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20 Feb 1989

Volume 54, Issue 8, pp. 681-777

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High critical currents in epitaxial YBa2Cu3O7−x thin films on silicon with buffer layers

X. D. Wu, A. Inam, M. S. Hegde, B. Wilkens, C. C. Chang, D. M. Hwang, L. Nazar, T. Venkatesan, S. Miura, S. Matsubara, Y. Miyasaka, and N. Shohata

Appl. Phys. Lett. 54, 754 (1989); http://dx.doi.org/10.1063/1.101471 (3 pages) | Cited 67 times

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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.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Millimeter wave surface resistance of epitaxially grown YBa2Cu3O7−x thin films

N. Klein, G. Müller, H. Piel, B. Roas, L. Schultz, U. Klein, and M. Peiniger

Appl. Phys. Lett. 54, 757 (1989); http://dx.doi.org/10.1063/1.101472 (3 pages) | Cited 79 times

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We have measured the surface resistance of two c‐axis oriented YBa2Cu3O7−x thin‐film samples in a copper host cavity at 86.7 GHz between 4.2 and 300 K. High quality films of 0.6 and 0.4 μm thickness have been grown epitaxially on SrTiO3 by pulsed excimer laser ablation. Their millimeter wave absorption drops sharply at a transition temperature of 86 and 88 K to a corresponding surface resistance at 77 K of 18 mΩ and less than 8 mΩ, respectively. These values exceed the best results on polycrystalline samples and come close to the expectation from classical superconductors. Therefore, applications of high Tc superconductors up to THz frequencies can be envisaged now.
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74.25.N- Response to electromagnetic fields
74.70.-b Superconducting materials other than cuprates
73.25.+i Surface conductivity and carrier phenomena
74.78.-w Superconducting films and low-dimensional structures

Highly oriented Tl2Ba2Ca2Cu3O10 thin films by pulsed laser evaporation

S. H. Liou, K. D. Aylesworth, N. J. Ianno, B. Johs, D. Thompson, D. Meyer, John A. Woollam, and Colleen Barry

Appl. Phys. Lett. 54, 760 (1989); http://dx.doi.org/10.1063/1.101473 (3 pages) | Cited 18 times

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We have fabricated superconducting thin films on MgO(100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and post‐annealing. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X‐ray microprobe fluorescence measurements indicate that a typical composition of films is Tl0.66Ba1.77Ca1.46Cu3Ox, which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 μm as revealed by scanning electron microscopy.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
68.55.-a Thin film structure and morphology
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Critical currents and thermally activated flux motion in high‐temperature superconductors

T. T. M. Palstra, B. Batlogg, R. B. van Dover, L. F. Schneemeyer, and J. V. Waszczak

Appl. Phys. Lett. 54, 763 (1989); http://dx.doi.org/10.1063/1.101474 (3 pages) | Cited 164 times

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We have measured the resistance below Tc of single crystals of the high‐temperature superconductors Ba2YCu3O7 and Bi2.2Sr2Ca0.8Cu2O8+δ in magnetic fields up to 12 T. The resistive transition of both compounds is dominated by intrinsic dissipation which is thermally activated, resulting in an exponential temperature dependence of the resistivity well below Tc. The dissipation is significantly larger and of different character in the Bi‐Cu compound than in Ba2YCu3O7. The relation between the activated behavior and the depinning critical current is discussed.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields

Fabrication of stable superconductive wires with YBa2Cu3Ox/Ag2O composite core

S. Sen, In‐Gann Chen, C. H. Chen, and D. M. Stefanescu

Appl. Phys. Lett. 54, 766 (1989); http://dx.doi.org/10.1063/1.101475 (3 pages) | Cited 26 times

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The problem of maintaining the oxygen stoichiometry of the Y1Ba2Cu3Ox (the so‐called 123) compound at the desired level of x=6.0±0.1 when fabricating superconducting wires using the powder‐in‐tube method is addressed. A solution to this problem appears to be incorporating an unstable oxide like Ag2O in the core material, such that it acts as an in situ oxygen donor during the final sintering or annealing stage. Moreover, the segregation of Ag at the grain boundaries of the 123 grains and at the porosities seems to be a possible reason for the considerable improvement of the critical current density Jc of these wires. The effect of processing parameters, like different sintering temperatures and addition of various percentages of either Ag or Ag2O, is presented. Finally, in order to test conservation of superconductive properties during handling, the wires were subjected to different degrees of bending, and the subsequent effect on superconducting transition temperature, Tc and Jc, is reported.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Growth of 200 Å superconducting Bi‐Sr‐Ca‐Cu oxide thin films

J.‐J. Yeh and M. Hong

Appl. Phys. Lett. 54, 769 (1989); http://dx.doi.org/10.1063/1.101476 (3 pages) | Cited 5 times

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Preferentially math‐axis oriented superconducting Bi‐Sr‐Ca‐Cu oxide films as thin as 200 Å have been successfully grown on MgO(100) substrates. Even though such thin films are only 6–7 unit cells thick, they still exhibit bulk superconducting properties. These films typically exhibit a superconducting transition temperature at 80 K and a critical current density of 105 A/cm2 at 50 K as determined by transport measurements. The ability to grow even thinner films is controlled by the exact film stoichiometry and the smoothness of the substrate surface.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
68.55.-a Thin film structure and morphology

X‐ray photoemission studies of the interfacial reactions of Pt and Au on anodic oxide of Hg0.8Cd0.2Te

W. M. Lau, J.‐W. He, and P. R. Norton

Appl. Phys. Lett. 54, 772 (1989); http://dx.doi.org/10.1063/1.101352 (3 pages) | Cited 2 times

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The metal‐oxide interfacial reactions of platinum and gold on anodic oxide of Hg0.8 Cd0.2 Te have been studied by x‐ray photoelectron spectroscopy. It was found that the depositions of these metals, which were expected to be inert, reduced the oxidized tellurium in the anodic oxide and extracted the reduced tellurium into the metal overlayer. In the case of platinum, reductions of oxidized cadmium and mercury also occurred. The resultant interfacial structures of gold and platinum on HgCdTe oxide seem to be determined by the kinetics of possible reactions but not by bulk thermodynamic data of the relevant reactants and the most stable reaction products.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Synthesis of composite thin films by simultaneous use of pulsed laser and conventional thermal evaporation

S. J. Dikshit, V. P. Godbole, S. M. Chaudhari, S. M. Kanetkar, and S. B. Ogale

Appl. Phys. Lett. 54, 775 (1989); http://dx.doi.org/10.1063/1.101477 (3 pages) | Cited 10 times

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The concept of simultaneous use of pulsed laser evaporation and conventional thermal evaporation has been used for the first time to synthesize composite thin‐film structures. It is shown that the use of pulsed laser evaporation of α‐Fe2O3 concurrently with thermal evaporation of aluminum leads to a composite state defined by the presence of clusters of iron‐related material in the aluminum matrix. The microstructural aspects of the physical state of the composite are studied by using conversion electron Mössbauer spectroscopy, glancing angle x‐ray diffraction, and scanning electron microscopy.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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