Showing papers by "S. R. Foltyn published in 1996"

Epitaxial growth of highly conductive ruo2 thin films on (100) si

Abstract: Conductive RuO2 thin films have been heteroepitaxially grown by pulsed laser deposition on Si substrates with yttria‐stabilized zirconia (YSZ) buffer layers. The RuO2 thin films deposited under optimized processing conditions are a‐axis oriented normal to the Si substrate surface with a high degree of in‐plane alignment with the major axes of the (100) Si substrate. Cross‐sectional transmission electron microscopy analysis on the RuO2/YSZ/Si multilayer shows an atomically sharp interface between the RuO2 and the YSZ. Electrical measurements show that the crystalline RuO2 thin films are metallic over a temperature range from 4.2 to 300 K and are highly conductive with a room‐temperature resistivity of 37±2 μΩ cm. The residual resistance ratio (R300 K/R4.2 K) above 5 for our RuO2 thin films is the highest ever reported for such films on Si substrates.

Characteristics of conductive SrRuO3 thin films with different microstructures

Abstract: Conductive SrRuO3 thin films were epitaxially grown on (100) LaAlO3 substrates by pulsed laser deposition over a temperature range from 650 °C to 825 °C. Well-textured films exhibiting a strong orientation relationship to the underlying substrate could be obtained at a deposition temperature as low as 450 °C. The degree of crystallinity of the films improved with increasing deposition temperature as confirmed by x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy. Scanning electron microscopy revealed no particulates on the film surface. The resistivity of the SrRuO3 thin films was found to be a strong function of the crystallinity of the film and hence the substrate temperature during film deposition. A residual resistivity ratio (RRR = ρ300 K/ρ4.2 K) of more than 8 was obtained for the SrRuO3 thin films deposited under optimized processing conditions.

ab‐plane anisotropy of the critical currents in twinned YBa2Cu3O7−δ superconductors

Abstract: We show that the in‐plane critical current density of heavily twinned YBa2Cu3O7−δ thick films is anisotropic, depending on the relative orientation between the transport electrical current and the twin boundary mosaic. We demonstrate that the critical current density in an applied magnetic field can be substantially increased by producing conductors with twin boundaries tilted 45° with respect to the electrical current flow. We show that these findings can be readily incorporated to improve the critical currents of biaxially textured YBa2Cu3O7−δ thick films deposited on metallic substrates.

Magnetotransport properties of SrRuO3 epitaxial thin films on (100) LaAlO3: Presence of localized magnetic moments.

Abstract: We report temperature and magnetic field dependences of the longitudinal and transverse magnetoresistances of high-quality epitaxial ${\mathrm{SrRuO}}_{3}$ thin films. We also report Hall effect measurements in the paramagnetic and ferromagnetic states. The magnetic field dependence of the longitudinal magnetoresistivity shows a simple scaling \ensuremath{\sim}${\mathit{H}}^{2}$/(T-${\mathit{T}}_{\mathit{c}}$${)}^{2}$ far above the ferromagnetic transition temperature ${\mathit{T}}_{\mathit{c}}$. This observation supports a presence of localized magnetic moments above ${\mathit{T}}_{\mathit{c}}$. \textcopyright{} 1996 The American Physical Society.

Bose glass vortex phase transition in twinned YBa2Cu3O7δ superconductors

Abstract: We show that twin boundaries, a ubiquitous c-axis-correlated (i.e., extending along the c axis throughout the thickness of the sample) crystallographic defect in some high-temperature superconductors, naturally induce a Bose glass vortex phase transition in the magnetic phase diagram of heavily twinned YBa2Cu3O7-δ thick films.

Edge-geometry SNS DC SQUIDs using Ag-doped YBa2Cu3O7-x electrodes

Abstract: Josephson junctions and DC SQUIDs were fabricated in an edge-geometry superconductor/normal-metal/superconductor configuration using Ag-doped YBa2Cu3O7-x electrodes and a PrBa2Cu3O7-x N-layer. A differential voltage modulation of over 150 µV/Φ0 at 75 K was achieved. The flux noise was 30~40 µΦ0Hz-1/2 measured with DC bias at a frequency of 1 Hz.

Microwave surface resistance of YBa2Cu3Cu3O7−x films on polycrystalline ceramic substrates with textured buffer layers

Abstract: We have used a parallel‐plate resonator technique to measure the microwave surface resist‐ ance Rs of YBa2Cu3O7−x (YBCO) films on buffered ceramic substrates at around 10 GHz, and studied the correlation between their Rs and materials properties. A 0.4‐μm‐thick YBCO film (with an in‐plane mosaic spread of 7°) grown on a polycrystalline alumina substrate with an ion‐beam‐assisted‐deposited yttria‐stabilized zirconia buffer layer showed an Rs of 1.89 mΩ at 76 K and 0.21 mΩ at 4 K. We have observed a strong correlation between the Rs of the samples and the in‐plane mosaic spread of the YBCO films. This correlation can be explained qualitatively in terms of a simple model in which the weak links between the grains of the YBCO film form an electrical network of Josephson junctions.

High-temperature superconductor edge-geometry SNS junctions with engineered normal-metal layers

Abstract: High-temperature superconductor Josephson junctions in an edge-geometry superconductor - normal-metal - superconductor (SNS) configuration were fabricated on substrates. The normal metal was composed of an engineered multilayer with different Pr-doping concentrations (x = 0.1, 0.3, or 0.5). Scanning tunnelling microscopy analysis on thin films provided supporting evidence for the use of such an engineered multilayer as N barrier to fabricate edge-geometry SNS junctions. The improved S - N or N - S interface, as revealed by cross-sectional transmission electron microscopy, explains the negligible interface resistance of the junctions.

Study of high-quality epitaxial YBCO thin films grown directly on Y-Cut LiNbO 3

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 (Tco) at 91K with a transition width of less than IK. Transport critical current densities were found to be ∼106 A/cm2 at 77K and zero field. An ion beam minimum channeling yield of 16% was obtained for YBCO films, indicating high crystallinity. High-resolution transmission electron microscopy studies showed that the 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 Tc 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.

Synthesis of low resistivity complex oxides on MgO using Pt as buffer layer

Abstract: Highly crystalline SrRuO3 (SRO) and La0.5Sr0.5CoO3 (LSCO) thin films were deposited on (100) Pt/ MgO by pulsed laser deposition. The films were mainly (001) textured normal to the substrate surface with a high degree of in-plane orientation with respect to the substrate’s major axes. These films were characterized using x-ray diffraction, Rutherford backscattering, four-point probe resistivity measurement, and transmission electron microscopy. The room temperature resistivity for LSCO and SRO films on Pt/MgO was found to be ∼35 and ∼40 μΩ-cm, respectively. An ion beam minimum channeling yield of ∼43% and ∼33% was obtained for LSCO and SRO films, respectively. The interface between Pt and oxide was found to be smooth and free from any interfacial diffusion. This result showed that high-quality low resistivity oxide thin films can be deposited on Pt.

YBa2Cu3O7-δ Thick Films on Ni-based Alloys

Abstract: YBa2Cu3O7-δ (YBCO) thick films were prepared on Ni based alloys with an ion beam assisted deposited and textured yttria-stabilized zirconia (YSZ) buffer layer. Transport critical current densities (Jc) over 1×106 A/cm2 at 75 K, and over l×l07A/cm2at 4 K were obtained in the 1 µm thick YBCO films. Zero field critical current of 198 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. It was also found that the thick films on Ni based alloys were quite flexible.