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  • 1985-1989  (8)
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  • 1
    ISSN: 1432-0630
    Keywords: 74 ; 66.30 ; 82.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The change in electrical resistance with time for bulk, thick-film, and thin-film Ba2YCu3Ox at atmospheric pressure is described as a function of the oxygen partial pressure (100 to 0.001%) and temperature (320°–750°C). The potential usefulness of these materials as oxygen sensors is demonstrated. The rate of equilibration is faster during oxygen uptake than during its loss. Time constants τ to reach equilibration (1/e remaining), qualitatively scale with sample dimensions. For a 1μm film at 600° C,τ 〈1 s for the range of PO2 (O2 being a shorthand for O2) from 100% to 0.001%. The rate increases markedly with increasing PO2. The actual resistance decreases with PO2 at a rate of logρ/log PO2 = 0.4 at 700° C showing adequate sensitivity for sensor purposes. Times for the transient resistance change in the sample where used to estimate the oxygen diffusion coefficient in the ceramic. The diffusivities obtained are 4·10−11−1·10−12 cm2/s in the 435°–320° C range, with an activation energy of ≅27 kcal/mole.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 919-921 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical and structural characteristics of thin thermally oxidized yttrium layers on Si and on Si covered with 40 A(ring) of SiO2 have been investigated. The factor of ∼ four advantage in the dielectric constant of Y2O3 over SiO2, coupled with extremely low leakage current density of better than 10−10 A/cm2 in a field of 1.9 MV/cm, sufficiently high breakdown strength, and well-behaved capacitance-voltage characteristics makes Y2O3 a viable candidate for Si very large scale integration applications, at least in passive devices. High-resolution transmission electron microscopy reveals the structure of the composite dielectric and provides good agreement between calculated and experimental capacitance.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 2103-2109 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Preparation and characteristics of refractory Nb/Al-oxide-Nb Josephson tunnel junctions with critical current densities jc from ∼103 to ∼4×104 A/cm2 were studied with respect to junction quality, uniformity, reproducibility and jc control. The key steps leading to improved junction parameters are emphasized and compared with previously used procedures. The results include jmaxc/jminc of 1.2, on a 1-in. chip, Vm up to 56 mV in junctions with jc∼103 A/cm2, and Vm up to 24 mV with jc∼6×103 A/cm2. Good run-to-run reproducibility and control of jc are also demonstrated. In particular, jc is shown to increase by a factor of ∼40 when the oxygen pressure during the in-situ oxidation of the Al overlayer is reduced from 1 to 0.01 Torr.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 618-619 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of A15 Nb3Al have been prepared by reactive diffusion of sputter-deposited Nb/Al multilayers. The diffusion reactions were studied by in situ annealing x-ray diffraction in the temperature range 50–950 °C. Initially the Nb and Al sublayers react to form the phase NbAl3. This interface reaction prevents the formation of the σ-phase Nb2Al, frequently found as a second phase in A15 Nb3Al materials; NbAl3 reacts with the remaining Nb to form the A15 phase. The highest Tc, 16.2 K measured resistively and 15.2 K inductively, was found in a Nb/Al multilayer with an A15 cell parameter a0=5.195 A(ring) which corresponds to ∼20 at. % Al. From a comparison with previous investigations of the Tc dependence on Al concentration and A15 cell parameter, it is concluded that a small amount of the A15 phase has a higher composition of 22–23 at. % Al.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5089-5097 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Al films deposited on Nb can be oxidized and used to make Josephson junction devices. We studied the structure of Al films deposited under "warm'' (estimated to be near 200 °C) and "cold'' (near room temperature) conditions because the cold films produced better Josephson junction devices. For the warm case, the Al film was composed of islands with open channels between them, which we attribute to a high mobility of the Al atoms that lowers the island nucleation density. The Nb surface was extremely flat, which we ascribe to the high surface atom mobility at the higher deposition temperature. The cold Al film was of uniform thickness which can be explained by a high island nucleation density. The cold Nb films had an undulating surface, caused by the lack of surface atom mobility during deposition. There was no evidence of Al-Nb interdiffusion, even after postdeposition heating to 300 °C. Auger spectroscopy, transmission electron microscopy, and scanning electron microscopy were needed to obtain these definitive conclusions.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3204-3210 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An emerging new class of superconductor-semiconductor devices requires Ohmic superconducting contacts which do not diffuse deeply into a semiconductor. We developed a contact to GaAs based on ∼150 A(ring) of AuGe covered with ∼2000 A(ring) of Nb annealed in reducing atmosphere at 390–420 °C for 1–5 s. The resulting contact has linear I-V characteristics at all temperatures down to 4.2 K, resistivity of ∼2×10−6 Ω cm2 (∼0.1 Ω mm), and superconducting transition temperature Tc (approximately-greater-than)8 K. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) studies revealed very shallow penetration of the active dopant Ge into GaAs; the upper limit for the thickness of the doped layer with Ge concentration over 1017 cm−3 is estimated as 200–300 A(ring). Gold, a nonactive dopant (deep level) drops to below 1018 cm−3 within the same distance, with the possible tail extending further. Morphology and uniformity of a contact, as revealed in TEM and optical microscopy, is good, owing to the Nb overlayer which prevents AuGe from "balling up'' upon melting. These contacts can be used in low-temperature devices and conventional devices based on GaAs.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1027-1029 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multiple metal-target dc magnetron sputter deposition of a metallic YBa2Cu3 alloy in pure Ar followed by ex situ oxygen annealing was used to prepare superconducting films on various substrates. This work particularly examines film-substrate reactions which are degrading to superconductivity. Better superconductors were obtained using predeposited buffer layers, notably on cubic zirconia and MgO substrates covered with Ag and Nb. Best films have Tc=80 K, metallic resistivities with resistance ratio(approximately-greater-than)2, and critical current density (approximately-less-than)10 kA cm−2 at 4.2 K. Normal-state resistivity measurements were made for O2 furnace temperatures up to 850 °C. Procedures for lithographically patterning these films are also described.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 311-313 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial YSi2−x films have been fabricated. The smooth 430-A(ring)-thick silicide films on Si (111) substrates were characterized by a Rutherford backscattering minimum channeling yield χmin =8%, establishing YSi2−x as one of the best known epitaxial silicides. Results of electrical measurements are also presented.
    Type of Medium: Electronic Resource
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