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26 Nov 1990

Volume 57, Issue 22, pp. 2285-2377

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Ideal tunneling characteristics in Ba1−xKxBiO3 point‐contact junctions with Au and Nb tips

Qiang Huang, J. F. Zasadzinski, K. E. Gray, D. R. Richards, and D. G. Hinks

Appl. Phys. Lett. 57, 2356 (1990); http://dx.doi.org/10.1063/1.104172 (3 pages) | Cited 13 times

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One important potential application of high‐temperature superconductors is for tunnel junctions, especially hysteretic Josephson junctions. Unfortunately, tunnel junctions of oxide superconductors with a useful Tc≳20 K have exhibited nonideal I(V) characteristics with a normalized zero‐bias conductance, σs/σn(0), of 15–50%. We present data on point‐contact junctions of Ba1−xKxBiO3 which clearly demonstrate that these problems are not intrinsic. Using a normal‐metal counterelectrode, σs/σn(0) was <1% and σs/σn(V) agreed with the BCS theory by including only thermal smearing. Using a superconducting Nb counterelectrode, the I(V) showed very sharp features with evidence of a proximity effect, and σs/σn(0) was <0.2%. These results prove that there is no fundamental limitation for tunnel junctions using this HTS material, and one can anticipate operation of devices with two Ba1−xKxBiO3 electrodes at 15–20 K.
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74.50.+r Tunneling phenomena; Josephson effects

Transport critical current density in epitaxial Bi2Sr2CaCu2O8+x films: Effects of the substrate twinning

G. Balestrino, V. Foglietti, M. Marinelli, E. Milani, A. Paoletti, and P. Paroli

Appl. Phys. Lett. 57, 2359 (1990); http://dx.doi.org/10.1063/1.104173 (3 pages) | Cited 19 times

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Epitaxial Bi2Sr2CaCu2O8+x films have been grown by the liquid phase technique on twinned LaGaO3 and untwinned SrTiO3 substrates. Crystallographic properties and transition temperatures are comparable, but the transport critical current density Jc depends dramatically on the substrate. Films grown on SrTiO3 have Jc comparable with single crystals, while films grown on LaGaO3 have Jc values extrapolated at 4.2 K in the 104–105 A cm−2 range. This effect is demonstrated to be a consequence of the presence of twinning domains in the 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
68.35.Dv Composition, segregation; defects and impurities

Bulk superconductivity in single CuO layer Bi‐Sr‐Cu‐O ceramics

L. F. Schneemeyer, S. A. Sunshine, R. M. Fleming, S. H. Glarum, R. B. van Dover, P. Marsh, and J. V. Waszczak

Appl. Phys. Lett. 57, 2362 (1990); http://dx.doi.org/10.1063/1.104174 (3 pages) | Cited 4 times

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Despite early recognition that a relatively low‐temperature superconductor occurs in samples of approximate composition Bi2Sr2CuO6, studies of this material have been plagued by difficulties in the preparation of single phase material with a large superconducting fraction. We report the first preparation of ceramic samples in the Bi‐Sr‐Cu‐O system that show bulk superconductivity at 4–15 K. Structural, chemical, and electronic characterizations of superconducting and nonsuperconducting ceramics of composition Bi2.05Sr1.95CuO6 are described.
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74.70.-b Superconducting materials other than cuprates
74.10.+v Occurrence, potential candidates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Defect formation caused by a transient decrease in the ambient oxygen concentration during growth of YBa2Cu3O7−δ films

A. Gupta, B. W. Hussey, A. Kussmaul, and A. Segmüller

Appl. Phys. Lett. 57, 2365 (1990); http://dx.doi.org/10.1063/1.104175 (3 pages) | Cited 25 times

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Thin films of YBa2Cu3O7−δ have been grown in an oxygen atmosphere by pulsed laser deposition using two synchronized lasers, separated by a variable delay (1 μs–10 ms). The ablated fragments from the first laser lead to formation of a blast wave in O2, leaving behind a rarefied ambient. If the second laser is triggered before the O2 pressure returns to equilibrium, the resulting films show a decrease in transition temperature with an expanded c‐lattice parameter caused by defects in the nonchain sites of YBa2Cu3O7−δ. This demonstrates the necessity of maintaining a sufficiently high concentration of oxygen within the time period that the fragments travel and deposit on the substrate.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
74.78.-w Superconducting films and low-dimensional structures

XeCl excimer laser ablation of a polyethersulfone film: Dependence of periodic microstructures on a polarized beam

Hiroyuki Niino, Masashi Shimoyama, and Akira Yabe

Appl. Phys. Lett. 57, 2368 (1990); http://dx.doi.org/10.1063/1.103873 (3 pages) | Cited 14 times

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Highly periodic stable microstructures appeared on the surface of polyethersulfone (PES) by XeCl excimer laser ablation with a single polarized beam in ambient air. Its formation mechanism was investigated using the time‐resolved light scattering technique with the pulsed light of an XeF excimer laser. In addition to the polarization of the ablating beam, thermal processes on the etched surface play a significant role in microstructure formation.
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78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Influence of surface topography on depth profiles obtained with secondary‐ion mass spectrometry

A. J. Walker, M. T. Borchert, C. J. Vriezema, and P. C. Zalm

Appl. Phys. Lett. 57, 2371 (1990); http://dx.doi.org/10.1063/1.103874 (3 pages) | Cited 1 time

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Lithographically generated well‐defined surface topography of submicron dimensions has been etched into silicon (100) previously implanted with 25 keV 11B to a fluence of 2×1014 atoms/cm2. The thus‐obtained samples were depth profiled via secondary‐ion mass spectrometry (SIMS). The boron concentration distributions measured were contrasted against those found on undisturbed flat parts of the target. From this intercomparison the otherwise trivial observation that surface topography causes profile distortion becomes suddenly alarming as an apparent improvement of depth resolution occurs. Scanning electron microscope images enable identification of the origin of this remarkable phenomenon. The present results imply that (i) the hitherto commonly accepted assumption in the interpretation of SIMS depth profiles that perceived gradients are never steeper than actual ones is subject to revision; (ii) it may prove very difficult, if not impossible, to construct SIMS equipment for reliable on‐chip analysis of submicron details.
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07.75.+h Mass spectrometers
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Improvement of rare‐gas solid moderators by using conical geometry

R. Khatri, M. Charlton, P. Sferlazzo, K. G. Lynn, A. P. Mills, and L. O. Roellig

Appl. Phys. Lett. 57, 2374 (1990); http://dx.doi.org/10.1063/1.103856 (3 pages) | Cited 22 times

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A slow positron beam with narrow energy spread can be obtained by moderating the β+ decay of a radioactive source. We report here the improvement in the efficiency of the rare‐gas solid positron moderators by using a different geometry. The efficiency for slow positrons, ϵ, was measured for the cylindrical and the cone configurations of the moderator with the latter yielding ϵ of (4.6±0.2)×10−3 for solid neon deposited on an encapsulated radioactive 22Na source deposited on a 5 μm Cu98/Be2 window. No corrections were applied for the attenuation caused by the window. The ϵ for the conical configuration is (2.7 ± 0.2) times higher than that for the cylindrical configuration. Other rare‐gas solids (e.g., Ar, Xe, Kr) yielded lower ϵ as compared to that for the solid neon in agreement with the earlier measured efficiencies of Mills and Gullikson [Appl. Phys. Lett. 49, 1121 <usb>(1986)].
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
78.70.Bj Positron annihilation
29.27.Eg Beam handling; beam transport
29.25.Rm Sources of radioactive nuclei
FREE

Erratum: Evidence for the existence of a negatively charged hydrogen species in plasma‐treated n‐type Si [Appl. Phys. Lett. 56, 949 (1990)]

A. J. Tavendale, S. J. Pearton, and A. A. Williams

Appl. Phys. Lett. 57, 2377 (1990); http://dx.doi.org/10.1063/1.104293 (1 page) | Cited 2 times

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Abstract Unavailable
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81.40.Rs Electrical and magnetic properties related to treatment conditions
71.55.Ht Other nonmetals
99.10.Cd Errata
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