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  • 2000-2004  (12)
  • 1985-1989  (37)
  • 11
    Electronic Resource
    Electronic Resource
    Preparation of Y-Ba-Cu oxide superconductor thin films using pulsed laser evaporation from high Tc bulk material (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 619-621 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first successful preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98366
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  • 12
    Electronic Resource
    Electronic Resource
    Imaging of current-induced superconducting-resistive transitions by scanning electron microscopy in laser-deposited superconducting thin films of Y1Ba2Cu3O7−x (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 911-913 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the transport current-induced resistive transitions in predominantly c-axis oriented crystalline Y1Ba2Cu3O7−x superconducting thin films with scanning electron microscopic (SEM) imaging and its correlation with dc current-voltage (I-V) measurements. We find that there is a nonlinear gradual transition region in the I-V curves that is caused by macroscopic effects (current "crowding'', substrate defects, film thickness variation, etc.) and by microscopic dissipation effects. At a high current there is an abrupt transition to the normal state in the I-V curve due to Joule heating. The SEM mapping provides a direct image of the above effects and is useful for characterization and study of fundamental transport properties of high Tc thin films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101620
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  • 13
    Electronic Resource
    Electronic Resource
    Surface layers on superconducting Y-Ba-Cu-O films studied with x-ray photoelectron spectroscopy (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1680-1682 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The chemical compositions of surface and bulk regions of pulsed laser deposited YBa2Cu3O7−x films on SrTiO3(001) substrates were examined. From the relative intensities of the surface and bulk components of the Ba 3d and Ba 4d spectra taken at different take-off angles and different escape depths [using Al Kα (1486.6 eV) and Mg Kα (1253.6 eV) excitations], we have concluded that there is a nonsuperconducting surface layer of 1 nm thickness with a composition of BaCuO2. This layer contains oxygen with a photoelectron binding energy of 531 eV, and Cu2+ ions. A superconducting film which was only 8 nm thick also had a layer of 1 nm thickness. By detecting the substrate Ti signal through this film, and ruling out a high density of pinholes, we provide evidence that the x-ray photoelectron spectroscopy data contain information from the superconducting phase. A polycrystalline pellet scraped in vacuum had a similar surface layer, which was only 0.4 nm thick.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102314
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  • 14
    Electronic Resource
    Electronic Resource
    High critical currents in epitaxial YBa2Cu3O7−x thin films on silicon with buffer layers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 754-756 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As-deposited superconducting thin films (∼0.1 μm) of YBa2Cu3O7−x have been prepared by pulsed laser deposition on (100) Si with buffer layers of BaTiO3/MgAl2O4. X-ray diffraction studies reveal that the films grow epitaxially with the c axis preferentially oriented normal to the substrate surface. This is confirmed by ion channeling measurements along the (100) (normal to the surface) and (110) directions of the Si substrate showing a minimum yield of 54% along the (100), and 78% along the (110) axes using 2.8 MeV He++. Preliminary transmission electron microscopy study also supports these results. The as-deposited films have zero resistance temperatures of 86–87 K, and critical current densities of 6×104 A/cm2 at 77 K and 1.2×105 A/cm2 at 73 K. Our results indicate that the superconducting properties of the films are limited primarily by the quality and degree of epitaxal growth of the buffer layers on the silicon substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101471
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  • 15
    Electronic Resource
    Electronic Resource
    High-temperature superconductivity in ultrathin films of Y1Ba2Cu3O7−x (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 581-583 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown ultrathin films of Y1Ba2Cu3O7−x in situ on (001) SrTiO3 by pulsed laser deposition. The zero resistance transition temperature (Tc0) is 〉90 K for films 〉300 A(ring) thick. The critical current density (Jc at 77 K) is 0.8×106 A/cm2 for a 300 A(ring) film and 4–5×106 A/cm2 for a 1000 A(ring) film. The Tc0 and Jc deteriorate rapidly below 300 A(ring), reaching values of 82 K and 300 A/cm2 at 77 K, respectively, for a 100 A(ring) film. Films only 50 A(ring) thick exhibit metallic behavior and possible evidence of superconductivity without showing zero resistance to 10 K. These results are understood on the basis of the defects formed at the film-substrate interface, the density of which rapidly decreases over a thickness of 100 A(ring). We have studied these defects by ion channeling measurements and cross-section transmission electron microscopy. Our results suggest that the superconducting transport in these films is likely to be two dimensional in nature, consistent with the short coherence length along the c axis of the crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101463
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  • 16
    Electronic Resource
    Electronic Resource
    Nature of the pulsed laser process for the deposition of high Tc superconducting thin films (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1431-1433 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pulsed laser thin-film deposition process can enable preparation of thin films of complex composition with good control over the film stoichiometry. The film compositions are similar to that of the target pellet and as a consequence this technique appears to be an ideal method for preparing high Tc thin films on a variety of substrates.The factors which contribute to this beneficial phenomenon have been explored by a laser ionization mass spectrometry (LIMS) and a post ablation ionization (PAI) neutral velocity analysis technique in order to determine the mass and velocities of the laser ejected material. In addition, x-ray absorption measurements on films deposited onto substrates at room temperature were performed in order to identify the presence of short-range crystalline order in the films. Both of these studies rule out the ejection of stoichiometric clusters of material from the pellet during the laser ablation/deposition process. Instead, binary and ternary suboxides are emitted from the target pellet. These suboxides most likely have unit sticking coefficient to the substrate which could contribute to the preservation of the film stoichiometry. The velocity distribution of several neutral species (e.g., BaO) indicates that particles have energies of several eV. Thus the effective temperatures of the emitted species are ∼15×103 K, and these energetic particles may facilitate growth of the crystalline films at low substrate temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100458
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  • 17
    Electronic Resource
    Electronic Resource
    InGaAs/InP superlattice mixing induced by Zn or Si diffusion (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1051-1053 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent studies have shown that Zn diffusion preferentially induces mixing (interdiffusion) of In and Ga in unstrained InGaAs/InP superlattices, with little diffusion of the anions. In the present study, a 3.1% lattice mismatch is accommodated in the mixed superlattice with no observable defects in layers on the order of the predicted critical layer thickness. At high concentrations, Zn resides preferentially in the InP layers in the form of Zn3P2. In marked contrast to this behavior of Zn, Si diffusion is observed to cause comparable interdiffusion on the cation and anion sublattices within a narrow range of dopant concentration. This result is at odds with some recent mixing models and is consistent with a divacancy mixing mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100406
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  • 18
    Electronic Resource
    Electronic Resource
    As-deposited high Tc and Jc superconducting thin films made at low temperatures (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 908-910 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 2000 A(ring) as-deposited high Tc superconducting Y1Ba2Cu3O7−x films with zero-resistance temperatures of ∼89 K and critical current densities about 0.7×106 A/cm2 at 77 K have been reproducibly fabricated at a substrate holder temperature of 650 °C, using pulsed laser deposition, with no post-annealing. One key to these results is the injection of gaseous oxygen into the laser-produced plume just in front of the target. In this way, the correct amount of oxygen is incorporated into the as-grown film so that post-deposition treatment becomes unnecessary. The in situ growth of such high Tc and Jc films is an important step in the use of the laser deposition technique to fabricate multilayer structures such as Josephson junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100155
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  • 19
    Electronic Resource
    Electronic Resource
    High Tc superconducting film as a fast nonlinear switch for noise discrimination in digital circuits (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2704-2706 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of fast nonlinear switching of a high Tc superconducting thin film at 70 K between the dissipative state (induced by an electrical current) and superconducting state are reported. System rise and fall times are measured to be about 1 ns and are limited by the parasitic components of the electrical circuitry. A novel scheme for noise discrimination in digital circuits using this switching has been proposed and experimentally demonstrated for speeds exceeding 200 Mb/s. This method allows significant reduction of amplitude noise and improvement of signal-to-noise ratio in digital circuits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100551
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  • 20
    Electronic Resource
    Electronic Resource
    Observation of two distinct components during pulsed laser deposition of high Tc superconducting films (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1193-1195 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using Rutherford backscattering technique, we have measured the angular distribution of the composition and thickness of the Y-Ba-Cu oxide film deposited by firing excimer laser (30 ns, 248 nm) pulses at a stoichiometric Y1Ba2Cu3O7−x pellet. The angular distribution consisted of two distinct components: one a cos θ component, a result of evaporation, and the other a highly forward directed component, a result of a secondary ejection process. The evaporated component is nonstoichiometric, as one would expect, whereas the forward-directed component has a composition close to that of the pellet. Further, the forward-directed stoichiometric component increases with the laser energy density in comparison with the evaporated component. These observations are discussed in the context of current models of laser-induced material ejection at surfaces.The laser energy dependence of the deposition is of critical importance in controlling the film stoichiometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99673
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