structures of sputtered c-axis-oriented YBa2Cu3O7−x (YBCO) thin films were studied by means of low-energy diffraction (LEED). The in situ analysis, without exposing the films to air, showed the formation of superstructures of the YBCO (001) 2×2 and YBCO (001) 4×1 type. Air-exposed surfaces showed no LEED pattern but could be transformed into the YBCO (001) 2×2 structure by annealing at 500 °C. The observed superstructures are interpreted as being due to oxygen loss of the YBCO surface region, causing an oxygen vacancy ordering in the basal CuO planes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107519
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Sputtering of YBa2Cu3O7−δ/NdAlO3/YBa2Cu3O7−δ trilayers (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 3304-3306 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial YBa2Cu3O7−δ/NdAlO3/YBa2Cu3O7−δ-trilayers were grown by sputtering from stoichiometric targets. The YBa2Cu3O7−δ (YBCO) films were deposited by dc-magnetron sputtering. For the NdAlO3 films, rf-magnetron sputtering was used. The individual YBCO films revealed critical-current densities up to 3×106 A/cm2 at 77 K. The bilayer and trilayer structures were characterized by x-ray diffraction, Rutherford backscattering spectroscopy, and transmission electron microscopy (TEM). The channel yield χmin of the YBCO film on top was 15% for an in situ deposited trilayer. The epitaxial growth of the subsequent layers was proved by cross-sectional TEM. Although the NdAlO3 layer contained misoriented grains, the top YBCO layer grows in single orientation over these areas. Preliminary electrical measurements show that NdAlO3 is a useful insulating dielectric for microelectronic applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106674
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    Paper (German National Licenses)
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