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5 Dec 1988

Volume 53, Issue 23, pp. 2251-2347

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Spiral hollow cathode plasma‐assisted diamond deposition

Y. Tzeng, P. J. Kung, R. Zee, K. Legg, H. Solnick‐Legg, D. Burns, and B. H. Loo

Appl. Phys. Lett. 53, 2326 (1988); http://dx.doi.org/10.1063/1.100268 (2 pages) | Cited 11 times

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High quality diamond films have been deposited on silicon and sapphire by means of a combined hot filament/electron beam/plasma‐assisted chemical vapor deposition technique. A spiral tantalum foil is used as the hot cathode to generate a high‐current dc discharge at a low sustaining voltage. Gas mixtures consisting of methane, hydrogen, and argon flowing through the spiral cathode towards the anode are effectively decomposed by the hot cathode and the high‐density plasma. Diamond particles and films, grown at a rate between 0.5 and 5 μm/h, have been characterized by scanning electron microscopy, x‐ray diffraction, and Raman spectroscopy.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.55.-g Dielectric thin films
78.30.Hv Other nonmetallic inorganics

Technique for selective etching of Si with respect to Ge

A. A. Bright, S. S. Iyer, S. W. Robey, and S. L. Delage

Appl. Phys. Lett. 53, 2328 (1988); http://dx.doi.org/10.1063/1.100269 (2 pages) | Cited 8 times

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A technique to selectively etch silicon with respect to germanium is described. The method relies on an observed small difference in the effects of polymeric etch‐inhibiting layers on the two materials. In a CF4/H2 plasma, the observed polymer point for Ge is 1–3% lower than for Si. This produces a narrow process window in which Si is etched while etching of Ge is suppressed. This technique has applications to etching of pure Si layers over Ge as well as Si‐Ge alloys for device applications.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Highly oriented as‐deposited superconducting laser ablated thin films of Y1Ba2Cu3O7−δ on SrTiO3, zirconia, and Si substrates

G. Koren, E. Polturak, B. Fisher, D. Cohen, and G. Kimel

Appl. Phys. Lett. 53, 2330 (1988); http://dx.doi.org/10.1063/1.100515 (3 pages) | Cited 57 times

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KrF excimer laser ablation of an Y1Ba2Cu3O7−δ pellet in 0.1–0.2 Torr of O2 ambient was used to deposit thin superconducting films onto SrTiO3, yttria‐stabilized zirconia (YSZ), and silicon substrates at 600–700 °C. The as‐deposited 1‐μm‐thick films at 650–700 °C substrate temperature were superconducting, without further high‐temperature annealing. All films had a similar Tc onset of ∼92 K but different zero‐resistance Tc of 90, 85, and 70 K for the films on SrTiO3, YSZ, and Si substrates, respectively. Angular x‐ray diffraction analysis showed that all the films were highly oriented with the c axis perpendicular to their surface. Critical current densities at 77 K were about 40 000 and 10 000 A/cm2 for the films on SrTiO3 and YSZ, respectively. Smooth surface morphology was observed in all films, with occasional defects and cracks in the films on YSZ, which seems to explain the lower critical current in these films.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Jj Ion and electron beam-assisted deposition; ion plating
74.25.Sv Critical currents
68.55.-a Thin film structure and morphology

Optical characterization of surface and interface oxygen content in YBa2Cu3Ox

M. K. Kelly, Siu‐Wai Chan, K. Jenkin, D. E. Aspnes, P. Barboux, and J.‐M. Tarascon

Appl. Phys. Lett. 53, 2333 (1988); http://dx.doi.org/10.1063/1.100516 (3 pages) | Cited 19 times

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Because YBa2Cu3Ox exists over a range of oxygen content and low oxygen material is nonsuperconducting, it is important to be able to measure and control this parameter for application purposes. We present an optical technique for determining oxygen loss at surfaces and interfaces, where processing and contacts with other materials may affect composition and where usual techniques are insensitive. Using a strong absorption feature at 4.1 eV which appears at low oxygen composition, we find that overlayers of Al and In remove oxygen from YBa2Cu3Ox, but Ag, Au, and room‐temperature exposure to moderate vacuum do not.
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68.35.Dv Composition, segregation; defects and impurities
74.70.-b Superconducting materials other than cuprates
73.40.Cg Contact resistance, contact potential
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Intrinsic superconductor/normal‐metal/superconductor‐like weak links in Y1Ba2Cu3O7−x thin films

P. England, T. Venkatesan, X. D. Wu, A. Inam, M. S. Hegde, T. L. Cheeks, and H. G. Craighead

Appl. Phys. Lett. 53, 2336 (1988); http://dx.doi.org/10.1063/1.100517 (3 pages) | Cited 23 times

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Magnetotransport measurements on micron‐sized wires of the thin‐film high Tc superconductor Y1 Ba2 Cu3 O7−x made by pulsed laser deposition reveal an exponential suppression of the critical current with magnetic field, and a power law dependence of the critical current on reduced temperature. We ascribe this behavior to crystallographic defects in the film which behave as superconductor/normal‐metal/superconductor weak links in a magnetic field. From the measurements we estimate a critical current density of 106 A cm−2 in a field of 16 T at 4.2 K.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.55.-a Thin film structure and morphology

Microstructure of epitaxial YbBa2Cu3O7 superconducting films grown by a new liquid‐gas‐solidification technique

C. H. Chen, H. S. Chen, and S. H. Liou

Appl. Phys. Lett. 53, 2339 (1988); http://dx.doi.org/10.1063/1.100518 (3 pages) | Cited 5 times

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We have studied the microstructures of epitaxial YbBa2Cu3O7 superconducting films grown on SrTiO3[100] and [110] substrates by a new liquid‐gas‐solidification processing technique. Films grown on SrTiO3[100] and [110] substrates are epitaxially oriented with [001] and [110] axes normal to the film surface. Twinned domains of ∼200 Å in size are observed in the [001] oriented films. Most defects observed can be attributed to the presence of stacking faults along the c axis. The presence of Cu‐O bilayer defects is also observed. Rapid oxygen diffusion in the liquid phase is found to play an important role in the microstructure of the thin films.
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68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates

Aluminum cladding of high Tc superconductor by thermocompression bonding

T. J. Richardson and L. C. DeJonghe

Appl. Phys. Lett. 53, 2342 (1988); http://dx.doi.org/10.1063/1.100519 (2 pages) | Cited 3 times

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Thermocompression bonding of aluminum to YBa2Cu3O7−x (YBCO) has been demonstrated. The superconductor is protected by a thin barrier layer of silver. The specific resistivity of the Al/Ag/YBCO interface was measured at 77 K as a function of current density and is below 3.2×10−5 Ω cm2 for electrode current densities of at least 400 A cm−2 . This technique provides a convenient means of cladding bulk superconducting ceramics with a strong, inexpensive, and highly conductive metal.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
73.40.Ns Metal-nonmetal contacts
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
74.70.-b Superconducting materials other than cuprates

Special grain boundaries in YBa2Cu3O7

D. A. Smith, M. F. Chisholm, and J. Clabes

Appl. Phys. Lett. 53, 2344 (1988); http://dx.doi.org/10.1063/1.100520 (2 pages) | Cited 19 times

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The orientation distribution produced in strings of YBa2Cu3O7−x often referred to as 123, crystals produced from a melt is not random. The individual crystals are kinematically free to rotate during the coalescence process and it is found that coincidence site lattice misorientations are selected. This observation suggests that grain boundaries in 123 have structures related to those in other crystalline materials.
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61.72.Mm Grain and twin boundaries
74.70.-b Superconducting materials other than cuprates
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Magnetic suspension of superconductors at 4.2 K

Ronald J. Adler and W. W. Anderson

Appl. Phys. Lett. 53, 2346 (1988); http://dx.doi.org/10.1063/1.100521 (2 pages) | Cited 6 times

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We have observed the stable suspension of superconductors at 4.2 K below a permanent magnet; the superconductors were the type II material Nb3Sn and the high transition temperature material YBa2Cu3Ox. Suspension below a magnet is to be distinguished from levitation above a magnet, which is the classic demonstration of the Meissner effect. Suspension at 4.2 K can be quantitatively explained as due to complete flux trapping in the superconductor. Suspension has previously been observed only at high temperatures in high transition temperature materials, in which the flux trapping is not complete.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.70.-b Superconducting materials other than cuprates
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