Showing papers by "S. R. Foltyn published in 1995"
TL;DR: In this paper, superconducting and mechanical properties of YBa2Cu3O7−δ (YBCO) films on Ni-based alloys with a textured yttria-stabilized zirconia (YSZ) buffer layer were reported.
Abstract: We report superconducting and mechanical properties of YBa2Cu3O7−δ (YBCO) thick films on Ni‐based alloys with a textured yttria‐stabilized zirconia (YSZ) buffer layer. The YBCO and YSZ layers were deposited by pulsed laser deposition and ion beam assisted deposition, respectively. It was found that the transport critical current density (Jc) correlates very well with the YBCO mosaic spread. Jc over 1×10 6 A/cm2 at 75 K and ∼1×107 A/cm2 at 4 K were obtained in the 1‐μm thick YBCO films. Zero field critical current of 120 amps at 75 K was obtained in a 2‐μm‐thick and 1‐cm‐wide YBCO film. Angular dependence measurement revealed Jc peaks for both H∥c and H∥a‐b. The peak for H∥c implies additional pinning due to defects such as small angle grain boundaries or twin boundaries. Bending tests at 75 K showed that the YBCO thick films on the metallic substrates could sustain a strain of 0.4% and over 1% for tension and compression, respectively.
342 citations
TL;DR: In this paper, the epitaxial nature of both Ba0.5Sr 0.5TiO3 (BST) thin films was determined by the measurement of inplane orientation with respect to the major axes of the substrate.
Abstract: Epitaxial Ba0.5Sr0.5TiO3 (BST) thin films were deposited on LaAlO3 substrates with the conductive metallic oxide SrRuO3 (SRO) as a bottom electrode by pulsed laser deposition. The BST and SRO films were (h00) and (00l) oriented normal to the substrate surface, respectively. The epitaxial nature of both BST and SRO layers was determined by the measurement of in‐plane orientation with respect to the major axes of the substrate. Ion beam channeling with a minimum yield of around 10% from Rutherford backscattering spectrometry demonstrated the films to be of high crystallinity. A dielectric constant around 500 and dielectric loss less than 0.01 at a frequency of 10 kHz were measured on the capacitors with a configuration of Ag/BST/SRO. Electrical measurements on such epitaxial BST films showed a breakdown voltage above 106 V/cm and a leakage current density of less than 5×10−8 A/cm at a field intensity of 2×105 V/cm. These results prove the BST/SRO heterostructure to be a good combination for microelectronic device applications.
133 citations
TL;DR: Overall, the critical current shows a clear Lorentz-force dependence and two distinctive peaks, one for fields parallel to the ab plane, due to bulk intrinsic pinning by the layered structure of the superconductor, and the other for fields Parallel to the c axis, which is attributed to twin-boundary c-axis correlated pinning.
Abstract: We investigate the angular dependence of the critical currents in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thick films deposited on metallic nickel-alloy substrates, with the aid of an yttria-stabilized zirconia buffer layer. Overall, the critical current shows a clear Lorentz-force dependence and two distinctive peaks, one for fields parallel to the ab plane, due to bulk intrinsic pinning by the layered structure of the superconductor, and the other for fields parallel to the c axis, which we attribute to twin-boundary c-axis correlated pinning, as suggested by its Lorentz-force dependence.
46 citations
TL;DR: In this article, RuO2 was epitaxially grown on LaAlO3 substrates by pulsed laser deposition, and the growth rate was demonstrated by the strong inplane orientation of thin films with respect to the major axes of the substrate.
Abstract: Highly conductive ruthenium oxide (RuO2) has been epitaxially grown on LaAlO3 substrates by pulsed laser deposition. The RuO2 film is (h00) oriented normal to the substrate surface. The heteroepitaxial growth of RuO2 on LaAlO3 is demonstrated by the strong in‐plane orientation of thin films with respect to the major axes of the substrate. High crystallinity of RuO2 thin films is also determined from Rutherford backscattering channeling measurements. Electrical measurements on the RuO2 thin films demonstrate a quite low room‐temperature resistivity of 35±2 μΩ cm at deposition temperatures of above 500 °C.
45 citations
TL;DR: An analytic {ital d}-wave theory, valid at {ital T}=0, finds that {lambda}(0) increases rapidly with disorder, but not as rapidly as observed; an analytic phenomenological model finds that one should expect this result.
Abstract: The penetration depth {lambda}({ital T}) in YBa{sub 2}(Cu{sub 1{minus}{ital x}}{ital M}{sub {ital x}}){sub 3}O{sub 7} films, with {ital M}=Ni or Zn and nominal concentrations, 0.02{le}{ital x}{le}0.06, is obtained from the mutual inductance of coaxial coils on opposite sides of the films. Both Ni and Zn increase {lambda}(0) very rapidly, such that the superfluid density, {ital n}{sub {ital s}}(0){proportional_to}{lambda}{sup {minus}2}(0), decreases by a factor of 2 for each percent of dopant. The rapid increase in {lambda}(0) implies that disorder fills in the superconducting density of states at low energy, so that {ital N}{sub {ital S}}(0) is roughly 80--95 % of the normal-state density of states. An analytic {ital d}-wave theory, valid at {ital T}=0, finds that {lambda}(0) increases rapidly with disorder, but not as rapidly as observed. It is striking that the dependence of {lambda}({ital T}/{ital T}{sub {ital c}}) on {ital T}/{ital T}{sub {ital c}} does not change significantly as {ital x} increases from 2% to 6%, although it is different from undoped YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. An {ital ad} {ital hoc} phenomenological model finds that one should expect this result. Finally, the values of {ital N}{sub {ital S}}(0) deduced from {lambda} are somewhat larger than values deduced from specific-heatmore » measurements on Zn-doped YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, which also indicate increasing gaplessness with doping.« less
36 citations
TL;DR: In this article, high current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films on flexible nickel substrates with textured buffer layers were fabricated.
Abstract: High current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria-stabilized-zirconia (YSZ) buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was/spl sim/10/spl deg/. A critical current density of 8/spl times/10/sup 5/ A/cm/sup 2/ was obtained at 75 K and zero field for thin YBCO films. It was also demonstrated that thick YBCO films with a high critical current and excellent magnetic field dependence at liquid nitrogen temperature can be obtained on flexible nickel substrates by using the textured buffer layers. Issues encountered in producing the films were discussed. >
24 citations
TL;DR: In this paper, a processing technique was developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) on amorphous SiO2 on (100) singlecrystal Si. This processing and the resulting multilayer structure might provide a new option for fabricating innovative microelectronic devices.
Abstract: A processing technique is developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) on amorphous SiO2 on (100) single-crystal Si. The YSZ layer shows high crystallinity with an ion beam channelling minimum of 11 % from Rutherford backscattering. Even though there is a thick intervening amorphous SiO2 layer between the Si and the YSZ, the single-crystal YSZ layer is aligned with the crystal Si. The tilt and rotation variations are 0·64° and 1·11° respectively, based on X-ray diffraction Ω-rocking curves on [100] and π scans on [202] of YSZ films. The epitaxial nature of the YSZ on the thick SiO2 layer (from 10 to 100 nm) is further confirmed by high-resolution cross-sectional transmission electron microscopy analysis. This processing and the resulting multilayer structure might provide a new option for fabricating innovative microelectronic devices.
19 citations
TL;DR: A diagonal-type epitaxy of RuO2 on yttria-stabilized zirconia (YSZ) substrates was confirmed from x-ray diffraction measurements as mentioned in this paper.
Abstract: Highly conductive metal-oxide RuO2 thin films have been successfully grown on yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition. Epitaxial growth of RuO2 thin films on YSZ and the atomically sharp interface between the RuO2 and the YSZ substrate are clearly evident from cross-sectional transmission electron microscopy. A diagonal-type epitaxy of RuO2 on YSZ is confirmed from x-ray diffraction measurements. The crystalline RuO2 thin films, deposited at temperatures in the range of 500 °C to 700 °C, have a room-temperature resistivity of 35 ± 2 μω-cm, and the residual resistance ratio (R
300 k/R
4.2 k) is around 5 for the crystalline RuO2 thin films.
18 citations
TL;DR: In this article, high crystallinity Ba0.5Sr0.3/SrRuO3 thin films were deposited on LaAlO3 substrates by pulsed laser deposition.
Abstract: High crystallinity Ba0.5Sr0.5TiO3 thin films were deposited on LaAlO3 substrates by pulsed laser deposition. A conductive metallic oxide, SrRuO3, provided not only a good bottom electrode for Ba0.5Sr0.5TiO3 but also an excellent seed layer for epitaxial growth of Ba0.5Sr0.5TiO3 on it. The epitaxial nature of the Ba0.5Sr0.5TiO3 thin films on the LaAlO3 substrate was confirmed by x-ray diffraction, Rutherford backscattering spectroscopy, and cross-sectional transmission electron microscopy. The quite good dielectric and electrical properties of crystalline Ba0.5Sr0.5TiO3 thin films suggest that Ba0.5Sr0.5TiO3/SrRuO3 is a good combination in terms of structural, electrical, and dielectric properties of Ba0.5Sr0.5TiO3 thin films.
10 citations
TL;DR: In this paper, the lattice mismatches from electrode and barrier layer are reduced to a very low level, which indicates that the junction performance is controlled by the normal metal (N) layer material instead of the interfaces.
Abstract: High‐temperature‐superconductor Josephson junctions with an edge geometry of superconductor/normal‐metal/superconductor have been fabricated on yttria‐stabilized zirconia substrates by engineering the electrode and N‐layer material to reduce the lattice mismatches (a, b, and c). With GdBa2Cu3O7−δ as electrodes and Pr‐doped Y0.6Pr0.4Ba2Cu3O7−δ as a barrier, the lattice mismatches from electrode and barrier layer are reduced to a very low level. The junctions fabricated with such a design demonstrate resistively shunted junction current‐voltage characteristics under dc bias at temperatures in the range of 77–88 K. The quite low specific interface resistivity on the order of 10−10 Ω cm2 indicates that the junction performance is controlled by the normal‐metal (N) layer material instead of the interfaces. The use of lattice‐matched electrode and N‐layer material is one of the key design rules to obtain controllable high‐temperature superconductor Josephson junctions.
3 citations
TL;DR: In this article, a unique normal-metal (N) layer construction was used to fabricate high temperature superconducting (S) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta/SNS Josephson junctions.
Abstract: A unique normal-metal (N) layer construction was used to fabricate high temperature superconducting (S) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// SNS Josephson junctions. The normal-metal included a gradient Pr-doped Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// layer which was composed of a light doping (x=0.1) next to both YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// electrodes, a slightly higher doping (x=0.3) towards the center, and a doping concentration of x=0.5 in the middle of the N-layer. A gradient of the doping profile of the N-layer instead of an abrupt one provides good thermal, structural, and chemical compatibility between adjacent regions. The multilayer configuration of the gradient Pr-doped N-layers on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// showed good growth structure as confirmed by X-ray diffraction and Rutherford backscattering channeling tests. The SNS junctions fabricated in such a way showed resistively shunted junction current vs voltage characteristics above 77 K. Microwave induced Shapiro steps above 77 K and voltage modulation of dc SQUIDs at 77 K were both demonstrated with this technology. >
TL;DR: In this article, multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy and the observed properties were discussed in terms of the excimer laser modification process and the microstructure and composition of resulting surfaces.
Abstract: Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1000 cycles, indicating wear=through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.
TL;DR: Li et al. as discussed by the authors used pulsesed laser deposition to deposit high-quality YBa2Cu3O7-δ (YBCO) thin films directly on y-cut LiNbO3 substrates.
Abstract: Pulsed laser deposition was used to deposit high-quality YBa2Cu3O7-δ (YBCO) thin films directly on y-cut LiNbO3 substrates. The as-deposited YBCO films had a high degree of in-plane orientation and showed superconducting transition temperature (T co) at 91 K with a transition width of less than 1 K. Transport critical current densities were found to be ∼ 106 A cm−2 at 77 K and zero field. An ion beam minimum channelling yield of 16% was obtained for YBCO films, indicating high crystallinity. High-resolution transmission electron microscopy studies showed that interface between the film and the substrate was quite smooth and free from interfacial interdiffusion. The defects in thin films are also identified. The work showed that high-quality high T c thin films can be deposited directly on LiNbO3. Novel devices based on the properties of both YBCO and LiNbO3 could be realized based on these results.