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  • 1
    Electronic Resource
    Electronic Resource
    Correlation of YBa2Cu3O7 step-edge junction characteristics with microstructure (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1131-1139 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current-voltage characteristics, Josephson radiation spectra, and critical current versus magnetic-field dependences were measured in epitaxial, c-axis YBa2Cu3O7 step-edge Josephson junctions (SEJs) on SrTiO3 and LaAlO3 substrates with various step angles α. The results were correlated with microstructural data to determine the origin of the observed weak-link behavior. It was shown that on steps with α(approximately-greater-than)45° the SEJ is a series connection of two weak links unambiguously correlated with the occurrence of two 90° tilt grain boundaries. On steep steps, α≥70°, the boundary at the upper step edge has, on average, the (103) symmetry, while the lower one is predominantly of the basal-plane-faced (010)(001) type. Correspondingly, one link is weaker than the other, with the weaker link originating on the (010)(001) boundary. However, others have shown that analogous grain boundaries in planar (103) and biepitaxial a-axis/c-axis films do not exhibit a strong magnetic-field dependence of critical current, which is characteristic of a weak link. Hence, it is proposed that the weak-link behavior of boundaries on step edges originates from their defect structure. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360347
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  • 2
    Electronic Resource
    Electronic Resource
    Low-resistivity epitaxial YBa2Cu3O7 thin films with improved microstructure and reduced microwave losses (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5572-5578 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of YBa2Cu3O7 have been prepared on SrTiO3 and LaAlO3 substrates by a high-pressure planar dc-sputtering technique. By covering the substrate heater with a frame of polycrystalline YBa2Cu3O7 substantial improvements of the YBa2Cu3O7 film properties were achieved. These are characterized by dc-resistivity values ρ(T) of less than 50 μΩ cm at 100 K and ρ(300 K)/ρ(100 K) values of up to 3.9. Significant deviations from the usual linear ρ(T) behavior were found. Critical temperatures above 90 K, resistive transition widths down to 0.3 K, and critical current densities of about 5 × 106 A/cm2 at 77 K confirm the high quality of the films. As indicated by Rutherford backscattering and high-resolution transmission electron microscopy the films exhibit a microstructure characterized by a reduced density of lattice defects. However, lattice-coherent precipitates with a diameter of about 5–10 nm were observed. As an outstanding feature the films exhibit, besides the initial steep falloff at Tc, a further gradual decrease of the microwave surface resistance at 87 GHz below 50 K by at least one order of magnitude. These results are very promising for millimeter-wave applications of epitaxial YBa2Cu3O7 thin films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350535
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  • 3
    Electronic Resource
    Electronic Resource
    Epitaxial growth of YBa2Cu3O7−x thin films on Si(100) with zirconia buffers of varying crystalline quality and structure (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5560-5564 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin epitaxial films of monoclinic pure and cubic yttria-stabilized (YSZ) ZrO2 were deposited onto Si(100) by electron-beam evaporation. The degree of crystalline perfection was controlled by the growth temperature. Epitaxial YBa2Cu3O7−x films were grown on these buffer layers by KrF excimer laser ablation. Optimum crystalline and electrical quality, characterized by a transition temperature Tc0 of 86–89 K, a critical current density jc of 106 A/cm2 at 77 K, and a channeling minimum yield of 12% was obtained on YSZ buffers showing a minimum yield of 7%. Even a 14-nm-thick YSZ buffer enabled the growth of an YBa2Cu3O7−x film with Tc0 of 86 K and a minimum yield of 12%. With decreasing quality of the YSZ buffer layers the crystalline quality of the superconductor also decreased. The disorder in the YBa2Cu3O7−x films, however, increased more slowly than in the buffer layers, so that even on an amorphous buffer the YBa2Cu3O7−x exhibited a pronounced texture with a minimum yield of 72%. The comparatively rough surface of the monoclinic pure ZrO2 severely hampered the c-axis alignment of the YBa2Cu3O7−x, resulting in superconductor films of inferior quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350532
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  • 4
    Electronic Resource
    Electronic Resource
    Conservative antiphase boundary in SrTiO3 films on LaAlO3 substrates with SrRuO3 buffer layers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5653-5656 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the microstructure of SrTiO3 films on LaAlO3 substrates with the SrRuO3 buffer layer using high-resolution transmission electron microscopy. While high density of defects due to lattice mismatch were found at the SrRuO3/LaAlO3 interface, no misfit dislocation was observed at the SrTiO3/SrRuO3 interface. The {111} stacking fault in the SrRuO3 buffer layer propagates into the SrTiO3 film, giving rise to a type of antiphase boundary on the {110} plane with a crystallographic shear vector of a/2〈001〉. The boundary is a conservative one which does not lead to any charge defects. A model based on dislocation interactions is proposed to explain the generation mechanism of the antiphase boundary. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1367881
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  • 5
    Electronic Resource
    Electronic Resource
    Structural and morphologic evolution of Pt/Ba0.7Sr0.3TiO3/Pt capacitors with annealing processes (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2728-2730 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure and chemistry of the as-grown, the postannealed and the forming-gas-atmosphere-treated Pt/Ba0.7Sr0.3TiO3/Pt capacitors are studied by means of high-resolution transmission electron microscopy and energy-disperse x-ray spectroscopy. It is found that the annealed Ba0.7Sr0.3TiO3 films have larger grain size and more smooth top film-electrode interfaces. High-resolution images reveal the presence of disordered or amorphous regions at the interfaces in the Ba0.7Sr0.3TiO3 film heated in the forming-gas atmosphere. These regions show a higher Ti/(Ba+Sr) ratio than the grain matrix. The effects of these amorphous regions on the electrical properties of Ba0.7Sr0.3TiO3 films are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1469683
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  • 6
    Electronic Resource
    Electronic Resource
    Fabrication of YBa2Cu3Ox thin-film flux transformers using a novel microshadow mask technique for in situ patterning (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3521-3523 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel microshadow mask technique for in situ patterning of multilayers is presented. It is ideally suited to fabricate YBa2Cu3Ox(YBCO) and insulator lines with gently sloping edges, needed for high quality insulated superconducting crossovers. The critical current density jc (T=77 K) of a YBCO/SrTiO3/YBCO crossover exceeds 2×106 A/cm2 in both the bottom and the top YBCO stripline. The insulating SrTiO3 layer of 200 nm thickness displays a high resistivity of ρ(approximately-greater-than)108 Ω cm (T=77 K). The extremely smooth morphology of the edges has been revealed by cross sectional transmission electron microscopy, indicating a stepflow mechanism of YBCO growth. Multiturn flux transformers with a 15 μm linewidth input coil spiral have been fabricated by this microshadow mask technique. A transformer with a pickup loop area of 7 mm2 has been coupled to a 1 mm2 washer dc SQUID in flip chip geometry. In comparison to the bare SQUID a magnetic flux gain factor of 9 has been obtained. The white noise level of this setup was determined to be 8×10−5 Φ0/Hz1/2 at 77 K. It was entirely due to the intrinsic noise of the employed dc SQUID itself. The 1/f noise level increased a factor of 2. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113784
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  • 7
    Electronic Resource
    Electronic Resource
    Josephson junctions, interconnects, and crossovers on chemically etched edges of YBa2Cu3O7−x (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2138-2140 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique of ultraviolet photolithography of YBa2Cu3O7−x and PrBa2Cu3O7−x films combined with nonaqueous Br-ethanol chemical etching was developed. Josephson junctions, interconnects, and crossovers on the basis of chemically etched edges of c-axis oriented YBa2Cu3O7−x thin films were prepared and investigated. For the Josephson junctions with a PrBa2Cu3O7−x barrier, the IcRn product values of about 10 mV at 4.2 K and up to about 0.6 mV at 77 K were achieved. Shapiro steps were observed in the temperature range up to about 89 K. Critical current spreads of about ±10% were observed. At 77 K, the electrodes of crossovers carried more than 106 A/cm2. For a 160-nm-thick SrTiO3 intermediate layer in crossovers, a resistivity of more than 109 Ω cm was achieved at T≤100 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110565
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  • 8
    Electronic Resource
    Electronic Resource
    Diamond epitaxy on (001) silicon: An interface investigation (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1197-1199 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In combination with scanning electron microscopy and x-ray pole-figure analysis high resolution electron microscope (HREM) observation of the diamond-silicon cross section in a 〈001〉 epitaxially oriented diamond film was carried out to investigate the atomic interfacial microstructure. The films were prepared by microwave plasma chemical vapor deposition using a bias-enhanced nucleation technique. Due to the multiple fit of diamond and silicon lattices, there is a periodic 3-to-2 registry of {111} atom planes of the epitaxial diamond-silicon interface. Planar defects on diamond {111} planes and interface misfit dislocations are shown for epitaxially oriented and for slightly misoriented diamond crystallites. A cubic silicon carbide "transition'' is found to be unnecessary for the epitaxy. The misorientation of the grown crystallites is also studied and found to be probably due to interface imperfection. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115005
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  • 9
    Electronic Resource
    Electronic Resource
    The coalescence of [001] diamond grains heteroepitaxially grown on (001) silicon (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3902-3904 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coalescence of diamond grains grown by microwave plasma chemical vapor deposition was observed at an atomic level using high resolution electron microscopy in combination with scanning electron microscopy. It was shown that large diamond crystals can be grown either by a coalescence of two [001]-oriented grains which have a slight misorientation or by a switch of the grain boundary, which is usually perpendicular to the surface plane, to a parallel direction. A single crystalline film might be deposited when the growing surface is fully covered by the (001) plane, i.e., no {111} top facet appears to separate the growing (001) surface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117564
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of chemical and ion-beam etching on the atomic structure of interfaces in YBa2Cu3O7/PrBa2Cu3O7 Josephson junctions (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3635-3637 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The atomic structure of the interfaces of Josephson junctions formed by epitaxial YBa2Cu3O7/PrBa2Cu3O7/YBa2Cu3O7 triple-layer films was investigated by high-resolution transmission electron microscopy. The samples were fabricated by sputter deposition on surfaces which were etched ex situ either chemically, using a nonaqueous Br-ethanol solution, or by an Ar ion beam. In the interfaces produced after ion etching a thin intermediate layer with a thickness of a few nanometers was observed. The main part of this layer consists of cubic PrBa2Cu3O7 or YBa2Cu3O7 which is cation disordered. The interfaces formed during deposition on Br-ethanol-etched surfaces did not contain such an intermediate layer but exhibited high structural perfection similar to that of interfaces produced in situ. These observations permit a qualitative explanation of the difference in the electrical properties of junctions produced by these two techniques. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115342
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