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13 Aug 1990

Volume 57, Issue 7, pp. 643-734

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Molecular beam epitaxy deposited thin films of bismuth compound superconductors

H. Bernhoff and A. S. Flodström

Appl. Phys. Lett. 57, 712 (1990); http://dx.doi.org/10.1063/1.104256 (3 pages) | Cited 2 times

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Thin films of superconducting BiCaSrCuO have been grown by molecular beam epitaxy depositions of Bi, Cu, and CaF2/SrF2 on MgO and SrTiO3 followed by a high‐temperature oxygen anneal. The films showed a fairly wide transition of 20 K at a Tc of 80 K. Residual amounts of fluorine, detected with secondary‐ion mass spectrometry, are believed to cause the broad superconducting transition. X‐ray diffraction analysis of the superconducting films revealed strongly c‐axis oriented films consisting of Bi2CaSr2Cu2O8 and Bi2Sr2Cu1O6 phase. Surface structure studies, with scanning electron microscopy and scanning tunneling microscopy, show oriented 1 μm sized very smooth flat grains of superconducting phase in the plane of the film with islands of CuOx scattered on top of these.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

Lanthanum‐substituted Y‐Ba‐Cu‐O superconductors synthesized at elevated oxygen pressures

D. E. Morris, P. K. Narwankar, A. P. B. Sinha, K. Takano, and V. T. Shum

Appl. Phys. Lett. 57, 715 (1990); http://dx.doi.org/10.1063/1.104257 (3 pages) | Cited 2 times

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Lanthanum substitution in the Y‐Ba‐Cu‐O system at elevated P(O2) results in superconducting compositions which throw interesting light on the effects of nonisovalent substitution in a Y‐Ba‐Cu‐O system. Like Ca substitution, La substitution also shifts the phase formation boundary between 123, 247, and 124 phases to higher P(O2), and stabilizes a tetragonal 123 structure at moderately elevated P(O2). However, in contrast with Ca substitution, Tc decreases continuously and rapidly with increasing La content. This can be only partly explained by a decrease of the hole concentration.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.66.Fn Inorganic compounds
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations

Ge on Bi2Sr2−xCa1+xCu2O8+y: Reduced reactivity through cluster assembly

T. R. Ohno, Y.‐N. Yang, J. H. Weaver, Y. Kimachi, and Y. Hidaka

Appl. Phys. Lett. 57, 718 (1990); http://dx.doi.org/10.1063/1.104287 (3 pages) | Cited 6 times

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Photoemission studies of low‐temperature deposition of ∼30‐Å‐diam Ge clusters on single‐crystal Bi2 Sr2−x Ca1+x Cu2 O8+y (100) show that an interface is produced with no evidence of substrate disruption. Analysis of the superconductor core level emission as a function of coverage indicates uniform overlayer growth and complete surface coverage. These cluster‐assembled interfaces were stable when warmed to 300 K, with only a slight reduction of Cu 2p3/2 satellite emission characteristic of the superconductor. In contrast, conventional atom‐by‐atom Ge deposition produces a Ge oxide layer and surface disruption.
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68.35.Fx Diffusion; interface formation
74.70.-b Superconducting materials other than cuprates
68.55.-a Thin film structure and morphology

In situ growth of YBa2Cu3O7−x high Tc superconducting thin films directly on sapphire by plasma‐enhanced metalorganic chemical vapor deposition

C. S. Chern, J. Zhao, Y. Q. Li, P. Norris, B. Kear, and B. Gallois

Appl. Phys. Lett. 57, 721 (1990); http://dx.doi.org/10.1063/1.104258 (3 pages) | Cited 13 times

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Highly c‐axis oriented YBa2Cu3O7−x superconducting thin films have been, in situ, deposited directly on sapphire substrate by a remote microwave plasma‐enhanced metalorganic chemical vapor deposition process (PE‐MOCVD). The films were deposited at a substrate temperature of 730 °C followed by a fast cooling. The as‐deposited films show attainment of zero resistance at 82 K and have critical current density of 104 A/cm2 at 70 K. ac susceptibility measurement indicated that the films contain a single superconducting phase. PE‐MOCVD was carried out in a commercial‐scale MOCVD reactor with capability of uniform deposition over 100 cm2 per growth run.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents

Remanent nonlinear magnetic response in superconducting Y‐Ba‐Cu‐O

A. Shaulov, D. Dorman, R. Bhargava, and Y. Yeshurun

Appl. Phys. Lett. 57, 724 (1990); http://dx.doi.org/10.1063/1.103599 (3 pages) | Cited 8 times

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We report a ‘‘memory’’ effect in the response of sintered Y‐Ba‐Cu‐O to alternating magnetic fields. The application of a steady bias field, above a certain threshold, causes the generation of harmonic components in the response. These harmonics persist after the field is removed, exhibiting a logarithmic decay with time. We explain these phenomena in the framework of the Bean model, taking into account the granularity of the sample. The memory phenomenon offers a principle for a new recording mechanism which may allow extremely high storage capacity.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.N- Response to electromagnetic fields
74.70.-b Superconducting materials other than cuprates
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Low noise YBa2Cu3O7−δ grain boundary junction dc SQUIDs

R. Gross, P. Chaudhari, M. Kawasaki, M. B. Ketchen, and A. Gupta

Appl. Phys. Lett. 57, 727 (1990); http://dx.doi.org/10.1063/1.103600 (3 pages) | Cited 107 times

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We have fabricated YBa2Cu3O7−δ grain boundary junction dc superconducting quantum interference devices (SQUIDs) with a square washer geometry design. The SQUIDs were formed in c‐axis oriented epitaxial films with a single grain boundary of predetermined nature. These SQUIDs show perfectly periodic voltage‐flux characteristics without hysteresis from 4.2 to 87 K. At 77 K intrinsic energy sensitivities of 1.5×10−30 and 3.0×10−30 J/Hz at 10 kHz were obtained for 60 and 110 pH SQUIDs, respectively. The intrinsic energy sensitivity limited by 1/f noise at 10 Hz was 1.2×10−28 and 5.5×10−28 J/Hz. The SQUID voltage noise was found to be almost identical to the voltage noise from one of its junctions. The flux focusing effect of the washer geometry was also measured.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.50.+r Tunneling phenomena; Josephson effects

Observation of large magneto‐optical effects in amorphous UxSb1−x films

M. W. McElfresh, T. S. Plaskett, R. J. Gambino, and T. R. McGuire

Appl. Phys. Lett. 57, 730 (1990); http://dx.doi.org/10.1063/1.103601 (3 pages) | Cited 3 times

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Amorphous films with the compositions UxSb1−x (for x between 0.2 and 0.8) prepared by magnetron sputtering show ferromagnetic properties with Curie temperatures as high as 135 K (for x=0.45) and ordered magnetic moments of about 1.5μB. Large positive Faraday rotation values of over 2×106 deg/cm and large negative Kerr rotation values of over 3° are reported. The values of Faraday rotation are correlated with a large Hall effect, having corresponding Hall angles of up to θH=17°.
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78.20.Ls Magneto-optical effects
75.50.Kj Amorphous and quasicrystalline magnetic materials

Rectifying metal‐polymer contacts formed by melt processing

M. Sundberg, G. Gustafsson, and O. Inganäs

Appl. Phys. Lett. 57, 733 (1990); http://dx.doi.org/10.1063/1.103602 (2 pages) | Cited 9 times

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Rectifying contacts between aluminum, indium, or titanium and a solution and melt processable conducting polymer, poly(3‐octylthiophene) have been formed by melt processing. The contacts are formed by heating a metal/polymer/metal structure to the melting point of the polymer and then pressing the metals to the melted polymer until adhesion is achieved, whereupon the whole structure is cooled to room temperature. Comparison of the current‐voltage and capacitance‐voltage characteristics of a melt processed device and a device manufactured by metal sputtering shows that no significant differences exist between these structures.
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73.40.Ns Metal-nonmetal contacts
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
85.30.De Semiconductor-device characterization, design, and modeling
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