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  • 1
    Electronic Resource
    Electronic Resource
    The critical current density in high fields in epitaxial thin films of Y1Ba2Cu3O7−δ : Flux pinning and pair breaking (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4220-4226 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current density (Jc) of two epitaxial thin films of Y1Ba2Cu3O7−δ has been measured as a function of temperature in magnetic fields up to 27 T. A detailed study of one of the films shows that when the transport current is in the a-b plane and the magnetic field is orthogonal to the c axis, the functional form of Jc is consistent with both a polynomial (flux pinning) description and an exponential (pair breaking) description. In contrast, when the current is in the a-b plane and the applied field is parallel to the c axis of the film, Jc is unambiguously exponential of the form Jc=α(T)exp[−μ0H/β(T)]. These results explain why there are conflicting suggestions in the literature as to the mechanism that determines Jc in high magnetic fields in thin films for J⊥H⊥c axis and provide evidence that pair breaking operates for J⊥ H(parallel)c axis. However, the standard phenomenological superconductor-normal-superconductor junction model derived in the clean limit for the normal metal cannot describe this pair-breaking mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352325
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  • 2
    Electronic Resource
    Electronic Resource
    Superconducting YBa2Cu3O7−x thin films on alkaline earth fluorides (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2032-2034 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alkaline earth fluorides have low dielectric constants and large band gaps. In addition, they are chemically compatible with and several can be grown epitaxially on silicon and compound semiconductors. We have deposited YBa2Cu3O7−x thin films (200–500 nm thick) directly on (001) SrF2, (001) BaF2, (001) MgF2, and unoriented CaF2 single crystals by laser deposition. The substrate temperature was about 720 °C and the vacuum chamber was at 350 mTorr of oxygen. For this work, no additional annealing outside the deposition chamber was done after deposition. The deposited YBa2Cu3O7−x films were superconducting and exhibited transition temperatures Tc (R=0) of 83, 73, and 74 K on MgF2, SrF2, and BaF2, respectively. Structural studies by x-ray diffraction showed that YBa2Cu3O7−x films on MgF2, SrF2, and BaF2 were polycrystalline and exhibited some (00L) textures. Deposition on CaF2 substrates resulted in yellowish, insulating films with Ca- and Ba-rich interfacial reaction products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101507
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: "The critical current density in high fields in epitaxial thin films of Y1Ba2Cu3O7−δ : Flux pinning and pair breaking'' [J. Appl. Phys. 72, 4220 (1992)] (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3117-3117 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354099
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  • 4
    Electronic Resource
    Electronic Resource
    Electrical Conductivities of (CeO2)1−x(Y2O3)x Thin Films (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Electrical properties of CeO2 thin films of different Y2O3 dopant concentration as prepared earlier were studied using impedance spectroscopy. The ionic conductivities of the films were found to be dominated by grain boundaries of high conductivity as compared with that of the bulk ceramic of the same dopant concentration sintered at 1500°C. The film grain-boundary conductivities were investigated with regard to grain size, grain-boundary impurity segregation, space charge at grain boundaries, and grain-boundary microstructures. Because of the large grain boundary and surface area in thin films, the impurity concentration is insufficient to form a continuous highly resistive Si-rich glassy phase at grain boundaries, such that the resistivity associated with space-charge layers becomes important. The grain-boundary resistance may originate from oxygen-vacancy-trapping near grain boundaries from space-charge layers. High-resolution transmission electron microscopy coupled with a trans-boundary profile of electron energy loss spectroscopy gives strong credence to the space-charged layers. Since the conductivities of the films were observed to be independent of crystallographic texture, the interface misorientation contribution to the grain-boundary resistance is considered to be negligible with respect to those of the impurity layer and space-charge layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00439.x
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  • 5
    Electronic Resource
    Electronic Resource
    Use of carbon films for passivation and environmental protection of superconducting YBa2Cu3O7−x (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6370-6376 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic device applications of high-temperature superconducting cuprates require the production of patterned thin films that are stable and inert in various processing and operating environments; however, the superconducting rare-earth barium cuprates have been shown to decompose in water and to degrade in superconducting properties in a humid atmosphere. The thermodynamics that forms the driving force for the degradation is reviewed. Protective coatings or removable protective films can realize many applications and facilitate processing of superconducting devices. Diamondlike carbon films as well as amorphous carbon films are investigated as possible protective layers for YBa2Cu3O7−x (YBCO). Amorphous carbon (a-carbon) films deposited by evaporation are shown to protect superconducting YBCO films from degradation by humidity. The YBCO films with a-carbon coatings have been shown to have critical current densities four orders of magnitude higher than the uncoated YBCO films after 2 h at a stressing of 100% relative humidity (RH). A similar stressing for 44.5 h has conducting YBCO films but no longer has a measurable critical current density. The a-carbon coating is an effective passivation layer for short-term storage (with time 〈2 h and 100% RH and time (approximately-greater-than)4 h at 50% RH) at room temperature. The critical current is shown to be a better indicator for the degree of degradation, since the transition temperature remains relatively constant as long as there is enough superconducting YBCO to provide a percolation path for the supercurrent. Degrees of degradation were also assessed by scanning electron microscopy. The versatility of these carbon films lies in that their deposition and removal by plasma oxidation at room temperature are compatible with YBCO films. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359109
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  • 6
    Electronic Resource
    Electronic Resource
    Al/Au and Cu/Au bilayer-metal contacts to YBa2Cu3O7−x thin films (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4082-4084 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical contact resistivities of both Al and Cu single layer contacts as well as Cu/Au and Al/Au bilayer metal contacts to YBa2Cu3O7−x (YBCO) thin film have been studied. It was found that aluminum and copper make poor electrical contacts to YBCO due to interface reactions. These contacts have large contact resistivity (10−1–1 Ω cm2), orders of magnitude higher than that of a gold/YBCO contact (10−6 Ω cm2). When an ultrathin Au interlayer (10–30 A(ring)) was inserted between an Al or Cu overlayer and a YBCO film, interface reaction was greatly reduced. The contact resistivities of Al/Au and Cu/Au bilayer-metal contacts dropped by five orders of magnitude when Au interlayer thickness was increased from 0 to 10 A(ring). With the gold interlayer thickness of 15 A(ring), the Al/Au and Cu/Au bilayer-metal contacts reached a minimum contact resistivity, approaching that of a thick single-layer Au metal contact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350834
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  • 7
    Electronic Resource
    Electronic Resource
    Microstructure of YBa2Cu3O7−x thin films grown on single-crystal SrTiO3 (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4719-4722 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: YBa2Cu3O7−x thin films on (001) and (014) SrTiO3 were prepared by coevaporation of Y, BaF2, and Cu, and annealing in oxygen at 850 °C. Cross-sectional samples prepared by cutting films and substrates along the SrTiO3 (100) plane were studied with transmission electron microscopy. The growth of YBa2Cu3O7−x in as-deposited films is extremely anisotropic with the [001] being the slow direction and the (001) plane being the fast growth plane. When the (001) planes of YBa2Cu3O7−x grains are parallel to the film plane, as on (001) SrTiO3, there is a dominance of this orientation over the whole film. Three types of YBa2Cu3O7−x grains, 90° misoriented from each other, are observed to grow on both (001) and (014) surfaces of single-crystal SrTiO3 substrates with their c directions aligned with one of the three 〈100〉 directions of cubic SrTiO3. This ambiguity creates a threefold degenerate epitaxy of YBa2Cu3O7−x on SrTiO3, which results in 90° grain boundaries in the final YBa2Cu3O7−x thin films. These boundaries are free of any second phase and decorations. While some extraneous phases were observed in these films, they were located away from the crystallographically special, 90° boundaries. Therefore, the presence of extraneous phases elsewhere in the films was not damaging to the superconducting transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343222
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  • 8
    Electronic Resource
    Electronic Resource
    Raman scattering as a contactless room-temperature test of the quality of YBa2Cu3O7−x thin films (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2381-2383 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The room-temperature Raman spectrum of YBa2Cu3O7−x is sensitive both to stoichiometry and to the transition from the semiconducting to the superconducting state as a function of oxygen annealing. In particular, it is shown that a good quality film with a Tc of ∼90 K and a sharp resistivity transition has not been produced if the frequency of the O(1) stretch along the c axis shifts from 500 cm−1 to lower frequencies. In this paper, two types of processing failures are illustrated: (1) lack of sufficient oxygen and (2) incorrect stoichiometry. No attempt has been made to predict Tc from the Raman data for less than optimum films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342803
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  • 9
    Electronic Resource
    Electronic Resource
    Transport in reversibly laser-modified YBa2Cu3O7−x superconducting thin films (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1802-1805 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A focused argon ion laser beam in a controlled ambient is used to modify the transport properties of superconducting YBa2Cu3O7−x thin films. The laser-modified region shows a sharp transition temperature (Tc≈76 K) that is reduced from the unmodified regions of the film (Tc≈87 K). In situ monitoring of the room-temperature electrical resistance is used to control the laser processing and prevent formation of the semiconducting phase. The original properties of the superconducting film can be recovered by plasma oxidation indicating that the laser-induced phase is oxygen deficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342911
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  • 10
    Electronic Resource
    Electronic Resource
    Visible thermal emission from sub-band-gap laser excited cerium dioxide particles (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1936-1941 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cerium dioxide particles excited in air with sub-band-gap radiation emit very broad radiation in the visible spectrum above a threshold intensity that decreases with increasing ambient temperature. Concomitant with this emission is the near disappearance of the Stokes and anti-Stokes Raman scattering peaks. Both phenomena are reversible in air up to just above threshold, and are seen for nanoparticles and several-micron-diameter particles with particle diameter comparable to or smaller than the laser focus. Temperature estimates using the Stokes/anti-Stokes scattering intensity ratio suggest there is laser heating due to small intragap absorption and possible nonlinear processes, given the very slow thermal conduction. The broad emission in this loose powder may well be due to thermal emission, on the basis of spectral fitting of the high-energy part of the spectrum to a blackbody radiator at ∼1200–1400 °C, although luminescence from a new phase is a possibility. The sudden decrease in Raman scattering and increase in emission in air are consistent with a transition to a new, possibly luminescent, phase, as is the continued disappearance of the Raman peaks in forming gas when the laser power is reduced below the upstroke threshold. Oxygen point defects and their complexes may play an important role in many of these processes. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1494130
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