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  • 1
    Electronic Resource
    Electronic Resource
    The influence of ambient magnetic environments on high-Tc superconducting quantum interference device gradiometers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8783-8791 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of high-temperature superconducting gradiometers have been evaluated in fields of up to 70 μT to determine their limitations in unshielded environments. The sensors incorporate first-order gradiometric superconducting quantum interference devices (SQUIDs) coupled to first-order gradiometric flux transformers. A gradiometer was operated successfully at all angles with respect to an ambient field with less than 20% variation in critical current and voltage/flux ratio. Magnetic hysteresis at 77 K was measured for field excursions up to 70 μT. The hysteresis factor, referred to the SQUID, averaged 10−3 Φ0/μT. Flux movement in the SQUID washers rather than the flux transformer was found to be the dominant cause of the hysteresis and the presence of the flux transformer reduced the hysteresis. This is interpreted as due to the coupling coil pinning the vortices against radial motion. The spectral noise density of the gradiometer was only weakly dependent on the orientation with respect to static fields of up to 70 μT except for narrow angular ranges where dominating random telegraph signal processes occurred. In contrast, field cooling the gradiometer above 15 μT was found to substantially increase the low-frequency noise. A gradiometer was successfully transported and operated out of doors with no shielding. Only a relatively minor degradation of performance was observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362504
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  • 2
    Electronic Resource
    Electronic Resource
    Electrolyte electroreflectance in the characterization of HgCdTe heterostructures (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4518-4522 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used the technique of electrolyte electroreflectance (EER) coupled with electrochemical etching to profile through epitaxial layers and heterostructures of Hg1−xCdxTe. The need for proper electrochemical control during EER measurements is discussed. The resolution achieved in both composition, Δx=±0.002, and etch depth, ±30 A(ring), has made possible the observation of the variations in composition at the ambient/epilayer, epilayer/substrate, and high-x/low-x interfaces. Good correlations of the profiles observed have been obtained with secondary ion mass spectroscopy, electron dispersive x-ray diffraction, and Rutherford backscattering measurements. The variation of the broadening parameter Γ at these interfaces is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339042
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  • 3
    Electronic Resource
    Electronic Resource
    The nonlinear surface impedance of YBa2Cu3O7−δ thin films in zero and large applied fields (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2137-2145 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present coplanar resonator measurements of the nonlinear microwave surface impedance of laser ablated and electron-beam coevaporated YBa2Cu3O7−δ thin films at 8 GHz in zero and applied magnetic fields, including the effects of irradiation with heavy ions. Correlations between the changes in surface resistance and reactance as a function of microwave current suggest that there are different contributions to the nonlinear behavior at low and high microwave currents in both zero and applied fields. In zero field, we suggest that microwave-induced flux lines are responsible for the observed nonlinear behavior, resulting in thermal runaway at large, sample dependent, microwave currents. The observed nonlinearity completely masks any possible contribution from the intrinsic pair breaking expected for a d-wave superconductor. In a magnetic field at relatively low currents, the nonlinearity can be described by the nonlinear dynamics of flux lines pinned by defects with a continuous range of pinning strengths. At higher currents, microwave field nucleation of flux lines is again considered important. On irradiation with 3.6 MeV/nucleon Xe-129 ions, the microwave losses and nonlinearity are significantly decreased in both zero and applied fields, which could have important implications for microwave device applications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371021
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of small changes in composition on the electrical and structural properties of YBa2Cu3O7 thin films (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2016-2018 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of YBa2Cu3O7 have been grown in situ by evaporation onto (001) MgO substrates. The composition was varied systematically to investigate the effects of changes in Cu content and Ba/Y ratio on the film properties. The results demonstrate that deviations from stoichiometry at the limit of resolution of most analytic techniques can have a large effect on structural and transport properties, as well as causing marked changes in surface morphology. The best properties (Jc(approximately-greater-than)3×106 A/cm2 at 77 K) are only found for a narrow range of compositions, which can be readily identified from the surface morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104152
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  • 5
    Electronic Resource
    Electronic Resource
    Narrow tracks in YBa2Cu3O7 thin films defined by laser ablation (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 75-77 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of cw laser ablation for defining narrow tracks in YBa2Cu3O7 thin films on (001) SrTiO3 substrates is described. Critical current densities have been observed up to 5×105 A/cm2 in 4-μm-wide tracks at 77 K. For these films, it is found that the value of critical current density calculated is insensitive to the length of track and the voltage criterion used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101438
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  • 6
    Electronic Resource
    Electronic Resource
    Electrolyte electroreflectance of HgCdTe at low temperatures (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 502-504 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrolyte electroreflectance measurements in ethanol/lithium perchlorate solutions over the temperature range 300–156 K have been used to derive the temperature dependence of the E1 transition of Hg1−xCdxTe (x=0.23–0.36). The temperature coefficient dE1/dT derived by third derivative line-shape fitting (6.6±0.5×10−4 eV K−1) is considerably higher than values reported previously in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98379
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  • 7
    Electronic Resource
    Electronic Resource
    Bit error probabilities in high temperature superconductor logic (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1366-1368 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present error rate simulations for a single flux quantum logic circuit which include statistical variations in the circuit parameters. We find that the fabrication yield, junction critical margins, and bit error probabilities of the nominal circuit can give a false impression of the performance of practical circuits. For our study circuit, the toggle flipflop, we find that, although the standard figures of merit may vary only marginally with design rules, the average error rate can differ by a factor of 104. Furthermore, for a state-of-the-art technology, the error rates of different realizations of the same design actually span 10 orders of magnitude. These results highlight the inadequacy of current figures of merit to gauge the performance of high temperature superconductor designs. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1285893
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  • 8
    Electronic Resource
    Electronic Resource
    YBa2Cu3O7 thin-film step junctions on MgO substrates (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2433-2435 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions have been made by the evaporation of epitaxial YBa2Cu3O7 over steps etched in (001) MgO. Such junctions differ from those grown on perovskite substrates in that the c-axis of the film grows approximately normal to the local substrate surface, so the junction comprises two tilt grain boundaries. Results are reported for junctions formed by this process which showed Josephson currents at temperatures up to 89 K and resistively shunted junctionlike current-voltage curves. A weak magnetic field applied normal to the substrate gave Fraunhofer patterns indicative of good current uniformity across the junction. The dc SQUIDs show deep modulation, and promising noise performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106996
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  • 9
    Electronic Resource
    Electronic Resource
    Low-noise YBa2Cu3O7 -PrBa2Cu3O7 multiturn flux transformers (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 366-368 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin-film YBa2Cu3O7 flux transformers with multiturn input coils have been constructed on 1 cm2 MgO substrates using PrBa2Cu3O7 as an insulator. By coupling these to high-temperature superconducting quantum interference devices (SQUIDs) using a flip-chip technology, several low-noise magnetometers and a gradiometer have been constructed. The yield of fully working flux transformers on 1 cm2 substrates exceeds 80%, and field sensitivities at 77 K of (520±30)fT/(square root of)Hz at 1 Hz and (165±8)fT/(square root of)Hz above 10 Hz have been achieved. No evidence for excess low-frequency noise above that of the uncoupled SQUID has been found in the flip-chip magnetometers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111149
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  • 10
    Electronic Resource
    Electronic Resource
    End point detection in ion beam milling of YBa2Cu3O7 thin films (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 228-230 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the processing of high temperature superconductor thin films into devices, the use of calibrated milling rates has proved unreliable as a means of determining the milled depth. This problem has been solved using in situ secondary ion mass spectrometry for identifying interfaces in multilayers based on YBa2Cu3O7. The depth resolution obtained during routine patterning of typical multilayers was ∼4 nm. Accurate termination of milling at an insulator/superconductor interface has been demonstrated. The presence of water vapor during milling has been shown to affect the proportions of the different secondary ion species, but has only a slight affect on the milling rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108192
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