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  • 1
    Electronic Resource
    Electronic Resource
    Temperature-dependent kinetic inductance of YBa2Cu3O7−δ thin films predicted by the coupled grain model in the strong-coupling limit (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7408-7413 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The introduction of a temperature dependence to the effective penetration depth as calculated in the strong-coupling limit of the coupled grain model is discussed. Assuming a phenomenological Gorter–Casimir behavior for the intrinsic penetration depth of YBa2Cu3O7−δ (YBCO) and a simple model for the temperature-dependent intergrain critical current density, the coupled grain model is found to predict a kinetic inductance which accurately fits the relative phase velocity, vφ(T)/vφ(T0), measured on coplanar YBCO transmission lines. This indicates that the coupled grain model provides an adequate physical interpretation of the empirical penetration depth proposed by, e.g., Rauch et al. [J. Appl. Phys. 73, 1866 (1993)] and suggests that the kinetic inductance is strongly influenced by boundaries between grains with minor relative misalignment. The average grain size and critical current density of the grain boundaries were estimated at a=140–240 nm and Jgc(0)=3.5×1010–1×1011 A m−2, respectively. We argue that the coupled grain model may prove suitable for implementation in microwave circuit design software, as thin film preparation techniques mature in the sense of providing samples with highly reproducible properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356656
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  • 2
    Electronic Resource
    Electronic Resource
    Lithographic processing of YBa2Cu3O7 thin films: Impact on electrical contacts (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 6167-6171 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silver contact pads to c-axis-oriented thin films of YBa2Cu3O7 (YBCO) were defined using three different techniques: (1) deposition through stencil masks; (2) liftoff; and (3) Ar plasma etching of in situ deposited Ag. A specific contact resistance of ρc(77 K) = 1 × 10−7 Ω cm2 was found for the in situ deposited contacts. Contacts defined with stencil masks and liftoff showed a ρc(77 K) ∼ 10−5 and ∼ 10−2 Ω cm2, respectively. Core-level photoelectron spectroscopy measurements indicate that the resist and acetone applied to the YBCO thin film during patterning do not introduce surface impurity phases in addition to those formed upon air exposure. Distinct chemical shifts originating from process-induced surface impurity phases were observed in photoelectron spectra taken on films prepared for contact definition by liftoff, i.e., exposed to the lithographic developer and deionized water. These findings correlate with the measured increase in contact resistance. Cross-sectional transmission electron microscopy images of an in situ deposited Ag contact unveil a 20–30-A(ring)-thick interface layer, in which the 12 A(ring) periodicity along the YBCO c axis vanishes. The presence of this layer could explain the absence of Josephson effects in YBCO/noble-metal/low-Tc superconductor junctions where the currents are forced to flow perpendicular to the a-b planes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350425
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  • 3
    Electronic Resource
    Electronic Resource
    X-ray photoelectron spectroscopy study of thin Ag overlayers on YBa2Cu3O7−xB: Effects of oxygen annealing (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1777-1781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray photoelectron spectroscopy was used to examine vapor deposited Ag overlayers on YBa2Cu3O7−x thin films and cleaved single-crystal surfaces (x=1), including the effects of subsequent heat treatment in oxygen. The core level spectra of the present tetragonal crystals were found to closely resemble those previously reported for nominally orthorhombic superconducting samples. Minor differences, notably an increased fraction of Cu in the +1 oxidation state and a slightly higher binding energy of the Ba 3d levels, may be attributed to the lower oxygen content of the tetragonal semiconducting phase. Deposition of Ag on clean monocrystal surfaces was found to cause some disruption of CuO bonds at the Ag/YBa2Cu3O7−x interface. We also find weak indications of surface band bending (i.e., Schottky barrier formation) from a uniform shift in the measured binding energies of the substrate core levels upon Ag deposition. Heat treatment in pure oxygen (1 h at 500 °C) of Ag-coated superconducting thin films was found to reduce efficiently the amount of superficial contaminant phases, initially present on the air-exposed thin-film surfaces, and to cause diffusion of Ag to a depth of ∼20 nm into the volume of the material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346608
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  • 4
    Electronic Resource
    Electronic Resource
    Removal of the surface contamination layer from CF4 plasma etched GaAs(100) substrate by thermal annealing in hydrogen (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4811-4815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Examination with x-ray photoelectron spectroscopy (XPS) of CF4 plasma etched GaAs(100) wafers unveils a residual surface reaction layer composed of Ga-fluoride and Ga-oxide. Efficient removal of this contamination layer by a brief immersion in a dilute NH4OH wet etch is demonstrated. The formation of a thin native oxide upon exposure to atmosphere of the clean substrate surface cannot be avoided, however. Prospective replacement of this wet etch processing by in situ thermal annealing in hydrogen was investigated. The recorded XPS spectra show almost complete desorption of fluorine after annealing at 200 °C, whereas a temperature of ∼600 °C is required for entire removal of residual surface Ga-oxide. Heat treatment in H2 also compares favorably with vacuum annealing, for which a noticeable reduction of the surface contamination layer was found only after annealing at 600 °C. The cleaning efficiency of hydrogen processing may be attributed to the reactive nature of this ambient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346138
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  • 5
    Electronic Resource
    Electronic Resource
    Processing dependence of the interfacial microstructure of Ag contacts to YBa2Cu3O7−δ thin films (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 836-838 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interfacial microstructure of three differently prepared silver contacts on c-axis oriented YBa2Cu3O7−δ (YBCO) thin films was examined using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintained at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomically sharp YBCO(001)/Ag interfaces were observed. In contrast, the cross-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 A(ring) thick. Scattered Y2O3 precipitates are found at the YBCO surface of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interface layer for in situ contacts to cold films must be ascribed to reactions with gaseous impurities in the sputter chamber ambient. In conclusion, we strongly emphasize the importance of using ultrahigh purity process gases in order to avoid formation of a resistive interfacial barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109870
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  • 6
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy study of Ag contacts to a- and c-axis oriented YBa2Cu3O7 thin films (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 498-500 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interface atomic structure of in situ sputter deposited silver contacts to a- and c-axis oriented thin films of YBa2Cu3O7 (YBCO) was investigated with cross-section transmission electron microscopy (TEM). A structurally disordered interface layer, approximately 25 A(ring) thick, was found for Ag contacts to c-axis oriented films. Electron diffraction analysis provides clear evidence for loss of the 11.7 A(ring) lattice periodicity along the YBCO c-axis in this zone. No such disordered interface layer could be identified in TEM images of Ag contacts to a-axis oriented films. These findings may have important bearing on fabrication of high Tc proximity coupled superconductor/normal metal/superconductor Josephson devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106612
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  • 7
    Electronic Resource
    Electronic Resource
    Photolithographic patterning of protective arsenic capping on molecular beam epitaxy grown AlxGa1−xAs(001) (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2124-2126 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Patterning of an arsenic capping layer deposited in situ on AlxGa1−xAs(100) epilayer surfaces is demonstrated, using standard photolithography and subsequent etching in a hydrogen radical (H*) beam. These data suggest that the protection offered by such capping during ambient storage, may be exploited for molecular beam epitaxy overgrowth and device processing purposes. The technique needs further refinement, however, as trace amounts of surface oxide and carbon impurities were found on the H* etched surfaces by core-level photoelectron spectroscopy. Moreover, the scanning electron micrographs unveil residues of the As cap along the photomask edges, after completed etching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111704
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  • 8
    Electronic Resource
    Electronic Resource
    XPS intensity analysis for assessment of thickness and composition of thin overlayer films: Application to chemically etched GaAs(100) surfaces (1989)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 14 (1989), S. 109-114 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Quantification by XPS intensity analysis of thin multicomponent overlayers, like the native oxides forming on compound semiconductor surfaces, is discussed in some detail. In particular, the advantage of exploiting the attenuated emission from substrate core levels with different probing depths is emphasized, in order to obtain a precise measure for the overlayer thickness dimension. For GaAs(100) treated with different chemical etches, estimates are obtained for the thickness of the native surface oxide formed after exposure to air, of 6-8 Å. The elemental composition of the surface oxide is close to the stoichiometric metal: oxygen ratio of the bulk oxides Ga2O3 and As2O3, in perfect agreement with the measured core-level shifts (1.4 ± 0.2 and 3.0 ± 0.1 eV for the Ga and As 2p levels, respectively). On a CF4 plasma-etched sample, a surface reaction layer of gallium fluoride was found with a composition close to GaF2 and an estimated thickness of ∼23 Å. This paper also discusses how to determine the kinetic energy dependence of the electron escape depth, expressed in terms of an exponent m (γ Em), by working out consistent estimates for the surface oxide (fluoride) thickness via two different approaches. Values for m are obtained in the range 0.5-0.6, in excellent agreement with previously reported data on electron escape depth for semiconductors.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740140303
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  • 9
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    Processing dependence of the interfacial microstructure of Ag contacts to YBa2Cu3O7−δthin films (1993)
    American Institute of Physics
    Details
    Publication Date: 1993-08-09
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Magnetic domain formation in ultrathin complex oxide ferromagnetic/antiferromagnetic bilayers (2018)
    American Institute of Physics
    Details
    Publication Date: 2018-09-24
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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