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Sample records for mocvd ybco films

  1. In-situ deposition of YBCO high-Tc superconducting thin films by MOCVD and PE-MOCVD

    NASA Technical Reports Server (NTRS)

    Zhao, J.; Noh, D. W.; Chern, C.; Li, Y. Q.; Norris, P. E.; Kear, B.; Gallois, B.

    1991-01-01

    Metal-Organic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T(sub c) greater than 90 K and J(sub c) of approximately 10(exp 4) A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metal-organic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology.

  2. In Situ deposition of YBCO high-T(sub c) superconducting thin films by MOCVD and PE-MOCVD

    NASA Technical Reports Server (NTRS)

    Zhao, J.; Noh, D. W.; Chern, C.; Li, Y. Q.; Norris, P.; Gallois, B.; Kear, B.

    1990-01-01

    Metalorganic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T( sub c) greater than 90 K and Jc approx. 10 to the 4th power A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology.

  3. High frequency properties of YBCO bridges fabricated by MOCVD

    SciTech Connect

    Chen, J.; Yamoshita, T. ); Suzuki, H.; Kurosawa, H. ); Yamane, H.; Hirai, T. . Inst. for Materials Research)

    1991-03-01

    This paper reports on the high frequency properties of YBCO bridges at 4.2% and 77K. The YBCO films were prepared by MOCVD. For small bridges with the width(w) of about 1 {mu}m and thickness(t) of less than 0.5{mu}m, the constant voltage steps at integral multiples of {phi}{sub 0}fr = 20 {mu}V were observed up to 1 mV, which is much higher than the IcR{sub N} ({lt}0.13 mV) product of these bridges at 77K. The magnitudes of the current steps as functions of the rf current at 4.2K and 77K were in quantitative agreement with the theoretical results based on the RSJ model.

  4. MOCVD and PE-MOCVD of HTSC thin films

    NASA Astrophysics Data System (ADS)

    Kirlin, Peter S.

    1992-04-01

    High quality YBaCuO and TlBaCaCuO thin films were deposited on MgO, LaAlO3 and Ag substrates by standard thermal and plasma enhanced MOCVD. The growth was done in inverted vertical reactors designed to achieve stagnation point flow and extremely uniform deposition rates were achieved (±0.5%) over large areas (5 cm2). The films were characterized by SEM-EDX, x-ray diffraction, four point probe, critical current density, dynamic impedance, and surface resistance measurements. C-axis oriented films with resistive transitions (R≤0.1 μV/cm) exceeding 110 K and 85 K were routinely obtained for the Tl- and Y-based superconductors grown on single crystal substrates. The best films had inductive transition widths less than 1 K and critical current densities (ambient field) as high as 106 A/cm2 at 77 K. The surface resistance of the films was measured using a cavity end wall replacement method and values as low as 10 mΩ were observed at 78 K and 35 GHz on both LaAlO3 (100) and Ag substrates.

  5. Epitaxial growth of biaxially oriented YBCO films on silver

    NASA Astrophysics Data System (ADS)

    Liu, Danmin; Zhou, Meiling; Wang, Xue; Suo, Hongli; Zuo, Tieyong; Schindl, Michael; Flükiger, René

    2001-09-01

    YBCO films were deposited on (100), (110) and (111) oriented silver single crystals and { 100} <100>, { 110} <211> and { 012} <100> biaxially textured Ag substrates by pulsed laser deposition. It is shown that the (100) and (110) orientated single crystals and the { 110} biaxially textured Ag tape are all suitable for the deposition of YBCO thin films with c-axis in-plane alignment. The Jc of YBCO film deposited on { 110} <211> biaxially textured Ag foil is 7×105A cm-2 at 77 K, 0 T. A scheme for the regular growth of YBCO on silver was put forward.

  6. Fast infrared response of YBCO thin films

    NASA Technical Reports Server (NTRS)

    Ballentine, P. H.; Kadin, A. M.; Donaldson, W. R.; Scofield, J. H.; Bajuk, L.

    1990-01-01

    The response to short infrared pulses of some epitaxial YBCO films prepared by sputter deposition and by electron-beam evaporation is reported. The response is found to be essentially bolometric on the ns timescale, with some indirect hints of nonequilibrium electron transport on the ps scale. Fast switching could be obtained either by biasing the switch close to the critical current or by cooling the film below about 20 K. These results are encouraging for potential application to a high-current optically-triggered opening switch.

  7. Fabrication of YSZ buffer layer by single source MOCVD technique for YBCO coated conductor

    NASA Astrophysics Data System (ADS)

    Jun, Byung-Hyuk; Sun, Jong-Won; Kim, Ho-Jin; Lee, Dong-Wook; Jung, Choong-Hwan; Park, Soon-Dong; Kim, Chan-Joong

    2003-10-01

    Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition technique using a single liquid source for the application of YBa 2Cu 3O 7- δ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (1 0 0) single crystal MgO substrate was used for searching the deposition conditions. Bi-axially oriented CeO 2 and NiO films were fabricated on {1 0 0} <0 0 1> textured Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660-800 °C) and oxygen flow rates (100-500 sccm) were changed to find the optimum deposition condition. The best (1 0 0) oriented YSZ film on MgO was obtained at 740 °C and O 2 flow rate of 300 sccm. For a YSZ buffer layer with this deposition condition on a CeO 2/Ni template, full width half maximum values of the in-plane ( ϕ-scan) and out-of-plane ( ω-scan) alignments were 10.6° and 9.8°, respectively. The SEM image of YSZ film on CeO 2/Ni showed surface morphologies without microcracks. The film deposition rate was about 100 nm/min.

  8. Study of high [Tc] superconducting thin films grown by MOCVD

    SciTech Connect

    Erbil, A.

    1990-01-01

    Work is described briefly, which was carried out on development of techniques to grow metal-semiconductor superlattices (artificially layered materials) and on the copper oxide based susperconductors (naturally layered materials). The current growth technique utilized is metalorganic chemical vapor deposition (MOCVD). CdTe, PbTe, La, LaTe, and Bi[sub 2]Te[sub 3] were deposited, mostly on GaAs. Several YBa[sub 2]Cu[sub 3]O[sub 7] compounds were obtained with possible superconductivity at temperatures up to 550 K (1 part in 10[sup 4]). YBa[sub 2]Cu[sub 3]O[sub 7[minus]x] and Tl[sub 2]CaBa[sub 2]Cu[sub 2]O[sub y] thin films were deposited by MOCVD on common substrates such as glass.

  9. Superconductivity of YBCO Thick Films Prepared by Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Kim, Youngha; Lee, Kyong H.; Sung, Tae-Hyun; Han, Sang-Chul; Han, Young-Hee; Jeong, Nyeon-Ho; No, Kwangsoo

    2007-10-01

    YBa2Cu3O x (YBCO) superconducting thick films have been fabricated on Cu substrates, using a simple screen-printing method from Cu-free powders (Y2O3 and BaCO3). However, such films have poor superconducting properties such as critical current density ( J c) due to the low film density. In this work, we investigate the effect of uniaxial c-axis pressure on the superconducting properties of these YBCO films using a spark plasma sintering (SPS) technique. The film screen-printed on Cu substrates was heat-treated at 850°C for 5 min in vacuum varying the pressure (15, 30, and 45 MPa). To form a superconducting YBCO phase, the film was reheat-treated at 930°C for 30 s in air followed by oxygen annealing at 450°C for 1 h. For heat-treatments performed under pressure, lower film porosity was obtained, and a higher crack density was also observed compared to films prepared without pressure. The densification of the YBCO thick films using the SPS technique was very effective in improving the superconducting properties of the films.

  10. Deposition of YBCO films by high temperature spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Shields, T. C.; Abell, J. S.; Button, T. W.; Chakalov, R. A.; Chakalova, R. I.; Cai, C.; Haessler, W.; Eickemeyer, J.; de Boer, B.

    2002-08-01

    The fabrication of YBCO coated conductors on flexible textured metallic substrates requires the deposition of biaxially textured buffer layers and superconducting films. In this study we have prepared YBCO thin films on single crystal SrTiO 3 substrates and cube textured Ni substrates by spray pyrolysis. The Ni substrates have been pre-buffered with CeO 2/YSZ/CeO 2, layers deposited by pulsed laser deposition. Spray pyrolysis of nitrate solutions has been performed directly on heated substrates at temperatures between 800 and 900 °C without need for a subsequent annealing step. YBCO films deposited on both types of substrate are biaxially textured. Full width half maximum values determined from φ-scans are 8° and 20° for films on SrTiO 3 and buffered Ni substrates respectively. A transport Jc value of 1.2×10 5 A/cm 2 at 77 K and zero field has been achieved on SrTiO 3 ( T c onset=91 K, ΔTc=6 K). χ ac susceptibility measurements of films on buffered Ni substrates show Tc onsets of 88 K with ΔTc=18 K.

  11. Pulsed laser deposition of YBCO thin films on IBAD-YSZ substrates

    NASA Astrophysics Data System (ADS)

    Li, M.; Ma, B.; Koritala, R. E.; Fisher, B. L.; Venkataraman, K.; Balachandran, U.

    2003-01-01

    High-quality YBa2Cu3O7-x (YBCO) films were fabricated on yttria-stabilized zirconia (YSZ)-buffered Hastelloy C276 substrates by pulsed laser deposition. YSZ was grown by ion-beam-assisted deposition. A thin (approx10 nm) CeO2 layer was deposited before the deposition of YBCO. The crystalline structure and biaxial texture of the YBCO film and the buffer layer were examined by x-ray diffraction 2theta-scan, phi-scan and pole-figure analysis. Epitaxial growth of the YBCO film on the buffer layer was observed. Full width at half maximum (FWHM) value of 7.4° was measured from the phi-scan of YBCO(103). Raman spectroscopy showed compositional uniformity and phase integrity in the YBCO films. Surface morphologies of the YBCO films were examined by scanning electron microscopy. Comparative studies indicated that the CeO2 buffer layer significantly improves the structural alignment and superconducting properties of YBCO films. Tc = 90 K, with sharp transition, and transport Jc = 2.2 × 106 A cm-2 at 77 K in zero-external field were obtained on the 0.5 mum thick YBCO films. The dependence of Jc on the FWHM of the YBCO(103) phi-scan indicated that high Jc is associated with low FWHM.

  12. Vortex creep in TFA-YBCO nanocomposite films

    NASA Astrophysics Data System (ADS)

    Rouco, V.; Bartolomé, E.; Maiorov, B.; Palau, A.; Civale, L.; Obradors, X.; Puig, T.

    2014-11-01

    Vortex creep in YBa2Cu3O7 - x (YBCO) films grown from the trifluoracetate (TFA) chemical route with BaZrO3 and Ba2YTaO6 second-phase nanoparticles (NPs) has been investigated by magnetic relaxation measurements. We observe that in YBCO nanocomposites the phenomenological crossover line from the elastic to the plastic creep regime is shifted to higher magnetic fields and temperatures. The origin of this shift lies on the new isotropic-strong vortex pinning contribution appearing in these nanocomposites, induced by local lattice distortions. As a consequence, we demonstrate that the addition of non-coherent NPs produces a decrease in the creep rate S in most of the phase diagram, particularly, in the range of fields and temperatures (T\\gt 60 K, {{μ }0}H\\gt 0.5 T) relevant for large scale applications.

  13. The preparation of high-J c Gd0.5Y0.5Ba2Cu3O7-δ thin films by the MOCVD process

    NASA Astrophysics Data System (ADS)

    Zhao, R. P.; Zhang, F.; Liu, Q.; Xia, Y. D.; Lu, Y. M.; Cai, C. B.; Tao, B. W.; Li, Y. R.

    2016-06-01

    A home-designed metal organic chemical vapor deposition (MOCVD) system has been employed to prepare high critical current density (J c) Gd0.5Y0.5Ba2Cu3O7-δ (GdYBCO) thin films on LaMnO3/epitaxial MgO/ion beam assisted deposition (IBAD)-MgO/solution deposition planarization (SDP)-Y2O3-buffered Hastelloy tapes; the thin films were directly heated by the Joule effect after applying an heating current (I h ) through the Hastelloy tapes. The effect of the mole ratio of the metal organic sources has been systematically investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated that the GdYBCO films crystallized better and became denser with the increasing of the Cu/Ba ratio from 1.0 to 1.1, yielding a J c at 77 K and 0 T of 200 nm GdYBCO film increasing from 2.5 MA cm-2 to 7 MA cm-2. In addition, SEM and energy dispersive spectrometer (EDS) characterizations revealed that more and more outgrowths appeared and the density of the film was reduced with an increase in the Cu/Ba ratio from 1.1 to 1.2. When the I h was 26.8 A and the mole ratio of Gd(tmhd)3, Y(tmhd)3, Ba(tmhd)2 and Cu(tmhd)2 in the precursor was 0.55:0.55:2:2.2, the critical current (I c) of the deposited 200 nm-thick GdYBCO film reached a 140 A cm-1 width (77 K, 0 T), corresponding to the J c 7 MA cm-2 (77 K, 0 T).

  14. YBCO thin film evaporation on as-deposited silver film on MgO

    NASA Astrophysics Data System (ADS)

    Azoulay, J.

    1999-11-01

    YBa 2Cu 3O 7- δ (YBCO) thin film was evaporated on as-deposited Ag buffer layer on MgO substrate. A simple, inexpensive vacuum system equipped with one resistively heated source was used. The subsequent heat treatment was carried out under low oxygen partial pressure at a relatively low temperature and short dwelling time. The films thus obtained were characterized for electrical properties using DC four-probe electrical measurements and inspected for structural properties and chemical composition by scanning electron microscopy (SEM). It is shown that YBCO thin film can grow on as-deposited thin silver layer on MgO substrate.

  15. On-line characterization of YBCO coated conductors using Raman spectroscopy methods.

    SciTech Connect

    Maroni, V. A.; Reeves, J. L.; Schwab, G.; Chemical Engineering; SuperPower, Inc.

    2007-04-01

    The use of Raman spectroscopy for on-line monitoring of the production of superconducting YBa2Cu3O6+X (YBCO) thin films on long-length metal tapes coated with textured buffer layers is reported for the first time. A methodology is described for obtaining Raman spectra of YBCO on moving tape exiting a metal-organic-chemical-vapor-deposition (MOCVD) enclosure. After baseline correction, the spectra recorded in this way show the expected phonons of the specific YBCO crystal orientation required for high supercurrent transport, as well as phonons of non-superconducting second-phase impurities when present. It is also possible to distinguish YBCO films that are properly textured from films having domains of misoriented YBCO grains. An investigation of the need for focus control on moving tape indicated that focusing of the laser on the surface of the highly reflective YBCO films exiting the MOCVD enclosure tends to produce aberrant photon bursts that swamp the Raman spectrum. These photon bursts are very likely a consequence of optical speckle effects induced by a combination of surface roughness, crystallographic texture, and/or local strain within the small grain microstructure of the YBCO film. Maintaining a slightly out-of-focus condition provides the best signal-to-noise ratio in terms of the obtained Raman spectra. In addition to examining moving tape at the post-MOCVD stage, Raman spectra of the film surface can also be recorded after the oxygen anneal performed to bring the YBCO to the optimum superconducting state. Consideration is given to data processing methods that could be adapted to the on-line Raman spectra to allow the tagging of out-of-specification tape segments and, at a more advanced level, feedback control to the MOCVD process.

  16. RF plasma enhanced MOCVD of yttria stabilized zirconia thin films using octanedionate precursors and their characterization

    NASA Astrophysics Data System (ADS)

    Chopade, S. S.; Nayak, C.; Bhattacharyya, D.; Jha, S. N.; Tokas, R. B.; Sahoo, N. K.; Deo, M. N.; Biswas, A.; Rai, Sanjay; Thulasi Raman, K. H.; Rao, G. M.; Kumar, Niranjan; Patil, D. S.

    2015-11-01

    Yttria stabilized zirconia thin films have been deposited by RF plasma enhanced MOCVD technique on silicon substrates at substrate temperature of 400 °C. Plasma of precursor vapors of (2,7,7-trimethyl-3,5-octanedionate) yttrium (known as Y(tod)3), (2,7,7-trimethyl-3,5-octanedionate) zirconium (known as Zr(tod)4), oxygen and argon gases is used for deposition. To the best of our knowledge, plasma assisted MOCVD of YSZ films using octanediaonate precursors have not been reported in the literature so far. The deposited films have been characterized by GIXRD, FTIR, XPS, FESEM, AFM, XANES, EXAFS, EDAX and spectroscopic ellipsometry. Thickness of the films has been measured by stylus profilometer while tribological property measurement has been done to study mechanical behavior of the coatings. Characterization by different techniques indicates that properties of the films are dependent on the yttria content as well as on the structure of the films.

  17. Thermal stability of NdBCO/YBCO/MgO thin film seeds

    NASA Astrophysics Data System (ADS)

    Volochová, D.; Kavečanský, V.; Antal, V.; Diko, P.; Yao, X.

    2016-04-01

    Thermal stability of the Nd1+x Ba2-x Cu3O7-δ (Nd-123 or NdBCO) thin films deposited on MgO substrate, with YBa2Cu3O7-δ (Y-123 or YBCO) buffer layer (NdBCO/YBCO/MgO thin film), has been experimentally studied in order to determine the optimal film thickness acting as seed for bulk YBCO growth. YBCO bulk superconductors with Y2BaCuO5 (Y-211) and CeO2 addition were prepared by the top seeded melt growth process in a chamber furnace using NdBCO/YBCO/MgO thin film seeds of different thicknesses (200-700 nm with 20 nm YBCO buffer layer) and different maximum temperatures, T max. The maximum temperatures varied in the range of 1040 °C-1125 °C. The highest thermal stability 1118 °C was observed in the case of NdBCO/YBCO/MgO thin film of 300 nm thickness. These results are corroborated with differential scanning calorimetry and high temperature x-ray diffraction measurements, as well as microstructure observations.

  18. Significance of microstructure for a MOCVD-grown YSZ thin film gas sensor

    SciTech Connect

    Vetrone, J.; Foster, C.; Bai, G.

    1996-11-01

    The authors report the fabrication and characterization of a low temperature (200--400 C) thin film gas sensor constructed from a MOCVD-grown yttria-stabilized zirconia (YSZ) layer sandwiched between two platinum thin film electrodes. A reproducible gas-sensing response is produced by applying a cyclic voltage which generates voltammograms with gas-specific current peaks and shapes. Growth conditions are optimized for preparing YSZ films having dense microstructures, low leakage currents, and maximum ion conductivities. In particular, the effect of growth temperature on film morphology and texture is discussed and related to the electrical and gas-sensing properties of the thin film sensor device.

  19. Metallization and interconnection of HTS YBCO thin film devices and circuits

    NASA Astrophysics Data System (ADS)

    Du, J.; Lam, S. K. H.; Tilbrook, D. L.

    2001-10-01

    A comprehensive study of specific contact resistivity and ultrasonic wire bonding yield and strength was carried out on noble metal-YBa2Cu3O7-x (YBCO) thin film contacts prepared by a variety of methods and with different YBCO surface conditions. The metallization techniques investigated include in situ and ex situ deposition of gold or silver on YBCO films. The ex situ contacts were made with and without lithographic processes. Contact resistivities of less than 5×10-8 Ω cm2 at 77 K were achieved for contacts made by the rapid ex situ deposition of gold or silver on fresh YBCO films with smooth surfaces. These contacts also gave a high wire bonding yield and strength of 10-19 g. High contact resistivities in excess of 5×10-4 Ω cm2 and poor wire bonding yield and strength were observed for the contacts made by standard lithographic lift-off processes on old YBCO films. Surface treatments using either argon ion beam etching or rf O2 plasma cleaning prior to metallization were found to be useful in reducing the contact resistivity and improving the wire bonding results for the lift-off contacts. The influence of YBCO film morphology on the contact resistance and wire bonding yield and strength was also studied.

  20. Detailed kinetics modeling of indium phosphide films in MOCVD reactors

    SciTech Connect

    Masi, M.; Cavallotti, C.; Radaelli, G.; Carra, S.

    1998-12-31

    The deposition kinetics of InP in MOCVD reactors is presented. The proposed chemical mechanism involves both gas phase and surface reactions. The fundamental hypothesis adopted in deriving the mechanism was a dual site dissociative adsorption of the precursors on the growing surface. In any case, all the rate constants either were taken from the literature or estimated through thermochemical methods. In addition, the deposition reactor was simulated by means of a monodimensional model that accounts for the main reactor features through the boundary layer theory.

  1. Deposition of YBCO thin films on silver substrate via a fluorine-free sol-gel synthesis

    NASA Astrophysics Data System (ADS)

    Xu, Yongli; Shi, Donglu; Lian, L.; Wang, M.; McClellan, Shaun M.

    2002-05-01

    To further develop grain-textured YBCO thin films for conductor development, we deposited, via a fluorine-free sol-gel synthesis, YBCO thin films on non-textured silver substrate. The interface structures were studied by both x-ray diffraction (XRD) and transmission electron microscopy (HRTEM). XRD data indicated that the YBCO films on silver substrate exhibited c-axis grain orientations. Experimental details are reported on the sol-gel synthesis chemistry and XRD and HRTEM characterization of the YBCO thin films.

  2. Optimization of GaN thin films via MOCVD

    NASA Technical Reports Server (NTRS)

    Dickens, Corey; Wilson, Sylvia L.

    1995-01-01

    A unique characteristic of every semiconductor is the amount of energy required to break an electron bond in the lowest band of allowed states, the valence band. The energy necessary to set an electron free and allow it to conduct in the material is termed the energy gap (Eg). Semiconductors with wide bandgap energies have been shown to possess properties for high power, high temperature, radiation resistance damage, and short wavelength optoelectronic applications. Gallium nitride, which has a wide gap of 3.39 eV, is a material that has demonstrated these characteristics. Various growth conditions are being investigated for quality gallium nitride heteroepitaxy growth via the technique of low pressure metal organic chemical vapor deposition (MOCVD) that can be used for device development.

  3. The preparation of high-J c Gd0.5Y0.5Ba2Cu3O7‑δ thin films by the MOCVD process

    NASA Astrophysics Data System (ADS)

    Zhao, R. P.; Zhang, F.; Liu, Q.; Xia, Y. D.; Lu, Y. M.; Cai, C. B.; Tao, B. W.; Li, Y. R.

    2016-06-01

    A home-designed metal organic chemical vapor deposition (MOCVD) system has been employed to prepare high critical current density (J c) Gd0.5Y0.5Ba2Cu3O7‑δ (GdYBCO) thin films on LaMnO3/epitaxial MgO/ion beam assisted deposition (IBAD)-MgO/solution deposition planarization (SDP)-Y2O3-buffered Hastelloy tapes; the thin films were directly heated by the Joule effect after applying an heating current (I h ) through the Hastelloy tapes. The effect of the mole ratio of the metal organic sources has been systematically investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated that the GdYBCO films crystallized better and became denser with the increasing of the Cu/Ba ratio from 1.0 to 1.1, yielding a J c at 77 K and 0 T of 200 nm GdYBCO film increasing from 2.5 MA cm‑2 to 7 MA cm‑2. In addition, SEM and energy dispersive spectrometer (EDS) characterizations revealed that more and more outgrowths appeared and the density of the film was reduced with an increase in the Cu/Ba ratio from 1.1 to 1.2. When the I h was 26.8 A and the mole ratio of Gd(tmhd)3, Y(tmhd)3, Ba(tmhd)2 and Cu(tmhd)2 in the precursor was 0.55:0.55:2:2.2, the critical current (I c) of the deposited 200 nm-thick GdYBCO film reached a 140 A cm‑1 width (77 K, 0 T), corresponding to the J c 7 MA cm‑2 (77 K, 0 T).

  4. Enhanced pinning in YBCO films with BaZrO.sub.3 nanoparticles

    DOEpatents

    Driscoll, Judith L.; Foltyn, Stephen R.

    2010-06-15

    A process and composition of matter are provided and involve flux pinning in thin films of high temperature superconductive oxides such as YBCO by inclusion of particles including barium and a group 4 or group 5 metal, such as zirconium, in the thin film.

  5. Propagation characteristics of the magnetostatic surface wave in the YBCO-YIG film-layered structure

    SciTech Connect

    Tsutsumi, M.; Fukusako, T.; Yoshida, S.

    1996-08-01

    Propagation characteristics of the magnetostatic surface wave (MSSW) in a YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO)-yttrium iron garnet (YIG) multilayered structure are investigated. Effects of the superconductor on the MSSW are discussed with regard to the dispersion characteristics of both the phase and attenuation constants as a function of the air gap between YIG and YBCO, taking into consideration the magnetic line-width of the YIG film. It was found that the nonreciprocity of MSSW is enhanced significantly by the superconductivity and depends on the magnetic line-width of the YIG film. To examine the effect of a YBCO on the MSSW propagation, experiments are carried out using a commercially available YIG film. Magnetic losses at low temperature are briefly discussed with experimentally observed nonreciprocity.

  6. Transient Electromagnetic Phenomena during Current Limiting Process in YBCO Thin Film

    NASA Astrophysics Data System (ADS)

    Ichiki, Y.; Ohsaki, H.

    2006-06-01

    In order to design a reliable and high-performance fault current limiter, it is necessary to estimate the influences of the inhomogeneous superconducting properties on the current limiting process and S-N transition. This paper describes the measurements of transient electromagnetic phenomena in YBCO thin film using pick-up coils to observe current-sharing process and change of current distribution. At first current distribution in a steady state was measured. And then transient phenomena caused by applying an overcurrent to YBCO thin film covered with a silver layer were measured.

  7. The role of Ag in the pulsed laser growth of YBCO thin films

    NASA Astrophysics Data System (ADS)

    Kalyanaraman, R.; Oktyabrsky, S.; Narayan, J.

    1999-05-01

    We have studied systematically the role of silver in improving microstructure and properties of Y1Ba2Cu3O7-δ (YBCO) thin films. We have more than doubled the grain size to nearly 1.8 μm and reduced processing temperatures by incorporating Ag in the YBCO films, which is accomplished by using a composite target containing 15% by weight of Ag. These films show approximately four times higher Jc than the best films obtained on MgO(001) substrates deposited from stoichiometric Y1Ba2Cu3O7-δ targets. Study of the silver content in the film as a function of the deposition temperature shows clearly a decreasing concentration with increasing temperature and a segregation of the Ag to the surface. The increased oxygen content in the films is also observed at lower processing temperatures, providing strong support for the efficient oxygenation of YBCO via the presence of silver. A qualitative model suggests that the formation of silver oxide, rapid surface diffusion of Ag on MgO surfaces, and the nonreactivity of Ag with YBCO are the key aspects to the improvement in microstructure. The possibility of extending these ideas to the growth of oxides is also discussed, along with the fabrication of in-situ superconducting-metal junctions with 3D geometries.

  8. Structural and electrical properties of epitaxial YBCO films on Si (Abstract Only).

    NASA Astrophysics Data System (ADS)

    Fork, David K.; Barrera, A.; Phillips, Julia M.; Newman, N.; Fenner, David B.; Geballe, Theodore H.; Connell, G. A. N.; Boyce, James B.

    1991-03-01

    Efforts to grow high quality films of YBCO on Si have been complicated by factors discussed in Ref. 1, chief among them being the reaction between YBCO and Si, which is damaging even at 550 C. This is well below the customary temperatures for YBCO film growth. To avoid the reaction problem, epitaxial YBCO films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ).2 Both layers are grown via an entirely in situ process by pulsed laser deposition (PLD). Although the buffer layer prevents reaction, another problem arises; the large difference in thermal expansion coefficients between silicon and YBCO causes strain at room temperature. Thin (<500 A) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Thicker films are cracked and have poorer electrical properties. The thermal strain may be reduced by growing on silicon-on-sapphire (SOS) rather than silicon.3 This allows the growth of films of arbitrary thickness. Ion channeling reveals a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12% on either silicon or SOS. The normal state resistivity is 250-300 i-cm at 300 K; the critical temperature, Tc (R=0), is 86-88 K with a transition width (ATc) of I K. Critical current densities (J)°f 2x107 A/cm2 at 4.2 K and >2x106 A/cm2 at 77 K have been achieved. In addition, the surface resistance of a YBCO film on SOS was measured against Nb at 4.2 K. At 10 GHz, a value of 45 was obtained. This compares favorably to values reported for LaAlO3. Application of this technology to produce reaction patterned microstrip lines has been tested.4 This was done by ion milling away portions of the YSZ buffer layer prior to the YBCO deposition. YBCO landing on regions of exposed Si reacts to form an insulator. This technique was used to make 3 micron lines 1.5 mm long. The resulting structure had a Jc of l.6xl06 A/cm2 at 77 K. Isolation of separate structures exceeded 20 M. Several

  9. YBCO thin films on CeO2 buffered silver substrates

    NASA Astrophysics Data System (ADS)

    Gallistl, B.; Gritzner, G.

    2008-02-01

    CeO2 was deposited on silver substrates by the chemical solution deposition method. Silver was dipped into a 0.05 M Ce(NO3)3 solution, dried in air and then annealed in air at 900 °C for 30 minutes. The CeO2 buffer layer was characterized by X-ray diffraction and scanning electron microscopy. YBCO was deposited onto the buffered substrate via screen printing. The YBCO films where sintered at temperatures of 880 °C and 890 °C. Dense and crack free YBCO layers were obtained with transition temperatures (Tc0) up to 83 K. Characterization of the superconducting film was performed by X-ray diffraction and SEM.

  10. Growth and properties of YBCO thin films on polycrystalline Ag substrates by inclined substrate pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Li, M.; Ma, B.; Koritala, R. E.; Fisher, B. L.; Dorris, S. E.; Venkataraman, K.; Balachandran, U.

    2002-06-01

    Fully c-axis-oriented YBCO films were directly deposited on polycrystalline silver substrates by inclined substrate pulsed laser ablation. The orientation and microstructure of the YBCO films were characterized by x-ray diffraction 2θ-scans, Ω-scans and pole figure analysis. Surface morphology was examined by scanning electron microscopy. Irregular-mosaic-shaped supergrains were observed in the films. Raman spectroscopy was used to evaluate the quality of the YBCO films. The superconducting transition temperature (Tc) and the critical current density (Jc) of the films were determined by inductive and transport measurements, respectively. Tc = 91 K with sharp transition and Jc = 2.7 × 105 A cm-2 at 77 K in zero field were obtained on a film that was 0.14 μm thick, 5 mm wide and 10 mm long. This work demonstrated a promising approach to obtain high-Jc YBCO films on nontextured polycrystalline silver substrate.

  11. Effects of thickness on superconducting properties and structures of Y2O3/BZO-doped MOD-YBCO films

    NASA Astrophysics Data System (ADS)

    Ding, Fa-Zhu; Gu, Hong-Wei; Wang, Hong-Yan; Zhang, Hui-Liang; Zhang, Teng; Qu, Fei; Dong, Ze-Bin; Zhou, Wei-Wei

    2015-05-01

    We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7-x (YBCO) films with BaZrO3 (BZO) and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD). Comparing with pure YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores. Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Beijing Natural Science Foundation, China (Grant No. 2152035).

  12. Biaxially aligned template films fabricated by inclined-substrate deposition for YBCO-coated conductor applications.

    SciTech Connect

    Ma, B.; Li, M.; Koritala, R. E.; Fisher, B. L.; Erck, R. A.; Dorris, S. E.; Miller, D. J.; Balachandran, U.

    2002-08-12

    Inclined substrate deposition (ISD) has the potential for rapid production of high-quality biaxially textured buffer layers, which are important for YBCO-coated conductor applications. We have grown biaxially textured MgO films by ISD at deposition rates of 20-100 {angstrom}/sec. Columnar grains with a roof-tile surface structure were observed in the ISD-MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD-MgO films are tilted at an angle from the substrate normal. A small {phi}-scan full-width at half maximum (FWHM) of {approx}9{sup o} was observed on MgO films deposited at an inclination angle of 55{sup o}. In-plane texture in the ISD MgO films developed in the first 0.5 {micro}m from the interface, then stabilized with further increases in film thickness. YBCO films deposited by pulsed laser deposition on ISD-MgO buffered Hastelloy C276 substrates were biaxially aligned with the c-axis parallel to the substrate normal. T{sub c} of 91 K with a sharp transition and transport J{sub c} of 5.5 x 10{sup 5} A/cm{sup 2} at 77 K in self-field were measured on a YBCO film that was 0.46-{micro}m thick, 4-mm wide, 10-mm long.

  13. MOCVD growth of CdO very thin films: Problems and ways of solution

    NASA Astrophysics Data System (ADS)

    Huerta-Barberà, Adelaida; Guia, Lluís Manel; Klymov, Oleksii; Marín-Borrás, Vicente; Martínez-Tomás, Carmen; Tamayo-Arriola, Julen; Kurtz, Alejandro; Montes Bajo, Miguel; Muñoz, Elias; Hierro, Adrian; Muñoz-Sanjosé, Vicente

    2016-11-01

    In this paper the growth of CdO by the MOCVD technique at atmospheric pressure has been studied in order to achieve very thin films of this material on r-sapphire substrates. The growth evolution of these films was discussed and the existence of a threshold thickness, below which island-shaped structures appear, was demonstrated. Some alternatives to reduce this threshold thickness have been proposed in the frame of the analysis of the crystal growth process. The morphology and structural properties of the films were analyzed by means of SEM and HRXRD. High-quality flat CdO samples were achieved with thicknesses up to 20 nm, which is five times thinner than the values previously reported in the literature.

  14. Enhancing critical current in YBCO thick films: Substrate decoration and quasi-superlattice approach

    NASA Astrophysics Data System (ADS)

    Sarkar, A.; Mikheenko, P.; Dang, V. S.; Abell, J. S.; Crisan, A.

    2009-10-01

    For power applications of superconducting films, the critical current density ( J c) and the thickness of the film ( d) should be as high as possible. Since J c decreases with both thickness and magnetic field, artificial pinning centres in addition to natural ones are required to keep J c high. The earliest cost-effective method used for introducing artificial pinning centres was the so-called substrate decoration, i.e., growing nano-scale islands (nano-dots) of certain materials on the substrate prior to the deposition of the superconducting thin film. Later on another version of this approach proved to be successful: building up a layered distribution of a second phase using a multilayer deposition (quasi-superlattices). Several materials have been used for the creation of artificial pinning centres. Here we report on the artificial pinning centres induced in YBCO thick films by substrate decoration and quasi-superlattice approaches using nano-dots of Pd and non-superconducting YBCO. The cross-sectional AFM images show evidence of c-axis correlated columnar defects. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films. We observed an important shift of the position of the maximum in the thickness dependence of J c( B) towards higher thicknesses compared with pure YBCO films by both approaches. A high J c( B) in our quite thick films provides a very high total critical current per cm of the film width. Critical current as high as 800 A/cm width was achieved in a 2.4 μm thick quasi-superlattice film with non-superconducting YBCO nano-dots.

  15. Versatility of metalorganic chemical vapor deposition process for fabrication of high quality YBCO superconducting thin films

    NASA Astrophysics Data System (ADS)

    Chern, C. S.; Kear, B. H.; Zhao, J.; Norris, P. E.; Li, Y. Q.

    1991-03-01

    YBCO films, having critical current densities in excess of 10 to the 6th A/sq cm at 77 K and transition temperatures of about 89 K, successfully deposited on close lattice matched substrate materials at substrate temperature in the range from 720 to 740 C, are presented. The critical current densities are 10,000 A/sq cm at 70 K and the critical temperatures are 82 K for the films deposited on sapphire substrates. Successful deposition of c-axis oriented YBCO films with a transition temperature of 85 K was also achieved on silver substrates. Detailed analyses of the films were carried out by X-ray diffraction, EDS, SEM, resistivity measurements, critical current density measurements, and magnetization susceptibility measurements.

  16. Micropatterning of TiO2 Thin Films by MOCVD and Study of Their Growth Tendency

    PubMed Central

    Hwang, Ki-Hwan; Kang, Byung-Chang; Jung, Duk Young; Kim, Youn Jea; Boo, Jin-Hyo

    2015-01-01

    In this work, we studied the growth tendency of TiO2 thin films deposited on a narrow-stripe area (<10 μm). TiO2 thin films were selectively deposited on OTS patterned Si(100) substrates by MOCVD. The experimental data showed that the film growth tendency was divided into two behaviors above and below a line patterning width of 4 μm. The relationship between the film thickness and the deposited area was obtained as a function of f(x) = a[1 − e(−bx)]c. To find the tendency of the deposition rate of the TiO2 thin films onto the various linewidth areas, the relationship between the thickness of the TiO2 thin film and deposited linewidth was also studied. The thickness of the deposited TiO2 films was measured from the alpha-step profile analyses and cross-sectional SEM images. At the same time, a computer simulation was carried out to reveal the relationship between the TiO2 film thickness and deposited line width. The theoretical results suggest that the mass (velocity) flux in flow direction is directly affected to the film thickness. PMID:25799219

  17. Development of Modified MOD-TFA Approach for YBCO Film Growth

    SciTech Connect

    Bhuiyan, Md S; Paranthaman, Mariappan Parans; Sathyamurthy, Srivatsan; Hunt, Rodney Dale; List III, Frederick Alyious; Duckworth, Robert C

    2007-01-01

    Low-cost coated-conductor fabrication methods are essential for various electric-power applications. Metal-organic-deposition (MOD) approach to grow both YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) and buffer layers on textured metal substrates is very promising towards fabrication of lower-cost second generation wires. YBCO coated conductors (CC) are being developed with high critical currents that should be sufficient for their extensive use in power applications. However, the present CC has high energy losses in ac magnetic field that are unacceptable. We have developed a modified MOD precursor route to deposit {approx} 0.8 {micro}m thick YBCO films in a single coat that requires less than one-fifth of the pyrolysis time compared to the traditional MOD approach. We have also developed a filamentization technique of CC using ink-jet printing to reduce ac losses due to applied ac fields. The preliminary results of YBCO films deposited on standard RABiTS template yielded an of 140 A/cm at 77 K and self- field. A modest reduction of ac loss was observed for the solution ink-jet printed filamentary conductor.

  18. Superconducting YBCO thin film on multicrystalline Ag film evaporated on MgO substrate

    NASA Astrophysics Data System (ADS)

    Azoulay, Jacob; Verdyan, Armen; Lapsker, Igor

    Superconducting YBa 2Cu 3O 7-δ films were grown by resistive evaporation on multicrystalline silver film which was evaporated on MgO substrate. A simple inexpensive vacuum system equipped with resistively heated boat was used for the whole process. Silver film was first evaporated on MgO substrate kept at 400°C during the evaporation after which with no further annealing a precursor mixture of yttrium small grains and Cu and BaF2 in powder form weighed in the atomic proportion to yield stoichiometric YBa 2Cu 3O 7 was evaporated. The films thus obtained were annealed at 740°C under low oxygen partial pressure of about 1Pa for 30 minutes to form the superconducting phase. X-ray diffraction and scanning electron microscopy techniques were used for texture and surface analysis. Electrical properties were determined using a standard dc four-probe for electrical measurements. The physical and electrical properties of the YBCO films are discussed in light of the fact that X-ray diffraction measurements done on the silver film have revealed a multicrystalline structure

  19. Design of a Cryogen Free Cryo-flipper using a High Tc YBCO Film

    NASA Astrophysics Data System (ADS)

    Parnell, S. R.; Kaiser, H.; Washington, A. L.; Li, F.; Wang, T.; Baxter, D. V.; Pynn, R.

    It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined non- adiabatic magnetic field transition that can be utilised to produce an efficient white beam neutron spin flipper. Typically these devices utilise niobium and hence require continuous use of liquid helium in order to maintain the device tem- perature. The use of high Tc materials removes the need for cryogens and has been explored previously and shown to provide efficient flipping of the neutron spin. Improvements in thin high Tc films over the past few years make these materials even more attractive. Here we present a design using a 350-nm-thick YBCO film capped with 100 nm of gold on a 78 x 100 x 0.5 mm sapphire substrate (Theva, Germany). The apparatus is compact (200 mm in length along the neutron beam), consisting of an oxygen-free high-conductivity copper frame, which holds the YBCO film and is mounted to the cold finger of a closed-cycle refrigerator. The part of the vacuum chamber, where the YBCO film is located, is ≈ 50 mm wide, which allows us to minimise the distance from the film to the external magnets. This distance is 26 mm on each side. The details of the guide field design are also discussed. In this design, the maximum neutron beam size that can be used is 40 × 40 mm2 and we can easily switch from a vertical to a horizontal guide field on either side of the YBCO film.

  20. MOCVD growth and structure of PbTiO{sub 3} thin films

    SciTech Connect

    Gao, Y.; Bai, G.; Merkle, K.L.; Chang, H.L.M.; Lam, D.J.

    1993-08-01

    PbTiO{sub 3} thin films grown on (001)MgO and (110)MgO by MOCVD have been characterized by x-ray diffraction and transmission electron microscopy. The PbTiO{sub 3} films deposited on (001)MgO under the optimum conditions always show a bi-layer structure. The top layer of the films near the free surface is c-axis oriented with the orientation relationship (001)[100]PbTiO{sub 3}{parallel}(001)[100]MgO. The bottom layer of the films near the substrate is a-axis oriented with (100)[001]PbTiO{sub 3}{parallel}(001)[100]MgO. 90{degrees} domains were observed, but only in the c-axis oriented layers. The thickness of the a-axis oriented layers near the substrate decreases with decreasing the cooling rate. PbTiO{sub 3} films deposited on (110) MgO, however, are single-layer, epitaxial films with (101)[001]PbTiO{sub 3}{parallel}(110)[001]MgO.

  1. MOCVD-SrTiO3 thin film microwave coplanar tunable devices: modelling of varactors

    NASA Astrophysics Data System (ADS)

    Gensbittel, A.; Dégardin, A. F.; Kreisler, A. J.

    2008-02-01

    SrTiO3 (STO) ferroelectric (FE) thin films associated with High Temperature Superconductor (HTSC) is a good compromise to realize electronically tunable microwave devices combining tunable dielectric properties of FE films with low loss microwave conductivity in HTSC. STO, which exhibits a perovskite structure, is suitable for epitaxial growth of YBaCuO films and has been widely studied to realize tunable components around 77 K. Up to now, STO thin films were essentially deposited by sputtering and pulsed laser deposition. In the framework of this study, we have explored the feasibility of microwave devices made from STO thin films prepared by metalorganic chemical vapour deposition (MOCVD). We have characterized Au/STO(250 nm thick)/MgO coplanar waveguide transmission lines and microwave variable capacitors (varactors) from 45 MHz up to 40 GHz, in the 300 K to 60 K temperature range. Dielectric characteristics of the STO films were extracted from measurements and studied as a function of frequency, electric field and temperature. The geometry of the interdigital capacitors (IDC) was chosen after evaluating their capacitances using an analytical theoretical model. We have used a de-embedding method to extract, from electromagnetic simulations using Sonnet® Software, the capacitance of the IDC alone.

  2. Tailoring the vortex pinning strength of YBCO thin films by systematic incorporation of hybrid artificial pinning centers

    NASA Astrophysics Data System (ADS)

    Jha, Alok K.; Matsumoto, Kaname; Horide, Tomoya; Saini, Shrikant; Mele, Paolo; Ichinose, Ataru; Yoshida, Yutaka; Awaji, Satoshi

    2015-11-01

    The effect of hybrid (columnar and spherical together) artificial pinning centers (APCs) on the vortex pinning properties of YBa2Cu3O7-δ (YBCO) thin films is investigated in detail on the basis of variation of critical current density (J C ) with applied magnetic field and also with the orientation of the applied magnetic field at 65 K and 77 K. Premixed YBCO + BaSnO3 composite targets are used for the deposition of the YBCO films which consist of self-assembled BaSnO3 nanocolumns (1D APCs); on the other hand, for the deposition of the YBCO films with hybrid APCs (BaSnO3 nanocolumns together with Y2O3 nanoparticles), the surface of the premixed YBCO + BaSnO3 composite targets are modified by putting a thin Y2O3 sectored piece on the premixed YBCO + BaSnO3 composite targets by means of silver paste. F pmax value increases systematically with incorporation of 1D and 1D and 3D APCs and it also shifts towards higher applied magnetic fields. Films with 1D APCs exhibit a strong J C peak at Θ = 0° (H//c-axis) whereas films consisting of hybrid APCs exhibit enhanced J C at all the investigated angular regimes. A possible mechanism of vortex pinning in samples with hybrid APCs is also discussed suggesting the role of 1D and 3D APCs.

  3. The mechanism of sputter-induced orientation change in YBCO films on MgO (001)

    SciTech Connect

    Huang, Y.; Vuchic, B.V.; Baldo, P.; Merkle, K.L.; Buchholz, D.B.; Mahajan, S.; Lei, J.S.; Markworth, P.R.; Chang, R.P.H.

    1996-12-01

    The mechanisms of the sputter-induced orientation change in YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}(YBCO) films grown on MgO (001) substrates by pulsed organometallic beam epitaxy (POMBE) are investigated by x-ray diffraction. Rutherford backscatter spectroscopy (RBS), cross-section TEM (XTEM) and microanalysis. It is found that the W atom implantation concurring with the ion sputtering plays an important role in effecting the orientation change. This implantation changes the surface structure of the substrate and induces an intermediate layer in the initial growth of the YBCO film, which in turn acts as a template that induces the orientation change. It seems that the surface morphology change caused by ion sputtering has only a minor effect on the orientation change.

  4. Synthesis, structure, microstructure and mechanical characteristics of MOCVD deposited zirconia films

    NASA Astrophysics Data System (ADS)

    Bernard, O.; Huntz, A. M.; Andrieux, M.; Seiler, W.; Ji, V.; Poissonnet, S.

    2007-03-01

    Zirconia (ZrO 2) thin films were deposited by metal organic chemical vapor deposition (MOCVD) on (1 0 0) Si over temperature and pressure ranges from 700 to 900 °C and 100 to 2000 Pa, respectively. The oxide films were characterized by field emission microscopy and X-ray diffraction so that microstructure and ratios of monoclinic and tetragonal phases could be estimated according to the process conditions. The mechanical behaviour of the substrate-film systems was investigated using Vickers micro-indentation and Berkovitch nano-indentation tests. The characteristics of silicon are not modified by the presence of a thin film of silicon oxide (10 nm), formed in the reactor during heating. Young's modulus and the hardness of tetragonal zirconia phase, 220 and 15 GPa, respectively, are greater than values obtained for monoclinic phase, 160 and 7 GPa, respectively. The zirconia films are well adherent and the toughness of tetragonal zirconia phase is greater than that of monoclinic phase.

  5. Two to six compound thin films by MOCVD for tandem solar cells

    NASA Astrophysics Data System (ADS)

    Britt, Jeffrey Scott

    Polycrystalline Cd(1-x)Zn(x)S and Hg(x)Zn(1-x)Te films have been deposited on a variety of substrates by MOCVD. Deposition conditions have been adjusted based on measurements of the material properties. Heterojunction solar cells have been formed from these materials and their potential application as the upper member of a tandem solar cell has been examined. The evaluation and optimization of a high efficiency CdTe/CdS solar cell has also been accomplished. Polycrystalline Cd(1-x)Zn(x)S films were deposited at 350-425 C by the reaction between DMCd, DEZn, and the novel source, propanethiol (PM) in a H2 flow. The growth rate and bandgap energy are strongly dependent on the growth temperature, DMCd/DEZn molar ratio, and the II/VI molar ratio. TMAl and octyl-chloride have been introduced into the reaction mixture to lower resistivities to values suitable for device operation. Polycrystalline ZnTe films have been deposited at 270-400 C by the reaction between DIPTe and DMZn or DEZn in a H2 flow. ZnTe films have been deposited by photoenhanced and conventional MOCVD. Polycrystalline Hg(x)Zn(1-x)Te films have been deposited at 350-410 C by the reaction between elemental Hg, DIPTe, and DMZn in a H2 flow. AsH3 was introduced to the reaction mixture to control the resistivity. Heterojunctions have been formed with Cd(1-x)Zn(x)S and ZnSe. The films and junctions have been characterized by x-ray, optical transmission, low temperature photoluminescence, SEM, and electrical measurements. The evaluation and optimization of a CSS CdTe/CdS solar cell has been formed. A technique for the formation of low-resistance contacts to CdTe with HgTe has also been developed. A pre-deposition heat treatment of CdS in H2 has been demonstrated beneficial to the photovoltaic characteristics of the junction. A post-deposition CdCl2 treatment has been shown to have a profound influence on the electrical characteristics of CSS CdTe/CdS junctions. The identification of optical losses in CSS Cd

  6. Epitaxial growth of YBCO films on metallic substrates buffered with yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Ma, B.; Li, M.; Fisher, B. L.; Koritala, R. E.; Balachandran, U.

    2002-05-01

    Biaxially textured yttria-stabilized zirconia (YSZ) films were grown on polished Hastelloy C (HC) substrates by ion-beam-assisted deposition (IBAD) and electron-beam evaporation. A water-cooled sample stage was used to dissipate heat generated by the Kaufman ion source and to maintain the substrate temperature below 100 °C during deposition. X-ray pole figures were used for texture analysis. In-plane texture measured from the YSZ (111) φ-scan full-width-at-half-maximum (FWHM) was 13.2° and out-of-plane texture from the YSZ (002) ω-scan FWHM was 7.7°. In-plane texture improved with lowered substrate temperature during IBAD deposition. RMS surface roughness of 3.3 nm was measured by atomic force microscopy. A thin CeO2 buffer layer (≈10 nm) was deposited to improve the lattice match between the YSZ and YBCO films and to enhance the biaxial alignment of YBCO films. YBCO films were epitaxially grown on IBAD-YSZ buffered HC substrates with and without CeO2 buffer layers by pulsed laser deposition (PLD). In-plane texture FWHMs of 12° and 9° were observed for CeO2 (111) and YBCO (103), respectively. Tc=90 K, with sharp transition, and Jc values of ≈2×106 A/cm2 at 77 K in zero field were observed on 0.5-μm-thick, 5-mm-wide, and 1-cm-long samples.

  7. A comparative study on in situ grown superconducting YBCO and YBCO-Ag thin films by PLD on polycrystalline SmBa2NbO6 substrate

    NASA Astrophysics Data System (ADS)

    Kurian, J.; John, Asha M.; Wariar, P. R. S.; Sajith, P. K.; Koshy, J.; Pai, S. P.; Pinto, R.

    2000-02-01

    The development and characterization of SmBa2NbO6, which is a new ceramic substrate material for the YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> superconductor, are reported. SmBa2NbO6 has a complex cubic perovskite structure with lattice constant a = 8.524 Å. The dielectric properties of SmBa2NbO6 are in a range suitable for its use as a substrate for microwave applications. SmBa2NbO6 was found to have a thermal conductivity of 77 W m-1 K-1 and a thermal expansion coefficient of 7.8 × 10-6 °C-1 at room temperature. Superconducting YBa2 Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> and YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> -Ag thin films have been grown in situ on polycrystalline SmBa2NbO6 by the pulsed laser ablation technique. The films exhibited (00l) orientation of an orthorhombic YBa2 Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> phase and gave a zero resistivity superconducting transition (TC(0)) at 90 K with a transition width of ~1.5 K. The critical current density of YBCO-Ag thin films grown on polycrystalline SmBa2NbO6 substrate was ~3 × 105 A cm-2 at 77 K. A comparative study of YBCO and YBCO-Ag thin films developed on polycrystalline SmBa2NbO6 substrate by PLD based on the crystallinity, orientation and critical current density of the YBCO film is discussed in detail.

  8. Effect of Deposition Temperature on the Properties of TIO2 Thin Films Deposited by Mocvd

    NASA Astrophysics Data System (ADS)

    Khalifa, Zaki S.

    2016-02-01

    Crystal structure, microstructure, and optical properties of TiO2 thin films deposited on quartz substrates by metal-organic chemical vapor deposition (MOCVD) in the temperature range from 250∘C to 450∘C have been studied. The crystal structure, thickness, microstructure, and optical properties have been carried out using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), atomic force microscope (AFM), and UV-visible transmittance spectroscopy, respectively. XRD patterns show that the obtained films are pure anatase. Simultaneously, the crystal size calculated using XRD peaks, and the grain size measured by AFM decrease with the increase in deposition temperature. Moreover, the texture of the films change and roughness decrease with the increase in deposition temperature. The spectrophotometric transmittance spectra have been used to calculate the refractive index, extinction coefficient, dielectric constant, optical energy gap, and porosity of the deposited films. While the refractive index and dielectric constant decrease with the increase of deposition temperature, the porosity shows the opposite.

  9. Microstructural, transport, and RF properties of multilayer-deposited YBCO films

    NASA Astrophysics Data System (ADS)

    Madhavrao, L. R.; Track, E. K.; Drake, R. E.; Patt, R.; Hohenwarter, G. K. G.

    1991-03-01

    Thin films of Y1Ba2Cu3O(7-x) (YBCO) have been fabricated by sequential multilayer RF magnetron sputter-deposition from Y2O3, BaCo3, and CuO targets and postannealing in oxygen. This approach readily allows precise control of the film stoichiometry and is promising for applications that require deposition over large areas. Films on different substrates-including SrTiO3, LaAlO3, MgO and sapphire-are found to be c-axis oriented for film thicknesses between 300 A and 10,000 A. Transport current densities in the range of 106 A/sq cm are obtained on SrTiO3 and LaAlO3 substrates and in the range of 105 A/sq cm on MgO and sapphire. Transition temperatures of 89 K (resistive) and 87 K (inductive) are obtained repeatably with LaAlO3 substrates. Copper cavity end wall measurements at 77 K and 35.6 GHz set an upper limit for the surface resistance of the YBCO films on LaAlO3 that is equal to the surface resistance of high-quality silver films. The fabrication and properties of these films are discussed.

  10. BIG films fabricated by PLD for magnetic flux visualisation of YBCO

    NASA Astrophysics Data System (ADS)

    Kawano, K.; Chakalov, R. A.; Kong, G.; Abell, J. S.; Kahl, S.; Grishin, A. M.

    2002-08-01

    Bi 3Fe 5O 12 (BIG) magneto-optic (MO) films have been grown onto (1 1 1) and (1 0 0) gadolinium gallium garnet substrates by pulsed laser deposition (PLD). X-ray and transmission electron microscopy measurements have confirmed the epitaxial growth of the BIG films on both substrate orientations. Faraday rotation angles of both films showed linear field dependence from -1600 to +1600 G and the saturated Faraday rotation angle values were ∼5 deg/μm and ∼7.8 deg/μm for the (1 1 1) and (1 0 0) oriented films, respectively. A change in the MO contrast of both films in applied magnetic field has been observed and magnetic flux distributions have been visualised in YBa 2Cu 3O 7- x (YBCO) bulk superconductor using the (0 0 1) oriented BIG film.

  11. High speed production of YBCO precursor films by advanced TFA-MOD process

    NASA Astrophysics Data System (ADS)

    Ichikawa, H.; Nakaoka, K.; Miura, M.; Sutoh, Y.; Nakanishi, T.; Nakai, A.; Yoshizumi, M.; Izumi, T.; Shiohara, Y.

    2009-10-01

    YBa 2Cu 3O 7-y (YBCO) long tapes derived from the metal-organic deposition (MOD) method using the starting solution containing trifluoroacetate (TFA) have been developed with high critical currents ( I c) over 200 A/cm-width. However, high speed production of YBCO films is simultaneously necessary to satisfy the requirements of electric power device applications in terms of cost and the amounts of the tapes. In this work, we developed a new TFA-MOD starting solution using F-free salt of Y, TFA salt of Ba and Cu-Octylate for application to the coating/calcination process and discussed several issues by using the Multi-turn (MT) Reel-to-Reel (RTR) system calcination furnace for the purpose of high throughput without degradation of the properties. The coating system was improved for uniform deposition qualities in both longitudinal and transversal directions. YBCO films using the new starting solution at the traveling rate of 10 m/h in coating/calcination by the MT-RTR calcination furnace showed the values of the critical current density of 1.6 MA/cm 2 as thick as 1.5 μm at 77 K under the self fields after firing at the high heating rate in the crystallization.

  12. Structural and optical properties of anatase TiO2 heteroepitaxial films prepared by MOCVD

    NASA Astrophysics Data System (ADS)

    Zhao, Wei; Feng, Xianjin; Xiao, Hongdi; Luan, Caina; Ma, Jin

    2016-11-01

    High-quality single-crystal anatase TiO2(a-TiO2) thin films have been obtained on SrTiO3 (STO) substrates using the metalorganic chemical vapor deposition (MOCVD) method. The optimal preparation process was explored. The lattice structure and epitaxial relationship were investigated by X-ray diffraction (XRD, both θ-2θ and Φ scans) and transmission electron microscopy (TEM). The results indicated that the film prepared at 550 °C with the Ti precursor molar flow rate of 4×10-7 mol/min had the best single crystalline quality, for which a clear epitaxial relationship of a-TiO2 (001)||STO (100) with a-TiO2 [100]||STO [001bar] could be inferred. The elemental composition and proportion were studied by the X-ray photoelectron spectroscopy (XPS) method, which proved the deposited film approximated stoichiometric TiO2. The samples showed high transparency of 70-80% in the visible range.

  13. Co-doping effects of Gd and Ag on YBCO films derived by metalorganic deposition

    NASA Astrophysics Data System (ADS)

    Sun, Meijuan; Liu, Zhiyong; Bai, Chuanyi; Guo, Yanqun; Lu, Yuming; Fan, Feng; Cai, Chuanbing

    2015-12-01

    Y1-xGdxBa2Cu3O7-δ-Ag (x = 0, 0.25, 0.5, 0.75, 1) thin films were prepared on oxide buffered Hastelloy substrates by low fluorine metalorganic depostion (MOD) process. The effects of co-doping of Ag and Gd on the microstructures and superconducting properties of YBCO thin films are investigated with respect to improvement on texture and superconducting performance in case of optimized doping content. It is found that optimum addition of Ag and Gd may lead to better c-axis orientation, superior surface microstructure and finally give rise to much improvement of superconducting performance.

  14. Inclined-substrate deposition of biaxially textured magnesium oxide thin films for YBCO coated conductors.

    SciTech Connect

    Ma, B.; Li, M.; Jee, Y. A.; Koritala, R. E.; Fisher, B. L.; Balachandran, U.; Energy Technology

    2002-02-01

    Highly textured MgO films were grown by the inclined-substrate deposition (ISD) technique at a high deposition rate. A columnar grain with a roofing-tile-shaped surface was observed in these MgO films. X-ray pole figure, and {phi}- and {omega}-scan were used to characterize in-plane and out-of-plane textures. MgO films deposited when the incline angle {alpha} was 55 and 30 degrees exhibited the best in-plane and out-of-plane texture, respectively. High-quality YBCO films were epitaxially grown on ISD-MgO-buffered Hastelloy C substrates by pulsed laser deposition. {Tc}=88 K, with sharp transition, and j{sub c} values of {approx}2x10{sup 5} A/cm{sup 2} at 77 K in zero field were observed on films 5 mm wide and 1 cm long. This work has demonstrated that biaxially textured ISD MgO buffer layers deposited on metal substrates are excellent candidates for fabrication of high-quality YBCO coated conductors.

  15. Performance of a polarised neutron cryo-flipper using a high TcYBCO film

    NASA Astrophysics Data System (ADS)

    Parnell, S. R.; Washington, A. L.; Kaiser, H.; Li, F.; Wang, T.; Hamilton, W. A.; Baxter, D. V.; Pynn, R.

    2013-09-01

    It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined, non-adiabatic, magnetic-field transition. This can be utilised to produce a highly efficient neutron spin flipper that is suitable for use with neutrons of multiple wavelengths. Devices of this type using superconducting niobium have been deployed on neutron diffractometers for several decades but have required liquid helium to maintain the correct temperature. The use of high Tc materials, which removes the need for cryogens and simplifies the device, was first explored by Fitzsimmons et al. in [1]. In this communication, we describe a π flipper which uses commercially available films consisting of a 350-nm-thick YBCO film capped with 100 nm of gold on a 78×100×0.5 mm sapphire substrate. We discuss the design and performance of this device. The apparatus is compact (≈200 mm in length along the neutron beam), consisting of an oxygen-free high-conductivity copper frame, which holds the YBCO film and is mounted to the cold finger of a closed-cycle He refrigerator. The part of the vacuum chamber, where the YBCO film is located, is 5 cm wide, which allows us to minimise the distance from the film to the magnetic guide fields. Negligible small angle neutron scattering is observed from the flipper and its transmission is measured to be greater than 98.5% over a wide band of neutron wavelengths. In this design, the maximum neutron beam size that can be used is 42×42 mm2 and we can easily switch from a vertical to a horizontal guide field (both perpendicular to the neutron beam) on either side of the YBCO film. Data are reported for neutron wavelengths between 4 and 8.5 Å and flipping efficiencies under a variety of conditions are discussed. Under optimum conditions an efficiency of 99.5±0.3% was achieved for 4-8 Å neutrons on a pulsed source and 99.4±0.5% was achieved at a monochromatic source using a neutron wavelength of 4.2 Å.

  16. Electronic Properties of Layered Oxides:. Pulsed Laser Deposition of YBCO Films for In-Situ Studies by Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pavuna, D.; Ariosa, D.; Berger, H.; Christensen, S.; Frazer, B.; Gatt, R.; Grioni, M.; Margaritondo, G.; Misra, S.; Onellion, M.; Schmauder, T.; Vobornik, I.; Xi, X.; Zacchigna, M.; Zwick, F.

    Due to imperfect surfaces of most cuprate samples, almost all Photoemission studies in the past decade were performed on Bi2Sr2CaCu2O8+x, even though a large fraction of other studies and electronic applications was reported for YBa2Cu3O7-δ (YBCO) family of superconducting compounds. In order to systematically study the gap parameter and the Fermi surface variation in high symmetry directions of YBCO and related oxide films we have constructed a new facility at the Wisconsin Synchrotron Radiation Center. We use the pulsed laser ablation (PLD) system that is directly linked to the photoemission chamber. In our unique approach, the samples never leave the controlled ambient and we oxidize our films, either by molecular oxygen or by ozone. In this paper, we, summarize some of the most relevant recent results on electronic properties of layered oxides and describe our new facility for the study of YBCO and related oxide films.

  17. Switching of YBCO thin films into the dissipative state at high current densities

    NASA Astrophysics Data System (ADS)

    Villard, Catherine; Devismes, Marie-Françoise; Carbone, Laurent; Bourgault, Daniel

    We report on the switching properties at high current densities of YBCO thin films shunted by an Ag layer. These experiments are performed either in liquid nitrogen or liquid argon (87.3K). Different transition regimes associated to specific electric field thresholds are observed. The nature of the thermal exchange with the bath and the role of the silver shunt and substrate are discussed. While only two regimes in the current-voltage characteristics are observed in liquid nitrogen, successively reversible and hysteretic, an intermediate behaviour appears at 87.3K associated with a total current diversion by the silver layer.

  18. Study of high {Tc} superconducting thin films grown by MOCVD. Final report, July 1, 1986--April 30, 1990

    SciTech Connect

    Erbil, A.

    1990-12-31

    Work is described briefly, which was carried out on development of techniques to grow metal-semiconductor superlattices (artificially layered materials) and on the copper oxide based susperconductors (naturally layered materials). The current growth technique utilized is metalorganic chemical vapor deposition (MOCVD). CdTe, PbTe, La, LaTe, and Bi{sub 2}Te{sub 3} were deposited, mostly on GaAs. Several YBa{sub 2}Cu{sub 3}O{sub 7} compounds were obtained with possible superconductivity at temperatures up to 550 K (1 part in 10{sup 4}). YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} and Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub y} thin films were deposited by MOCVD on common substrates such as glass.

  19. Nucleation of stable superconductivity in YBCO-films

    NASA Astrophysics Data System (ADS)

    Kötzler, J.

    By means of the linear dynamic conductivity, inductively measured on epitaxial films between 30mHz and 30 MHz, the transition line T g (B) to generic superconductivity is studied in fields between B=0 and 19T. It follows closely the melting line T m (B) described recently in terms of a blowout of thermal vortex loops in clean materials. The critical exponents of the correlation length and time near T g (B), however, enem to be dominated by some intrinsic disorder. Columnar defects produced by heavy-ion irradiation up to field-equivalent-doses of B ϕ =10T lead to adisappointing reduction of T g (B→0) while for B>B ϕ the generic line of the pristine film is recovered. These novel results are also discussed in terms of a loop-driven destruction of generic superconductivity.

  20. Microstructural analysis on growth and crystallization mechanism of YBCO films deposited by advanced TFA-MOD process

    NASA Astrophysics Data System (ADS)

    Matsuda, J.; Nakaoka, K.; Sutoh, Y.; Nakanishi, T.; Yoshizumi, M.; Yamada, Y.; Izumi, T.; Shiohara, Y.

    2007-10-01

    We have investigated effects of the heating rate in the crystallization process on Ic values and microstructures of YBa2Cu3O7-δ (YBCO) films, which were fabricated by the advanced metalorganic deposition (MOD) method using trifluoroacetates. As a result, it was found that the slow heating rate less than 2 °C/min in the crystallization process increases the volume of randomly oriented YBCO crystals, which results in a low Ic value of the YBCO film. TEM observations of quenched samples prepared by cooling rapidly during the crystallization process revealed that unreacted phase particles such as CuO, Y2Cu2O5 and Ba-O-F crystallize and coarsen to large crystals before the nucleation and growth of YBCO crystals in the case of slow heating. We conclude that it is important to control the size and distributions of the unreacted phase particles in the crystallization process, in order to fabricate the YBCO coated conductor with high Ic.

  1. High velocity vortex channeling in vicinal YBCO thin films.

    PubMed

    Puica, I; Lang, W; Durrell, J H

    2012-09-01

    We report on electrical transport measurements at high current densities on optimally doped YBa2Cu3O7-δ thin films grown on vicinal SrTiO3 substrates. Data were collected by using a pulsed-current technique in a four-probe arrangement, allowing to extend the current-voltage characteristics to high supercritical current densities (up to 24 MA cm(-2)) and high electric fields (more than 20 V/cm), in the superconducting state at temperatures between 30 and 80 K. The electric measurements were performed on tracks perpendicular to the vicinal step direction, such that the current crossed between ab planes, under magnetic field rotated in the plane defined by the crystallographic c axis and the current density. At magnetic field orientation parallel to the cuprate layers, evidence for the sliding motion along the ab planes (vortex channeling) was found. The signature of vortex channeling appeared to get enhanced with increasing electric field, due to the peculiar depinning features in the kinked vortex range. They give rise to a current-voltage characteristics steeper than in the more off-plane rectilinear vortex orientations, in the electric field range below approximately 1 V/cm. Roughly above this value, the high vortex channeling velocities (up to 8.6 km/s) could be ascribed to the flux flow, although the signature of ohmic transport appeared to be altered by unavoidable macroscopic self-heating and hot-electron-like effects.

  2. Microstructure of artificial 45{sup degree} [001] tilt grain boundaries in YBCO films grown on (001) MgO

    SciTech Connect

    Huang, Y.; Vuchic, B.V.; Merkle, K.L.; Buchholz, D.B.; Chang, R.P.H.

    1996-03-01

    High-angle grain boundaries in YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) show weak-link effects and behave as Josephson junctions. This kind of grain boundary junction (GBJs) has potential applications in magnetic field measurement and electronic devices. This work studies the microstructure of artificially made GBJs in YBCO films on (001) MgO and the mechanism of boundary formation, with the goal to improve GBJ quality and obtain a better understanding of the junctions` transport properties.

  3. In-situ integrated processing and characterization of thin films of high temperature superconductors, dielectrics and semiconductors by MOCVD

    NASA Technical Reports Server (NTRS)

    Singh, R.; Sinha, S.; Hsu, N. J.; Thakur, R. P. S.; Chou, P.; Kumar, A.; Narayan, J.

    1991-01-01

    In this strategy of depositing the basic building blocks of superconductors, semiconductors, and dielectrics having common elements, researchers deposited superconducting films of Y-Ba-Cu-O, semiconductor films of Cu2O, and dielectric films of BaF2 and Y2O3 by metal oxide chemical vapor deposition (MOCVD). By switching source materials entering the chamber, and by using direct writing capability, complex device structures like three terminal hybrid semiconductor/superconductor transistors can be fabricated. The Y-Ba-Cu-O superconducting thin films on BaF2/YSZ substrates show a T(sub c) of 80 K and are textured with most of the grains having their c-axis or a-axis perpendicular to the substrate. Electrical characteristics as well as structural characteristics of superconductors and related materials obtained by x-ray deffraction, electron microscopy, and energy dispersive x-ray analysis are discussed.

  4. Planar tunneling into Zn and Ni-doped YBCO thin films

    NASA Astrophysics Data System (ADS)

    Badica, E.; Greene, L. H.

    2001-03-01

    Superconducting thin films of Y_1Ba_2Cu_3-xM_xO_7-delta (M = Zn, Ni; x = 0, 0.01, 0.02, 0.08, and 0, 0.01, 0.02, 0.24 respectively) are grown in different crystallographic orientations, classified into c-axis and ab-oriented. The critical temperatures of the films are 90, 84, 81, 60K, and 90, 81 77K, for Zn and Ni doping, respectively. Planar tunneling spectroscopy into the ab-planes, using Pb and Bi counter-electrodes, shows that the gap-like feature scales with the critical temperature, and the magnitude of the surface-induced Andreev bound states (ABS) seen at zero bias decreases with increasing doping concentration. In the case of Zn-doping, the surface-induced ABS are quenched for the highest doping concentration used, consistent with previous measurements on ion-irradiated (1) and Pr-doped (2) YBCO thin films. A detailed comparison (3) of the influence of doping and disorder on the low-energy density of states of YBCO, as a function of temperature and externally applied magnetic field, will be presented. We acknowledge support from NSF (DMR 94-21957) and NSF (DMR 99-72087). 1. M. Aprili, M. Covington, E. Paraoanu, B. Niedermeier, and L. H. Greene, Phys. Rev. B 57, R8139 (1998); 2. M. Covington, and L. H. Greene, Phys. Rev. B 62, 12 440 (2000); 3. E. Badica, M. Aprili, M. Covington, and L. H. Greene, Proceedings for the SPIE 2000 Aerosense Symposium, 'Oxide Superconductors: Physics and Nano-engineering IV', April 24-28, 2000, Orlando, Florida.

  5. Self-assembled artificial pinning centres in thick YBCO superconducting films

    NASA Astrophysics Data System (ADS)

    Mikheenko, P.; Abell, J. S.; Sarkar, A.; Dang, V. S.; Awang Kechik, M. M.; Tanner, J. L.; Paturi, P.; Huhtinen, H.; Babu, N. Hari; Cardwell, D. A.; Crisan, A.

    2010-06-01

    Strong, artificial pinning centres are required in superconducting films of large thickness for power applications in high magnetic fields. One of the methods for the introduction of pinning centres in such films is substrate decoration, i.e., growing nanoscale islands of certain materials on the substrate prior to the deposition of the superconducting film. Two other methods are building up a layered distribution of a second phase and homogeneous incorporation of second phase inclusions from a compositional target. In this paper, we compare the effectiveness of these methods in terms of the type of the self-assembly of nanoparticles. The comparison is made over a large set of YBa2Cu3O7 films of thickness up to 6.6 μm deposited with Au, Ag, Pd, LaNiO3, PrBa2Cu3O7, YBCO, BaZrO3 and Gd2Ba4CuWOy nanoparticles. It is found that substrate-decoration self-assembly is able to provide higher critical current in low magnetic field than the incorporation of homogeneous second phase in the sample microstructure. By specific modification of substrate decoration we achieved the self-field critical current per centimetre of width of 896 A/cm at 77.3 K and 1620 A/cm at 65 K in a film of thickness of 4.8 μm.

  6. MOCVD Growth and Characterization of n-type Zinc Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Ben-Yaacov, Tammy

    , and we investigate the n-ZnO/p-GaN interface. We show that ZnO has potential as an effective p-contact for these devices, and determine properties that still need improvement in order for ZnO to compete with other contact materials. We also compare the device performance to metal-contacted devices. In summary, this thesis describes the growth of ZnO(0001) films by MOCVD, the progress in developing ZnO material with excellent surface morphology, high crystal quality, and controllable n-type doping, as well as its application to GaN-based optoelectronic devices as a p-contact material.

  7. MOCVD growth of magnesium zinc oxide films and nanostructures for photovoltaics

    NASA Astrophysics Data System (ADS)

    Duan, Ziqing

    MgxZn1-xO, which is formed by alloying ZnO with MgO, has been developed as a promising window layer in chalcopyrite thin film solar cells and hybrid polymer solar cells for enhanced open-circuit voltage and solar conversion efficiency because of its bandgap tunability. The surface morphology of MgxZn1-xO layers in those photovoltaic applications plays important roles on the performances of solar cells. Two-dimensional (2-D) dense and smooth film is preferred in the inorganic p-n junction solar cells while one-dimensional (1-D) nanostructures are favorable for the hybrid polymer solar cells. In this dissertation, metal-organic chemical vapor deposition (MOCVD) is used to grow both of MgxZn1-xO polycrystalline 2-D films and single crystalline 1-D nanostructures for solar cells. A low-temperature (~250°C) ZnO buffer layer, followed by the high-temperature (~500°C) growth of MgxZn1-xO, is found to be beneficial for the formation of a 2-D dense and smooth film. On the other hand, a high-temperature (~520°C) ZnO buffer layer followed by a high temperature (530°C-560°C) growth of MgxZn1-xO is needed to grow the 1-D Mg xZn1-xO (0≤x≤0.15) nanostructures on Si. For the first time, 1-D MgxZn1-xO nanostructures (0≤x≤0.1) are sequentially grown on a Ga-doped ZnO (GZO) 2-D film to form the 3-D photoelectrode, which is used to fabricate the P3HT-MgxZn1-xO hybride solar cells. The preliminary testing results of solar cells show that Mg xZn1-xO is promising to be used in hybrid polymer solar cells for the enhancement of open circuit voltage (VOC). MgxZn1-xO (0≤x≤0.1) polycrystalline films are used in Cu2O-MgxZn1-x O heterojunction solar cells. The current density-voltage (J-V) measurements of solar cells under illumination show that VOC, shunt resistance Rsh and the solar conversion efficiency η are improved with increasing of Mg% until 10%. A relatively high solar conversion efficiency, η AM1.5 = 0.71 % with a short circuit current JSC = 3.0 mA/cm 2 and VOC

  8. Preparation and microstructures of high-current density YBCO films by no-water post-annealing of precursor films including BaF 2

    NASA Astrophysics Data System (ADS)

    Ichinose, Ataru; Kikuchi, Akihiro; Kiss, Takanobu; Tachikawa, Kyoji; Akita, Shirabe; Inoue, Kiyoshi

    2003-10-01

    Precursor films are deposited on SrTiO 3 single crystals at room temperature by the co-evaporation technique using Y, BaF 2 and Cu as evaporation sources. Then, the precursor films are annealed in a low-pressure oxygen atmosphere without introduction of water vapor. A sample with a reflection high-energy electron diffraction (RHEED) pattern exhibiting some streaks, Kikuchi lines and Kikuchi zone, which resembles that of a single crystal, is successfully prepared. According to the cross-sectional TEM observation results, epitaxial growth of this YBCO film is achieved for the entire film thickness. The transport properties are measured using a small bridge with a width of 0.1 mm and a length of 1 mm by a standard four-probe method. The obtained YBCO film has a high Jc of over 1 MA/cm 2 at 77 K and a self-field. Furthermore, we discuss the relationship between the epitaxial YBCO layer thickness and the annealing conditions. Approximately 300- and 400-nm-thick epitaxial YBCO films are successfully prepared.

  9. In-plane aligned YBCO film on textured YSZ buffer layer deposited on NiCr alloy tape by laser ablation with only O+ ion beam assistance

    NASA Astrophysics Data System (ADS)

    Tang Huang, Xin; Qing Wang, You; Wang, Qiu Liang; Chen, Qing Ming

    2000-02-01

    High critical current density and in-plane aligned YBa2 Cu3 O7-x (YBCO) film on a textured yttria-stabilized zirconia (YSZ) buffer layer deposited on NiCr alloy (Hastelloy c-275) tape by laser ablation with only O+ ion beam assistance was fabricated. The values of the x-ray phi-scan full width at half-maximum (FWHM) for YSZ(202) and YBCO(103) are 18° and 11°, respectively. The critical current density of YBCO film is 7.9 × 105 A cm-2 at liquid nitrogen temperature and zero field, and its critical temperature is 90 K.

  10. Engineered oxide thin films as 100% lattice match buffer layers for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Akin, Y.; Heiba, Z. K.; Sigmund, W.; Hascicek, Y. S.

    2003-12-01

    One of the most important qualities of buffer layers for RE-BCO coated conductors' growth is close lattice match with RE-BCO. However, there is no natural material with a 100% lattice match with RE-BCO. In this study mixtures of europium oxide (Eu 2O 3) and ytterbium oxide (Yb 2O 3), (Eu 1- uYb u) 2O 3 (0.0⩽ u⩽1.0), were investigated as a candidate buffer layer that could have same lattice parameter as YBa 2Cu 3O 7- δ(YBCO). Because the pseudocubic lattice parameter of Eu 2O 3 is bigger, and that of Yb 2O 3 is smaller than lattice parameter of YBCO, and the mixed oxides with appropriate ratio would have same lattice parameter of YBCO. The mixtures were prepared using metal-organic precursor by sol-gel process, and it was found that all mixed samples are single phase, complete solid solutions, and have same crystal system over the whole range of " u". Lattice parameters of mixed (Eu 1- uYb u) 2O 3 oxide powders were changed between 10.86831 and 10.42828 Å which are lattice parameter of Eu 2O 3 and Yb 2O 3, respectively by changing the ratio of Eu/Yb in the mixture. Phase and lattice parameter analysis revealed that pseudocubic lattice parameter of (Eu 0.893Yb 0.107) 2O 3 is 3.82 Å which is same as the lattice parameter of YBCO. Textured (Eu 0.893Yb 0.107) 2O 3 buffer layers were grown on biaxially textured-Ni (1 0 0) substrates. The solution was prepared from Europium and Ytterbium 2,4-pentadioanate, and was deposited on the Ni substrates using a reel-to-reel sol-gel dip coating system. The textured films were annealed at 1150 °C for 10 min under 4% H 2-Ar gas flow. Extensive texture analysis has been done to characterize the texture of (Eu 0.893Yb 0.107) 2O 3 buffer layers. X-ray diffraction (XRD) of the buffer layer showed strong out-of-plane orientation on Ni tape. The (Eu 0.893Yb 0.107) 2O 3 (2 2 2) pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full

  11. Resistive switching phenomena of HfO2 films grown by MOCVD for resistive switching memory devices

    NASA Astrophysics Data System (ADS)

    Kim, Hee-Dong; Yun, Min Ju; Kim, Sungho

    2016-08-01

    The resistive switching phenomena of HfO2 films grown by using metal organic chemical vapor deposition (MOCVD) was studied for the application of resistive random access memory (ReRAM) devices. In the fabricated Pt/HfO2/TiN memory cells, bipolar resistive switching characteristics were observed, and the set and reset states were measured to be as low as 7 μA and 4 μA, respectively, at V READ = 1 V. Regarding the resistive switching performance, stable resistive switching (RS) performance was observed under 40 repetitive dc cycles with small variations of set/reset voltages and the currents and good retention characteristics of over 105 s in both the low-resistance state (LRS) and the high-resistance state (HRS). These results show the possibility of using MOCVDgrown HfO2 films as a promising resistive switching materials for ReRAM applications.

  12. Solid source MOCVD system

    DOEpatents

    Hubert, B.N.; Wu, X.D.

    1998-10-13

    A system for MOCVD fabrication of superconducting and non-superconducting oxide films provides a delivery system for the feeding of metallorganic precursors for multi-component chemical vapor deposition. The delivery system can include multiple cartridges containing tightly packed precursor materials. The contents of each cartridge can be ground at a desired rate and fed together with precursor materials from other cartridges to a vaporization zone and then to a reaction zone within a deposition chamber for thin film deposition. 13 figs.

  13. Solid source MOCVD system

    DOEpatents

    Hubert, Brian N.; Wu, Xin Di

    1998-01-01

    A system for MOCVD fabrication of superconducting and non-superconducting oxide films provides a delivery system for the feeding of metalorganic precursors for multi-component chemical vapor deposition. The delivery system can include multiple cartridges containing tightly packed precursor materials. The contents of each cartridge can be ground at a desired rate and fed together with precursor materials from other cartridges to a vaporization zone and then to a reaction zone within a deposition chamber for thin film deposition.

  14. Strong vortex matching effects in YBCO films with periodic modulations of the superconducting order parameter fabricated by masked ion irradiation

    NASA Astrophysics Data System (ADS)

    Haag, L. T.; Zechner, G.; Lang, W.; Dosmailov, M.; Bodea, M. A.; Pedarnig, J. D.

    2014-08-01

    We report on measurements of the magnetoresistance and of the critical current in thin films of the high-temperature superconductor YBa2Cu3O7-δ (YBCO). A square array of regions with suppressed superconducting order parameter has been created in these films by introducing point defects via irradiation with He+ ions through a silicon stencil mask. In such a structure distinct peaks of the critical current can be observed at commensurate arrangements of magnetic flux quanta with the artificial defect lattice. Concurrently, the magnetoresistance shows pronounced minima. Both observations demonstrate that the strong intrinsic pinning in YBCO can be overcome by a periodic array of ion-damage columns with 300 nm spacing.

  15. Characterization of MgO substrates for growth of epitaxial YBCO thin films

    NASA Astrophysics Data System (ADS)

    Du, J.; Gnanarajan, S.; Bendavid, A.

    2005-08-01

    YBCO films were grown on magnesium oxide (MgO) substrates for fabricating step-edge junction SQUIDs and other Josephson junction-based devices. In-plane 45° grain misorientation was frequently observed in films grown on degraded or contaminated MgO substrates. The appearance of these misoriented grains results in a decrease of the thin-film critical-current density and reduces the device yield. In this work, we investigated the chemical properties of MgO substrates with various surface conditions due to different substrate preparation methods and environmental degradation, by using x-ray photoelectron spectroscopy (XPS). The XPS characteristics of the surface are compared before and after a thermal annealing at 760 °C resembling the thin-film deposition heating cycle. The MgO substrates, after lithographic processing or only weeks of exposure to the laboratory environment, showed surface degradation characterized by the presence of hydroxyl groups, carbonate, and other possible carbon compounds such as bicarbonate, alcohols and carboxyl. Heating of the substrates to 760 °C improves the surface quality to a certain degree with the removal of some of the above contaminants, but is not sufficient to recover the MgO surfaces. A final Ar ion-beam etch cleaning process at low ion energy proved to be very effective in refreshing the MgO substrate surface that had been degraded due to lithographic processing or storage. Films grown on MgO with this pre-treatment showed perfect grain alignment and high critical-current densities.

  16. Y-Ba-Cu-O film deposition by metal organic chemical vapor deposition on buffered metal substrates.

    SciTech Connect

    Selvamanickam, V.; Galinski, G.; DeFrank, J.; Trautwein, C.; Haldar, P.; Balachandran, U.; Lanagan, M.; Chudzik, M.

    1999-10-12

    YBa{sub 2}Cu{sub 3}O{sub 2} (YBCO) films have been deposited on buffered metal substrates by Metal Organic Chemical Vapor Deposition (MOCVD). Cube-textured nickel substrates were fabricated by a thermomechanical process. Epitaxial CeO{sub 2}films were deposited on these substrates by thermal evaporation. Nickel alloy substrates with biaxially-textured Yttria-Stabilized Zirconia (YSZ) buffer layers deposited by Ion Beam Assisted Deposition were also prepared. Highly biaxially-textured YBCO films were deposited by MOCVD on both types of metal substrates. A critical current density greater than 10{sup 5} A/cm{sup 2} at 77 K has been achieved in YBCO films on metal substrates.

  17. Improvements in Crystal Structure of Two Inch Double-Sided YBCO Thin Films by Preseeded Self-Template Layer

    NASA Astrophysics Data System (ADS)

    Li, Yanrong; Liu, Xingzhao; Tao, Bowan; Zhang, Ying; Deng, Xinwu

    2003-03-01

    A self-template layer was employed to improve the crystal structure and microwave properties of large-area double-sided YBCO thin films. Two-inch double-sided YBCO thin films with excellent out-of-plane orientation and lateral homogeneity of microwave surface resistance were prepared by using a preseeded self-template layer. The full width at half maximum (FWHM) value of the rocking curve as low as 0.15° was achieved. The electronic channeling pattern was very sharp, clear and symmetric. The values of microwave surface resistance Rs (75 K, 145 GHz, 0 T) below 55 mΩ were obtained over the entire YBCO thin films on 2-inch LaAlO3 wafers. The majority of the wafer area given in percent has Rs (75 K, 145 GHz, 0 T) values in the range from 15 mΩ to 40 mΩ. The high frequency (HF) power handling capability was demonstrated by a breakdown field higher than 6 mT at 8.5 GHz and 77 K.

  18. Vortex dynamics of 250 MeV Ag ions irradiated YBCO films

    NASA Astrophysics Data System (ADS)

    Khatua, Sanghamitra; Kumar, Ravi; Mishra, P. K.; Sahni, V. C.; Pinto, R.

    YBCO thin films with c-axis orientation were grown in-situ by KrF laser on LaAIO 3 substrate. The films were irradiated with 250 MeV Ag ions at doses equivalent to B φ ranging from 1 T to 4 T. Critical currents were measured using SQUID magnetometer with field parallel to columnar defects. There is a marked enhancement of vortice pinning due to generation of additional pinning centres. There seems to be an upper limit to the irradiation doses beyond which there is a 'smearing effect' on Jc. We also find a shift in Irreversibility Line towards higher field which is attributed to better pinning induced by columnar defects. Defect production is examined in the framework of "Coulomb explosion" model and the consequences are analysed in terms of defect-induced behaviour within the purview of models such as "Bean model", 'Exponential model' and "Vortex Glass" model. We point out that the 'stress model' provides a qualitative explanation for the reduced Tc and a broad transition at high fluence.

  19. Irreversible properties of YBCO thick films deposited by liquid phase epitaxy on single crystalline substrates

    NASA Astrophysics Data System (ADS)

    Vostner, A.; Tönies, S.; Weber, H. W.; Cheng, Y. S.; Kurumovic, A.; Evetts, J. E.; Mennema, S. H.; Zandbergen, H. W.

    2003-10-01

    We report on the field and temperature dependence of the critical transport current density Jc, the angular dependence of the transport current at various external magnetic fields and the irreversibility fields in YBa2Cu3O7-delta (Y-123) thick films prepared by liquid phase epitaxy (LPE). A comparison of the irreversible properties between specimens produced with and without silver additions to the melt is also presented. Transmission electron microscopy (TEM) was employed to obtain information on the correlation between the transport properties and the microstructure. The samples were deposited either directly on NdGaO3 (NGO) or on seeded (100) MgO substrates, where a 200 nm thin YBCO film deposited by pulsed laser deposition (PLD) acts as seed layer for the LPE process. The final thickness of the Y-123 layer is of the order of 1 µm for the NGO and between 2 and 10 µm for the MgO samples. The critical current densities reach 3 × 109 A m-2 at zero field and 77 K in the best case.

  20. Structural, optical and electrical properties of Al-N codoped ZnO films by RF-assisted MOCVD method

    NASA Astrophysics Data System (ADS)

    Su, Jianfeng; Zang, Chunhe; Cheng, Chunxiao; Niu, Qiang; Zhang, Yongsheng; Yu, Ke

    2010-10-01

    N-doped ZnO films were produced using N 2 as N source by metal-organic chemical vapor deposition (MOCVD) system which has been improved with radio-frequency (RF)-assisted equipments. The data of secondary ion mass spectroscopy (SIMS) indicate that the concentration of N in N-doped ZnO films is around 5 × 10 20 cm -3, implying that sufficient incorporation of N into ZnO can be obtained by RF-assisted equipment. On this basis, the structural, optical and electrical properties of Al-N codoped ZnO films were studied. Then, the effect of RF power on crystal quality, surface morphologies, optical properties was analyzed using X-ray diffraction, atomic force microscopy and photo-luminescence methods. The results illustrate that the RF plasma is the key factor for the improvement of crystal quality. Then the observation of A 0X recombination associated with N O acceptor in low-temperature PL spectrum proved that some N atoms have occupied the positions of O atoms in ZnO films. Hall measurements shown that p-type ZnO film deposited on quartz glasses was obtained when RF power was 150 W for the Al-N codoped ZnO films, while the resistivity of N-doped ZnO films was rather high. Compared with the Al-doped ZnO film, the obviously increased resistivity of codoped films indicates that the formation of N O acceptors compensate some donors in ZnO films effectively.

  1. Initial stages of TiO 2 thin films MOCVD growth studied by in situ surface analyses

    NASA Astrophysics Data System (ADS)

    Brevet, A.; Peterlé, P. M.; Imhoff, L.; Marco de Lucas, M. C.; Bourgeois, S.

    2005-02-01

    In situ chemical surface analyses using X-ray photoelectron spectroscopy (XPS) were performed to understand the initial stages of TiO 2 thin-film MOCVD growth. Deposits on Si (1 0 0), a few nanometres thick, were obtained at a fixed temperature of 650 °C and for two different pressures, 2.9 and 0.05 mbar, using titanium tetraisopropoxide (TTIP) as precursor. Pressure lowering led to a higher deposit growth rate. Reduction of titanium with respect to stoichiometric titanium dioxide and oxidation of the wet-cleaned silicon substrate are observed from decomposition of the Ti 2p and Si 2p peaks. The formation of a TiSi xO y mixed oxide is also pointed out and confirmed by the presence of a characteristic component in the O 1 s peak.

  2. Pulsed laser deposition of c-axis untilted YBCO films on c-axis tilted ISD MgO-buffered metallic substrates

    NASA Astrophysics Data System (ADS)

    Li, M.; Ma, B.; Koritala, R. E.; Fisher, B. L.; Venkataraman, K.; Maroni, V. A.; Vlasko-Vlasov, V.; Berghuis, P.; Welp, U.; Gray, K. E.; Balachandran, U.

    2003-05-01

    Biaxially textured MgO template layer was deposited on nontextured metal substrates by inclined-substrate deposition (ISD) at a deposition rate of 24-600 nm/min. c-axis untilted YBa 2Cu 3O 7- x (YBCO) films were deposited on these MgO-buffered substrates by pulsed laser deposition. The crystalline structures of the YBCO films and MgO layers were examined by X-ray pole figure analysis, X-ray φ-scans, and χ-scans. A tilt angle of 33° of the MgO[0 0 1] with respect to the substrate normal and c-axis untilted YBCO films were observed, respectively. Good biaxial texture of these films with full-width-at-half-maximum values of 13.8° and 10.6° for the φ-scans of YBCO(1 0 3) and MgO(2 2 0), respectively, were obtained. Morphologies were examined by scanning electron microscopy, which revealed a unique roof-tile feature and columnar grain growth for the ISD MgO layer. Raman spectroscopy and magneto-optical image technique were also used to evaluate the quality of the YBCO film. An angular dependence of Jc on the direction of an applied magnetic field confirmed the c-axis untilted orientation of the YBCO films. Tc=90 K with sharp transition and Jc=3.0×10 5 A/cm 2 at 77 K in zero field were obtained on 0.4-μm-thick YBCO films.

  3. Effect of copper content in precursor solution on the superconducting properties of YBCO films derived from low-fluorine solution

    NASA Astrophysics Data System (ADS)

    Zhao, Gaoyang; Lei, Li; Liu, Xiaomei; Chen, Yuanqing

    2008-12-01

    Four low-fluorine solutions with different stoichiometry of Y:Ba:Cu = 1:2: ξ ( ξ = 3, 3.5, 4, 4.5) were prepared using Ba-TFA, yttrium and copper acetate as precursors. YBa 2Cu 3O 7-δ (YBCO) films derived from these low-fluorine solutions were coated on LaAlO 3 (LAO) single crystal substrates by dip-coating process. The effect of copper stoichiometry in precursor solution on the microstructure and superconductivity of YBCO films was studied. The growth orientation and microstructure of the films were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results show that there are large volume fraction of a-axis oriented YBCO grains in the films derived from precursor solutions with stoichiometry of Y:Ba:Cu = 1:2: ξ ( ξ = 3, 3.5, 4.5), while the films from the solution with stoichiometry of Y:Ba:Cu = 1:2:4 mainly grow along c-axis orientation and the volume fraction of c-axis oriented grains is 96.33%. Superconductivity test indicate that the film derived from the precursor solution with stoichiometry of Y:Ba:Cu = 1:2:4 exhibits excellent superconducting properties with the critical transition temperature Tc approximate 90 K, the sharp transition temperature Δ T below 1 K and the critical current density Jc over 1 MA/cm 2 (77 K, 0 T).

  4. Aspects of passive magnetic levitation based on high-T(sub c) superconducting YBCO thin films

    NASA Astrophysics Data System (ADS)

    Schoenhuber, P.; Moon, F. C.

    1995-04-01

    Passive magnetic levitation systems reported in the past were mostly confined to bulk superconducting materials. Here we present fundamental studies on magnetic levitation employing cylindrical permanent magnets floating above high-T(sub c) superconducting YBCO thin films (thickness about 0.3 mu m). Experiments included free floating rotating magnets as well as well-established flexible beam methods. By means of the latter, we investigated levitation and drag force hysteresis as well as magnetic stiffness properties of the superconductor-magnet arrangement. In the case of vertical motion of the magnet, characteristic high symmetry of repulsive (approaching) and attractive (withdrawing) branches of the pronounced force-displacement hysteresis could be detected. Achievable force levels were low as expected but sufficient for levitation of permanent magnets. With regard to magnetic stiffness, thin films proved to show stiffness-force ratios about one order of magnitude higher than bulk materials. Phenomenological models support the measurements. Regarding the magnetic hysteresis of the superconductor, the Irie-Yamafuji model was used for solving the equation of force balance in cylindrical coordinates allowing for a macroscopic description of the superconductor magnetization. This procedure provided good agreement with experimental levitation force and stiffness data during vertical motion. For the case of (lateral) drag force basic qualitative characteristics could be recovered, too. It is shown that models, based on simple asymmetric magnetization of the superconductor, describe well asymptotic transition of drag forces after the change of the magnet motion direction. Virgin curves (starting from equilibrium, i.e. symmetric magnetization) are approximated by a linear approach already reported in literature only. This paper shows that basic properties of superconducting thin films allow for their application to magnetic levitation or - without need of levitation

  5. Aspects of passive magnetic levitation based on high-T(sub c) superconducting YBCO thin films

    NASA Technical Reports Server (NTRS)

    Schoenhuber, P.; Moon, F. C.

    1995-01-01

    Passive magnetic levitation systems reported in the past were mostly confined to bulk superconducting materials. Here we present fundamental studies on magnetic levitation employing cylindrical permanent magnets floating above high-T(sub c) superconducting YBCO thin films (thickness about 0.3 mu m). Experiments included free floating rotating magnets as well as well-established flexible beam methods. By means of the latter, we investigated levitation and drag force hysteresis as well as magnetic stiffness properties of the superconductor-magnet arrangement. In the case of vertical motion of the magnet, characteristic high symmetry of repulsive (approaching) and attractive (withdrawing) branches of the pronounced force-displacement hysteresis could be detected. Achievable force levels were low as expected but sufficient for levitation of permanent magnets. With regard to magnetic stiffness, thin films proved to show stiffness-force ratios about one order of magnitude higher than bulk materials. Phenomenological models support the measurements. Regarding the magnetic hysteresis of the superconductor, the Irie-Yamafuji model was used for solving the equation of force balance in cylindrical coordinates allowing for a macroscopic description of the superconductor magnetization. This procedure provided good agreement with experimental levitation force and stiffness data during vertical motion. For the case of (lateral) drag force basic qualitative characteristics could be recovered, too. It is shown that models, based on simple asymmetric magnetization of the superconductor, describe well asymptotic transition of drag forces after the change of the magnet motion direction. Virgin curves (starting from equilibrium, i.e. symmetric magnetization) are approximated by a linear approach already reported in literature only. This paper shows that basic properties of superconducting thin films allow for their application to magnetic levitation or - without need of levitation

  6. Manufacture of YBCO Superconducting Flexible Tapes from Nanoparticle Films Derived from Sedimentation and by Flame Deposition of Nanoparticles from Solution

    SciTech Connect

    Wiesmann, Harold

    2008-02-24

    The objective of this CRADA was to develop the experimental and theoretical basis of a technology to produce yttrium barium copper oxide (YBCO) superconducting flexible tapes derived from nanoparticle metal oxide sols. The CRADA was a joint effort between Oxford Superconducting Technology, Brookhaven National Laboratory and Karpov Institute of Physical Chemistry. The effort was divided into three main tasks, the synthesis of a heteroepitaxial oxide buffer layer, and the manufacture of a flexible biaxially textured metallic substrate and the synthesis of a heteroepitaxial crystalline YBCO layer. The formation of a heteroepitaxial buffer layer was implemented using technology developed at the Karpov Institute of Physical Chemistry for the synthesis, stabilization and deposition of polymer stabilized nanoparticle metal oxide sols. Using this technology, flexible oriented RABiTS nickel tapes, manufactured and supplied by the CRADA partner, Oxford Superconducting Technology, Carteret, New Jersey, were coated with a film of metal oxide nanoparticles. After coating the RABiTS nickel tapes with the nanoparticle sols the nickel tape/nanoparticle composite structure was sintered in order to form a dense crystalline heteroepitaxial oxide layer on the surface of the tape, also known as a ‘buffer’ layer. The final phase of the research was the formation of a heteroepitaxial YBCO layer, grown on top of the metal oxide buffer layer. This work was scheduled to follow the development of the heteroepitaxial oxide buffer layer as described above. Three different polymer stabilized sols, yttrium hydroxide, Y(OH){sub 3}, copper hydroxide, Cu(OH){sub 2}, and barium fluoride, BaF{sub 2}, were synthesized and combined in the appropriate stoichiometric ratio. This metal oxide sol was then be deposited onto the buffer layer and reacted to form a crystalline heteroepitaxial YBCO film ranging from 1–5 microns thick.

  7. Thickness-Dependent Properties of YBCO Films Grown on GZO/CLO-Buffered NiW Substrates

    NASA Astrophysics Data System (ADS)

    Malmivirta, M.; Huhtinen, H.; Zhao, Y.; Grivel, J.-C.; Paturi, P.

    2016-07-01

    To study the role of novel Gd_2 Zr_2 O_7 /Ce_{0.9} La_{0.1} O_2 buffer layer structure on a biaxially textured NiW substrate, a set of YBa_2 Cu_3 O_{7-δ } (YBCO) films with different thicknesses were prepared by pulsed laser deposition (PLD). Interface imperfections as well as thickness-dependent structural properties were observed in the YBCO thin films. The structure is also reflected into the improved superconducting properties with the highest critical current densities in films with intermediate thicknesses. Therefore, it can be concluded that the existing buffer layers need more optimization before they can be successfully used for films with various thicknesses. This issue is linked to the extremely susceptible growth method of PLD when compared to the commonly used chemical deposition methods. Nevertheless, PLD-grown films can give a hint on what to concentrate to be able to further improve the buffer layer structures for future coated conductor technologies.

  8. Anomalous current-voltage characteristics along the c-axis in YBaCuO thin films prepared by MOCVD and AFM lithography

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shuu'ichirou; Kawaguchi, Atsushi; Oda, Shunri

    1997-12-01

    We have proposed a fabrication process of intrinsic Josephson junctions (IJJs) using AFM lithography and successfully obtained IJJs in YBaCuO thin films deposited by MOCVD. A sample shows clear hysteresis and 23 voltage steps related to IJJs in the I- V curve. The maximum width of a step is about 2 mV at 5 K. We discuss the I- V characteristics and estimate the order of the parameters for the IJJ.

  9. Studies of Solution Deposited Cerium Oxide Thin Films on Textured Ni-Alloy Substractes for YBCO Superconductor

    SciTech Connect

    Stewart, Erin L; Bhuiyan, Md S; Sathyamurthy, Srivatsan; Paranthaman, Mariappan Parans

    2006-01-01

    Cerium oxide (CeO2) buffer layers play an important role for the development of YBa2Cu3O7-x (YBCO) based superconducting tapes using the rolling assisted biaxially textured substrates (RABiTS) approach. The chemical solution deposition (CSD) approach has been used to grow epitaxial CeO2 films on textured Ni-3 a 4% W alloy substrates with various starting precursors of ceria. Precursors such as cerium acetate, cerium acetylacetonate, cerium 2-ethylhexanoate, cerium nitrate, and cerium trifluoroacetate were prepared in suitable solvents. The optimum growth conditions for these cerium precursors were Ar-4% H2 gas processing atmosphere, solution concentration levels of 0.2-0.5 M, a dwell time of 15 min, and a process temperature range of 1050-1150 degrees C. X-ray diffraction, AFM, SEM, and optical microscopy were used to characterize the CeO2 films. Highly textured CeO2 layers were obtained on Ni-W substrates with both cerium acetate and cerium acetylacetonate as starting precursors. YBCO films with a Jc of 1.5 MA/cm2 were obtained on cerium acetylacetonate-based CeO2 films with sputtered YSZ and CeO2 cap layers.

  10. The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates

    SciTech Connect

    Huang, Y.; Vuchic, B.V.; Carmody, M.; Baldo, P.M.; Merkle, K.L.; Buchholz, D.B.; Mahajan, S.; Lei, J.S.; Markworth, P.R.; Chang, R.P.; Marks, L.D.

    1998-12-01

    The sputter-induced epitaxy change of in-plane orientation occurring in YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a Ba{sub x}Mg{sub 1{minus}x}O buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45{degree} oriented growth to the 0{degree} oriented growth. {copyright} {ital 1998 Materials Research Society.}

  11. Recycling failed bulk YBCO superconductors using the NdBCO/YBCO/MgO film-seeded top-seeded melt growth method

    NASA Astrophysics Data System (ADS)

    Xu, H. H.; Cheng, L.; Yan, S. B.; Yu, D. J.; Guo, L. S.; Yao, X.

    2012-05-01

    REBa2Cu3Oy (RE123 or REBCO, RE = rare earth elements) bulk high-temperature superconductors have a potential perspective for large-scale engineering applications. However, the cost of REBCO bulk production is rather high, considering high failure rates, expensive RE materials, and Pt or Ag addition. Using the cold-seeding in the top-seeded melt growth, a simple and feasible process, we succeeded in recycling the failed REBCO (RE = Y) bulks. The distinctive feature of this recycling process is the use of YBCO-buffered NdBCO films as seeds, which have high thermal stability and can endure a maximum processing temperature (Tmax) up to 1120 °C to enable full decomposition of solid REBCO. Three typical microstructures were recognized in the failed samples attributed to the inherent differences in the non-optimized growth heating profiles. Preferential recycling procedures were chosen according to the difficulty of the failed-samples decomposition, which has a certain connection with the microstructures of the failed bulks. Finally, after oxygenation, the recycled bulks demonstrate good superconducting properties.

  12. Preparation of ZnO:CeO{sub 2-x} thin films by AP-MOCVD: Structural and optical properties

    SciTech Connect

    Torres-Huerta, A.M.; Dominguez-Crespo, M.A.; Brachetti-Sibaja, S.B.; Dorantes-Rosales, H.; Hernandez-Perez, M.A.; Lois-Correa, J.A.

    2010-09-15

    The growth of columnar CeO{sub 2}, ZnO and ZnO:CeO{sub 2-x} films on quartz and AA6066 aluminum alloy substrates by economic atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) is reported. A novel and efficient combination of metal acetylacetonate precursors as well as mild operating conditions were used in the deposition process. The correlation among crystallinity, surface morphology and optical properties of the as-prepared films was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and UV-vis spectroscopy. The synthesized films showed different crystallographic orientations depending on the ZnO and CeO{sub 2} lattice mismatch, cerium content and growth rate. The CeO{sub 2} films synthesized in this work showed plate-like compact structures as a result of the growth process typical of CVD. Both pure and ZnO:CeO{sub 2-x} films were obtained with a hexagonal structure and highly preferred orientation with the c-axis perpendicular to both substrates under the optimal deposition conditions. The microstructure was modified from dense, short round columns to round structures with cavities ('rose-flower-like' structures) and the typical ZnO morphology by controlling the cerium doping the film and substrate nature. High optical transmittance (>87%) was observed in the pure ZnO films. As for the ZnO:CeO{sub 2-x} films, the optical transmission was decreased and the UV absorption increased, which subsequently was affected by an increase in cerium content. This paper assesses the feasibility of using ZnO:CeO{sub 2-x} thin films as UV-absorbers in industrial applications. - Graphical abstract: TEM micrographs and their corresponding SAED pattern obtained for the as-deposited ZnO-CeO{sub 2-x} thin films for a Zn/Ce metallic ratio 16:9.

  13. BaHfO3 artificial pinning centres in TFA-MOD-derived YBCO and GdBCO thin films

    NASA Astrophysics Data System (ADS)

    Erbe, M.; Hänisch, J.; Hühne, R.; Freudenberg, T.; Kirchner, A.; Molina-Luna, L.; Damm, C.; Van Tendeloo, G.; Kaskel, S.; Schultz, L.; Holzapfel, B.

    2015-11-01

    Chemical solution deposition (CSD) is a promising way to realize REBa2Cu3O7-x (REBCO; RE = rare earth (here Y, Gd))-coated conductors with high performance in applied magnetic fields. However, the preparation process contains numerous parameters which need to be tuned to achieve high-quality films. Therefore, we investigated the growth of REBCO thin films containing nanometre-scale BaHfO3 (BHO) particles as pinning centres for magnetic flux lines, with emphasis on the influence of crystallization temperature and substrate on the microstructure and superconductivity. Conductivity, microscopy and x-ray investigations show an enhanced performance of BHO nano-composites in comparison to pristine REBCO. Further, those measurements reveal the superiority of GdBCO to YBCO—e.g. by inductive critical current densities, J c, at self-field and 77 K. YBCO is outperformed by more than 1 MA cm-2 with J c values of up to 5.0 MA cm-2 for 265 nm thick layers of GdBCO(BHO) on lanthanum aluminate. Transport in-field J c measurements demonstrate high pinning force maxima of around 4 GN m-3 for YBCO(BHO) and GdBCO(BHO). However, the irreversibility fields are appreciably higher for GdBCO. The critical temperature was not significantly reduced upon BHO addition to both YBCO and GdBCO, indicating a low tendency for Hf diffusion into the REBCO matrix. Angular-dependent J c measurements show a reduction of the anisotropy in the same order of magnitude for both REBCO compounds. Theoretical models suggest that more than one sort of pinning centre is active in all CSD films.

  14. Quantitative magneto-optical analysis of the role of finite temperatures on the critical state in YBCO thin films

    NASA Astrophysics Data System (ADS)

    Albrecht, Joachim; Brück, Sebastian; Stahl, Claudia; Ruoß, Stephen

    2016-11-01

    We use quantitative magneto-optical microscopy to investigate the influence of finite temperatures on the critical state of thin YBCO films. In particular, temperature and time dependence of supercurrents in inhomogeneous and anisotropic films are analyzed to extract the role of temperature on the supercurrents themselves and the influence of thermally activated relaxation. We find that inhomogeneities and anisotropies of the current density distribution correspond to a different temperature dependence of local supercurrents. In addition, the thermally activated decay of supercurrents can be used to extract local vortex pinning energies. With these results the modification of vortex pinning introduced by substrate structures is studied. In summary the local investigation of supercurrent densities allows the full description of the vortex pinning landscape with respect to pinning forces and energies in superconducting films with complex properties under the influence of finite temperatures.

  15. Preparation of Sr2AlTaO6 Insulating Films on YBa2Cu3O7-δ by Metalorganic Chemical Vapor Deposition with Purified Sr Source

    NASA Astrophysics Data System (ADS)

    Takahashi, Yoshihiro; Zama, Hideaki; Ishimaru, Yoshihiro; Inoue, Nobuyoshi; Wu, Yuan; Morishita, Tadataka; Tanabe, Keiichi

    2002-02-01

    200-nm-thick Sr2AlTaO6 (SAT) insulating films were prepared on 10-μm-thick superconducting YBa2Cu3O7-δ (YBCO) films by metalorganic chemical vapor deposition (MOCVD). By employing a purified Sr(thd)2 metalorganic source, instead of Sr(thd)2-2tetraene, and a higher evaporation temperature, we could reproducibly obtain stoichiometric SAT films with high crystallinity as revealed by the full-width at half maximum value of the SAT (004) X-ray rocking curve which was as small as 0.2°. Moreover, a 200-nm-thick c-axis-oriented YBCO film with a Tc of 90 K and a Jc higher than 107 A/cm2 below 60 K could be grown on the SAT film. These results confirm that the SAT films prepared by MOCVD are suitable for use as insulating layers in high-Tc multilayer electronic devices.

  16. MOCVD of ceramic and metallic films on porous substrates for dense membrane applications

    NASA Astrophysics Data System (ADS)

    Xia, Changfeng

    Fabrication of thin, dense films on porous substrates is of interest for gas separation membranes, membrane reactor, gas sensors and solid oxide fuel cells. In this study, Chemical Vapor Deposition (CVD) was used to deposit CeOsb2-doped Ysb2Osb3-stabilized ZrOsb2, perovskite SrCosb1-xFesbxOsb{3-delta} and copper films on porous substrates for the purposes of fabricating dense inorganic membranes and studying membrane fabrication process. Aerosol-assisted precursor delivery was employed to overcome the drawbacks of conventional precursor delivery and to provide better control in film composition of multicomponent membrane materials. Thin membrane films of CeOsb2-doped Ysb2Osb3-stabilized ZrOsb2 were grown under atmospheric and reduced pressures from the toluene solutions of the precursors of Zr, Y and Ce 2,2,6,6-tetramethyl-3,5-heptanedionate (tmhd). The effects of system pressure on film morphology, structure and gas-tightness were investigated. The film composition was controlled by selecting the right ratios of precursors in the solutions. Thin membrane films of perovskite SrCosb1-xFesbxOsb{3-delta} were grown under atmospheric pressure and reduced pressure from Sr, Co and Fe tmhd precursors. The relationship between film composition and the composition of precursor solution was developed. The effects of deposition pressure on film morphology, structure and gas-tightness were also studied. The influence of phase purity of SrCosb1-xFesbxOsb{3-delta} films by the system total pressure was also studied. Copper films were deposited on porous substrates for the purpose of investigating the membrane fabrication process using Cu as a model material. The film morphology, microstructure, gas-tightness and other physical properties were characterized in a systematic manner. The copper deposition rates were investigated at different precursor concentrations and the deposition temperatures by using Aerosol-Assisted CVD (AACVD) of toluenen solutions of Cu(hfac)sb2 (hfac

  17. Reduced pressure MOCVD of C-axis oriented BiSrCaCuO thin films

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Norihito; Vigil, J.; Gardiner, R.; Kirlin, P. S.

    1990-01-01

    BiSrCaCuO thin films were deposited on MgO (100) single-crystal substrates by metalorganic chemical vapor deposition at 500 C and 2 torr using fluorinated beta-diketonate complexes of Sr, Ca, and Cu and triphenylbismuth. An inverted vertical reaction chamber allowed uniform film growth over large areas (7.7 cm diameter). The as-deposited films were amorphous mixtures of oxides and fluorides; a two-step annealing protocol (750 C + 850-870 C) was developed which gives c-axis oriented films of Bi2Sr2Ca1Cu2O(x). The postannealed films showed onsets in the resistive transition of 110 K, and zero resistivity was achieved by 83 K. Critical current densities as high as 11,000 A/sq cm were obtained at 25 K.

  18. Synthesis, characterization, and thermal properties of homoleptic rare-earth guanidinates: promising precursors for MOCVD and ALD of rare-earth oxide thin films.

    PubMed

    Milanov, Andrian P; Fischer, Roland A; Devi, Anjana

    2008-12-01

    Eight novel homoleptic tris-guanidinato complexes M[(N(i)Pr)(2)CNR(2)](3) [M = Y (a), Gd (b), Dy (c) and R = Me (1), Et (2), (i)Pr (3)] have been synthesized and characterized by NMR, CHN-analysis, mass spectrometry and infrared spectroscopy. Single crystal structure analysis revealed that all the compounds are monomers with the rare-earth metal center coordinated to six nitrogen atoms of the three chelating guanidinato ligands in a distorted trigonal prism geometry. With the use of TGA/DTA and isothermal TGA analysis, the thermal characteristics of all the complexes were studied in detail to evaluate their suitability as precursors for thin film deposition by MOCVD and ALD. The (i)Pr-Me(2)N-guanidinates of Y, Gd and Dy (1a-c) showed excellent thermal characteristics in terms of thermal stability and volatility. Additionally, the thermal stability of the (i)Pr-Me(2)N-guanidinates of Y and Dy (1a, c) in solution was investigated by carrying out NMR decomposition experiments and both the compounds were found to be remarkably stable. All these studies indicate that (i)Pr-Me(2)N-guanidinates of Y, Gd and Dy (1a-c) have the prerequisites for MOCVD and ALD applications which were confirmed by the successful deposition of Gd(2)O(3) and Dy(2)O(3) thin films on Si(100) substrates. The MOCVD grown films of Gd(2)O(3) and Dy(2)O(3) were highly oriented in the cubic phase, while the ALD grown films were amorphous.

  19. Electroluminescent ZnS:Mn films prepared by an MOCVD method based on dithiocarbamate precursors

    NASA Astrophysics Data System (ADS)

    Zavyalova, L. V.; Beletski, A. I.; Svechnikov, G. S.

    1999-05-01

    It is shown that electroluminescent ZnS:Mn films with luminance more than 0268-1242/14/5/013/img6 and luminous efficiency 0268-1242/14/5/013/img7 can be obtained by low-temperature deposition from Mn and Zn dithiocarbamates; subsequent thermal treatment of these films is not necessary. Starting materials were deposited on the substrate heated to a temperature of 220-0268-1242/14/5/013/img8C by spraying organic solution in air at atmospheric pressure. As a result homogeneous polycrystalline layers of ZnS:Mn with a growth rate of 60-0268-1242/14/5/013/img9 have been obtained. The electroluminescent characteristics of the thin films and structures based on various preparation and excitation conditions are presented. The possibility of application of these films as a planar light source is discussed.

  20. Double-sided reel-to-reel metal-organic chemical vapor deposition system of YBa{sub 2}Cu{sub 3}O{sub 7-δ} thin films

    SciTech Connect

    Zhang, Fei; Xiong, Jie Liu, Xin; Zhao, Ruipeng; Zhao, Xiaohui; Tao, Bowan; Li, Yanrong

    2014-07-01

    Two-micrometer thick YBa{sub 2}Cu{sub 3}O{sub 7-δ} (YBCO) films have been successfully deposited on both sides of LaAlO{sub 3} single crystalline substrates by using a home-made reel-to-reel metal-organic chemical vapor deposition (MOCVD) system, which has two opposite symmetrical shower heads and a special-designed heater. This technique can simultaneously fabricate double-sided films with high deposition rate up to 500 nm/min, and lead to doubling current carrying capability of YBCO, especially for coated conductors (CCs). X-ray diffraction analysis showed that YBCO films were well crystallized and highly epitaxial with the full width at half maximum values of 0.2° ∼ 0.3° for the rocking curves of (005) YBCO and 1.0° for Φ-scans of (103) YBCO. Scanning electron microscope revealed dense, crack-free, slightly rough surface with Ba-Cu-O precipitates. The films showed critical current density (J{sub c}, 77 K, 0 T) of about 1 MA/cm{sup 2}, and overall critical current of 400 A/cm, ascribed to the double-sided structure. Our results also demonstrated that the temperature and composition in the deposition zone were uniform, which made MOCVD preparation of low cost and high performance double-sided YBCO CCs more promising for industrialization.

  1. Effects of ambient background gases on YBCO plume propagation under film growth conditions: Spectroscopic, ion probe, and fast photographic studies

    SciTech Connect

    Geohegan, D.B.

    1991-09-01

    The formation, composition, and propagation of KrF laser-produced plasmas from Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-x} have been studied with emphasis on topics relevant to film growth by pulsed-laser deposition. Spatially and temporally resolved, high-resolution optical absorption and emission spectroscopy, fast ion probes, and fast photography (obtained with a gated, image-intensified CCD array detector (ICCD)) are employed to investigate both emitting and non-emitting species in the laser plume as well as the overall shape and propagation of the laser plasma in background gases of oxygen and xenon. Transient optical absorption spectroscopy is applied to study the composition of the plume of ejected material from the dense layer near the target surface to distances of several centimeters. Optical absorption persists long after the decay of plasma fluorescence, indicating a slower component to plume transport. The absorption of YO formed by YBCO ablation in vacuum and by-yttrium ablation in oxygen is presented. Fast electric ion probes are utilized to measure velocities and total collected charge of the positive ions in the expanding YBCO laser plasma from near-threshold, vacuum conditions into the high fluence, background gas conditions utilized for thin-film growth. The exponential attenuation of the positive ion flux transmitted through 50--300 mTorr background oxygen is measured and used to define an attenuation coefficient. The showing of the laser plasma and formation of shock structures due to gas collisions is studied by ion probe measurements and fast ICCD photography. A comparison between shock wave propagation and drag models is presented to describe the arrival time and shape of the ion probe current waveform with distance. 11 refs, 11 figs.

  2. Surface Passivation for 3-5 Semiconductor Processing: Stable Gallium Sulphide Films by MOCVD

    NASA Technical Reports Server (NTRS)

    Macinnes, Andrew N.; Jenkins, Phillip P.; Power, Michael B.; Kang, Soon; Barron, Andrew R.; Hepp, Aloysius F.; Tabib-Azar, Massood

    1994-01-01

    Gallium sulphide (GaS) has been deposited on GaAs to form stable, insulating, passivating layers. Spectrally resolved photoluminescence and surface recombination velocity measurements indicate that the GaS itself can contribute a significant fraction of the photoluminescence in GaS/GaAs structures. Determination of surface recombination velocity by photoluminescence is therefore difficult. By using C-V analysis of metal-insulator-semiconductor structures, passivation of the GaAs with GaS films is quantified.

  3. Control of carbon content in amorphous GeTe films deposited by plasma enhanced chemical vapor deposition (PE-MOCVD) for phase-change random access memory applications

    NASA Astrophysics Data System (ADS)

    Aoukar, M.; Szkutnik, P. D.; Jourde, D.; Pelissier, B.; Michallon, P.; Noé, P.; Vallée, C.

    2015-07-01

    Amorphous and smooth GeTe thin films are deposited on 200 mm silicon substrates by plasma enhanced—metal organic chemical vapor deposition (PE-MOCVD) using the commercial organometallic precursors TDMAGe and DIPTe as Ge and Te precursors, respectively. X-ray photoelectron spectroscopy (XPS) measurements show a stoichiometric composition of the deposited GeTe films but with high carbon contamination. Using information collected by Optical Emission Spectroscopy (OES) and XPS, the origin of carbon contamination is determined and the dissociation mechanisms of Ge and Te precursors in H2 + Ar plasma are proposed. As a result, carbon level is properly controlled by varying operating parameters such as plasma radio frequency power, pressure and H2 rate. Finally, GeTe films with carbon level as low as 5 at. % are obtained.

  4. Growth condition dependence of Mg-doped GaN film grown by horizontal atmospheric MOCVD system with three layered laminar flow gas injection

    NASA Astrophysics Data System (ADS)

    Tokunaga, H.; Waki, I.; Yamaguchi, A.; Akutsu, N.; Matsumoto, K.

    1998-06-01

    We developed a novel atmospheric pressure horizontal MOCVD system (SR2000) for the growth of III-nitride film. This system was designed for high-speed gas flow in order to suppress thermal convection and undesirable reactant gas reaction. We have grown Mg-doped GaN films using SR2000. We studied the bis-cyclopentadienyl magnesium (Cp 2Mg) flow rate dependence and growth temperature ( Tg) dependence of Mg-doped GaN. As a result, we have obtained p-type GaN film with hole carrier density of 8×10 17 cm -3 with a mobility of 7.5 cm 2/(V s) at the growth condition with Cp 2Mg flow rate of 0.1 μmol/min at Tg of 1025°C.

  5. The magnetisation profiles and ac magnetisation losses in a single layer YBCO thin film caused by travelling magnetic field waves

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Coombs, Timothy

    2015-05-01

    This paper studies the magnetisation and ac magnetisation losses caused by a travelling magnetic wave on a single-layer YBCO thin film. This work provides thorough investigations on how the critical magnetic field gradient has been changed by the application of a travelling wave. Several conditions were studied such as zero-field cooling (ZFC), field cooling (FC) and a delta-shaped trapped field. It was found that the travelling wave tends to attenuate the existing critical magnetic field gradients in all these conditions. This interesting magnetic behaviour can be well predicted by the finite element (FEM) software with the E-J power law and Maxwell’s equations. The numerical simulations show that the existing critical current density has been compromised after applying the travelling wave. The magnetisation profile caused by the travelling wave is very different from the standing wave, while the magnetisation based on the standing wave can be interpreted by the Bean model and constant current density assumption. Based on the numerical method, which has reliability that has been solidly proven in the study, we have extended the study to the ac magnetisation losses. Comparisons were made between the travelling wave and the standing wave for this specific YBCO sample. It was found that by applying the magnetic wave of the same amplitude, the ac magnetisation loss caused by the travelling wave is about 1/3 of that caused by the standing wave. These results are helpful in understanding the general magnetism problems and ac magnetisation loss in the travelling magnetic wave conditions such as inside a high temperature superconducting (HTS) rotating machine, etc.

  6. MOCVD (Ba{sub x}Sr{sub 1-x})Ti{sub 1+y}O{sub 3+z} (BST) thin films for high frequency tunable devices.

    SciTech Connect

    Baumann, P. K.; Kaufman, D. Y.; Im, J.; Auciello, O.; Streiffer, S. K.; Erck, R. A.; Giumarra, J.

    2001-01-01

    We have investigated the structural and electrical characteristics of (Ba{sub x}Sr{sub 1-x})Ti{sub 1+y}O{sub 3+z} (BST) thin films synthesized at 650{sup o}C on Pt/SiO{sub 2}/Si substrates using a large area, vertical metalorganic chemical vapor deposition (MOCVD) reactor equipped with a liquid delivery system. Films with a Ba/Sr ratio of 70/30 were studied, as determined using X-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). A substantial reduction of the dielectric loss was achieved when annealing the entire capacitor structure in air at 700{sup o}C. Dielectric tunability as high as 2.3:1 was measured for BST capacitors with the currently optimized processing conditions.

  7. Progress in fabrication of large magnetic sheilds by using extended YBCO thick films sprayed on stainless steel with the HVOF technique

    SciTech Connect

    Pavese, F.; Bergadano, E.; Ferri, D.

    1997-06-01

    Fabricating a full box-type magnetic shield, by spraying a thick film of commercial YBCO powder on stainless steel with the oxygen-fuel high-velocity technique (HVOF, also referred to as {open_quotes}continuous detonation spray{close_quotes} (CDS)), requires the solution of several specific problems since the design stage of the project. The design problems of this type of shield are examined and the results obtained in the early stages of the realization are discussed.

  8. Properties variation with composition of single-crystal Pb(Zr{sub x}Ti{sub 1-x})O{sub 3} thin films prepared by MOCVD

    SciTech Connect

    Foster, C.M.; Bai, G.R.; Li, Z.; Jammy, R.; Wills, L.A.; Hiskes, R.

    1995-12-01

    Single-crystal thin films covering the full range of PZT 0{le}x{le}1 have been deposited by metal-organic chemical vapor deposition (MOCVD). The films were grown on epitaxial, RF-sputter-deposited SrRuO{sub 3} thin film electrodes on (001) SrTiO{sub 3} substrates. X-ray diffraction, energy-dispersive electron spectroscopy and optical waveguiding were used to characterize the crystalline structure, composition, refractive index, and film thickness. We found that the PZT films were single-crystalline for all compositions exhibiting cube-on-cube epitaxy with the substrate with very high degrees of crystallinity and orientation. We report the systematic variations in the optical, dielectric, polarization, and transport properties as a function of composition and the epitaxy-induced modifications in the solid-solution phase diagram of this system. These films exhibited electronic properties which showed clear systematic variations with composition. High values of remnant polarization (30--55 {mu}C/cm{sup 2}) were observed at all ferroelectric compositions. Unlike previous studies, the dielectric constant exhibited a clear dependence on composition with values ranging from 225--650. Coercive fields decreased with increasing Zr concentration to a minimum of 20 kV/cm at the (70/30) composition. In addition, these films exhibited both high resistivity and dielectric-breakdown strength ({approximately}10{sup 13} {Omega}-cm at 100 kV/cm and >300 kV/cm, respectively) without any compensative doping.

  9. Investigation of the bulk pinning force in YBCO superconducting films with nano-engineered pinning centres

    NASA Astrophysics Data System (ADS)

    Crisan, A.; Dang, V. S.; Yearwood, G.; Mikheenko, P.; Huhtinen, H.; Paturi, P.

    2014-08-01

    For practical applications of superconducting materials in applied magnetic fields, artificial pinning centres in addition to natural ones are required to oppose the Lorentz force. These pinning centres are actually various types of defects in the superconductor matrix. The pinning centres can be categorised on their dimension (volume, surface, or point) and on their character (normal cores or Δκ cores). We have used the Dew Hughes approach to determine the types of pinning centres present in various samples, with various thicknesses, temperatures and nanostructured additions to the superconducting matrix. Results show that normal surface pinning centres are present throughout almost all the samples, as dominant pinning mechanism. Such 2D extended pinning centres are mainly due to dislocations, grain boundaries, nanorods. Strong normal point pinning centres were found to be common in BZO doped YBCO samples. Other types of pinning centres, in various (minor) concentrations were also found in some of the samples.

  10. Critical current anisotropy and pinning in (103) YBCO superconducting thin films on SrTiO3(110) substrates

    NASA Astrophysics Data System (ADS)

    Wu, K. H.; Huang, S. J.; Wang, S. J.; Chen, S. P.; Juang, J. Y.; Uen, T. M.; Gou, Y. S.

    1996-03-01

    High quality (103) oriented YBCO superconducting thin films with T c ≈89 K have been prepared by pulsed laser deposition on SrTiO3(110) substrates. The grain morphology of the films, as revealed by both scanning electron microscopy and atomic force microscopy, shows distinct brick wall structure. The critical current densities measured along (001) direction of the substrates are about an order of magnitude higher than that measured on the other in-plane direction with no apparent weak- link behavior observed. The critical current densities in both directions, however, show a similar linear temperature dependence over a wide temperature range, indicative of a flux-creep limited mechanism. The creep rate in both cases, as fit to the Anderson-Kim creep model, is of order of 1 which is about an order of magnitude higher than that of conventional type-II superconductors. Samples co-ablated with silver were also studied. Detail mechanisms of pinning as wall as grain morphology evolutions are discussed.

  11. Structural and optical properties of Ga{sub 2}O{sub 3}:In films deposited on MgO (1 0 0) substrates by MOCVD

    SciTech Connect

    Kong Lingyi; Ma Jin; Luan Caina; Zhu Zhen

    2011-08-15

    Ga{sub 2}O{sub 3}:In films with different indium (In) content x [x=In/(Ga+In) atomic ratio] have been deposited on MgO (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). Structural analyses revealed that the film deposited with actual In content (x') of 0.09 was an epitaxial film and the films with x'=0.18 and 0.37 had mixed-phase structures of monoclinic Ga{sub 2}O{sub 3} and bixbyite In{sub 2}O{sub 3}. The absolute average transmittance of the obtained films in the visible region exceeded 95%, and the band gap was in the range of 4.74-4.87 eV. Photoluminescence (PL) measurements were performed at room temperature, in which the visible luminescences were strong and could be seen by the naked eye. The strong emissions in the visible light region were proposed to originate from the gallium vacancies, oxygen deficiencies and other defects in these films. - Graphical abstract: Low magnification XTEM (a), HRTEM (b) and SAED (c) micrographs of the interface area between Ga{sub 1.82}In{sub 0.18}O{sub 3} film and MgO substrate have showed the Ga{sub 1.82}In{sub 0.18}O{sub 3} is an epitaxial film. Highlights: > Ga{sub 1.82}In{sub 0.18}O{sub 3} epitaxial film was deposited on MgO(1 0 0) substrate. > The transmittance of the Ga{sub 2}O{sub 3}:In films in the visible region exceeded 95%. > Strong emissions were observed in the photoluminescence measurements of the films.

  12. Chemical Solution Based Epitaxial Oxide Filmes on Biaxially Textured Ni-W Substrates with Improved Out-of-Plane Texture for YBCO Coated Conductors

    SciTech Connect

    Bhuiyan, Md S; Paranthaman, Mariappan Parans; Sathyamurthy, Srivatsan

    2007-01-01

    Epitaxial films of rare-earth (RE) niobates (where the rare earth includes La, Ce, and Nd) and lanthanum tantalate with pyrochlore structures were grown directly on biaxially textured nickel-3 at.% tungsten (Ni-W) substrates using a chemical solution deposition (CSD) process. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis revealed the surface morphology of the films to be smooth and homogeneous. Detailed X-ray diffraction analysis showed that the films of pyrochlore RE niobate and La-tantalate are highly textured with cube-on-cube epitaxy. The overall texture quality of the films was investigated by measuring the full-width half-maximum (FWHM) of the (004) and (222) rocking curves. We observed a sharper texture for both lanthanum niobate (La{sub 3}NbO{sub 7}) and lanthanum tantalate (La{sub 3}TaO{sub 7}) films compared to the underlying Ni-W substrate, though they have a larger lattice misfit with the Ni-W substrates. These results were comparable to the texture improvement observed in vacuum-deposited Y{sub 2}O{sub 3} seed layers. Texture improvement in the seed layer is the key towards obtaining YBCO films with a higher critical current density. Hence, solution-deposited La{sub 3}NbO{sub 7} and La{sub 3}TaO{sub 7} films can be used as a seed layer towards developing all metalorganic-deposited (MOD) buffer/YBCO architectures.

  13. Advanced high temperature superconductor film-based process using RABiTS

    SciTech Connect

    Goyal, A.; Hawsey, R.A.; Hack, J.; Moon, D.

    2000-01-01

    The purpose of this Cooperative Research and Development Agreement (CRADA) between Lockheed Martin Energy Research Corporation (Contractor), Managing contractor for Oak Ridge National Laboratory (ORNL) and Midwest Superconductivity, Inc. (MSI) and Westinghouse Science and Electric Company (WEC) was to develop the basis for a commercial process for the manufacturing of superconducting tape based on the RABiTS technology developed at ORNL. The chosen method for deposition of YBCO films on RABiTS was Metal Organic chemical Vapor Deposition (MOCVD).

  14. MOCVD-derived highly transparent, conductive zinc- and tin-doped indium oxide thin films: precursor synthesis, metastable phase film growth and characterization, and application as anodes in polymer light-emitting diodes.

    PubMed

    Ni, Jun; Yan, He; Wang, Anchuang; Yang, Yu; Stern, Charlotte L; Metz, Andrew W; Jin, Shu; Wang, Lian; Marks, Tobin J; Ireland, John R; Kannewurf, Carl R

    2005-04-20

    Four diamine adducts of bis(hexafluoroacetylacetonato)zinc [Zn(hfa)(2).(diamine)] can be synthesized in a single-step reaction. Single crystal X-ray diffraction studies reveal monomeric, six-coordinate structures. The thermal stabilities and vapor phase transport properties of these new complexes are considerably greater than those of conventional solid zinc metal-organic chemical vapor deposition (MOCVD) precursors. One of the complexes in the series, bis(1,1,1,5,5,5-hexafluoro-2,4-pentadionato)(N,N'-diethylethylenediamine)zinc, is particularly effective in the growth of thin films of the transparent conducting oxide Zn-In-Sn-O (ZITO) because of its superior volatility and low melting point of 64 degrees C. ZITO thin films with In contents ranging from 40 to 70 cation % (a metastable phase) were grown by low-pressure MOCVD. These films exhibit conductivity as high as 2900 S/cm and optical transparency comparable to or greater than that of commercial Sn-doped indium oxide (ITO) films. ZITO films with the nominal composition of ZnIn(2.0)Sn(1.5)O(z)() were used in fabrication of polymer light-emitting diodes. These devices exhibit light outputs and current efficiencies almost 70% greater than those of ITO-based control devices. PMID:15826201

  15. Vaporization of a mixed precursors in chemical vapor deposition for YBCO films

    NASA Technical Reports Server (NTRS)

    Zhou, Gang; Meng, Guangyao; Schneider, Roger L.; Sarma, Bimal K.; Levy, Moises

    1995-01-01

    Single phase YBa2Cu3O7-delta thin films with T(c) values around 90 K are readily obtained by using a single source chemical vapor deposition technique with a normal precursor mass transport. The quality of the films is controlled by adjusting the carrier gas flow rate and the precursor feed rate.

  16. Growth and barium zirconium oxide doping study on superconducting M-barium copper oxide (M = yttrium, samarium) films using a fluorine-free metal organic decomposition process

    NASA Astrophysics Data System (ADS)

    Lu, Feng

    We present a fluorine-free metal organic deposition (F-free MOD) process - which is possibly a rapid and economic alternative to commercial trifluoroacetates metal organic deposition (TFA-MOD) and metal organic chemical vapor deposition (MOCVD) processes - for the fabrication of high quality epitaxial high temperature superconducting YBa2Cu3O7-x (YBCO) films on both Rolling-Assisted Biaxially Textured Substrates (RABiTS) and single crystal substrates. We first studied the growth of YBCO and SmBCO films, and their resulting microstructure and superconducting properties. We produced epitaxial c-axis YBCO films with high critical current density (Jc) in excess of 106 A/cm2 at 77K in self field at the thickness of ˜1 mum. Because industrial applications demand high quality YBCO films with very high Jc, we investigated introducing BaZrO3 (BZO) nano-pinning sites in HTS thin films by our F-free MOD technique to improve Jc and the global pinning force (Fp). BZO-doped YBCO films were fabricated by adding extra Ba and Zr in the precursor solutions, according to the molar formula 1 YBCO + x BZO. We found the BZO content affects the growth of YBCO films and determined the optimum BZO content which leads to the most effective pinning enhancement and the least YBCO degradation. We achieved the maximum pinning force of ˜ 10 GN/m3 for x = 0.10 BZO-doped, 200 nm thick YBCO film on SrTiO3 single crystal substrates by modifying the pyrolysis from a one-step to a two-plateau decomposition during the F-free MOD process. For growing optimum BZO-doped YBCO films on RABiTS substrates, the F-free MOD process was also optimized by adjusting the maximum growth temperature and growth time to achieve stronger pinning forces. Through-process quenching studies indicate that BZO form 10--25 nm nanoparticles at the early stage of the process and are stable during the following YBCO growth, demonstrating that chemically doping YBCO films with BZO using the F-free MOD process is a very effective

  17. Novel Neo-Pentoxide Precursors for MOCVD Thin Films of TiO(2) and ZrO(2).[1

    SciTech Connect

    Boyle, Timothy J.; Francisco, Laila P.; Gallegos, Jesus J.; Rodriguez, Mark A.; Ward, Timothy L.

    1999-07-14

    Two novel Group IV precursors, titanium (IV) neo-pentoxide, [Ti({mu}-ONep)(ONep){sub 3}]{sub 2} (l), and zirconium (IV) neo-pentoxide, [Zr({mu}-ONep)(ONep){sub 3}]{sub 2} (2), were reported to possess relatively high volatility at low temperatures. These compounds were therefore investigated as MOCVD precursors using a lamp-heated cold-wall CVD reactor and direct sublimation without carrier gas. The ONep derivatives proved to be competitive precursors for the production of thin films of the appropriate MO{sub 2} (M = Ti or Zr) materials in comparison to other metallo-organic precursors. Compound 1 was found to sublime at 120 C with a deposition rate of {approximately}0.350 {mu}m/min onto a substrate at 330 C forming the anatase phase with < 1% residual C found in the final film. Compound 2 was found to sublime at 160 C and deposited as crystalline material at 300 C with < 1% residual C found in the final film. A comparison to standard alkoxide and {beta}-diketonates is presented where appropriate.

  18. Photodetectors of slit and sandwich types based on CdS and CdS1-xSex films obtained using MOCVD method from dithiocarbamates

    NASA Astrophysics Data System (ADS)

    Zavyalova, Ludmila V.; Svechnikov, Sergey V.; Tchoni, Vladimir G.

    1997-04-01

    Here we report the results of working out an original, simple in control and not requiring expensive equipment MOCVD-method for depositing films of semiconductor compounds A2B6. Dithiocarbamates (DTC) are used as starting materials. The compounds are stable, easily synthesized, cheap and low toxic. Atoms of metal and sulfur in the DTC are strongly bonded. The DTC could be easily dissolved in various organic solvents. The experimental unit for film deposition comprises a spraying apparatus, a substrate heater, and a quartz cylinder for separation of a reaction zone from ambience. The process of film deposition is carried out in air conditions. Films of CdS, bright-yellow, transparent, having mirror smooth surface at thickness less than 2 mkm and rough surface at thickness 8-12 mkm, were deposited by spraying cadmium dithiocarbamate, that is DTC with radical C2H5, solution in pyridine on substrates heated to 240-280 degrees C. Deposition rate was 60-90 nm/min. Films obtained were of hexagonal modification, polycrystalline, textured, with low, at the level of centipercents content of oxygen and carbon. Slit type photodetectors based on CdS and CdS1-xSex of 1.0 mkm thickness have dark conductivity (sigma) d equals 10-9 divided by 10-8 Ohm-1cm-1 and photoconductivity (sigma) ph equals 10-2 divided by 10-1 Ohm-1cm-1 at 200 lux. Industrially suitable technology for production of photopotentiometer on the base of these films was developed. Sandwich-type photodetectors In2S3 - CdS: Cu, Cl - In with 8-12 mkm thickness have the same value of photoconductivity and the light-to-dark ratio is 106 divided by 107. Based on sandwich-type photodetectors, a hybrid structure of pyroelectric-photodetector as a resonant-type coordinate-sensitive detector was developed.

  19. Compact spherical neutron polarimeter using high-T(c) YBCO films.

    PubMed

    Wang, T; Parnell, S R; Hamilton, W A; Li, F; Washington, A L; Baxter, D V; Pynn, R

    2016-03-01

    We describe a simple, compact device for spherical neutron polarimetry measurements at small neutron scattering angles. The device consists of a sample chamber with very low (<0.01 G) magnetic field flanked by regions within which the neutron polarization can be manipulated in a controlled manner. This allows any selected initial and final polarization direction of the neutrons to be obtained. We have constructed a prototype device using high-T(c) superconducting films and mu-metal to isolate regions with different magnetic fields and tested device performance in transmission geometry. Finite-element methods were used to simulate the device's field profile and these have been verified by experiment using a small solenoid as a test sample. Measurements are reported using both monochromatic and polychromatic neutron sources. The results show that the device is capable of extracting sample information and distinguishing small angular variations of the sample magnetic field. As a more realistic test, we present results on the characterization of a 10 μm thick Permalloy film in zero magnetic field, as well as its response to an external magnetic field. PMID:27036785

  20. Interplay between as grown defects and heavy ion induced defects in YBCO films

    SciTech Connect

    Crescio, E.; Gerbaldo, R.; Ghigo, G.; Gozzelino, L.; Camerlingo, C.; Monaco, A.; Nappi, C.; Cuttone, G.; Rovelli, A.

    1999-04-20

    The dominating pinning mechanism in YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} thin film has been investigated by means of resistivity and ac susceptibility measurements and by structural characterizations. The aim of the work is to determine optimal pinning conditions in order to prevent the field-induced drop of the critical current density. The Clem and Sanchez model is used to extract critical current values from the susceptibility data. In this framework, the role of columnar-like defects is extensively studied. The formation of columnar pins was promoted by a suitable modification in the preparation process. In addition, columnar tracks of different density were induced by Au-ion irradiation. Analysis of the critical current dependence on the magnetic field reveals that linearly-correlated defects are effective in improving the vortex lattice stability in matching regions of field and temperature.

  1. Advanced light-scattering materials: Double-textured ZnO:B films grown by LP-MOCVD

    NASA Astrophysics Data System (ADS)

    Addonizio, M. L.; Spadoni, A.; Antonaia, A.

    2013-12-01

    Double-textured ZnO:B layers with enhanced optical scattering in both short and long wavelength regions have been successfully fabricated using MOCVD technique through a three step process. Growth of double-textured structures has been induced by wet etching on polycrystalline ZnO surface. Our double-layer structure consists of a first ZnO:B layer wet etched and subsequently used as substrate for a second ZnO:B layer deposition. Polycrystalline ZnO:B layers were etched by utilizing diluted solutions of fluoridic acid (HF), chloridric acid (HCl) and phosphoric acid (H3PO4) and their effect on surface morphology modification was systematically investigated. The morphology of the second deposited ZnO layer strongly depended on the surface properties of the etched ZnO first layer. Growth of cauliflower-like texture was induced by protrusions presence on the HCl etched surface. Optimized double-layer structure shows a cauliflower-like double texture with higher RMS roughness and increased spectral haze values in both short and long wavelength regions, compared to conventional pyramidal-like single texture. Furthermore, this highly scattering structure preserves excellent optical and electrical properties.

  2. High flux pinning efficiency by columnar defects dispersed in three directions in YBCO thin films

    NASA Astrophysics Data System (ADS)

    Sueyoshi, Tetsuro; Nishimura, Takahiro; Fujiyoshi, Takanori; Mitsugi, Fumiaki; Ikegami, Tomoaki; Ishikawa, Norito

    2016-10-01

    A systematic investigation of flux pinning by widely direction-dispersed columnar defects (CDs) in YBa2Cu3O y thin films was carried out by using heavy-ion irradiation: a parallel configuration of CDs aligned along the c-axis, and two trimodal splay configurations composed of CDs crossing at 0° and ± 45° relative to the c-axis, where the splay plane defined by the three irradiation angles is perpendicular (trimodal-A) or parallel (trimodal-B) to the transport current direction. The trimodal configurations show high pinning efficiency over a wide range of magnetic field orientations compared to the parallel one at low magnetic field. In particular, trimodal-B shows the higher critical current density of the two trimodal configurations. The crossed CDs at ± 45° in the trimodal configurations provide uncorrelated flux pinning at B || c due to the large tilting angle off the c-axis, which effectively reinforce the flux pinning of CDs parallel to the c-axis. This assist effect is more remarkable for trimodal-B: a kink sliding motion of flux lines along the CDs is more effectively reduced by the splay plane, not only at B || c but also at inclined magnetic fields off the c-axis.

  3. Metal-Organic Chemical Vapor Deposition (MOCVD) Synthesis of Heteroepitaxial Pr0.7Ca0.3MnO3 Films: Effects of Processing Conditions on Structural/Morphological and Functional Properties

    PubMed Central

    Catalano, Maria R; Cucinotta, Giuseppe; Schilirò, Emanuela; Mannini, Matteo; Caneschi, Andrea; Lo Nigro, Raffaella; Smecca, Emanuele; Condorelli, Guglielmo G; Malandrino, Graziella

    2015-01-01

    Calcium-doped praseodymium manganite films (Pr0.7Ca0.3MnO3, PCMO) were prepared by metal-organic chemical vapor deposition (MOCVD) on SrTiO3 (001) and SrTiO3 (110) single-crystal substrates. Structural characterization through X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) analyses confirmed the formation of epitaxial PCMO phase films. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) characterization was used to confirm lateral and vertical composition and the purity of the deposited films. Magnetic measurements, obtained in zero-field-cooling (ZFC) and field-cooling (FC) modes, provided evidence of the presence of a ferromagnetic (FM) transition temperature, which was correlated to the transport properties of the film. The functional properties of the deposited films, combined with the structural and chemical characterization collected data, indicate that the MOCVD approach represents a suitable route for the growth of pure, good quality PCMO for the fabrication of novel spintronic devices. PMID:26478849

  4. Metal-Organic Chemical Vapor Deposition (MOCVD) Synthesis of Heteroepitaxial Pr0.7Ca0.3MnO3 Films: Effects of Processing Conditions on Structural/Morphological and Functional Properties.

    PubMed

    Catalano, Maria R; Cucinotta, Giuseppe; Schilirò, Emanuela; Mannini, Matteo; Caneschi, Andrea; Lo Nigro, Raffaella; Smecca, Emanuele; Condorelli, Guglielmo G; Malandrino, Graziella

    2015-08-01

    Calcium-doped praseodymium manganite films (Pr0.7Ca0.3MnO3, PCMO) were prepared by metal-organic chemical vapor deposition (MOCVD) on SrTiO3 (001) and SrTiO3 (110) single-crystal substrates. Structural characterization through X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) analyses confirmed the formation of epitaxial PCMO phase films. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) characterization was used to confirm lateral and vertical composition and the purity of the deposited films. Magnetic measurements, obtained in zero-field-cooling (ZFC) and field-cooling (FC) modes, provided evidence of the presence of a ferromagnetic (FM) transition temperature, which was correlated to the transport properties of the film. The functional properties of the deposited films, combined with the structural and chemical characterization collected data, indicate that the MOCVD approach represents a suitable route for the growth of pure, good quality PCMO for the fabrication of novel spintronic devices. PMID:26478849

  5. Indium droplet formation in InGaN thin films with single and double heterojunctions prepared by MOCVD

    NASA Astrophysics Data System (ADS)

    Chen, Yung-Sheng; Liao, Che-Hao; Kuo, Chie-Tong; Tsiang, Raymond Chien-Chao; Wang, Hsiang-Chen

    2014-07-01

    Indium gallium nitride (InGaN) samples with single heterojunction (SH) and double heterojunction (DH) were prepared using metal-organic chemical vapor deposition. SH has a layer of InGaN thin film (thicknesses, 25, 50, 100, and 200 nm) grown on an uGaN film (thickness, 2 μm). The DH samples are distinguished by DH uGaN film (thickness, 120 nm) grown on the InGaN layer. Reciprocal space mapping measurements reveal that the DH samples are fully strained with different thicknesses, whereas the strain in the SH samples are significantly relaxed with the increasing thickness of the InGaN film. Scanning electron microscopy results show that the surface roughness of the sample increases when the sample is relaxed. High-resolution transmission electron microscopy images of the structure of indium droplets in the DH sample indicate that the thickness of the InGaN layer decreases with the density of indium droplets. The formation of these droplets is attributed to the insufficient kinetic energy of indium atom to react with the elements of group V, resulting to aggregation. The gallium atoms in the GaN thin film will not be uniformly replaced by indium atoms; the InGaN thin film has an uneven distribution of indium atoms and the quality of the epitaxial layer is degraded.

  6. Metal-organic chemical vapor deposition of cerium oxide, gallium-indium-oxide, and magnesium oxide thin films: Precursor design, film growth, and film characterization

    NASA Astrophysics Data System (ADS)

    Edleman, Nikki Lynn

    A new class of volatile, low-melting, fluorine-free lanthanide metal-organic chemical vapor deposition (MOCVD) precursors has been developed. The neutral, monomeric cerium, neodymium, gadolinium, and erbium complexes are coordinatively saturated by a versatile, multidentate, ether-functionalized beta-ketoiminate ligand, and complex melting point and volatility characteristics can be tuned by altering the alkyl substituents on the ligand periphery. Direct comparison with lanthanide beta-diketonate complexes reveals that the present precursor class is a superior choice for lanthanide oxide MOCVD. Epitaxial CeO 2 buffer layer films have been grown on (001) YSZ substrates by MOCVD at significantly lower temperatures than previously reported using one of the newly developed cerium precursors. High-quality YBCO films grown on these CeO2 buffer layers by POMBE exhibit very good electrical transport properties. The cerium complex has therefore been explicitly demonstrated to be a stable and volatile precursor and is attractive for low-temperature growth of coated conductor multilayer structures by MOCVD. Gallium-indium-oxide thin films (GaxIn2-xO 3), x = 0.0˜1.1, have been grown by MOCVD using the volatile metal-organic precursors In(dpm)3 and Ga(dpm)3. The films have a homogeneously Ga-substituted, cubic In2O3 microstructure randomly oriented on quartz or heteroepitaxial on (100) YSZ single-crystal substrates. The highest conductivity of the as-grown films is found at x = 0.12. The optical transmission window and absolute transparency of the films rivals or exceeds that of the most transparent conductive oxides known. Reductive annealing results in improved charge transport characteristics with little loss of optical transparency. No significant difference in electrical properties is observed between randomly oriented and heteroepitaxial films, thus arguing that carrier scattering effects at high-angle grain boundaries play a minor role in the film conductivity mechanism

  7. Low-cost and high-power-density resistive fault-current limiting elements using YBCO thin films and Au-Ag alloy shunt layers

    NASA Astrophysics Data System (ADS)

    Yamasaki, H.; Arai, K.; Furuse, M.; Kaiho, K.; Nakagawa, Y.

    2006-06-01

    We propose a new design for the high-temperature superconducting thin-film faultcurrent limiter (FCL), which uses high-resistivity Au-Ag alloy shunt layers instead of the pure gold (or silver) shunt layers conventionally used. An FCL element (5 mm wide and 40 mm long) with a YBCO thin film (THEVA) and a parallel inductively-wound shunt resistor successfully withstood very high electric field (> 44 Vpeak/cm) for 5 cycles (0.1 sec) after switching, and achieved a very high switching power density, ~2.0 kVA/cm2. We confirmed similar maximum tolerable electric field (>40 Vpeak/cm, limited by power supply) in a larger sample (1 cm × 6 cm). The composition of our FCL element is very simple, and the achieved power density is more than five times higher than conventional devices, which leads to a dramatic reduction in the amount of expensive superconducting thin films. We made a conceptual design and cost estimation of our FCL elements used in a typical 6.6 kV FCL.

  8. Preparation and characterization of Al{sub 2x}In{sub 2−2x}O{sub 3} films deposited on MgO (1 0 0) by MOCVD

    SciTech Connect

    Li, Zhao; Ma, Jin Zhao, Cansong; Du, Xuejian; Mi, Wei; Luan, Caina; Feng, Xianjin

    2015-07-15

    Highlights: • Ternary Al{sub 2x}In{sub 2−2x}O{sub 3} alloy films were deposited on MgO (1 0 0) by MOCVD. • The microstructure of the Al{sub 2x}In{sub 2−2x}O{sub 3} films were studied upon HRTEM. • Al{sub 2x}In{sub 2−2x}O{sub 3} alloy films exhibited great optical transparency in the visible wavelength range. • The band gap of the Al{sub 2x}In{sub 2−2x}O{sub 3} films can be modulated by controlling the Al contents in the samples. - Abstract: The ternary Al{sub 2x}In{sub 2−2x}O{sub 3} films with different compositions x[Al/(Al + In) atomic ratio] have been fabricated on the MgO (1 0 0) substrates by the metal organic chemical vapor deposition (MOCVD) method. The influence of different Al contents on the structural, optical and electrical properties of Al{sub 2x}In{sub 2−2x}O{sub 3} films has been studied. The structural studies reveal a change from single crystalline structure of cubic In{sub 2}O{sub 3} to amorphous as the Al content increases. The average transmittances of all samples in the visible range are over 80%. The optical band gap is observed to increase monotonically from 3.67 to 5.38 eV as the Al content increases from 0.1 to 0.9.

  9. Photoelectron spectroscopy study of AlN films grown on n-type 6H-SiC by MOCVD

    NASA Astrophysics Data System (ADS)

    Liang, F.; Chen, P.; Zhao, D. G.; Jiang, D. S.; Zhao, Z. J.; Liu, Z. S.; Zhu, J. J.; Yang, J.; Liu, W.; He, X. G.; Li, X. J.; Li, X.; Liu, S. T.; Yang, H.; Liu, J. P.; Zhang, L. Q.; Zhang, Y. T.; Du, G. T.

    2016-09-01

    Photoelectron spectroscopy has been employed to analyze the content and chemical states of the elements on the surface of AlN films with different thickness, which are synthesized by metalorganic chemical vapor deposition on the n-type SiC substrates under low pressure. It is found that, besides the carbon and gallium on the AlN surface, the atom percentage of surface oxygen increases from 4.9 to 8.4, and the electron affinity also increases from 0.36 to 0.97 eV, when the thickness of AlN films increase from 50 to 400 nm. Furthermore, accompanying with the high-resolution XPS spectra of the O 1s, it is speculated that surface oxygen may be the major influence on the electron affinity, where the surface oxygen changes the surface chemical states through replacing N to form Al-O bond and Ga-O bond, although there are also a few of Ga and C contaminations in the chemical sate of Ga-O and C-C, respectively.

  10. Cryolubricity of YBCO powder deposits

    NASA Astrophysics Data System (ADS)

    Stevens, Keeley M.; Krim, Jacqueline

    2010-03-01

    Motivated by recent reports of superconductivity-dependent friction [1] in macroscopic pin-on-disk measurements of steel on YBCO, [2] we have investigated the tribological properties of YBCO powder deposits on metal electrodes of a quartz crystal microbalance (QCM). Measurements are performed as a function of temperature over the range 80 - 300K, by monitoring the frequency and amplitude of the QCM both in the presence and absence of adsorbed nitrogen film layers. A pulsed magnetic field was applied to isolate the effect of superconductivity at and around the transition temperature. The powder deposits produce negative shifts in the QCM fundamental frequency, an indication of the strength of their attachment to the surface. The shifts exhibit structure as the temperature passes through the superconducting transition temperature, but the presumed drop in friction is not so large as to produce a decoupling effect which would lead to positive shifts. [3] Measurements on alternate QCM electrodes in the presence of adsorbed film layers are ongoing and will be reported on. Funding provided by NSF DMR. [4pt] [1] Highland, M. and Krim, J. Phys. Rev. Lett. 2006, 96, 226107.[0pt] [2] Ding, Q. et al. Wear 2008, 265, 1136.[0pt] [3] Dybwad, G.L. J. Appl. Phys. 1985, 58, 2789.

  11. MOCVD growth and characterization of (Ba{sub x}Sr{sub 1{minus}x})Ti{sub 1+y}O{sub 3+z} thin films for high frequency devices

    SciTech Connect

    Baumann, P. K.; Streiffer, S. K.; Im, J.; Baldo, P.; McCormick, A.; Auciello, O.; Kaufman, D. Y.; Erck, R. A.; Giumarra, J.; Zebrowski, J.

    2000-01-18

    The authors have investigated the structural and electrical characteristics of (Ba{sub x}Sr{sub 1{minus}x})Ti{sub 1+y}O{sub 3+z} (BST) thin films. The BST thin films were deposited at 650 C on platinized silicon with good thickness and composition uniformity using a large area, vertical liquid-delivery metalorganic chemical vapor deposition (MOCVD) system. The (Ba+Sr)/Ti ratio of the BST films was varied from 0.96 to 1.05 at a fixed Ba/Sr ratio of 70/30, as determined using x-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). Patterned Pt top electrodes were deposited onto the BST films at 350 C through a shadow mask using electron beam evaporation. Annealing the entire capacitor structure in air at 700 C after deposition of top electrodes resulted in a substantial reduction of the dielectric loss. Useful dielectric tunability as high as 2.3:1 was measured.

  12. YBCO coated conductors on highly textured Pd-buffered Ni-W tape

    NASA Astrophysics Data System (ADS)

    Celentano, G.; Galluzzi, V.; Mancini, A.; Rufoloni, A.; Vannozzi, A.; Augieri, A.; Petrisor, T.; Ciontea, L.; Gambardella, U.

    2006-06-01

    High critical current density YBa2Cu3O7-x (YBCO) coated conductors were obtained on cube textured Ni-W. The use of a Pd transient layer as a first buffer led to a sharp out-of-plane grains alignment of the CeO2/YSZ/CeO2 buffer layer. YBCO films grown on this template exhibit an out-of-plane orientation with a full width at half maximum of about 3°, less than 50% of the respective starting Ni-W value. Despite the complete interdiffusion between Ni-W and Pd after the YBCO film deposition, the coated conductors exhibit good film adherence as well as a crack free and smooth surface of the YBCO film. YBCO thin films show critical temperature values above than 88 K and a critical current density of 2.1 MA/cm2 at 77 K and self field.

  13. Reel-to-reel fabrication of meter-long YBCO coated conductor

    NASA Astrophysics Data System (ADS)

    Yang, J.; Zhang, H.; Wang, S. M.; Lin, C. G.; Shi, D. Q.; Dou, S. X.

    2011-04-01

    YBa 2Cu 3O 7-δ (YBCO) superconductors were coated on the CeO 2/YSZ/Y 2O 3 buffered Ni-5at%W tapes by a reel-to-reel pulsed laser deposition (PLD). The process of a multi-layer deposition of YBCO film was explored. X-ray diffraction texture measurements showed good both in-plane and out of plane crystalline orientations in YBCO films. The average values calculated at a full width at half maximum (FWHM) of the peaks from phi-scans ( φ) and omega ( ω) scans for one meter-long YBCO tape were 7.49° and 4.71°, respectively. The critical current ( Ic) was over 200 A/cm-width at 77 K and under self-field for meter-long YBCO tape. The critical transition temperature of the YBCO tape was typically as 90.1 K with 0.5 K transition widths.

  14. Effect of Co-doping on Microstructural, Crystal Structure and Optical Properties of Ti1-xCOxO2 Thin films Deposited on Si Substrate by MOCVD Method

    NASA Astrophysics Data System (ADS)

    Supriyanto, E.; Sutanto, H.; Subagio, A.; Saragih, H.; Budiman, M.; Arifin, P.; Sukirno, Barmawi, M.

    2008-03-01

    Ti1-xCOxO2 thin films have been grown on n-type Si(100) substrates by metal organic vapor deposition (MOCVD) using titanium (IV) isopropoxide (TTIP) and tris (2,2,6,6-tetramethyl-3, 5-heptanedionato) cobalt (III) as metal organic precursors. The parameter deposition, such as: bubbler temperature of TTIP Tb(Ti) = 50 °C; substrate temperature Ts = 450 °C; bubbler pressure Pb(Ti) = 260 Torr; flow rate of Ar gas through TTIP precursor Ar(Ti) = 100 sccm (standard cubic centimeters per minute) and flow rate of oxygen gas O2 = 60 sccm were found as optimal deposition parameters. The thin films deposited were have rutile (002) crystal plane, whereas those deposited at other parameter were mixing of anatase and rutile phases. Co dopant with concentration of up to 5.77% was not changes the structure of TiO2. Increase of Co incorporated in thin films was decreasing of band-gap energy.

  15. Mechanism of thickness dependence of critical current density in HTS YBCO film and its elimination using nano-engineering

    NASA Astrophysics Data System (ADS)

    Wang, Xiang

    The most promising characteristic of a High Temperature Superconductor (HTS) is its ability to carry larger electrical current at liquid nitrogen boiling temperature and strong applied magnetic field with minimal dissipation. Numerous large scale applications such as HTS transmission cables, HTS magnets and HTS motors have been developed using HTS materials. The major limitation that prevents its wide commercialization is its high cost-to-performance ratio. However, the effort to further improve HTS current carrying capability is jeopardized by a mysterious thickness dependence of the critical current density (Jc) --- Jc monotonically decreases with increasing thickness (t) at 77 K and self-field (SF). This poses a great challenge for both HTS applications and the understanding of vortex dynamics. What further complicates this issue is the complex defect structure in HTS films as well as the creep nature of magnetic vortices at a finite temperature. After a systematic study of the temperature and magnetic field effects on Jc--t, we conclude that Jc--t is most likely the result of a collective pinning effect dictated by a random pinning potential. Besides that, thermal fluctuations also alter Jc--t in a predictable way. Therefore, by either modifying the vortex structure or pinning structure, J c--t can be eliminated. Indeed, a thin film J c has been restored in a HTS/insulator/HTS trilayer while the magnetic coupling is weakened. Moreover, Jc--t has been removed when the random distributed point pins are overpowered by strong linear defects.

  16. Grain morphology of YBCO coated superconductors prepared by spin process on Ni substrate

    NASA Astrophysics Data System (ADS)

    Liu, C. F.; Du, S. J.; Yan, G.; Xi, W.; Wu, X.; Pang, Y.; Wang, F. Y.; Liu, X. H.; Feng, Y.; Zhang, P. X.; Wu, X. Z.; Zhou, L.

    2003-04-01

    The YBCO thick films with c-axis preferred orientation were prepared by spin and printing processes on Ni substrates (including cold rolling Ni, cube textured Ni, and cube textured Ni+ self-oxided NiO ). The results show that the chrysanthemum (or spherulite) and polygon morphology grains dominate the microstructure of YBCO films. The chrysanthemum size is about 0.2-0.5 mm range, some reaches 1 mm, and polygon grains normally are placed in the center of the chrysanthemum grains. No chrysanthemum grains appear in the thick films prepared on the substrate with Ag or YBCO intermediate layers.

  17. Influence of Al content on the properties of ternary Al{sub 2x}In{sub 2−2x}O{sub 3} alloy films prepared on YSZ (1 1 1) substrates by MOCVD

    SciTech Connect

    Feng, Xianjin; Zhao, Cansong; Li, Zhao; Luo, Yi; Ma, Jin

    2015-10-15

    Highlights: • Al{sub 2x}In{sub 2−2x}O{sub 3} films were prepared on the Y-stabilized ZrO{sub 2} (1 1 1) substrates by MOCVD at 700 °C. • A phase transition from the bixbyite In{sub 2}O{sub 3} structure to the amorphous structure was observed. • The lowest resistivity of 4.7 × 10{sup −3} Ω cm was obtained for the Al{sub 0.4}In{sub 1.6}O{sub 3} film. • Tunable optical band gap from 3.7 to 4.8 eV was obtained. - Abstract: The ternary Al{sub 2x}In{sub 2−2x}O{sub 3} films with different Al contents of x [Al/(Al + In) atomic ratio] have been fabricated on the Y-stabilized ZrO{sub 2} (1 1 1) substrates by metal organic chemical vapor deposition at 700 °C. The structural, electrical and optical properties of the films as a result of different Al contents (x = 0.1–0.9) were investigated in detail. With the increase of Al content from 10% to 90%, a phase transition from the bixbyite In{sub 2}O{sub 3} structure with a single orientation along (1 1 1) to the amorphous structure was observed. The minimum resistivity of 4.7 × 10{sup −3} Ω cm, a carrier concentration of 1.4 × 10{sup 20} cm{sup −3} and a Hall mobility of 9.8 cm{sup 2} v{sup −1} s{sup −1} were obtained for the sample with x = 0.2. The average transmittances for the Al{sub 2x}In{sub 2−2x}O{sub 3} films in the visible range were all over 78% and the optical band gap of the films could be tuned from 3.7 to 4.8 eV.

  18. Study of the optical properties and structure of ZnSe/ZnO thin films grown by MOCVD with varying thicknesses

    NASA Astrophysics Data System (ADS)

    Jabri, S.; Amiri, G.; Sallet, V.; Souissi, A.; Meftah, A.; Galtier, P.; Oueslati, M.

    2016-05-01

    ZnSe layers were grown on ZnO substrates by the metal organic chemical vapor deposition technique. A new structure appeared at lower thicknesses films. The structural properties of the thin films were studied by the X-ray diffraction (XRD) and Raman spectroscopy methods. First, Raman selection rules are explicitly put forward from a theoretical viewpoint. Second, experimentally-retrieved-intensities of the Raman signal as a function of polarization angle of incident light are fitted to the obtained theoretical dependencies in order to confirm the crystallographic planes of zinc blend ZnSe thin film, and correlate with DRX measurements. Raman spectroscopy has been used to characterize the interfacial disorder that affects energy transport phenomena at ZnSe/ZnO interfaces and the Photoluminescence (PL) near the band edge of ZnSe thin films.

  19. AC and DC transport currents in melt-grown YBCO

    SciTech Connect

    Yi, Z.; Ashworth, S.; Becluz, C.; Scurlock, R.G. )

    1991-03-01

    It has been suggested that the transport J{sub c} in multi-grain samples of bulk YBCO are limited by the intergrain links. This paper reports on preliminary measurements of intergrain currents. The intergrain critical currents in melt grown YBCO do not appear to be as sensitive to the precise crystallographic alignment of adjacent grains a has been reported for thin films. The measured critical current of similar grain boundaries varies widely, between 15000 A/cm{sup 2} and 200A/Cm{sub 2} for adjacent boundaries in the same sample.

  20. Synthesis and properties of highly c-axis oriented PbTiO3 thin films prepared by and MOCVD method

    NASA Astrophysics Data System (ADS)

    Chen, Xian-Tong; Yamane, Hisanori; Kaya, Kiyoshi

    1992-08-01

    Thin films of PbTiO3 were prepared on MgO(100) substrates by chemical vapor deposition using Pb(C2H5)4 (PbEt) and Ti(OC3H7)4 (TTIP) as sources. With decreasing Pb/Ti molar ratio from 1.2 to 1 the degree of c-axis orientation increased. Highly c-axis oriented PbTiO3 thin films were epitaxially grown at 500°C and 2 kPa. The films were transparent and had a refractive index (n) of 2.64 at 632.8 nm which was about 2% lower than that of a single PbTiO3 crystal (n ≈ 2.7). The films prepared on (100)-oriented Pt electrodes deposited on MgO(100) substrates at 600°C and 2 kPa also showed a prominent c-axis orientation and had a dielectric constant of 90.

  1. Equilibrium composition in II?VI telluride MOCVD systems

    NASA Astrophysics Data System (ADS)

    Ben-Dor, L.; Greenberg, J. H.

    1999-03-01

    Thermodynamic calculations, or computer simulation of the equilibrium composition, offer an excellent possibility to reduce drastically the elaborate trial-and-error experimental efforts of finding the optimal preparation conditions for MOCVD processes (temperature T, pressure P, initial composition of the vapors X), to limit them only to the P- T- X field of existence of the solid to be prepared and an acceptable yield of the product. In this communication equilibrium composition was investigated for MOCVD processes of CdTe, ZnTe, HgTe and solid solutions Cd xZn 1- xTe and Hg xCd 1- xTe. A number of volatile organometallic compounds have been used as precursors for MOCVD growth. These are dimethylcadmium (CH 3) 2Cd, DMCd; diethylzinc (C 2H 5) 2Zn, DEZn; diisopropylzinc [CH(CH 3) 2] 2Zn, DiPZn; diethyltellurium (C 2H 5) 2Te, DETe; diisopropyltellurium [CH(CH 3) 2] 2Te, DiPTe; methylallyltellurium CH 3TeCH 2CHCH 2, MATe. A choice of the particular combination of the precursors largely depends on the desired composition of the film to be prepared, especially in cases of solid solutions Cd xZn 1- xTe and Hg xCd 1- xTe where the vapor pressure of the precursors is instrumental for the composition of the vapor in the reaction zone and, ultimately, for the composition x of the solid solution. Equilibrium composition for II-VI telluride MOCVD systems was investigated at temperatures up to 873 K in hydrogen and inert gas atmospheres at pressures up to 1 atm. P- T- X regions of existence were outlined for each of the five materials.

  2. Direct deposition of YBCO on polished Ag substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Ma, B.; Li, M.; Koritala, R. E.; Fisher, B. L.; Dorris, S. E.; Maroni, V. A.; Miller, D. J.; Balachandran, U.

    2002-09-01

    YBCO thin films were directly deposited on mechanically polished nontextured silver (Ag) substrates at elevated temperature by pulsed laser deposition with various inclination angles of 35°, 55°, and 72°. Strong fiber texture, with the c-axis parallel to the substrate normal was detected by X-ray diffraction pole figure analysis. Atomic force microscopy and scanning electron microscopy images revealed that a few a-axis-oriented grains were dispersed on the top surface of the YBCO films. Transmission electron microscopy revealed dense amorphous layer at the interface between the YBCO film and the Ag substrate. Energy dispersive spectrum analysis indicates that the YBCO film deposited on the Ag substrate is slightly Cu-deficient. A YBCO film deposited at 755 °C and an inclination angle of 55° exhibited Tc=90 K. Transport critical current density measured by the four-probe method at 77 K in self-field was ≈2.7×10 5 A/cm 2. This work demonstrated a simple and inexpensive method to fabricate YBCO-coated conductors with high critical current density.

  3. Preparation and characterization of YBCO coating on metallic RABiT substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Gonal, M. R.; Prajapat, C. L.; Igalwar, P. S.; Maji, B. C.; Singh, M. R.; Krishnan, M.

    2016-05-01

    Superconducting YBCO films are coated on metallic Rolling Assisted Bi-axially Textured Substrates (RABiTS) Ni-5wt % W (NiW) (002) substrate using pulsed laser deposition (PLD) system. Targets of YBa2Cu3O7-δ (YBCO) and buffer layers of Ceria and 8 mole % Yttria Stabilized Zirconia (YSZ) of high density are synthesized. At each stage of deposition coatings are characterized by XRD. Transport studies show superconducting nature of YBCO only when two successive buffer layers of YSZ and CeO2 are used.

  4. Investigation on orientation, epitaxial growth and microstructure of a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7-δ films prepared on (001), (110) and (111) SrTiO3 single crystal substrates by spray atomizing and coprecipitating laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Wang, Ying; Huang, Zhi liang; Mao, Yangwu; Xu, Yuan Lai

    2015-04-01

    a-axis-, c-axis-, (103)/(110)- and (113)-oriented YBa2Cu3O7-δ (YBCO) films were pareared by spray atomizing and coprecipitating laser chemical vapor deposition. The surface of the a-axis-oriented YBCO film consisted of rectangular needle-like grains whose in-plane epitaxial growth relationship was YBCO [100] // STO [001] (YBCO [001] // STO [100]), and that of the c-axis-oriented YBCO film consisted of dense flat surface with epitaxial growth relationship of YBCO [001] // STO [001] (YBCO [100] //STO [100]). For the (103)/(110)-oriented and (113)-oriented YBCO film, they showed wedge-shaped and triangle-shaped grains, with corresponding in-plane epitaxial growth relationship of YBCO [110] // STO [110] (YBCO [010] // STO [010]) and YBCO [100] // STO [100] (YBCO [113] // STO [111], respectively.

  5. Obtention and characterization of YBCO/Ag/YBCO welds at different misorientation angles

    NASA Astrophysics Data System (ADS)

    Bozzo, B.; Bartolomé, E.; Granados, X.; Puig, T.; Obradors, X.

    2006-06-01

    The microstructural and magnetic properties of YBa2Cu3O7 (YBCO) welds with different crystallographic [001]-tilt misorientation, prepared by the Ag surface melting induced welding technique, have been studied. The inter- and intra-grain critical current densities have been simultaneously obtained by solving the Inverse Problem from the remanent local magnetization magnetic field maps measured by Hall Probe imaging. The obtained dependence of the inter-grain current density with the angle, JcGB(θ), is compared to previous results for thin-film bicrystals and bulk boundaries.

  6. Study on Quench Protection of HTS Coil Wound of YBCO Conductor

    NASA Astrophysics Data System (ADS)

    Fu, Youkun; Tsukamoto, Osami; Furuse, Mitsuho

    Recent progress of long YBCO coated conductors is remarkable and coils wound of YBCO conductors will be developed in near future. YBCO coated conductors that are made by deposition of thin YBCO film on high resistance metal substrates such as Hastelloy and nickel tapes are highly resistive when they are quenched. Therefore, measures for stabilization and quench protection are more important for YBCO conductors than for Bi/Ag sheathed tapes which have low resistive silver matrix. Though HTS conductors working at liquid nitrogen temperature are hard to be quenched, the conductors still have possibilities of quenches due to local defects for example. We studied necessary amount of copper stabilizer to protect the YBCO conductors in coils from damages caused by hot spots due to quenches. In the work we numerically calculated maximum hot spot temperature of a YBCO conductor quenched by a local disturbance during the sequence of quench detection and energy dump. In the analysis, necessary amounts of copper to keep the maximum hot spot temperature below a threshold are calculated. Based on the analysis, optimum conductor design is discussed to obtain safe and high current density conductors.

  7. Development of YBCO Superconductor for Electric Systems: Cooperative Research and Development Final Report, CRADA Number CRD-04-150

    SciTech Connect

    Bhattacharya, R.

    2013-03-01

    The proposed project will be collaborative in exploration of high temperature superconductor oxide films between SuperPower, Inc. and the National Renewable Energy Laboratory. This CRADA will attempt to develop YBCO based high temperature oxide technology.

  8. Epitaxial Pb(Zr{sub 0.40}Ti{sub 0.60})O{sub 3}/SrRuO{sub 3} and PbTiO{sub 3}/SrRuO{sub 3} multilayer thin films prepared by MOCVD and rf sputtering

    SciTech Connect

    Foster, C.M.; Csencsits, R.; Baldo, P.M.

    1994-12-01

    Epitaxial SrRuO{sub 3} thin films were deposited by RF sputtering on SrTiO{sub 3} or MgO substrates for use as underlying electrodes. On these conductive substrates, epitaxial Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3} (PZT) and PbTiO{sub 3} (PT) thin films were, deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. 90{degree} domains, interfacial misfit dislocations and dislocations and threading dislocations were the primary structural defects, and the films showed a 70% RBS channeling reduction. Hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag or ITO glass top electrode showed: a remanent polarization of 46.2 mC/cm{sup 2}, a coercive field of 54.9 KV/cm, a dielectric constant of 410, a bipolar resistivity of {approximately}5.8 {times} 10{sup 9} {Omega}-cm at a field of 275 KV/cm, and a breakdown strength of >400 KV/cm.

  9. Nonvacuum Deposition of Silver Doped YBCO Coated Conductor on %100 Lattice Match Buffered Ni Tapes

    NASA Astrophysics Data System (ADS)

    Arda, L.; Cakiroglu, O.; Keskin, S.; Sacli, O. A.

    2007-04-01

    Silver doped YBa2Cu3O7-δ (YBCO) coated conductors were fabricated on Gd1.624Ho0.376O3 (100 % lattice match with YBCO) textured buffer layers on Ni tape by reel-to-reel sol-gel dip coating system. Sample were prepared with different wt(1-5) % Ag doped ratio. The surface morphologies and microstructure of all sample were characterized by ESEM, EDS and XRD. Pole figure texture analyses have been done to characterize texture of buffer layer and YBCO superconducting film . The critical current Ic measurement was performed using four wire method with the 1 μV/cm criterion. The critical current density, Jc was measured to be 2.2 × 104 A/cm2 at 77 K self field for 1 wt % Ag doped YBCO sample.

  10. Comparison of crystalline and superconducting properties of sputtered a-axis oriented YBCO films on MgO and SrTiO 3 substrates

    NASA Astrophysics Data System (ADS)

    Mahajan, S.; Wen, J. G.; Ito, W.; Cho, C. H.; Takenaka, T.; Kubota, N.; Yoshida, Y.; Morishita, T.

    1994-05-01

    The crystalline and superconducting properties of sputtered a-axis oriented thin films of Y 1Ba 2Cu 3O 7- x on SrTiO 3(100) and MgO (100) substrates are compared using X-ray diffraction (XRD), high-resolution electron microscopy (HREM), atomic force microscopy, critical current ( Jc) and surface resistance ( Rs) measurements. A two step self-template method was used for deposition, and HREM measurements revealed that the bulk film beyond the template was pure a-axis oriented on SrTiO 3 and also on lattice-mismatched MgO. However, the nature of the template layer on the two substrates was completely different and the crystallinity of the film was found to be dependent on the crystallinity of the template. The Jc and Rs measurements indicated that the superconducting properties of the film on MgO owing to its poor crystallinity, were dominated by weak links in contrast to well-coupled grains for the film on SrTiO 3.

  11. Real-time physico-neural solutions for MOCVD

    SciTech Connect

    Kelkar, A.S.; Mahajan, R.L.; Sani, R.L.

    1995-12-31

    This paper presents an integrated physical neural network approach for the modeling and optimization of a vertical MOCVD reactor. A first-principles physical model for the reactor was solved numerically using the Fluid Dynamics Analysis Package (FIDAP). This transient model included property variation and thermodiffusion effects. Artificial Neural Network (ANN) models were then trained to predict the growth rate profiles within the reactor. The data used to train the network was obtained from FIDAP simulations for combinations of process parameters determined by statistical Design of Experiments (DOE) methodology. It is shown that the trained ANN predicts the behavior of the reactor accurately. Optimum process conditions to obtain a uniform thickness of the deposited film were determined and tested using the ANN model. The results demonstrate the power and robustness of ANNs for obtaining fast on-line responses to changing input conditions. This capability of ANNs is particularly important for implementing run-to-run and on-line control of the MOCVD process.

  12. Monitoring of MOCVD reactants by UV absorption

    SciTech Connect

    Baucom, K.C.; Killeen, K.P.; Moffat, H.K.

    1995-07-01

    In this paper, we describe how UV absorption measurements can be used to measure the flow rates of metal organic chemical vapor deposition (MOCVD) reactants. This method utilizes the calculation of UV extinction coefficients by measuring the total pressure and absorbance in the neat reactant system. The development of this quantitative reactant flow rate monitor allows for the direct measurement of the efficiency of a reactant bubbler. We demonstrate bubbler efficiency results for TMGa, and then explain some discrepancies found in the TMAl system due to the monomer to dimer equilibrium. Also, the UV absorption spectra of metal organic and hydride MOCVD reactants over the wavelength range 185 to 400 nm are reported.

  13. AC over-current characteristics of YBCO coated conductor with copper stabilizer layer considering insulation layer

    NASA Astrophysics Data System (ADS)

    Du, H.-I.; Kim, M.-J.; Kim, Y.-J.; Lee, D.-H.; Han, B.-S.; Song, S.-S.

    2010-11-01

    Compared with the first-generation BSCCO wire, the YBCO thin-film wire boasts low material costs and high Jc and superior magnetic-field properties, among other strengths. Meanwhile, the previous BSCCO wire material for superconducting cables has been researched on considerably with regard to its post-wire quenching characteristics during the application of an alternating over-current. In this regard, the promising YBCO thin-film wire has yet to be further researched on. Moreover, still lacking is research on the YBCO thin-film wire with insulating layers, which is essential in the manufacture of superconducting cables, along with the testing of the application of an alternating over-current to the wire. In this study, YBCO thin-film wires with copper-stabilizing layers were used in testing alternating over-current application according to the presence or absence of insulating layers and to the thickness of such layers, to examine the post-quenching wire resistance increase and quenching trends. The YBCO thin-film wire with copper-stabilizing layers has a critical temperature of 90 K and a critical current of 85 A rms. Moreover, its current application cycle is 5.5 cycles, and its applied currents are 354, 517, 712, and 915 A peak. These figures enabled the YBCO thin-film wires with copper-stabilizing layers to reach 90, 180, 250, and 300 K, respectively, in this study. These temperatures serve as a relative reference to examine the post-quenching wire properties following the application of an alternating over-current.

  14. Zone refining of sintered, microwave-derived YBCO superconductors

    SciTech Connect

    Warrier, K.G.K.; Varma, H.K.; Mani, T.V.; Damodaran, A.D.; Balachandran, U.

    1993-07-01

    Post-sintering treatments such as zone melting under thermal gradient has been conducted on sintered YBCO tape cast films. YBCO precursor powder was derived through decomposition of a mixture of nitrates of cations in a microwave oven for {approx}4 min. The resulting powder was characterized and made into thin sheets by tape casting and then sintered at 945 C for 5 h. The sintered tapes were subjected to repeated zone refining operations at relatively high speeds of {approx}30 mm/h. A microstructure having uniformly oriented grains in the a-b plane throughout the bulk of the sample was obtained by three repeated zone refining operations. Details of precursor preparation, microwave processing and its advantages, zone refining conditions, and microstructural features are presented in this paper.

  15. Trapped Field Characteristics of Stacked YBCO Thin Plates for Compact NMR Magnets: Spatial Field Distribution and Temporal Stability

    PubMed Central

    Hahn, Seungyong; Kim, Seok Beom; Ahn, Min Cheol; Voccio, John; Bascuñán, Juan; Iwasa, Yukikazu

    2010-01-01

    This paper presents experimental and analytical results of trapped field characteristics of a stack of square YBCO thin film plates for compact NMR magnets. Each YBCO plate, 40 mm × 40 mm × 0.08 mm, has a 25-mm diameter hole at its center. A total of 500 stacked plates were used to build a 40-mm long magnet. Its trapped field, in a bath of liquid nitrogen, was measured for spatial field distribution and temporal stability. Comparison of measured and analytical results is presented: the effects on trapped field characteristics of the unsaturated nickel substrate and the non-uniform current distribution in the YBCO plate are discussed. PMID:20585463

  16. Trapped Field Characteristics of Stacked YBCO Thin Plates for Compact NMR Magnets: Spatial Field Distribution and Temporal Stability.

    PubMed

    Hahn, Seungyong; Kim, Seok Beom; Ahn, Min Cheol; Voccio, John; Bascuñán, Juan; Iwasa, Yukikazu

    2010-06-01

    This paper presents experimental and analytical results of trapped field characteristics of a stack of square YBCO thin film plates for compact NMR magnets. Each YBCO plate, 40 mm × 40 mm × 0.08 mm, has a 25-mm diameter hole at its center. A total of 500 stacked plates were used to build a 40-mm long magnet. Its trapped field, in a bath of liquid nitrogen, was measured for spatial field distribution and temporal stability. Comparison of measured and analytical results is presented: the effects on trapped field characteristics of the unsaturated nickel substrate and the non-uniform current distribution in the YBCO plate are discussed.

  17. Electrospinning of superconducting YBCO nanowires

    NASA Astrophysics Data System (ADS)

    Duarte, Edgar A.; Rudawski, Nicholas G.; Quintero, Pedro A.; Meisel, Mark W.; Nino, Juan C.

    2015-01-01

    YBa2Cu3O7-δ (YBCO) nanowires with critical transition temperature Tc = 91.7 K were synthesized by an electrospinning process with the use of sol-gel precursors. A homogeneous polymeric solution containing Y, Ba, and Cu acetates was electrospun, resulting in collections of randomly oriented nanowires as well as bundles of aligned nanowires. Fully crystallized YBCO nanowires were obtained after calcination at temperatures as low as 820 °C. The morphology, microstructure, and crystal structure were investigated, and the diameters of the polycrystalline nanowires varied between 120 and 550 nm depending on the viscosity of the precursors. Thinner individual wires, with diameters in the 50-80 nm range, were synthesized with a single grain structure across the entire wire cross-section.

  18. A novel MOCVD reactor for growth of high-quality GaN-related LED layers

    NASA Astrophysics Data System (ADS)

    Hu, Shaolin; Liu, Sheng; Zhang, Zhi; Yan, Han; Gan, Zhiyin; Fang, Haisheng

    2015-04-01

    Gallium nitride (GaN), a direct bandgap semiconductor widely used in bright light-emitting diodes (LEDs), is mostly grown by metal-organic chemical vapor deposition (MOCVD) method. A good reactor design is critical for the production of high-quality GaN thin films. In this paper, we presented a novel buffered distributed spray (BDS) MOCVD reactor with vertical gas sprayers and horizontal gas inlets. Experiments based on a 36×2″ BDS reactor were conducted to examine influence of the process parameters, such as the operating pressure and the gas flow rate, on the growth efficiency and on the layer thickness uniformity. Transmission electron microscopy (TEM) and photoluminescence (PL) are further conducted to evaluate quality of the epitaxial layers and to check performance of the reactor. Results show that the proposed novel reactor is of high performance in growing high-quality thin films, including InGaN/GaN multiquantum wells (MQWs) structures.

  19. Pd layer on cube-textured substrates for MOD-TFA and PLD YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Mancini, A.; Celentano, G.; Galluzzi, V.; Rufoloni, A.; Vannozzi, A.; Augieri, A.; Ciontea, L.; Petrisor, T.; Gambardella, U.; Longo, G.; Cricenti, A.

    2008-01-01

    Pd films were deposited on rolling assisted biaxially textured substrate (RABiTS) Ni-5 at.% W in order to exploit the Pd effect of the texture sharpening with respect to that of the substrate, for the development of YBa2Cu3O7-x (YBCO) coated conductors. The Pd sharpening effect was relevant in the out-of-plane direction where the reduction for the ω-scans' full width at half maximum (FWHM) ranged from 55 to 65%, depending on the substrate roughness. The obtained minimum values of the FWHM in the transverse rolling direction of the (002) Pd ω-scan and in the (111) Pd phi-scan were of about 2.5° and 5°, respectively. The CeO2/YSZ/CeO2 (YSZ is Y2O3-stabilised ZrO2) heterostructure of the buffer layer was developed by pulsed laser deposition (PLD). In order to transfer the sharp orientation of the Pd film, both the seed CeO2 layer and the YSZ layer were deposited at low temperatures (450 °C), low enough to avoid Pd/Ni-W interdiffusion. The YBCO, films deposited by both PLD and metal-organic deposition (MOD) using metal trifluoroacetate acid (TFA), exhibited rolling direction (005) ω-scan and the (113) phi-scan FWHM values of about 2° and 5°, respectively. In spite of the complete interdiffusion between Ni and Pd during the YBCO film deposition, the coated conductors exhibit good adherence, as well as a smooth and crack-free surface. A zero-resistance critical temperature (TC0) of 90.8 K for the MOD-TFA YBCO films and critical current-density (JC) up to 2.2 MA cm-2 at 77 K and self-field for PLD YBCO films have been obtained.

  20. Fabrication and Characterization of YBCO Coated Conductors by Inclined Substrate Deposition

    NASA Astrophysics Data System (ADS)

    Ma, B.; Balachandran, U.; Xu, Y.; Bhattacharya, R.

    2006-03-01

    Inclined substrate deposition (ISD) is an effective method for rapid fabrication of high-quality template layers for YBCO-coated conductors. We have deposited biaxially textured ISD-MgO films on flexible metallic tapes in a reel-to-reel system by electron-beam evaporation at rapid deposition rates, 2-10 nmṡs-1. Strontium ruthenium oxide (SRO) buffer and YBCO films were grown by pulsed laser deposition (PLD). Pole figure analysis of a meter-long ISD-MgO tape was carried out by X-ray diffraction using a Bruker's D8 DISCOVER equipped with GADDS (general area detection diffraction system). The c-axis of the ISD-MgO film was tilted away from substrate normal. A full-width at half maximum (FWHM) of ≈10° was observed from the φ-scan of the MgO (002) diffraction measured on samples deposited with 35° inclination angle. Surface morphology measured by atomic force microscopy revealed a roof-tile shaped structure for the ISD-MgO films. Through the use of the SRO buffer, biaxial alignment in the YBCO film deposited on the ISD-MgO template was improved. The φ-scan FWHM was 5.8° for the YBCO (005) diffraction. We have measured the critical transition temperature Tc = 91 K and transport critical current density Jc >1.6×106 Aṡcm-2 at 77 K in self-field on a SRO-buffered YBCO film grown with ISD-MgO architecture.

  1. Long length oxide template for YBCO coated conductor prepared by surface-oxidation epitaxy method

    NASA Astrophysics Data System (ADS)

    Watanabe, Tomonori; Matsumoto, Kaname; Maeda, Toshihiko; Tanigawa, Toru; Hirabayashi, Izumi

    2001-08-01

    A 50 m long, biaxially textured NiO buffer layer for epitaxial growth ofYBa 2Cu 3O 7- δ (YBCO) film has been fabricated on the long cube textured nickel tape using surface-oxidation epitaxy (SOE) method. The SOE-NiO layers were highly {1 0 0} <0 0 1> textured. The full width at half maximum of 10-14.5° from X-ray φ-scan ( Δφ) was in the range of 10-14.5° through the whole length. The critical current density ( Jc) values exceeding 0.3 MA/cm 2 (77 K, 0 T) have been obtained in short samples of YBCO films on NiO/Ni tapes, by using thin MgO cap layer. Thirty meters long Ni-clad Ni-20wt.%Cr (Ni/NiCr) and Ni-clad austenitic stainless steel (Ni/SS) tapes were also prepared for YBCO coated conductors with higher strength and lower magnetism than those of pure nickel tape. Highly {1 0 0} <0 0 1> textured NiO layers were formed on those textured composite tapes by SOE method as same as on cube textured pure nickel tapes. YBCO films with Jc of 0.1 MA/cm 2 (77 K, 0 T) have been obtained on MgO/SOE-NiO layer of short Ni/NiCr composite tape.

  2. All MOD buffer/YBCO approach to coated conductors

    NASA Astrophysics Data System (ADS)

    Parans Paranthaman, M.; Sathyamurthy, S.; Heatherly, L.; Martin, P. M.; Goyal, A.; Kodenkandath, T.; Li, X.; Thieme, C. L. H.; Rupich, M. W.

    2006-10-01

    RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7-δ (YBCO) approach has been considered as one of the potential, low-cost approaches to fabricate high performance second generation coated conductors. The most commonly used RABiTS architectures consisting of a starting template of biaxially textured Ni-W (5 at.%) substrate with a seed layer of Y2O3, a barrier layer of YSZ, and a CeO2 cap. In this three layer architecture, all the buffers are deposited using physical vapor deposition (PVD) techniques. Using these PVD deposited templates, 0.8-μm thick MOD-YBCO films with an Ic (critical current) of 250 A/cm have been achieved routinely in short lengths. We have developed a low-cost, non-vacuum, MOD process to grow epitaxial buffer layers on textured Ni-5W substrates. The main challenge in this effort is to match the performance of MOD templates to that of PVD templates. We have recently shown that the properties of MOD-La2Zr2O7 (LZO) layers can be improved by inserting a thin Y2O3 seed layer. Using MOD-CeO2 cap layers, we have demonstrated the growth of high performance MOD-YBCO films with an Ic of 200 A/cm-width on MOD-La2Zr2O7/Y2O3/Ni-5W substrates. This approach could potentially decrease the overall cost of the coated conductor fabrication.

  3. All MOD Buffer/YBCO Approach to Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Sathyamurthy, Srivatsan; Heatherly Jr, Lee; Martin, Patrick M; Goyal, Amit; Kodenkandath, Thomas; Li, Xiaoping; Thieme, C. L. H.; Rupich, Marty

    2006-01-01

    RABiTS based metal-organic deposition (MOD) buffer/YBa2Cu3O7-d (YBCO) approach has been considered as one of the potential, low-cost approaches to fabricate high performance second generation coated conductors. The most commonly used RABiTS architectures consisting of a starting template of biaxially textured Ni-W (5 at.%) substrate with a seed layer of Y2O3, a barrier layer of YSZ, and a CeO2 cap. In this three layer architecture, all the buffers are deposited using physical vapor deposition (PVD) techniques. Using these PVD deposited templates, 0.8-{mu}m thick MOD-YBCO films with an Ic (critical current) of 250 A/cm have been achieved routinely in short lengths. We have developed a low-cost, non-vacuum, MOD process to grow epitaxial buffer layers on textured Ni-5W substrates. The main challenge in this effort is to match the performance of MOD templates to that of PVD templates. We have recently shown that the properties of MOD-La2Zr2O7 (LZO) layers can be improved by inserting a thin Y2O3 seed layer. Using MOD-CeO2 cap layers, we have demonstrated the growth of high performance MOD-YBCO films with an Ic of 200 A/cm-width on MOD-La2Zr2O7/Y2O3/Ni-5W substrates. This approach could potentially decrease the overall cost of the coated conductor fabrication.

  4. Passivation of Flexible YBCO Superconducting Current Lead With Amorphous SiO2 Layer

    NASA Technical Reports Server (NTRS)

    Johannes, Daniel; Webber, Robert

    2013-01-01

    across a thermal gradient with as little flow of heat as possible to make an efficient current lead. By protecting YBCO on a flexible substrate of low thermal conductivity with SiO2, a thermally efficient and flexible current lead can be fabricated. The technology is also applicable to current leads for 4 K superconducting electronics current biasing. A commercially available thin-film YBCO composite tape conductor is first stripped of its protective silver coating. It is then mounted on a jig that holds the sample flat and acts as a heat sink. Silicon dioxide is then deposited onto the YBCO to a thickness of about 1 micron using PECVD (plasma-enhanced chemical vapor deposition), without heating the YBCO to the point where degradation occurs. Since SiO2 can have good high-frequency electrical properties, it can be used to coat YBCO cable structures used to feed RF signals across temperature gradients. The prime embodiment concerns the conduction of DC current across the cryogenic temperature gradient. The coating is hard and electrically insulating, but flexible.

  5. The non-epitaxial growth of c-axis YBa 2Cu 3O x films on high-index planes of silver

    NASA Astrophysics Data System (ADS)

    Huang, D. X.; Yamada, Y.; Hirabayashi, I.

    2000-11-01

    YBa 2Cu 3O x (YBCO) thin films were deposited by the pulsed-laser ablation on polycrystalline Ag substrates. The c-axis-oriented YBCO films on various high-index silver crystal planes have been observed using cross-sectional transmission electron microscopy (TEM). The obtained results show that, differing from the epitaxial growth of the YBCO films on low-index planes, the YBCO films grown on high-index planes have not a good epitaxial relationship. The c-axes of the YBCO grains keep to vertical to the substrate surface plane but the a- and b- axes of the grains are randomly oriented.

  6. Vacuum MOCVD fabrication of high efficience cells

    NASA Technical Reports Server (NTRS)

    Partain, L. D.; Fraas, L. M.; Mcleod, P. S.; Cape, J. A.

    1985-01-01

    Vacuum metal-organic-chemical-vapor-deposition (MOCVD) is a new fabrication process with improved safety and easier scalability due to its metal rather than glass construction and its uniform multiport gas injection system. It uses source materials more efficiently than other methods because the vacuum molecular flow conditions allow the high sticking coefficient reactants to reach the substrates as undeflected molecular beams and the hot chamber walls cause the low sticking coefficient reactants to bounce off the walls and interact with the substrates many times. This high source utilization reduces the materials costs power device and substantially decreases the amounts of toxic materials that must be handled as process effluents. The molecular beams allow precise growth control. With improved source purifications, vacuum MOCVD has provided p GaAs layers with 10-micron minority carrier diffusion lengths and GaAs and GaAsSb solar cells with 20% AMO efficiencies at 59X and 99X sunlight concentration ratios. Mechanical stacking has been identified as the quickest, most direct and logical path to stacked multiple-junction solar cells that perform better than the best single-junction devices. The mechanical stack is configured for immediate use in solar arrays and allows interconnections that improve the system end-of-life performance in space.

  7. Properties of YBCO on LaMnO3-capped IBAD MgO-templates without Homo-epitaxial MgO layer.

    SciTech Connect

    Aytug, Tolga; Paranthaman, Mariappan Parans; Kim, Kyunghoon; Zhang, Yifei; Cantoni, Claudia; Zuev, Yuri L; Goyal, Amit; Thompson, James R; Christen, David K

    2009-01-01

    Previously, it has been well established that in an IBAD architecture for coated conductors, (1) LaMnO3 (LMO) buffer layers are structurally and chemically compatible with an underlying homo-epitaxial MgO layer and (2) high current density YBCO films can be grown on these LMO templates. In the present work, the homo-epi MgO layer has been successfully eliminated and a LMO cap layer was grown directly on the IBAD (MgO) template. The performance of the LMO/IBAD (MgO) samples has been qualified by depositing 1 m-thick YBCO coatings by pulsed laser deposition. Electrical transport measurements of YBCO films on the standard (with homo-epi MgO) and simplified (without homo-epi MgO) IBAD architectures were carried out. The angular dependencies of critical current density (Jc) are similar for both IBAD architectures. XRD measurements indicate good, c-axis aligned YBCO films. Transmission electron microscopy (TEM) images reveal that microstructures of YBCO/LMO/IBAD (MgO) and YBCO/LMO/homo-epi MgO/IBAD (MgO) templates are similar. These results demonstrate the strong potential of using LMO as a single cap layer directly on IBAD (MgO) for the development of a simplified IBAD architecture.

  8. A YBCO RF-SQUID magnetometer and its applications

    NASA Technical Reports Server (NTRS)

    Luwei, Zhou; Jingwu, Qiu; Xienfeng, Zhang; Zhiming, Tank; Yongjia, Qian

    1990-01-01

    An applicable RF-superconducting quantum interference detector (SQUID) magnetometer was made using a bulk sintered yttrium barium copper oxide (YBCO). The temperature range of the magnetometer is 77 to 300 K and the field range 0 to 0.1T. At 77 K, the equivalent flux noise of the SQUID is 5 x 10 to minus 4 power theta sub o/square root of Hz at the frequency range of 20 to 200 Hz. The experiments show that the SQUID noise at low-frequency end is mainly from 1/f noise. A coil test shows that the magnetic moment sensitivity delta m is 10 to the minus 6th power emu. The RF-SQUID is shielded in a YBCO cylinder with a shielding ability B sub in/B sub ex of about 10 to the minus 6th power when external dc magnetic field is about a few Oe. The magnetometer is successfully used in characterizing superconducting thin films.

  9. Modified Lanthanum Zirconium Oxide buffer layers for low-cost, high performance YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Parans Paranthaman, M.; Sathyamurthy, S.; Li, Xiaoping; Specht, E. D.; Wee, S. H.; Cantoni, C.; Goyal, A.; Rupich, M. W.

    2010-03-01

    The pyrochlore Lanthanum Zirconium Oxide, La 2Zr 2O 7 (LZO), has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO 2 cap/YSZ barrier/Y 2O 3 seed on Ni-5%W metal tape. The main focus of this research is to ascertain whether: (i) we can further improve the barrier properties of LZO; (ii) we can modify the LZO cation ratio and still achieve a high level of performance; and (iii) it is possible to reduce the number of buffer layers. We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La 2O 3-ZrO 2 system. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of La xZr 1-xO y ( x = 0.2-0.6) on standard Y 2O 3 buffered Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase with only (0 0 1) texture can be achieved in a broad compositional range of x = 0.2-0.6 in La xZr 1-xO y. Both CeO 2 cap layers and MOD-YBCO films were grown epitaxially on these modified LZO barriers. High critical currents per unit width, Ic of 274-292 A/cm at 77 K and self-field were achieved for MOD-YBCO films grown on La xZr 1-xO y ( x = 0.4-0.6) films. These results indicate that LZO films can be grown with a broad compositional range and still support high performance YBCO coated conductors. In addition, epitaxial MOD La xZr 1-xO y ( x = 0.25) films were grown directly on biaxially textured Ni-3W substrates. About 3 μm thick YBCO films grown on a single MOD-LZO buffered Ni-3W substrates using pulsed laser deposition show a critical current density, Jc, of 0.55 MA/cm 2 ( Ic of 169 A/cm) at 77 K and 0.01 T. This work holds promise for a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.

  10. Modified Lanthanum Zirconium Oxide Buffer for Low-Cost, High Performance YBCO Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Sathyamurthy, Srivatsan; Li, Xiaoping; Specht, Eliot D; Wee, Sung Hun; Cantoni, Claudia; Goyal, Amit; Rupich, M. W.

    2010-01-01

    Lanthanum Zirconium Oxide, La2Zr2O7 (LZO) has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed/Ni-5W. The main focus of this research is to see (i) whether we can improve further the barrier properties of LZO; (ii) can we widen the LZO composition and still achieve the high performance?; and (iii) is it possible to reduce the number of buffer layers? We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La2O3-ZrO2 system. Using metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of LaxZr1-xOy (x = 0.2-0.6) on standard Y2O3 buffered Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase without the (111) texture can be achieved in a wider compositional window of x = 0.2-0.6 in LaxZr1-xOy. Both CeO2 cap layers and MOD-YBCO films were grown 2 epitaxially on these modified LZO barriers. Transport property measurements indicate that we can achieve a higher critical current, Ic of 274-292 A/cm at 77 K and self-field on MOD-YBCO films grown on LaxZr1-xOy (x = 0.4-0.6) films. These results indicate that LZO films can be grown with a wider compositional window and still achieve high performance YBCO coated conductors. In addition, epitaxial MOD LaxZr1-xOy (x = 0.25) films were grown directly on biaxially textured Ni-3W substrates. About 3 m thick YBCO films with a Jc of 0.55 MA/cm2 at 77 K and 0.01 T were grown on a single MOD LZO buffered Ni-3W substrate using pulsed laser deposition. This work promises a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.

  11. Nickel-copper alloy tapes as textured substrates for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Vannozzi, A.; Celentano, G.; Angrisani, A.; Augieri, A.; Ciontea, L.; Colantoni, I.; Galluzzi, V.; Gambardella, U.; Mancini, A.; Petrisor, T.; Rufoloni, A.; Thalmaier, G.

    2008-02-01

    NiCuCo alloy tape was studied as textured substrates for YBCO coated conductors application. The addition of a small amount of cobalt was pursued in order to enhance the microstructure of the NiCu alloy. The use of different thermal treatments during the recrystallization process permitted to obtain area densities of cube orientation as high as 95%. The substrate was thoroughly characterized by means of x-ray diffraction, EBSD and SEM analyses. Further, the mechanical properties and the magnetic behaviour of this substrate have been investigated and compared with those exhibited by Ni, NiW and NiCu tapes. The suitability of this alloy substrate for YBCO coated conductors has been tested through the deposition of a conventional CeO2/YSZ/CeO2 buffer layer architecture using a Pd transient layer. Apart from passivating Ni-Cu-Co substrate, the use of a Pd transient layer produces a relevant texture sharpening in the out-of-plane orientation and the full width at half maximum of the ?-scan drops from about 9° of NiCuCo to 2° of Pd layer. This sharp texture is transferred to the YBCO film and the results indicate that NiCuCo alloy is a promising alternative substrate for the realization of YBCO coated conductors.

  12. A new direct process to prepare YBa 2Cu 3O 7- δ films on biaxially textured Ag{110}<211>

    NASA Astrophysics Data System (ADS)

    Wang, Rongping; Zhou, Yueliang; Pan, Shaohua; He, Meng; Chen, Zhenghao; Yang, Guozhen

    1999-12-01

    YBa 2Cu 3O 7- δ (YBCO) films were successfully prepared on biaxially textured Ag{110}<211> substrates by using pulsed laser deposition. X-ray diffraction results showed that the degree of preferential orientation of Ag{110}<211> substrates varied with increasing annealing temperature. With a thin template layer deposited at low temperature, YBCO film with c-axis orientation and in-plane biaxial alignment could be obtained at high deposition temperature. Scanning electron microscopy observation revealed that YBCO grains enlarged, but Ag grains on the surface of the YBCO films became smaller with increasing deposition temperature. At optimal deposition conditions, Ag atoms diffuse into the YBCO grain boundaries, and then fill in the weak-link regions in the YBCO film, resulting in the easier conduction. Jc value of 5×10 5 A/cm 2 was obtained at 77 K and zero magnetic field for the best YBCO film in our work.

  13. The influence of strain on the dielectric behavior of (Ba, Sr) Ti{sub 1+x}O{sub 3} thin films grown by LS-MOCVD on Pt/SiO{sub 2}/Si.

    SciTech Connect

    Streiffer, S. K.

    1998-10-14

    The strain state and its coupling to dielectric behavior have been investigated for (100) BST thin films deposited on Pt/SiO{sub 2}/Si at 640 C. It is estimated from x-ray diffraction that the in-plane biaxial strain is approximately 0.7%. We postulate that this is of sufficient magnitude to confine any spontaneous polarization to the plane of the film. The thickness-corrected dielectric behavior perpendicular to the substrate for these samples shows evidence of coupling to such an in-plane phase transition at approximately 390K, as manifested by deviation from Curie-Weiss-like behavior at this temperature.

  14. Direct observation of surface plasmons in YBCO by attenuated total reflection of light in the infrared

    NASA Astrophysics Data System (ADS)

    Walmsley, D. G.; Smyth, C. C.; Sellai, A.; McCafferty, P. G.; Dawson, P.; Morrow, T.; Graham, W. G.

    1994-02-01

    Surface plasmons have been observed directly in YBCO films in an Otto-geometry attenuated total reflection measurement at a wavelength of 3.392 μm. The laser deposited films are c-axis oriented on an MgO substrate. This observation confirms theoretical deductions from complex dielectric function data. Measured data have been fitted to a theoretical model and are compared with the optical constants determined by Bozovic [1]. The investigations have been extended to films with other orientations to investigate whether material anisotropy is reflected in the results and non-metallic behaviour is found.

  15. Development of Solution Buffer Layers for RABiTS Based YBCO Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Qiu, Xiaofeng; Kim, Kyunghoon; Shi, D.; Zhang, Yifei; Li, Xiaoping; Sathyamurthy, Srivatsan; Thieme, C. L. H.; Rupich, M. W.

    2010-01-01

    The main objective of this research is to find a suitable alternate solution based seed layer for the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni-5%W metal tape. In the present work, we have identified CeO2 buffer layer as a potential replacement for Y2O3 seeds. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of CeO2 (both pure and Zr, Cu and Gd-doped) directly on biaxially textured Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial CeO2 phase with slightly improved out-of-plane texture compared to the texture of underlying Ni-W substrates can be achieved in pure, undoped CeO2 samples. We have also demonstrated the growth of YSZ barrier layers on pure CeO2 seeds using sputtering. Both sputtered CeO2 cap layers and MOD-YBCO films were grown epitaxially on these YSZ-buffered MOD-CeO2/Ni-5W substrates. High critical currents per unit width, Ic of 264 A/cm (critical current density, Jc of 3.3 MA/cm2) at 77 K and 0.01 T was achieved for 0.8 m thick MOD-YBCO films grown on MOD-CeO2 seeds. These results indicate that CeO2 films can be grown directly on Ni-5W substrates and still support high performance YBCO coated conductors. This work holds promise for a route for producing low-cost buffer architecture for RABiTS based YBCO coated conductors.

  16. Development of Solution Buffer Layers for RABiTS Based YBCO Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Qiu, Xiaofeng; List III, Frederick Alyious; Zhang, Yifei; Li, Xiaoping; Sathyamurthy, Srivatsan; Thieme, C. L. H.; Rupich, M. W.

    2011-01-01

    Abstract The main objective of this research is to find a suitable alternate solution based seed layer for the standard RABiTS three-layer architecture of physical vapor deposited CeO cap/YSZ barrier/Y O seed on Ni-5%W metal tape. In the present work, we have identified CeO buffer layer as a potential replacement for Y O seeds. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of CeO (pure and Zr, Cu and Gd-doped) directly on biaxially textured Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial CeO phase with slightly improved out-of-plane texture compared to the texture of the underlying Ni-W substrates can be achieved in pure, undoped CeO samples. We have also demonstrated the growth of YSZ barrier layers on pure CeO seeds using sputtering. Both sputtered CeO cap layers and MOD-YBCO films were grown epitaxially on these YSZ-buffered MOD-CeO /Ni-5W substrates. High critical currents per unit width, of 264 A/cm (critical current density, of 3.3 MA/cm ) at 77 K and 0.01 T was achieved for 0.8 m thick MOD-YBCO films grown on MOD-CeO seeds. These results indicate that CeO films can be grown directly on Ni-5W substrates and still support high performance YBCO coated conductors. This work holds promise for a route for producing low-cost buffer architecture for RABiTS based YBCO coated conductors.

  17. High-material yield fabrication of YBCO coated conductors by Nd:YAG-PLD system

    NASA Astrophysics Data System (ADS)

    Ono, I.; Ichino, Y.; Yoshida, Y.; Yoshizumi, M.; Izumi, T.; Shiohara, Y.

    In order to fabricate superconducting coated conductors with lower cost, fabrication processes are required high material yield. We report an improvement of the material yield of YBCO films prepared by inside-plume Nd:YAG pulsed laser deposition method on metal substrates with an architecture of CeO2/LMO/IBAD-MgO/GZO/HastelloyTM. In this study, we shortened a distance from the target to the substrate (dT-S) in order to improve the material yield. Additionally, we have used Nd:YAG laser because initial and running costs are anticipated to be lower than those of excimer laser. As a result, by shorting the dT-S from 40 mm to 20 mm, the material yield increased on 10 mm×10 mm substrates. Additionally, by changing the O2 pressure (PO2) from 40 Pa to 400 Pa at dT-S = 20 mm, the material yield had a local maximal value of 18.6% at PO2=200 Pa. On multi-turn (MT) metal substrates, the material yield reached 56.0%. However, the critical current density (Jc) of the YBCO film which was deposited at dT-S = 20 mm and PO2=200 Pa on the 10 mm×10 mm substrate was 1.2 MA/cm2 at the edges and 0.2 MA/cm2 at the center at 77 K in self-field, although the YBCO films showed good aligned crystal textures. In order to improve this non-uniformity, we tilted the surface normal of the target 15 degree from a line connecting target and substrate. As a result, we achieved the uniformity in deposition rate. Then, we prepared YBa1.78Cu2.9Oy target to fabricate YBCO films with stoichiometric composition and obtained the uniform-high Jc.

  18. Fast epitaxial growth of a-axis- and c-axis-oriented YBa 2Cu 3O 7- δ films on (1 0 0) LaAlO 3 substrate by laser chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Pei; Ito, Akihiko; Tu, Rong; Goto, Takashi

    2011-02-01

    a-axis- and c-axis-oriented YBa2Cu3O7-δ (YBCO) films were epitaxially grown on (1 0 0) LaAlO3 substrates by laser chemical vapor deposition. The preferred orientation in the YBCO film changed from the a-axis to the c-axis with increasing laser powers from 77 to 158 W (the deposition temperatures from 951 to 1087 K). The a-axis-oriented YBCO film showed in-plane epitaxial growth of YBCO [0 0 1]//LAO [0 0 1], and the c-axis-oriented YBCO film showed that of YBCO [0 1 0]//LAO [0 0 1]. A c-axis-oriented YBCO film with a high critical temperature of 90 K was prepared at a deposition rate of 90 μm h-1, about 2-1000 times higher than that of metalorganic chemical vapor deposition.

  19. Study of the Nucleation and Growth of YBCO on Oxide Buffered Metallic Tapes

    SciTech Connect

    Solovyov, Vyacheslav

    2009-04-10

    The CRADA collaboration concentrated on developing the scientific understanding of the factors necessary for commercialization of high temperature superconductors (HTS) based on the YBCO coated conductor technology for electric power applications. The project pursued the following objectives: 1. Establish the correlations between the YBCO nuclei density and the properties of the CeO{sub 2} layer of the RABiTS{trademark} template; 2. Compare the nucleation and growth of e-beam and MOD based precursors on the buffered RABiTS{trademark} templates and clarify the materials science behind the difference; and 3. Explore routes for the optimization of the nucleation and growth of thick film MOD precursors in order to achieve high critical current densities in thick films. The CRADA work proceeded in two steps: 1. Detailed characterization of epitaxial ceria layers on “model” substrates, such as (001) YSZ and on RABiTS tapes; and 2. Study of YBCO nucleation on well-defined substrates and on long-length RABiTS.

  20. Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation

    SciTech Connect

    Biswas, Pranab; Banerji, P.; Halder, Nripendra N.; Kundu, Souvik; Shripathi, T.; Gupta, M.

    2014-05-15

    The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-à-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 ºC and 700 ºC showed p-type conductivity with a hole concentration of 1.1 × 10{sup 18} cm{sup −3} and 2.8 × 10{sup 19} cm{sup −3} respectively, whereas those annealed at 800 ºC showed n-type conductivity with a carrier concentration of 6.5 × 10{sup 16} cm{sup −3}. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (As{sub Zn}–2V{sub Zn}), by substituting Zn atoms (As{sub Zn}) and thereby creating two zinc vacancies (V{sub Zn}). Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 ºC, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, Ga{sub Zn}. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.

  1. Hybrid quantum systems with YBCO coplanar resonators and spin ensembles of organic radicals

    NASA Astrophysics Data System (ADS)

    Ghirri, Alberto; Bonizzoni, Claudio; Troiani, Filippo; Cassinese, Antonio; D'Arienzo, Massimiliano; Beverina, Luca; Affronte, Marco

    We have studied the coherent coupling of microwave photons in a superconducting coplanar resonator with a spin ensemble of stable open-shell organic radicals. We fabricated YBCO/sapphire coplanar resonators that show quality factors ~= 3*104 at 1.8 K, that remain remarkably stable in high magnetic field applied parallel to the YBCO film [QL (7 T) = 90% QL (0 T)]. Spin ensembles of (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl organic radical (PyBTM) show sharp EPR linewidth (8 MHz) due to the effect of the exchange narrowing. The frequency of the spin transition is tuned by means of the external magnetic field. We show the achievement of the strong collective coupling with the resonant photons with coupling rates exceeding 90 MHz at 1.8 K.

  2. Ion beam codeposition of HTSC films on SrTiO3 and ITO/Si

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor; Kellett, Bruce J.; Dwir, Benjamin; James, Jonathan H.; Gauzzi, Andrea; Faulkner, James R., Jr.; Affronte, M.; Reinhardt, F. K.

    1990-10-01

    Superconducting YBa2Cu3O 7 (YBCO) thin films were grown on Si with transparent, conducting Indium Tin Oxide (ITO) buffer layers The onset temperature at 92K and zero resistance at 68K were measured. Both, ITO and YBCO films were deposited by ion beam co-deposition. The YBCO/ITO films exhibit metallic resistivity with positive slopes (''O.O55 &square/K). The YBCO is uniform, textured and polycrystalline. The relevance for hybrid opto-electronic device structures is briefly discussed.

  3. Ion beam codeposition of HTSC films on SrTiO3 and ITO/Si

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor; Kellett, Bruce J.; Dwir, Benjamin; James, Jonathan H.; Gauzzi, Andrea; Faulkner, James R., Jr.; Affronte, M.; Reinhardt, F. K.

    1990-10-01

    Superconducting YBa2C u 3 0 7 (YBCO) thin films were grown on Si with transparent, conducting Indium Tin Oxide (ITO) buffer layers The onset temperature at 92K and zero resistance at 68K were measured. Both, ITO and YBCO films were deposited by ion beam co-deposition. The YBCO/ITO films exhibit metallic resistivity with positive slopes (r0.055 1K). The YBCO is uniform, textured and polycrystalline. The relevance for hybrid opto-electronic device structures is briefly discussed.

  4. MOD Buffer/YBCO Approach to Fabricate Low-Cost Second Generation HTS Wires

    SciTech Connect

    Paranthaman, Mariappan Parans; Sathyamurthy, Srivatsan; Bhuiyan, Md S; Martin, Patrick M; Aytug, Tolga; Kim, Kyunghoon; Fayek, Mostafa; Leonard, Keith J; Li, Jing; Zhang, W.; Rupich, Marty

    2007-01-01

    The metal organic deposition (MOD) of buffer layers on RABiTS substrates is considered a potential, low-cost approach to manufacturing high performance Second Generation (2G) high temperature superconducting (HTS) wires. The typical architecture used by American Superconductor in their 2G HTS wire consists of a Ni-W (5 at.%) substrate with a reactively sputtered Y2O3 seed layer, YSZ barrier layer and a CeO2 cap layer. This architecture supports critical currents of over 300 A/cm-width (77 K, self-field) with 0.8 mum YBCO films deposited by the TFA-MOD process. The main challenge in the development of the MOD buffers is to match or exceed the performance of the standard vacuum deposited buffer architecture. We have recently shown that the texture and properties of MOD - La2Zr2Ogamma (LZO) barrier layers can be improved by inserting a thin sputtered Y2O3 seed layer and prepared MOD deposited LZO layers followed by MOD or RF sputtered CeO2 cap layers that support MOD-YBCO films with Ic's of 200 and 255 A/cm-width, respectively. Detailed X-ray and microstructural characterizations indicated that MOD - CeO2 cap reacted completely with MOD YBCO to form BaCeOs. However, sputtered CeO2 cap/MOD YBCO interface remains clean. By further optimizing the coating conditions and reducing the heat-treatment temperatures, we have demonstrated an Ic of 336 A/cm with improved LZO layers and sputtered CeO2 cap and exceeded the performance of that of standard vacuum deposited buffers.

  5. YBCO High-Temperature Superconducting Filters on M-Plane Sapphire Substrates

    NASA Technical Reports Server (NTRS)

    Sabataitis, J. C.; Mueller, C. H.; Miranda, F. A.; Warner, J.; Bhasin, K. B.

    1996-01-01

    Since the discovery of High Temperature Superconductors (HTS) in 1986, microwave circuits have been demonstrated using HTS films on various substrates. These HTS-based circuits have proven to operate with less power loss than their metallic film counterparts at 77 K. This translates into smaller and lighter microwave circuits for space communication systems such as multiplexer filter banks. High quality HTS films have conventionally been deposited on lanthanum aluminate (LaAlO3) substrates. However, LaAlO3 has a relative dielectric constant (epsilon(sub r)) of 24. With a epsilon(sub r) approx. 9.4-11.6, sapphire (Al2O3) would be a preferable substrate for the fabrication of HTS-based components since the lower dielectric constant would permit wider microstrip lines to be used in filter design, since the lower dielectric constant would permit wider microstrip lines to be used for a given characteristic impedance (Z(sub 0)), thus lowering the insertion losses and increasing the power handling capabilities of the devices. We report on the fabrication and characterization of YBa2Cu3O(7-delta) (YBCO) on M-plane sapphire bandpass filters at 4.0 GHz. For a YBCO 'hairpin' filter, a minimum insertion loss of 0.5 dB was measured at 77 K as compared with 1.4 dB for its gold counterpart. In an 'edge-coupled' configuration, the insertion loss went down from 0.9 dB for the gold film to 0.8 dB for the YBCO film at the same temperature.

  6. Superconducting YBa2Cu3O7 films on Si and GaAs with conducting indium tin oxide buffer layers

    NASA Astrophysics Data System (ADS)

    James, J. H.; Kellett, B. J.; Gauzzi, A.; Dwir, B.; Pavuna, D.

    1991-03-01

    Superconducting YBa2Cu3O7-delta (YBCO) thin films have been grown in situ by ion beam sputtering on Si and GaAs substrates with intermediate, conducting Indium Tin Oxide (ITO) buffer layers. Uniform, textured YBCO films on ITO exhibit Tc onset at 92K and Tc0 at 68K and 60K on Si and GaAs substrates respectively, the latter value is the highest Tc reported on GaAs. YBCO/ITO films exhibit metallic resistivity behavior. In situ YBCO films on SrTiO3 show Tc onset = 92K and Tc0 = 90.5K, transition widths are less than 1K. A simple optical bolometer has been constructed from YBCO films on SrTiO3. Tunnelling measurements have also been carried out using the first YBCO-Pb window-type tunnel junctions.

  7. Fabrication of high T(sub c) superconductor thin film devices: Center director's discretionary fund

    NASA Technical Reports Server (NTRS)

    Sisk, R. C.

    1992-01-01

    This report describes a technique for fabricating superconducting weak link devices with micron-sized geometries etched in laser ablated Y1Ba2Cu3O(x) (YBCO) thin films. Careful placement of the weak link over naturally occurring grain boundaries exhibited in some YBCO thin films produces Superconducting Quantum Interference Devices (SQUID's) operating at 77 K.

  8. High Jc YBCO coated conductors on non-magnetic metallic substrate using YSZ-based buffer layer architecture

    NASA Astrophysics Data System (ADS)

    Celentano, G.; Boffa, V.; Ciontea, L.; Fabbri, F.; Galluzzi, V.; Gambardella, U.; Mancini, A.; Petrisor, T.; Rogai, R.; Rufoloni, A.; Varesi, E.

    2002-08-01

    Biaxially aligned YBa 2Cu 3O 7- δ (YBCO) thick films were deposited by pulsed laser ablation technique on cube textured non-magnetic Ni 89V 11 (Ni-V) substrate, using CeO 2/YSZ/CeO 2/NiO buffer layer architecture. The first NiO seed layer was formed by epitaxial oxidation of the Ni-V substrate. Structural analyses show typical full width at half maximum values of φ- and ω-scans less than 10° and 8°, respectively. The highest value obtained for the critical current density at 77 K and zero magnetic field was 6×10 5 A cm -2, which is close to that obtained for YBCO films grown on CeO 2/NiO buffer layer architecture.

  9. Transport phenomena and the effects of reactor geometry for epitaxial GaN growth in a vertical MOCVD reactor

    NASA Astrophysics Data System (ADS)

    Tseng, Chien-Fu; Tsai, Tsung-Yen; Huang, Yen-Hsiu; Lee, Ming-Tsang; Horng, Ray-Hua

    2015-12-01

    In this study a numerical simulation was carried out to analyze the transport phenomena in a vertical type metal organic chemical vapor deposition (MOCVD) reactor for Gallium Nitride (GaN) growth. The simulated results were compared and validated by experiment. The effects of showerhead design and chamber height are investigated and discussed. It was found that, by properly adjusting the height of the chamber, both the growth rate and film uniformity could be significantly improved. This is attributed to the suppression of the thermal and mass transfer boundary layers by the injection flow of reacting gas mixtures, as well as the confined vertical vortices caused by the geometry of the reduced space. However, inappropriate design of the distance between the showerhead and the susceptor can result in uneven distribution of the organic source in the vicinity of the substrate surface resulting in an uneven growth rate of the GaN film. Consequently, there exists an optimal chamber height that will give the best growth rate and uniformity to the GaN film as discussed in this study. This study provides comprehensive insight into the transport phenomena of GaN growth that includes coupled heat and mass transfer as well as chemical reactions. The results provide important information in a succinct format and enable decisions to be made about the showerhead and the geometrical design and size of a vertical MOCVD reactor.

  10. Growth and superconducting properties of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} films on conductive SrRuO{sub 3} and LaNiO{sub 3} multilayers for coated conductor applications

    SciTech Connect

    Aytug, T.; Wu, J. Z.; Cantoni, C.; Verebelyi, D. T.; Specht, E. D.; Paranthaman, M.; Norton, D. P.; Christen, D. K.; Ericson, R. E.; Thomas, C. L.

    2000-02-07

    Conductive multilayers of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}/SrRuO{sub 3}/LaNiO{sub 3} (YBCO/SRO/LNO), YBCO/SRO, and YBCO/LNO were grown epitaxially on single-crystal LaAlO{sub 3} and SrTiO{sub 3} substrates. Property characterizations revealed that the YBCO films on SRO and SRO/LNO buffer structures have excellent structural and superconducting properties. The YBCO/LNO, however, suffers degradation in superconducting transition temperatures and critical current densities, despite a good crystalline structure. The SRO/LNO bilayer showed excellent electrical contact with YBCO. These results have demonstrated the structural and chemical compatibility of SRO/LNO multilayers with YBCO and their potential use as conductive buffer layers for YBCO-based coated conductors as well as for other high-temperature superconducting applications. (c) 2000 American Institute of Physics.

  11. Maximum permissible voltage of YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Wen, J.; Lin, B.; Sheng, J.; Xu, J.; Jin, Z.; Hong, Z.; Wang, D.; Zhou, H.; Shen, X.; Shen, C.

    2014-06-01

    Superconducting fault current limiter (SFCL) could reduce short circuit currents in electrical power system. One of the most important thing in developing SFCL is to find out the maximum permissible voltage of each limiting element. The maximum permissible voltage is defined as the maximum voltage per unit length at which the YBCO coated conductors (CC) do not suffer from critical current (Ic) degradation or burnout. In this research, the time of quenching process is changed and voltage is raised until the Ic degradation or burnout happens. YBCO coated conductors test in the experiment are from American superconductor (AMSC) and Shanghai Jiao Tong University (SJTU). Along with the quenching duration increasing, the maximum permissible voltage of CC decreases. When quenching duration is 100 ms, the maximum permissible of SJTU CC, 12 mm AMSC CC and 4 mm AMSC CC are 0.72 V/cm, 0.52 V/cm and 1.2 V/cm respectively. Based on the results of samples, the whole length of CCs used in the design of a SFCL can be determined.

  12. Remarkable weakness against cleavage stress for YBCO-coated conductors and its effect on the YBCO coil performance

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Y.; Nakagome, H.; Takematsu, T.; Takao, T.; Sato, N.; Takahashi, M.; Maeda, H.

    2011-08-01

    Cleavage strength for an YBCO-coated conductor at 77 K was investigated with a model experiment. The nominal cleavage strength for an YBCO-coated conductor is extremely low, typically 0.5 MPa. This low nominal cleavage strength is due to stress concentration on a small part of the YBCO-coated conductor in cleavage fracture. Debonding by the cleavage stress occurs at the interface between the buffer layer and the Hastelloy substrate. The nominal cleavage strength for a slit edge of the conductor is 2.5-times lower than that for the original edge of the conductor; cracks and micro-peel existing over the slit edge reduce the cleavage strength for the slit edge. Cleavage stress and peel stress should be avoided in coil winding, as they easily delaminate the YBCO-coated conductor, resulting in substantial degradation of coil performance. These problems are especially important for epoxy impregnated YBCO-coated conductor coils. It appears that effect of cleavage stress and peel stress are mostly negligible for paraffin impregnated YBCO-coated conductor coils or dry wound YBCO-coated conductor coils.

  13. P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Jin, Y. J.; Chia, C. K.; Liu, H. F.; Wong, L. M.; Chai, J. W.; Chi, D. Z.; Wang, S. J.

    2016-07-01

    In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures.

  14. Fabrication of Filamentary YBCO Coated Conductor by Inkjet Printing

    SciTech Connect

    List III, Frederick Alyious; Kodenkandath, Thomas; Rupich, Marty

    2007-01-01

    Inkjet printing is a potentially low cost, high rate method for depositing precursors for filamentary YBCO coated conductors. The method offers considerable flexibility of filament pattern, width, and thickness. Using standard solution precursors and RABiTSTM substrates, the printing, processing, and properties of some inkjet-derived filamentary YBCO coated conductors for Second Generation (2G) wire are demonstrated on a laboratory scale. Some systematic variations of growth rate and critical transport current with filament width are observed and discussed.

  15. On the use of copper-based substrates for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Vannozzi, A.; Fabbri, F.; Augieri, A.; Angrisani Armenio, A.; Galluzzi, V.; Mancini, A.; Rizzo, F.; Rufoloni, A.; Padilla, J. A.; Xuriguera, E.; De Felicis, D.; Bemporad, E.; Celentano, G.

    2014-05-01

    It is well known that the recrystallization texture of heavily cold-rolled pure copper is almost completely cubic. However, one of the main drawbacks concerning the use of pure copper cube-textured substrates for YBCO coated conductor is the reduced secondary recrystallization temperature. The onset of secondary recrystallization (i.e., the occurrence of abnormal grains with unpredictable orientation) in pure copper substrate was observed within the typical temperature range required for buffer layer and YBCO processing (600-850 °C). To avoid the formation of abnormal grains the effect of both grain size adjustment (GSA) and recrystallization annealing was analyzed. The combined use of a small initial grain size and a recrystallization two-step annealing (TSA) drastically reduced the presence of abnormal grains in pure copper tapes. Another way to overcome the limitation imposed by the formation of abnormal grains is to deposit a buffer layer at temperatures where secondary recrystallization does not occur. For example, La2Zr2O7 (LZO) film with a high degree of epitaxy was grown by metal-organic decomposition (MOD) at 1000 °C on pure copper substrate. In several samples the substrate underwent secondary recrystallization. Our experiments indicate that the motion of grain boundaries occurring during secondary recrystallization process does not affect the quality of LZO film.

  16. Heavy p-type carbon doping of MOCVD GaAsP using CBrCl3

    NASA Astrophysics Data System (ADS)

    Heidelberger, Christopher; Fitzgerald, Eugene A.

    2016-07-01

    CBrCl3 is shown to be a useful precursor for heavy p-type carbon doping of GaAsxP1-x grown via metalorganic chemical vapor deposition (MOCVD) across a range of compositions. Structural and electrical properties of the GaAsP films were measured for various processing conditions. Use of CBrCl3 decreased the growth rate of GaAsP by up to 32% and decreases x by up to 0.025. The dependence of these effects on precursor inputs is investigated, allowing C-doped GaAsP films to be grown with good thickness and compositional control. Hole concentrations of greater than 2×1019 cm-3 were measured for values of x from 0.76 to 0.90.

  17. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  18. The use of metalorganics in the preparation of semiconductor materials. VIII - Feasibility studies of the growth of Group III-Group V compounds of boron by MOCVD

    NASA Technical Reports Server (NTRS)

    Manasevit, H. M.; Hewitt, W. B.; Nelson, A. J.; Mason, A. R.

    1989-01-01

    The MOCVD growth of B-As and B-P films on Si, sapphire, and Si-on-sapphire substrates is described; in this process, trimethylborane (TMB) or triethylborane (TEB) is pyrolyzed in the presence of AsH3 or PH3 in an H2 atmosphere. The procedures employed are outlined, and the results are presented in graphs, tables, and micrographs. It is found that the growth rate of the primarily amorphous films is dependent on the TMB or TEB concentration but approximately constant for TEB and AsH3 at 550-900 C. The nominal compositions of films grown using TMB are given as B(12-16)As2 and B(1-1.3)P. Carbon impurities and significant stress, bowing, and crazing are observed in the films grown on Si substrates, with the highest carbon content in the films grown from TMB and PH3.

  19. Hetero-epitaxy of ε-Ga2O3 layers by MOCVD and ALD

    NASA Astrophysics Data System (ADS)

    Boschi, F.; Bosi, M.; Berzina, T.; Buffagni, E.; Ferrari, C.; Fornari, R.

    2016-06-01

    Growth of gallium oxide thin films was carried out by Metalorganic Chemical Vapor Deposition (MOCVD) at different temperatures. Pure ε-phase epilayers of Ga2O3, with good morphology and structural properties, were obtained, for the first time with this technique, on sapphire at the temperature of 650 °C. XRD analysis performed by high-resolution diffractometry confirmed the good crystallographic quality of the grown layers. At temperatures higher than 700 °C the usual stable β-Ga2O3 phase was obtained. The ε-films were successfully deposited also on (0001)-oriented GaN and (111)- and (001)-oriented 3C-SiC templates, provided that the appropriate temperature was chosen. This indicates that the temperature, rather than substrate structure, is the growth parameter which decides what phase actually forms. The growth proceeds via coalescence of hexagonal islands and is favored when a substrate with an in-plane hexagonal arrangement of the atoms is employed. By applying Atomic Layer Deposition (ALD), epitaxial growth of the ε-phase was achieved at lower temperature, while the overall uniformity resulted improved, even on large sapphire substrates.

  20. Enhanced 77 K vortex-pinning in Y Ba2Cu3O7-x films with Ba2Y TaO6 and mixed Ba2Y TaO6 + Ba2Y NbO6 nano-columnar inclusions with irreversibility field to 11 T

    NASA Astrophysics Data System (ADS)

    Rizzo, F.; Augieri, A.; Angrisani Armenio, A.; Galluzzi, V.; Mancini, A.; Pinto, V.; Rufoloni, A.; Vannozzi, A.; Bianchetti, M.; Kursumovic, A.; MacManus-Driscoll, J. L.; Meledin, A.; Van Tendeloo, G.; Celentano, G.

    2016-06-01

    Pulsed laser deposited thin Y Ba2Cu3O7-x (YBCO) films with pinning additions of 5 at. % Ba2Y TaO6 (BYTO) were compared to films with 2.5 at. % Ba2Y TaO6 + 2.5 at. % Ba2Y NbO6 (BYNTO) additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO) and 11 T (YBCO-BYNTO), representing the highest ever achieved values in YBCO films.

  1. MOCVD growth of vertically aligned InGaN nanowires

    NASA Astrophysics Data System (ADS)

    Kuo, H. C.; Su Oh, Tae; Ku, P.-C.

    2013-05-01

    In this work, we report the growth of vertically aligned bulk InGaN nanowires (NWs) on r-plane sapphire substrate by metal organic chemical vapor deposition (MOCVD). Through the optimization process of growth conditions, such as growth temperature and pressure, we obtained high density InGaN NWs consisting of one (0001) polar- and two equivalent {1101} semi-polar planes. We have shown the highest InGaN NWs wire density of 8×108 cm-2,with an average diameter of 300 nm and a length of 2 μm. From results of photoluminescence (PL) at 30 K and 300 K, we observed the intense and broad emission peak from InGaN NWs at around 595 nm, and confirmed that the luminescence could be tuned from 580 nm to 660 nm by controlling the indium flow (TMIn) rate. Our results indicate that MOCVD-grown InGaN NWs can be effective absorbers of the blue-green range of solar spectrum and may be one of the good candidates for high efficiency photovoltaic devices targeting at blue-green photons.

  2. YBCO grain boundary Josephson junction coupled with a slot dipole antenna for terahertz wave detectors

    NASA Astrophysics Data System (ADS)

    Yamada, H.; Hayasaka, T.; Toya, G.; Saito, A.; Ohshima, S.; Nakajima, K.

    2014-05-01

    We examined terahertz wave detectors that used YBa2Cu3O7-δ (YBCO) grain boundary Josephson junctions (GBJJs) coupled with a slot dipole antenna (SDA). The detectors consisted of a 220-GHz full-wavelength SDA patterned on a Au layer and a GBJJ patterned on an YBCO/bicrystal MgO film, which were separated by an insulating benzocyclobutene layer. The microbridge of the fabricated junction was 5-μm wide and was trimmed to 2 μm using an ultraviolet laser cutter to modify the junction parameters. The critical current IC, normal resistance RN, and ICRN product after the trimming at 30 K were 0.62 mA, 1.42 Ω, and 0.88 mV, respectively. The current-voltage characteristics and radio frequency (RF) wave responses of these detectors for a millimeter wave of 180-240 GHz were measured at 30 K. The coupling efficiency between the GBJJ and the SDA and the system sensitivity were obtained as -19.0 dB and 630 V/W, respectively, at 193 GHz. For the RF wave response of 180-240 GHz, the coupling efficiency was relatively flat.

  3. MOD approach for the growth of epitaxial CeO2 buffer layers on biaxially textured Ni W substrates for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Bhuiyan, M. S.; Paranthaman, M.; Sathyamurthy, S.; Aytug, T.; Kang, S.; Lee, D. F.; Goyal, A.; Payzant, E. A.; Salama, K.

    2003-11-01

    We have grown epitaxial CeO2 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors using a newly developed metal organic decomposition (MOD) approach. Precursor solution of 0.25 M concentration was spin coated on short samples of Ni-3 at%W (Ni-W) substrates and heat-treated at 1100 °C in a gas mixture of Ar-4%H2 for 15 min. Detailed x-ray studies indicate that CeO2 films have good out-of-plane and in-plane textures with full-width-half-maximum values of 5.8° and 7.5°, respectively. High temperature in situ XRD studies show that the nucleation of CeO2 films starts at 600 °C and the growth completes within 5 min when heated at 1100 °C. SEM and AFM investigations of CeO2 films reveal a fairly dense microstructure without cracks and porosity. Highly textured YSZ barrier layers and CeO2 cap layers were deposited on MOD CeO2-buffered Ni-W substrates using rf-magnetron sputtering. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A critical current, Jc, of about 1.5 MA cm-2 at 77 K and self-field was obtained on YBCO (PLD)/CeO2 (sputtered)/YSZ (sputtered)/CeO2 (spin-coated)/Ni-W.

  4. Superconducting YBa2Cu3O7 films for novel (opto)electronic device structures

    NASA Astrophysics Data System (ADS)

    Pavuna, D.; Dwir, B.; Gauzzi, A.; James, J. H.; Kellett, B. J.

    1991-02-01

    This short overview briefly summarizes the most important parameters for successful preparation and associated properties of thin films of YBa2Cu3O(7-delta) (YBCO) superconductors. The principles are illustrated by using the example of monotarget ion beam sputtering technique: YBCO films grown in situ on SrTiO3 show Tc(onset) = 92 K and Tco = 91 K. Magnetron sputtering, E-beam evaporation, laser ablation and molecular beam epitaxy are discussed. In situ ion beam sputtering of YBCO on Si and GaAs substrates with intermediate, conducting Indium Tin Oxide (ITO) buffer layers is also presented. Uniform, textured YBCO films on ITO exhibit Tc(onset) at 92 K and Tco at 68 K and 60 K on Si and GaAs substrates, respectively; the latter is the highest Tc reported on GaAs. YBCO/ITO films exhibit metallic resistivity behavior. Finally, the performance of a simple optical bolometer demonstrated on YBCO films and the results of tunneling measurements on the window-type YBCO-Pb tunnel junctions are discussed.

  5. Demonstration of High Current Density YBCO Coated Conductors on RE2O3-Buffered Ni Substrates with Two New Alternative Architectures

    SciTech Connect

    Beach, D.B.; Chirayil, T.G.; Christen, D.K.; Cui, X.; Feenstra, R.; Goyal, A.; Kroeger, D.M.; Lee, D.F.; Martin, P.M.; Mathis, J.E.; Morrell, J.S.; Norton, D.P.; Paranthaman, M.; Specht, E.D.; Verebelyi, D.T.

    1999-07-12

    In continuation of our effort to develop single buffer layer architectures for YBCO (YBa2Cu3O7-g) coated tape conductors, we have studied RE2O3 (RE = Y, and rare earths) as candidate materials. Three types of crystal structures including the preferred cubic phase are known for the rare earth oxides. High quality simple cubic RE2O3 buffer layers were grown epitaxiahy on {100}<001> textured Ni substrates using both reactive evaporation and sol-gel processing. Detailed X-ray studies have shown that the Y2O3, Eu2O3, Gd2O3, and Yb2O3 were grown with a single epitaxial orientation. SEM micrographs indicated that both e-beam and sol-gel grown films were dense, continuous and crack free. High Jc YBCO films were grown on RE2O3-buffered Ni substrates with sputtered cap layers. Two new alternative buffer layer architectures were developed. A high Jc of 1.8 MA/cm2 at 77 K and self-field was obtained on YBCO films with a layer sequence of YBCO (pulsed laser deposition)/Yb2O3 (sputtered)/Y2O3 (e-beam)/Ni. Also, a high Jc of over 1 MA/cm2 at 77 K and self-field was obtained on YBCO films with a layer sequence of YBCO (ex-situ BaF2 process)/CeO2 (sputtered)YSZ sputtered)/RE2O3 (sol-gel or e-beam)Ni. The performance of sol-gel grown buffers approached the quality of e-beam grown buffers.

  6. Raman and x-ray absorption spectroscopy characterization of Zr-doped MOCVD YBa2Cu3O6+δ

    NASA Astrophysics Data System (ADS)

    Maroni, V. A.; Kropf, A. J.; Aytug, T.; Paranthaman, M.

    2010-01-01

    Metal-organic chemical vapor deposited YBa2Cu3O6+δ (YBCO) films (about 0.9 µm thick) containing varying amounts of added zirconium were examined by Raman microscopy and synchrotron x-ray absorption spectroscopy. The self-field and in-field (1 T, B\\parallel c ) Jc performance of the YBCO films at 77 K (reported by the group at Oak Ridge National Laboratory that fabricated the samples) exhibited an increase on going from 0 mol% (m/o) Zr-added to 2.5 m/o Zr-added but then decreased sharply with increasing Zr content. Raman measurements on these films showed that the added Zr had little effect on YBCO cation disorder up to about 7.5 m/o Zr-added. Cation disorder increased while Ba-Cu-O content remained relatively constant for Zr additions >=7.5 m/o. In the region of sharpest descent of Jc with increasing Zr content (2.5-7.5 m/o Zr-added) neither the cation disorder nor the Ba-Cu-O content showed a systematic variation with Jc. Zirconium K edge x-ray absorption near-edge spectroscopy revealed that virtually all of the added Zr in each sample was present as a BaZrO3-like phase (BZO). The Jc performance of the Zr-added films showed a high correlation with the variations in the next-nearest-neighbor Zr-M (M = Zr, Y) scattering path amplitude from the extended x-ray absorption fine structure (EXAFS) and the critical temperature over the full range of Zr additions and with cation disorder at the higher Zr-added levels (>7.5 m/o). There was no obvious correlation with the amount of residual barium cuprate or CuO. Approximate ranges for the BZO particle dimensions estimated from the EXAFS data indicated that the mean particle size gets larger with increasing Zr addition.

  7. Microstructure Characteristics of High Lift Factor MOCVD REBCO Coated Conductors With High Zr Content

    SciTech Connect

    Galstyan, E; Gharahcheshmeh, MH; Delgado, L; Xu, AX; Majkic, G; Selvamanickam, V

    2015-06-01

    We report the microstructural characteristics of high levels of Zr-added REBa2Cu3O7-x (RE = Gd, Y rare earth) coated conductors fabricated by Metal Organic Chemical Vapor Deposition (MOCVD). The enhancements of the lift factor defined as a ratio of the in-field (3 T, B parallel to c-axis) critical current density (J(c)) at 30 K and self-field J(c) at 77 K have been achieved for Zr addition levels of 20 and 25 mol% via optimization of deposition parameters. The presence of strong flux pinning is attributed to the aligned nanocolumns of BaZrO3 and nanoprecipitates embedded in REBa2Cu3O7-x matrix with good crystal quality. A high density of BZO nanorods with a typical size 6-8 nm and spacing of 20 nm has been observed. Moreover, the high Zr content was found to induce a high density of intrinsic defects, including stacking faults and dislocations. The correlation between in-field performance along the c-axis and microstructure of (Gd, Y) BCO film with a high level of Zr addition is discussed.

  8. Growth and Superconducting Properties of YBa2Cu3O 7-d Films on Conductive SrRuO3 and LaNiO3 Multilayers for

    SciTech Connect

    Aytug, T.

    2000-02-07

    Conductive multilayers of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}/SrRuO{sub 3}/LaNiO{sub 3} (YBCO/SRO/LNO), YBCO/SRO, and YBCO/LNO were grown epitaxially on single-crystal LaAlO{sub 3} and SrTiO{sub 3} substrates. Property characterizations revealed that the YBCO films on SRO and SRO/LNO buffer structures have excellent structural and superconducting properties. The YBCO/LNO, however, suffers degradation in superconducting transition temperatures and critical current densities, despite a good crystalline structure. The SRO/LNO bilayer showed excellent electrical contact with BCO. These results have demonstrated the structural and chemical compatibility of SRO/LNO multilayers with YBCO and their potential use as conductive buffer layers for YBCO-based coated conductors as well as for other high-temperature superconducting applications.

  9. Growth of epitaxial Y 2O 3 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors by MOD approach

    NASA Astrophysics Data System (ADS)

    Bhuiyan, M. S.; Paranthaman, M.; Kang, S.; Lee, D. F.; Salama, K.

    2005-06-01

    We have grown epitaxial Y 2O 3 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors using a newly developed metal organic decomposition (MOD) approach. Y 2O 3 precursor solution of 0.25 M concentration was spin coated on short samples of Ni-3 at.%W (Ni-W) substrates and heat-treated at 1150 °C in a gas mixture of Ar-4% H 2 for an hour. Detailed X-ray studies indicate that Y 2O 3 films have good out-of-plane and in-plane textures with full-width-half-maximum values of 6.22° and 7.51°, respectively. SEM and AFM investigations of Y 2O 3 films reveal a fairly dense and smooth microstructure without cracks and porosity. Highly textured YSZ barrier layers and CeO 2 cap layers were deposited on MOD Y 2O 3-buffered Ni-W substrates using rf-magnetron sputtering. Pulsed laser deposition was used to grow YBCO films on these substrates. A critical current, Jc, of about 1.21 MA/cm 2 at 77 K and self-field was obtained on YBCO (PLD)/CeO 2 (sputtered)/YSZ (sputtered)/Y 2O 3 (spin-coated)/Ni-W.

  10. MOCVD growth of AlGaN UV LEDs

    SciTech Connect

    Han, J.; Crawford, M.H.

    1998-09-01

    Issues related to the MOCVD growth of AlGaN, specifically the gas-phase parasitic reactions among TMG, TMA, and NH{sub 3}, are studied using an in-situ optical reflectometer. It is observed that the presence of the well-known gas phase adduct (TMA: NH{sub 3}) could seriously hinder the incorporation behavior of TMGa. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN SCH QW p-n diode structure. The UV emission at 360 nm (FWHM {approximately} 10 nm) represents the first report of LED operation from an indium-free GaN QW diode.

  11. Radiation induced modifications on microstructure and related properties of high temperature superconductor YBCO

    NASA Astrophysics Data System (ADS)

    Marhas, Manmeet Kaur; Balakrishnan, K.; Saravanan, P.; Ganesan, V.; Srinivasan, R.; Kanjilal, D.; Mehta, G. K.; Vedwyas, M.; Ogale, S. B.; Pai, S. P.; Ramachandra Rao, M. S.; Pinto, R.; Mohan Rao, G.; Senthilnathan, S.; Mohan, S.

    Role of swift heavy ion irradiation on the modification of transport and structural properties of high temperature superconductors is studied. Good quality YBCO thin films prepared by high pressure oxygen sputtering and laser ablation were used in this investigation. Resistivity and atomic force microscopy (AFM) were mainly used to probe superconducting and microstructural modifications resulted from the irradiation of high energy and heavy ions like 100 MeV oxygen and 200 MeV silver. Radiation induced sputtering or erosion is likely to be a major disastrous component of such high energy irradiation that could be powerful in masking phase coherence effects, atleast in grain boundaries. The extent of damage/nature of defects other than columnar defects produced by swift heavy ions is discussed in the light of AFM measurements. The effect of high energy oxygen ion irradiation is anomalous. A clear annealing effect at higher doses is seen.

  12. Study of TiO2 nanomembranes obtained by an induction heated MOCVD reactor

    NASA Astrophysics Data System (ADS)

    Crisbasan, A.; Chaumont, D.; Sacilotti, M.; Crisan, A.; Lazar, A. M.; Ciobanu, I.; Lacroute, Y.; Chassagnon, R.

    2015-12-01

    Nanostructures of TiO2 were grown using the metal oxide chemical vapor deposition (MOCVD) technique. The procedure used induction heating on a graphite susceptor. This specific feature and the use of cobalt and ferrocene catalysts resulted in nanomembranes never obtained by common MOCVD reactors. The present study discusses the preparation of TiO2 nanomembranes and the dependence of nanomembrane structure and morphology on growth parameters.

  13. High Tc YBCO superconductor deposited on biaxially textured Ni substrate

    DOEpatents

    Budai, John D.; Christen, David K.; Goyal, Amit; He, Qing; Kroeger, Donald M.; Lee, Dominic F.; List, III, Frederick A.; Norton, David P.; Paranthaman, Mariappan; Sales, Brian C.; Specht, Eliot D.

    1999-01-01

    A superconducting article includes a biaxially-textured Ni substrate, and epitaxial buffer layers of Pd (optional), CeO.sub.2 and YSZ, and a top layer of in-plane aligned, c-axis oriented YBCO having a critical current density (J.sub.c) in the range of at least 100,000 A/cm.sup.2 at 77 K.

  14. Magnetic moment of single vortices in YBCO nano-superconducting particle: Eilenberger approach

    NASA Astrophysics Data System (ADS)

    Zakharchuk, I.; Sharafeev, A.; Belova, P.; Safonchik, M.; Traito, K. B.; Lähderanta, E.

    2013-12-01

    Temperature dependence of single vortex magnetic moment in nanosize superconducting particles is investigated in the framework of quasiclassical Eilenberger approach. Such nanoparticles can be used for preparation of high-quality superconducting thin films with high critical current density. In contrast to bulk materials where the vortex magnetic moment is totally determined by flux quantum, in nano-sized specimens (with characteristic size, D, much less than effective penetration depth, λeff) the quantization rule is violated and magnetic moment is proportional to D2/λ2eff(T). Due to strong repulsion between vortices in nanoparticles only a single vortex can be trapped in them. Because of small size of particles the screening current of the vortex is located near the vortex core where the current is quite high and comparable to depairing currents. Therefore, the superconducting electron density, ns, depends on the current value and the distance from the vortex core. This effect is especially important for superconductors having gap nodes, such as YBCO. The current dependence of ns in nanoparticles is analogous to the Volovik effect in flux-line lattice in bulk samples. The magnitude of the effect can be obtained by comparing the temperature dependence of magnetic moment in the vortex and in the Meissner states. In the last case the value of screening current is small and superconducting response to the external field is determined by London penetration depth. Because of importance of nonlinear and nonlocal effects, the quantum mechanical Eilenberger approach is applied for description of the vortex in nanoparticles. The flattening of 1/λ2eff(T) dependence has been found. A comparison of the theoretical results with experimental magnetization data in Meissner and mixed states of YBCO nanopowders has been done. The presence of nonlinear and nonlocal effects in vortex current distribution is clearly visible. The obtained results are important for the description

  15. Thermal diffusion and quench propagation in YBCO pancake coils wound with ZnO and Mylar insulations

    NASA Astrophysics Data System (ADS)

    Sumption, M. D.; Majoros, M.; Susner, M.; Lyons, D.; Peng, X.; Clark, C. F.; Lawless, W. N.; Collings, E. W.

    2010-07-01

    The thermal diffusion properties of several different kinds of YBCO (yttrium barium copper oxide) insulations and the quench properties of pancake coils made using these insulations were studied. Insulations investigated include Nomex, Kapton, and Mylar, as well as insulations based on ZnO, Zn2GeO4, and ZnO-Cu. Nomex, Kapton, and Mylar, chosen for their availability and ease of use, were obtained as thin ribbons, while the ZnO based insulations were chosen for their high thermal conductivity and were applied by a thin film technique. Initially, short stacks of YBCO conductors with interlayer insulation, epoxy, and a central heater strip were made and later measured as regards their thermal conductivity in liquid nitrogen. Subsequently, three different pancake coils were made. The first two were smaller, each using one meter total of YBCO tape present as four turns around a G-10 former. One of these smaller coils used Mylar insulation co-wound with the YBCO tape, the other used YBCO tape onto which ZnO based insulation had been deposited. One larger coil was made which used 12 total meters of ZnO insulated tape and had 45 turns. Temperature gradients were measured and thermal conductivities were estimated from these coils; the results obtained were compared to those for the short stacks. Quench propagation velocity measurements were performed on the coils (77 K, self-field) by applying a DC current and then using a heater pulse to initiate a quench. Radial NZP (normal zone propagation velocity) values (0.02-1 mm s - 1) were two orders of magnitude lower than axial values (~10-20 mm s - 1). Nevertheless, the quenches were generally seen to propagate radially within the coils, in the sense that any given turn in the coil is driven normal by the turn underneath it. This was due to the fact that while the radial NZP is much lower than the NZP along the conductor (~100 ×) the distance by which the normal zone must expand longitudinally is much larger than the distance

  16. Effects of process parameters on sheet resistance uniformity of fluorine-doped tin oxide thin films

    PubMed Central

    2012-01-01

    An alternative indium-free material for transparent conducting oxides of fluorine-doped tin oxide [FTO] thin films deposited on polyethylene terephthalate [PET] was prepared by electron cyclotron resonance - metal organic chemical vapor deposition [ECR-MOCVD]. One of the essential issues regarding metal oxide film deposition is the sheet resistance uniformity of the film. Variations in process parameters, in this case, working and bubbler pressures of ECR-MOCVD, can lead to a change in resistance uniformity. Both the optical transmittance and electrical resistance uniformity of FTO film-coated PET were investigated. The result shows that sheet resistance uniformity and the transmittance of the film are affected significantly by the changes in bubbler pressure but are less influenced by the working pressure of the ECR-MOCVD system. PMID:22221518

  17. X-ray diffraction characterization of thin superconductive films

    SciTech Connect

    Kozaczek, K.J.; Watkins, T.R.; Book, G.W.; Carter, W.B.

    1995-12-31

    The physical and mechanical properties of thin films are often different from the properties of bulk material and are dictated by the film/substrate orientation relationship, crystal anisotropy and crystalgraphic texture of the film. X-ray diffraction texture analysis provides information about preferential film growth and can be used for optimization of deposition parameters and prediction of properties of thin films. An x-ray back reflection technique using the Braga-Brentano geometry with experimental corrections for absorption and defocusing was used to study thin ceramic films deposited by combustion chemical vapor deposition (CCVD). The film/substrate orientation relationships of YBa{sub 2}Cu{sub 3}O{sub x} (YBCO) superconducting thin films deposited via CCVD on single crystal MgO and polycrystalline silver substrates were studied. The as-deposited films on single crystal (100) MgO substrates showed strong preferential growth with the basal plane parallel to the substrate surface (c-axis up growth). Texture analysis showed two in-plane alignment orientations of the film with respect to the substrate, with YBCO [100] and [110] aligned with the [100] MgO substrate. YBCO films deposited on cold-rolled polycrystalline silver displayed c-axis up growth indicating that the orientation of the polycrystalline substrate (brass type texture) did not induce detectable in-plane preferential growth of the YBCO.

  18. Temperature and Magnetic Field Dependence of Critical Currents in YBCO Coated Conductors with Processing-Induced Variations in Pinning Properties

    SciTech Connect

    Gapud, Albert Agcaoili; Feenstra, Roeland; Christen, David K; Thompson, James R; Holesinger, T. G.

    2005-01-01

    Several applications of high-temperature super-conducting wire require high currents at intermediate magnetic fields B and over a range of orientations; however, such conditions are at present achievable only at low temperatures (-30 K). The goal of this study is to determine the feasibility of higher operating temperatures for these applications by investigating temperature dependent, low- and high-field pinning properties of YBCO coated conductor samples. The YBCO films were grown on RABiTS templates by a PVD ex situ BaF{sub 2} process. Variations in pinning properties were induced by introducing excess yttrium (Y) in the precursor and controllably increasing the growth rate. The main result is a more uniform dependence of J{sub c} over all orientations of B, along with high irreversibility field B{sub irr} and high critical current densities J{sub c}. Results also show that for films with various pinning properties and processed under different conditions the self-field J{sub c} at 77 K is an effective indicator of performance in the temperatures and fields of interest.

  19. Microwave surface resistance of high Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Apte, Prakash R.; Pinto, R.; Kumar, Dhananjay; Vijayaraghavan, R.

    1995-09-01

    The surface resistance, Rs, at microwave frequencies has been an important qualification parameter for high temperature superconductor (HTS) thin films. HTS thin films with low Rs have been realized on many substrates, and many groups have realized Rs values in the range 300 - 400 (mu) (Omega) at 10 GHz at 77 K with YBa2Cu3O7-(delta ) (YBCO) films on <100> LaAlO3 substrates. Both microstrip resonator and parallel plate resonator techniques are being used to measure Rs values of HTS thin films. It has been observed that the value of Rs at given frequency and temperature critically depends upon the epitaxial quality and granularity of the films. For example, YBCO films grown on <100> MgO have been found to be granular and weak link limited with a significant microwave power dependence of Rs. On the other hand, YBCO films insitu grown on <100> LaAlO3 have shown better epitaxy with low Rs. This is obviously due to the much better lattice match of YBCO with <100> LaAlO3 if the targets used for laser deposition are doped with Ag. Extensive work carried out in our laboratory has shown that a Ag-doping level of around 5 wt.% in YBCO is the optimum which results in YBCO films of much improved quality. We have realized Ag-doped YBCO films with Jc values of 6 - 8 X 106 Acm-2 at 77 K and a low Rs value of 210 (mu) (Omega) at 10 GHz at 77 K on <100> LaAlO3. Both these values are the best realized on LaAlO3 to date. What is equally important is the fact that with Ag-doping the reproducibility of the epitaxial quality of the films improves significantly. This has been found to be due to the enhanced oxygenation of films during growth and the surfactant effect of Ag. Experiments have shown that even the optimum temperature for insitu growth in reduced considerably by Ag-doping. It must be mentioned, however, that the only negative aspect of Ag-doping is the higher microwave residual surface resistance, Rres, observed in these films at (very) low temperatures. This is obviously due

  20. Physical and Material Properties of Yttrium Barium Copper Oxide High Critical Temperature Superconducting Thin Films.

    NASA Astrophysics Data System (ADS)

    Ma, Qiyuan

    1990-01-01

    A simple method of using layered structures and rapid thermal annealing to produce Y_1 Ba_2 Cu_3 O_{7-x} (YBCO) superconducting thin films is presented. Material properties of the films depend strongly on the processing conditions, the film stoichiometry, and the substrates. The films with critical temperature (T_{ rm c}) higher than liquid nitrogen temperature (77 K) have been made on various substrates including magnesium oxide, sapphire, and silicon. The best film was obtained on a MgO substrate with T_{rm c} of 84 K. Silicon diffusion and reaction with oxygen during a high temperature anneal degrade the superconductivity of the film on a Si substrate. Using a buffer layer of gold, the Si-YBCO interaction is greatly reduced. Typical resistivity of the film shows a linear temperature dependence which may be attributed to an electron -phonon interaction. Anisotropic resistance behavior has been observed due to the layered structures. Different metal contacts to the YBCO films have been used to study the chemical and electrical properties of metal-YBCO film interfaces. Gold has been found nonreactive to YBCO film, thus, it has the lowest contact resistivity. Near the T_{rm c}, the contact resistivity of a Au-YBCO contact approaches zero. This may be due to the proximity effect. Other metals such as Pt, Pd, Sn and Ti, react with the YBCO film and form thin oxide layers at the interfaces. The oxide layer acts as an insulating barrier which forbids the proximity effect and causes a large contact resistivity. The structural and electrical properties of the Si-YBCO intermixed film have been studied for different thicknesses of the silicon layers. A novel patterning technique of using Si-YBCO intermixing has been developed for fabricating the YBCO superconducting device structures. A superconductor sample has a critical current value I _{rm c}. Below the I _{rm c} the material is superconducting, and above I_{rm c} the sample has a finite resistance. Based on this effect

  1. Doping Effect of Nano-Ybco Additive on MgB2

    NASA Astrophysics Data System (ADS)

    Rui, X. F.; Sun, X. F.; Xu, X. L.; Zhang, L.; Zhang, H.

    The effect of YBCO nanoparticles added into MgB2 on Tc, Jc, and flux pinning was studied for MgB2(YBCO)x with x=0, 5, 10, 15 wt%. Phase analysis shows that none of elements are doped into the MgB2 lattice in the samples with YBCO addition. For the samples with YBCO addition, the Jc-H characteristics behave poorly in comparison with the pure sample. Our experimental results show that the nanoscale size of addition dosen't comprise the only condition for its effectiveness as pinning centers.

  2. Influence of oxygen partial pressure and silver additions on microstructure and related properties of YBCO superconductors

    SciTech Connect

    Singh, J.P.; Joo, J.; Guttschow, R.; Poeppel, R.B.

    1992-02-01

    Microstructure has a great influence on the mechanical and superconducting properties of YBCO. Mechanical properties of YBCO can be improved by both modifying the monolithic microstructure and developing composites of YBCO with silver (Ag). When monolithic YBCO was sintered to high densities ({approx} 91%) at a relatively low temperature ({approx} 910{degrees}C) by controlling oxygen partial pressure during sintering, the result was a small-grain microstructure (average grain size {approx} 5 {mu}m) and hence a high strength of 191 {plus_minus} 7 MPa. Addition of Ag as a second phase further improved the strength of YBCO. Composites of YBCO with 10 to 15 vol % Ag has a strength of 225 {plus_minus} 6 MPa and a fracture toughness of 3.3 {plus_minus} 0.2 MPa{radical}m. These improvements are believed to be due to compressive stresses in the YBCO matrix as a result of thermal mismatch between the YBCO and Ag phases. Furthermore, the Ag particles may provide increased resistance to crack propagation by pinning the crack. On the other hand, addition of Ag as a dopant to substitute for Cu sites in YBCO has a profound but nonmonotonic effect on grain microstructure and the resulting critical current density.

  3. Influence of oxygen partial pressure and silver additions on microstructure and related properties of YBCO superconductors

    SciTech Connect

    Singh, J.P.; Joo, J.; Guttschow, R.; Poeppel, R.B.

    1992-02-01

    Microstructure has a great influence on the mechanical and superconducting properties of YBCO. Mechanical properties of YBCO can be improved by both modifying the monolithic microstructure and developing composites of YBCO with silver (Ag). When monolithic YBCO was sintered to high densities ({approx} 91%) at a relatively low temperature ({approx} 910{degrees}C) by controlling oxygen partial pressure during sintering, the result was a small-grain microstructure (average grain size {approx} 5 {mu}m) and hence a high strength of 191 {plus minus} 7 MPa. Addition of Ag as a second phase further improved the strength of YBCO. Composites of YBCO with 10 to 15 vol % Ag has a strength of 225 {plus minus} 6 MPa and a fracture toughness of 3.3 {plus minus} 0.2 MPa{radical}m. These improvements are believed to be due to compressive stresses in the YBCO matrix as a result of thermal mismatch between the YBCO and Ag phases. Furthermore, the Ag particles may provide increased resistance to crack propagation by pinning the crack. On the other hand, addition of Ag as a dopant to substitute for Cu sites in YBCO has a profound but nonmonotonic effect on grain microstructure and the resulting critical current density.

  4. Unique magnetic structure of YbCo2Si2

    NASA Astrophysics Data System (ADS)

    Mufti, N.; Kaneko, K.; Hoser, A.; Gutmann, M.; Geibel, C.; Krellner, C.; Stockert, O.

    2016-07-01

    We report on the results of powder and single-crystal neutron diffraction to investigate the magnetic order in YbCo2Si2 below the Néel temperature TN=1.7 K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector k1=(0.25 0.25 1 ) is found, while the intermediate phase (T >0.9 K) is characterized by an incommensurate magnetic structure with k2=(0.25 0.086 1 ) . The magnetic structure in YbCo2Si2 is in marked contrast to all other known R Co2Si2 compounds (R = rare earth element) likely due to some itineracy of the Yb 4 f states being responsible for the magnetism.

  5. Temperature dependence of nanoscale friction for Fe on YBCO

    NASA Astrophysics Data System (ADS)

    Altfeder, Igor; Krim, Jacqueline

    2012-05-01

    A magnetic probe microscopy study of levitation and atomic-scale friction is reported for Fe on YBCO (Tc = 92.5 K) in the temperature range 65-293 K. Below Tc, the friction coefficient is constant and exhibits no correlation with the strength of superconducting levitation forces. Above Tc, the friction coefficient increases progressively, and nearly doubles between Tc and room temperature. The results are discussed within the context of the underlying atomic-scale electronic and phononic mechanisms that give rise to friction, and it is concluded that contact electrification and static electricity may play a significant role in the non-superconducting phase. Given that the properties of YBCO can be finely tuned, the results point the way to a variety of interesting studies of friction and superconductors.

  6. STANFORD IN-SITU HIGH RATE YBCO PROCESS: TRANSFER TO METAL TAPES AND PROCESS SCALE UP

    SciTech Connect

    Malcolm R. Beasley; Robert H.Hammond

    2009-04-14

    Executive Summary The materials science understanding of high rate low cost processes for Coated Conductor will benefit the application to power utilities for low loss energy transportation and power generation as well for DOD applications. The research in this program investigated several materials processing approaches that are new and original, and are not being investigated elsewhere. This work added to the understanding of the material science of high rate PVD growth of HTSC YBCO assisted by a liquid phase. A new process discovered uses amorphous glassy precursors which can be made at high rate under flexible conditions of temperature and oxygen, and later brought to conditions of oxygen partial pressure and temperature for rapid conversion to YBCO superconductor. Good critical current densities were found, but further effort is needed to optimize the vortex pinning using known artificial inclusions. A new discovery of the physics and materials science of vortex pinning in the HTSC system using Sm in place of Y came at growth at unusually low oxygen pressure resulting in clusters of a low or non superconducting phase within the nominal high temperature phase. The driving force for this during growth is new physics, perhaps due to the low oxygen. This has the potential for high current in large magnetic fields at low cost, applicable to motors, generators and transformers. The technical demands of this project were the motivation for the development of instrumentation that could be essential to eventual process scale up. These include atomic absorption based on tunable diode lasers for remote monitoring and control of evaporation sources (developed under DARPA support), and the utility of Fourier Transform Infrared Reflectivity (FTIR) for aid in the synthesis of complex thin film materials (purchased by a DURIP-AFOSR grant).

  7. MOCVD grown hexagonal BN epilayers for DUV photonics

    NASA Astrophysics Data System (ADS)

    Majety, Sashikanth; Li, Jing; Lin, Jingyu; Jiang, Hongxing

    2013-03-01

    Hexagonal boron nitride (hBN) has attracted a lot of interest recently owing to its excellent physical properties and its potential use as a template in graphene electronics. We report on the successful growth of hBN epilayers using metal organic chemical vapor deposition (MOCVD) on sapphire and n-AlGaN substrates. P-type conductivity control was also achieved by in-situ Mg doping. This provides us with an opportunity to solve the problem of low quantum efficiency of DUV devices using Al-rich AlGaN alloys due to their extremely low p-type conductivity. Mg doped hBN epilayers grown on insulating templates were p-type with an in-plane resistivity of 2.3 Ω cm. Diode behavior in the p-n structures of p-hBN/n-Al0.62Ga0.38N has been demonstrated. Our results indicate that hBN epilayers have potential for DUV optoelectronic devices and also demonstrate the feasibility of using highly conductive p-type hBN as electron blocking and p-contact layers for AlGaN based deep UV emitters. This work is supported by DOE.

  8. The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

    NASA Technical Reports Server (NTRS)

    Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

    1991-01-01

    Thin films of YBa2Cu3O(7-x) (YBCO) were temperature cycled to simulate conditions of a low earth orbit satellite. In one series of tests, epitaxial and polycrystalline YBCO films were cycled between temperatures of +/- 80 C in vacuum and in nitrogen for hundreds of cycles. The room temperature resistance of an epitaxial YBCO film increased by about 10 percent, but the superconducting transition temperature was unchanged. The largest changes were for a polycrystalline YBCO film on oxidized silicon with a zirconia buffer layer, for which the transition temperature decreased by 3 K. An extended test was carried out for epitaxial films. After 3200 cycles (corresponding to about 230 days in space), transition temperatures and critical current densities remained unchanged.

  9. The Effect of Axial Stress on YBCO Coils

    SciTech Connect

    Sampson, W.; Anerella, M.; Cozzolino, J.P.; Gupta, R.C.; Shiroyanagi, Y.; Evangelou, E.

    2011-03-28

    The large aspect ratio of typical YBCO conductors makes them ideal for constructing solenoids from pancake style coils. An advantage of this method is that each subunit can be tested before assembly into the finished magnet. The fact that conductors are available in relatively short lengths is another reason for using such a fabrication technique. The principal drawback is the large number of joints required to connect the coils together. When very high field solenoids such as those contemplated for the muon collider are built in this way the magnetic forces between pancakes can be very large. Extensive measurements have been made on the effect of stress on short lengths of conductor, but there is little or no data on the effect of intercoil loading. The experiment described in this paper was designed to test the ability of YBCO coils to withstand these forces. A spiral wound 'pancake' coil made from YBCO coated conductor has been stressed to a pressure of 100MPa in the axial direction at 77K. In this case axial refers to the coil so that the force is applied to the edge of the conductor. The effect on the critical current was small and completely reversible. Repeatedly cycling the pressure had no measureable permanent effect on the coil. The small current change observed exhibited a slight hysteretic behaviour during the loading cycle.

  10. Superconducting YBa 2Cu 3O 7- δ thin film grown on metallic film evaporated on MgO

    NASA Astrophysics Data System (ADS)

    Verdyan, A.; Azoulay, J.; Lapsker, I.

    2001-03-01

    At present it is commonly accepted that thin film formation of YBa 2Cu 3O 7- δ (YBCO) on conducting substrate is one of the keys to further development of advanced devices in the microelectronic and other applications. We have grown YBCO thin films by resistive evaporation technique on MgO coated with metallic layers (Ni or Ag). A simple inexpensive vacuum system equipped with resistively heated boats for metal and precursor mixture of yttrium, copper and barium fluoride powders was used. X-ray diffraction (XRD) and scanning electron microscopy techniques were used for texture, morphology and surface analyses respectively. Electrical and magnetical properties were determined by a standard dc four-probe method. The way of heating process is shown to be critical parameter in the film quality. The physical and electrical properties of the YBCO films are discussed in light of the fact that XRD measurements done on the metallic buffer layers have revealed a multicrystalline structure.

  11. Superconducting Yttrium Barium Copper Oxide Thin Films and Thin Film Devices

    NASA Astrophysics Data System (ADS)

    Stamper, Anthony Kendall

    Superconducting thin films of YBa_2 Cu_3O_{7 -delta} (YBCO) have been deposited using rf diode sputtering from a single composite target. These films were deposited on silicon substrates at substrate temperatures up to 600^circC using either 100% argon or a 90% argon and 10% oxygen sputtering gas mixture. Yttria-stabilized ZrO_2 (YSZ) buffer layers were employed both for electrical isolation and to minimize the reaction between the silicon and the superconductor. The YSZ crystal structure was highly dependent on the deposition parameters and films with (111) and (100) cubic texturing were grown on oxidized silicon substrates. The composition and electrical properties of the YBCO films, which were deposited on-axis from 5 cm targets, were approximately constant over most of the 5 cm substrates when oxygen was in the sputtering gas and were reproducible. The effect of the sputtering gas pressure, the presence of 10% oxygen in the sputtering gas, the target composition, and the substrate temperature on the film composition have been studied. We demonstrated that neutral oxygen bombardment was responsible for composition differences between the target and the thin film. YBCO films deposited on in-situ heated substrates had zero-transition temperatures up to 87K with 10% to 90% transition widths of less than 5K and were c-axis oriented. Films deposited on unheated substrates required processing at higher temperatures, had zero-transition temperatures up to 85K, and were randomly oriented. Lithographic processes and contact technologies were developed for device fabrication. Using these processes, we fabricated simple YBCO microstrip structures, YBCO/Au/n-Si Schottky diodes, Pb/Ag/YBCO Josephson junctions, and Au/YSZ/YBCO multi-layer structures. After optimization of the process, we were able to fabricate high quality diodes and ohmic contacts without degrading the electrical properties of the YBCO. Finally, we fabricated flux transformer structures, with winding widths

  12. Enhancement of high-TC superconducting thin film devices by nanoscale polishing

    NASA Astrophysics Data System (ADS)

    Michalowski, P.; Shapoval, T.; Meier, D.; Katzer, C.; Schmidl, F.; Schultz, L.; Seidel, P.

    2012-11-01

    The effects of mechanical nanoscale polishing on the superconducting parameters of YBa2Cu3O7-δ (YBCO) thin films and bi-crystal grain boundary Josephson junctions have been investigated. We prepared samples with additional gold nanocrystallites in the YBCO film. As they are distributed throughout the whole YBCO film, they provide a low-resistance ohmic contact even if parts of the film are removed. Polishing was performed either before or after the patterning and did not change the properties of the grain boundary. However, nanopolishing reduces the film roughness in a significant way, which makes it an indispensable tool for the preparation of integrated superconducting circuits. We also succeeded in tuning the IC and RN of the Josephson junctions of direct current superconducting quantum interference devices (dc-SQUIDs) by systematically reducing the film thickness, which opens up new possibilities in the application of magnetic field sensors.

  13. Influence of Natural Convection and Thermal Radiation Multi-Component Transport in MOCVD Reactors

    NASA Technical Reports Server (NTRS)

    Lowry, S.; Krishnan, A.; Clark, I.

    1999-01-01

    The influence of Grashof and Reynolds number in Metal Organic Chemical Vapor (MOCVD) reactors is being investigated under a combined empirical/numerical study. As part of that research, the deposition of Indium Phosphide in an MOCVD reactor is modeled using the computational code CFD-ACE. The model includes the effects of convection, conduction, and radiation as well as multi-component diffusion and multi-step surface/gas phase chemistry. The results of the prediction are compared with experimental data for a commercial reactor and analyzed with respect to the model accuracy.

  14. Buffer layers for deposition of superconducting YBaCuO thin film on polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Beetz, Charles P.; Cui, G. J.; Lincoln, B. A.; Kirlin, Peter S.

    1992-09-01

    In an attempt to combine the properties of high temperature superconductors with the high thermal conductivity and low specific heat of diamond, we have explored the deposition of in- situ YBa(subscript 2)Cu(subscript 3)O(subscript 7-(delta) ) (YBCO) superconducting films on polycrystalline diamond thin films. We demonstrate for the first time superconducting YBCO films on diamond employing multiple layer buffer layer systems. Three different composite buffer layer systems were explored for this purpose: (1) Diamond/Zr/YSZ/YBCO, (2) Diamond/Si(subscript 3)N(subscript 4)/YSZ/YBCO, and (3) Diamond/SiO(subscript 2)/YSZ/YBCO. Adherent thin Zr films were deposited by dc sputtering on the diamond films at 450 to 820 degree(s)C. The yttria stabilized zirconia (YSZ) was deposited by reactive RF sputtering at 680 to 750 degree(s)C. The Si(subscript 3)N(subscript 4) and SiO(subscript 2) were also deposited by on-axis RF sputtering at 400 to 700 degree(s)C. YBCO films were grown on the buffer layers by off-axis RF sputtering at substrate temperatures between 690 degree(s)C and 750 degree(s)C. In all cases, the as-deposited YBCO films were superconducting above 77 K. This demonstration enables the fabrication of low heat capacity, fast response time bolometric far IR detectors and paves the way for the use of HTSC as a high frequency interconnect metallization on thick diamond film based multichip modules.

  15. Investigation on preparation and properties of Pb(Zr 0.95Ti 0.05)O 3 thin films

    NASA Astrophysics Data System (ADS)

    Zeng, Hui; Wu, Ping; Dong, Daxing; Zhang, Peng

    2011-01-01

    The preparation process, micro-structure and electrical properties of Pb(Zr xTi 1-x)O 3 (PZT) thin films were investigated in this paper. The Ag/PZT( x = 0.95)/YBCO/Si thin films were prepared by pulsed laser deposition (PLD). Si was the substrate; Ag and YBCO were the top electrode and the bottom electrode respectively. The bottom electrode YBCO was deposited on the Si substrate by PLD, and PZT was epitaxially deposited on YBCO also by PLD. After rapidly annealing, the AFM, XRD and the analysis of their electrical characters showed the films had good ferroelectric and pyroelectric properties. At 50 °C, the pyroelectric coefficient ( p) was 3.5 × 10 -8 C/(cm 2 K), the remanent polarization ( P r) and the coercive field ( E c) were 43.6 μC/cm 2 and 19.3 kV/cm respectively.

  16. CVD method for forming B.sub.i -containing oxide superconducting films

    DOEpatents

    Wessels, Bruce W.; Marks, Tobin J.; Richeson, Darrin S.; Tonge, Lauren M.; Zhang, Jiming

    1994-01-01

    Films of high T.sub.c Bi-Sr-Ca-Cu-O superconductor have been prepared by MOCVD using volatile metal organic precursors and water vapor. The metal organic precursors are volatized along with a bismuth source, such as Bi(C.sub.6 H.sub.5).sub.3, deposited on a heated substrate to form a film, and annealed.

  17. Interactions of Y2BaCuO5 particles and the YBCO matrix within melt-textured YBCO samples studied by means of electron backscatter diffraction

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Mücklich, F.; Ogasawara, K.; Murakami, M.

    2005-02-01

    By means of automated electron backscatter diffraction (EBSD) analysis, we studied the local orientations of embedded Y2BaCuO5(211) particles within melt-textured YBa2Cu3Ox (YBCO) samples. On both components, we obtained high-quality Kikuchi patterns, thus allowing the automated mapping of the crystal orientations and a two-phase analysis of the samples. Investigations were performed on a variety of melt-textured YBCO samples. In melt-textured YBCO with (001) orientation, we find that the embedded 211 particles do not have any preferred orientation. The EBSD maps also reveal that at certain orientations of the 211 particles the YBCO growth is not altered. From the obtained EBSD mappings, we can conclude that the formation of small 211 particles will not disturb the YBCO matrix growth, whereas the presence of large 211 particles causes severe changes in the YBCO growth, leading to the formation of subgrains. The EBSD results are presented in the form of local orientation maps and local pole figures.

  18. High hole concentration Li-doped NiZnO thin films grown by photo-assisted metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhao, Y. D.; Dong, X.; Ma, Z. Z.; Zhang, Y. T.; Wu, B.; Zhuang, S. W.; Zhang, B. L.; Li, W. C.; Du, G. T.

    2016-11-01

    High hole concentration Li-doped NiZnO thin films were grown by metal-organic chemical vapor deposition (MOCVD). The crystalline, optical, electrical, and morphological characteristics of the NiZnO films were studied as a function of lithium content. The resistance of the films decreased and the hole concentration greatly increased with increasing lithium content. However, the crystalline and optical properties were observed to degrade as the lithium content was increased. To relieve the degradation, a photo-assisted MOCVD method was used in order to restrict this degradation and this represents a new way to obtain stable high hole concentration NiZnO films.

  19. Thin film cadmium telluride, zinc telluride, and mercury zinc telluride solar cells

    SciTech Connect

    Chu, T.L. )

    1992-04-01

    This report describes research to demonstrate (1) thin film cadmium telluride solar cells with a quantum efficiency of 75% or higher at 0. 44 {mu}m and a photovoltaic efficiency of 11.5% or greater, and (2) thin film zinc telluride and mercury zinc telluride solar cells with a transparency to sub-band-gap radiation of 65% and a photovoltaic conversion efficiency of 5% and 8%, respectively. Work was directed at (1) depositing transparent conducting semiconductor films by solution growth and metal-organic chemical vapor deposition (MOCVD) technique, (2) depositing CdTe films by close-spaced sublimation (CSS) and MOCVD techniques, (3) preparing and evaluating thin film CdTe solar cells, and (4) preparing and characterizing thin film ZnTe, CD{sub 1-x}Zn{sub 1-x}Te, and Hg{sub 1-x}Zn{sub x}Te solar cells. The deposition of CdS films from aqueous solutions was investigated in detail, and their crystallographic, optical, and electrical properties were characterized. CdTe films were deposited from DMCd and DIPTe at 400{degrees}C using TEGa and AsH{sub 3} as dopants. CdTe films deposited by CSS had significantly better microstructures than those deposited by MOCVD. Deep energy states in CdTe films deposited by CSS and MOCVD were investigated. Thin films of ZnTe, Cd{sub 1- x}Zn{sub x}Te, and Hg{sub 1-x}Zn{sub x}Te were deposited by MOCVD, and their crystallographic, optical, and electrical properties were characterized. 67 refs.

  20. Surface resistance measurements of surface and interface sides of YBa2Cu3O7 films on sapphire and LaAlO3

    NASA Astrophysics Data System (ADS)

    Jacob, Mohan V.; Mazierska, Janina; Lorenz, Michael

    2003-03-01

    We have measured the surface resistance of YBCO superconducting thin films deposited on sapphire and lanthanum aluminate substrates at the film side and at the interface between the substrate and the film. The measured difference in the Rs values of the interface and the film sides was between 30% and 60% for the YBCO films on LAO in the temperature range 15-80 K. For the Ag-doped films on sapphire the difference in Rs monotonically varied from 10% to 65% when temperature increased from 30 K to 80 K.

  1. Superconducting YBa2Cu3O(7-delta) thin films on GaAs with conducting indium-tin-oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Kellett, B. J.; Gauzzi, A.; James, J. H.; Dwir, B.; Pavuna, D.

    1990-12-01

    Superconducting YBa2Cu3O(7-delta) (YBCO) thin films have been grown in situ on GaAs with conducting indium-tin-oxide (ITO) buffer layers. Superconducting onset is about 92 K with zero resistance at 60 K. ITO buffer layers usually form Schottky-like barriers on GaAs. The YBCO film and ITO buffer layer, grown by ion beam sputter codeposition, are textured and polycrystalline with a combined room-temperature resistivity of about 1 milliohm cm.

  2. The use of monolithic YBCO in electromagnetic launchers

    NASA Astrophysics Data System (ADS)

    Putman, Philip T.

    One of the fundamental barriers to the use of electromagnetic launchers is the high power required to reach launch speed in a reasonable distance. It has been proposed that large external power supplies can be avoided by using superconducting persistent currents in the barrel of the launcher to store energy. This study examines the use of monolithic YBCO for these persistent current magnets. Monolithic magnets, unlike wound magnets, can have a nonuniform current distribution, which causes energy transfer between the stationary energy storage magnets and the accelerated magnet to be inefficient. This problem can be overcome by optimization of the magnet shape. This requires a model for computation of current distribution, force vs. distance, and efficiency. A model is presented for calculating the current distribution and magnetic force for two YBCO rings, each with a trapped field such that an attractive force is developed between them. Two different methods were used to find current as a function of time. The first is a system of differential equations for the time dependence of the current distribution, which is solved using the 4-step vector Runge-Kutta method. The second is a speed-independent approximation that is less computationally intensive. The integral equation for force at each time step is solved using the finite sum method. After verifying the speed-dependent model by comparing computations to measured force vs. distance curves for twenty-eight pairs of YBCO magnets, the model was used to examine behavior at speeds up to 10,000 m/s. It was found that energy transfer is almost independent of speed for a properly designed launcher. Also, heating due to flux flow was found to be minimal. The fact that energy transfer did not depend on speed allowed the speed-independent model to be used with an optimizer to find a more efficient shape for the accelerated YBCO magnet. A magnet of this shape was fabricated, and efficiency was measured to be 84%, compared

  3. Investigation of Radiation Affected High Temperature Superconductors - YBCO

    NASA Astrophysics Data System (ADS)

    Veterníková, J.; Chudý, M.; Slugeň, V.; Sojak, S.; Degmová, J.; Snopek, J.

    In this paper, high temperature superconductors are studied in terms of radiation stability, which is necessary for application in fusion reactors. Perspective superconducting materials based on YBCO (Perkovskite structure) were measured by positron annihilation lifetime spectroscopy. Measurements were performed for samples prior to and after fast neutron irradiation in TRIGA MARK II reactor in Vienna. The samples demonstrated accumulation of Cu-O di-vacancies due to the irradiation. Nevertheless, the structure showed regeneration during thermal treatment by defects recombination. Positron spectroscopy results were complemented with values of critical temperature, which also showed changes of superconducting properties after the irradiation and the annealing.

  4. CFD simulation of pulsed MOCVD to reduce gas-phase parasitic reaction

    NASA Astrophysics Data System (ADS)

    Zhou, Ning; Lowry, Samuel A.; Krishnan, Anantha

    1999-07-01

    A Computational Fluid Dynamics (CFD) code is used to determine the potential benefit of pulsed Metal-Organic Chemical Vapor Deposition (MOCVD). When AlN is grown using MOCVD over a range of pressures (30 to 270 Torr) and substrate temperatures (400°C to 900°C), gas-phase mixing of the precursor (TMA1) and ammonia hydride (NH3)leads to adduct formation. This adduct formation may produce some undesired particulate by-products and deplete the precursors at elevated pressure and temperature. In order to reduce this gas-phase parasitic reaction, the pulsed inlet condition as proposed by Bachmann et al. is utilized to effectively separate the precursor form ammonia in gas- phase. It is predicted that for high reactor pressure (270 Torr), the growth efficiency of AlN can be enhanced by a factor of 3 through the pulsed MOCVD technique while simultaneously reducing the particle formation. The improvement by pulsed MOCVD is also demonstrated for a proposed 3D (North Carolina State University) research reactor.

  5. Method for Improving Mg Doping During Group-III Nitride MOCVD

    DOEpatents

    Creighton, J. Randall; Wang, George T.

    2008-11-11

    A method for improving Mg doping of Group III-N materials grown by MOCVD preventing condensation in the gas phase or on reactor surfaces of adducts of magnesocene and ammonia by suitably heating reactor surfaces between the location of mixing of the magnesocene and ammonia reactants and the Group III-nitride surface whereon growth is to occur.

  6. In situ study through electrical resistance of growth rate of trifluoroacetate-based solution-derived YBa2Cu3O7 films

    NASA Astrophysics Data System (ADS)

    Sánchez-Valdés, C. F.; Puig, T.; Obradors, X.

    2015-02-01

    In this work, we have studied by means of in situ electrical measurements the nucleation, growth and sintering stages of epitaxial YBa2Cu3O6+δ (YBCO) superconducting thin films prepared using a chemical solution deposition approach based on metal-organic trifluoroacetate-based (TFA) precursors. Single crystal substrates (LaAlO3 and CeO2/YSZ) were used in this study. Analysis of isothermal time dependences, at different temperatures, of in situ electrical resistance of films allowed to evidence that the growth rate G is strongly temperature dependent, i.e. G is enhanced by a factor ˜15 when going from 700 to 810 °C. Additionally, we demonstrate that adding Ag-TFA in the solution may enhance the growth rate by as much as 50%, as compared to pure YBCO, thus confirming previous assessments of the strong influence of Ag doping on YBCO film growth and microstructure. In situ electrical resistance measurements show as well that an incubation time exists and we infer the origin of its temperature dependence. Finally, a thermodynamic analysis allows proposing a single equation for the growth rate of YBCO films integrating all the relevant processing parameters. Our analysis has validated the solid-gas reaction-diffusion model describing the growth of YBCO films from TFA precursors and thus enlarges the knowledge required to enhance the control of the microstructure and superconducting properties of solution-derived YBCO films.

  7. Formation of superconducting junctions in MT-YBCO

    NASA Astrophysics Data System (ADS)

    Prikhna, T. A.; Gawalek, W.; Novikov, N. V.; Moshchil, V. E.; Sverdun, V. B.; Sergienko, N. V.; Surzhenko, A. B.; Uspenskaya, L. S.; Viznichenko, R.; Kordyuk, A. A.; Litzkendorf, D.; Habisreuther, T.; Krachunovska, S.; Vlasenko, A. V.

    2005-02-01

    The formation of superconducting junctions between MT-YBCO using TmBa2Cu3O7-δ powder as a solder has been studied. The method proposed excludes the step of a very slow cooling (at a rate of several degrees per hour) during seam formation. The heating and cooling rate for joining parts produced from single-domain material without visible cracks (macrocracks) can be rather high (500-1000 K h-1) and a holding time at the highest temperature (1010 °C) of several minutes (0.05 h) is enough to form a reliable junction. Reasonable rates of heating and cooling are however around 100 K h-1 if crack propagation is to be avoided in joined blocks used for practical application. Modelling experiments on rings and studies of the ring properties by vibrating sample magnetometer (VSM), field mapping with a Hall probe and magneto-optical microscopy have shown that superconducting properties of the junction were not lower than that of the joined material (jc of about 30 kA cm-2 was observed in zero field at 77 K) and that the proposed process of joining did not adversely affect the properties of the material. The structure of the resulting junction was in good agreement with the structure of MT-YBCO.

  8. Limitations for the trapped field in large grain YBCO superconductors

    NASA Astrophysics Data System (ADS)

    Eisterer, M.; Haindl, S.; Zehetmayer, M.; Gonzalez-Arrabal, R.; Weber, H. W.; Litzkendorf, D.; Zeisberger, M.; Habisreuther, T.; Gawalek, W.; Shlyk, L.; Krabbes, G.

    2006-07-01

    The actual limitations for the trapped field in YBa2Cu3O7-δ (YBCO) monoliths are discussed. The influence of the sample geometry and of the critical current density on the trapped field is investigated by numerical calculations. The field dependence of the critical current density strongly influences the trapped field. A nonlinear relationship between the sample size, the critical current density and the resulting trapped field is derived. The maximum achievable trapped field in YBCO at 77 K is found to be around 2.5 T. This limit is obtained for reasonable geometries and high but realistic critical current densities. Such high fields have not been reached experimentally so far, due to non-optimized flux pinning and material inhomogeneities. These inhomogeneities can be directly assessed by the magnetoscan technique, and their influence is discussed. Significant differences between the a- and the c-growth sectors were found. Limitations due to cracks and non-superconducting inclusions (e.g. 211 particles) are estimated and found to be candidates for variations of Jc on a millimetre length scale, as observed in experiments.

  9. Broad Temperature Pinning Study of 15 mol.% Zr-Added (Gd, Y)-Ba-Cu-O MOCVD Coated Conductors

    SciTech Connect

    Xu, AX; Khatri, N; Liu, YH; Majkic, G; Galstyan, E; Selvamanickam, V; Chen, YM; Lei, CH; Abraimov, D; Hu, XB; Jaroszynski, J; Larbalestier, D

    2015-06-01

    BaZrO3 (BZO) nanocolumns have long been shown to be very effective for raising the pinning force F-p of REBa2Cu3Ox (REBCO, where RE = rare earth) films at high temperatures and recently at low temperatures too. We have successfully incorporated a high density of BZO nanorods into metal organic chemical vapor deposited (MOCVD) REBCO coated conductors via Zr addition. We found that, compared to the 7.5% Zr-added coated conductor, dense BZO nanorod arrays in the 15% Zr-added conductor are effective over the whole temperature range from 77 K down to 4.2 K. We attribute the substantially enhanced J(c) at 30 K to the weak uncorrelated pinning as well as the strong correlated pinning. Meanwhile, by tripling the REBCO layer thickness to similar to 2.8 mu m, the engineering critical current density J(e) at 30 K exceeds J(e) of optimized Nb-Ti wires at 4.2 K.

  10. Structural and morphological qualities of InGaN grown via elevated pressures in MOCVD on AlN/Si(111) substrates

    NASA Astrophysics Data System (ADS)

    Ho, Jian Wei; Zhang, Li; Wee, Qixun; Tay, Andrew A. O.; Heuken, Michael; Chua, Soo-Jin

    2013-11-01

    We examine the structural and morphological qualities of InxGa1-xN grown directly on AlN/Si(111) substrates by MOCVD as a function of growth pressure and temperature. The use of elevated pressures (up to 300 Torr) resulted in the suppression of InGaN phase separation and indium droplet formation allowing single phase, textured epitaxial (0002)-oriented InxGa1-xN to be grown on the highly mismatched substrates. Various indium compositions x, up to ~0.4, can subsequently be achieved by adjusting the growth temperature over the range of 655 °C-795 °C. Increase in growth temperature reduces the indium composition x but is accompanied by a decrease in the FWHM of the (002)-ω and asymmetric (105)-ω rocking curves indicating lower crystallographic tilt and improved crystal quality. The reduction in tilt saturates at ~705 °C. This corroborates with room-temperature photoluminescence (PL) measurements where PL is not detectable below ~705 °C but emerges above this temperature and narrows in FWHM with further temperature increase. SEM shows that films grown at low pressure are compositionally and morphologically non-uniform, while films grown at elevated pressure are homogeneous, single phase and composed of densely packed, interconnected epitaxial islands, with lower temperature favouring a smaller island size. We conclude that while lower temperatures favour increased indium incorporation, the ensuing smaller island size and greater extent of island boundaries, arising from larger lattice mismatch and lower surface mobility of species, degrades crystal quality appreciably. Above 705 °C, improvement in crystallographic quality is limited by the AlN growth template and requires innovative MOCVD growth strategies.

  11. Deposition of High-Temperature Superconducting Thin Films on Metallic and Nometallic Substrates by Laser Ablation.

    NASA Astrophysics Data System (ADS)

    Wu, Anqi

    This dissertation covers my research in four steps: basic understanding of the theory of superconductors, development of the experimental setup, deposition of high temperature superconducting thin films (HTSTF) on metallic and nonmetallic substrates by laser ablation, and characterization HTSTFs on metallic and nonmetallic substrates. High quality HTSTFs have been grown on metallic and nonmetallic substrates, including SrTiO_3 , MgO, YSZ, Cu, Ag, Ni, and Stainless Steel. Of particular note, there have been no other successful reports of a superconducting YBa_2Cu _3O_{rm 7-x} (YBCO) film on Cu. Cu is a unique candidate for a YBCO substrate material. My investigation shows that it is possible, using laser ablation, to make good YBCO films on Cu substrates, possessing a natural oxide layer interface. The films on Cu exhibit a metallic normal state, and a resistive transition width of 6 K to zero resistance (R ~ 0) at 84 K. We determined the critical current density, J_{rm c}, to be 1,300 A/cm^2 at 13 K by the 4-probe transport method. The Naval Research Laboratory found J_{rm c} of another film to be about 3,880 A/cm ^2 at 4.2 K using the contactless single coil method. Analysis of the film compositions and structures have been made using XRD, EDAX, SEM, and AFM. STM, AFM, and high-magnification SEM images of the YBCO films on Cu show random orientation and rough surface relative to similar films on SrTiO_3, MgO, and YSZ. Due to the formation of a natural, irregular Cu oxide layer between the film and Cu substrate, the gaps between grains of YBCO on polycrystalline Cu are definitely larger than those of films deposited on single crystal such as SrTiO_3 (J_{ rm c} = 1.4 times 10^6 A/cm^2 at 77 K). This may explain the differences in J _{rm c}. The Cu-oxide layer significantly affects the quality of YBCO film on Cu because of larger lattice mismatches and thermal expansion differences between the Cu-oxide and YBCO film compared to Cu and YBCO. Applying an electric field

  12. High-Temperature Superconductivity in the Yttrium Barium-Copper System: Thin Film Growth, Grain Boundary Effects and Interlayer Coupling Mechanisms

    NASA Astrophysics Data System (ADS)

    Chen, Ling

    The present work addresses key scientific and technical issues pertaining to the establishment of an improved understanding of the physical mechanisms of superconductivity and the development of a technologically useful process for the growth of YBCO films. The first section describes the successful development of a technologically useful CVD process for the growth of high quality YBCO ultrathin and multilayered structures on metallic and insulating substrates for energy-related, microwave, and microelectronic applications. In particular, the process was employed to deposit epitaxial YBCO films on single-crystal dielectric substrates, such as LaAlO _3 and SrTiO_3 at growth rates >700 A/min. Films above 500 A on SrTiO_3 exhibited a T _{rm c} of 92 K, a J _{rm c} of 2times10 ^6 A/cm^2 (77K, B = 0), no weak-link behavior in magnetic field up to 1 Tesla, and a surface resistance R_{rm s} of 309 muOmega (10 GHz, 77 K), which is comparable to the best PVD YBCO films. Corresponding investigations of the mechanisms of early film nucleation and growth led to the identification of appropriate growth modes and the successful production of high quality superconducting ultrathin YBCO layers down to 60 A. In particular, it is shown that the nature of YBCO growth is greatly influenced by substrate morphology, chemical condition and lattice mismatch, with the early stages of growth on LaAlO_3 and MgO following, respectively, the Frank-van der Merwe and Volmer Weber modes. Additionally, the improved quality of YBCO films on silver substrates was partially explained by the key role of the substrate processing temperature in not only affecting YBCO nucleation and growth but also in the recrystallization of silver substrates, which in turn greatly influenced film growth. In addition, experimental observations concerning the existence of a T_{rm c} ~ 30 K in a unit-cell thick YBCO layer and the effects on T_{rm c} of composition and dimensions of multilayered superconductor structures

  13. Effects of Seed Layer on YBa2Cu3Ox Films Grown by Liquid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Zama, Hideaki; Miyakoshi, Masayuki; Yamamoto, Hiroshi; Morishita, Tadataka

    1999-11-01

    Crack-free YBa2Cu3Ox (YBCO) films were grown by liquid phaseepitaxy (LPE) on MgO(100) substrates with a YBCO seed layer. Thecrystalline property of LPE was crucially dependent on that of theseed layer. On the purely c-axis-oriented seed layer, reasonable YBCOfilms were grown with a full-width at half maximum of the (005)reflection rocking curve, Δω, of 0.07°. In the case of the seedincluding an a-axis-oriented grain, the value of Δω of LPE films waspoor in reproducibility and larger than 0.1° on average. For thea-axis-oriented seed, no YBCO films grew under the growth conditionsin this study. X-ray topographic observations revealed that thecrystalline quality of MgO substrates limited the Δω of LPE films grownon them.

  14. Influence of YBa2HfO5.5 - 'derived secondary phase' on the critical current density and flux-Pinning force of YBa2Cu3O7-δ thick films

    NASA Astrophysics Data System (ADS)

    Rejith, Pullanhiyodan Puthiyaveedu; Vidya, Sukumariamma; Thomas, Jijimon Kumbukkattu

    2015-12-01

    Enhancement in critical current density (Jc) and flux pinning force (Fp) in superconducting thick films of YBa2Cu3O7-δ (YBCO) added with small quantities of nanopowders of HfO2, BaHfO3 and YBa2HfO5.5, coated on YBa2ZrO5.5 substrate by dip-coating technique is reported. Critical current density measurements were done over an applied magnetic field using standard four probe technique and the results are compared with that of pure YBCO. High critical current density (Jc) of ∼4.84 MA/cm2 at 77 K in self-field was obtained for 2 wt% of YBa2HfO5.5 added YBCO. A systematic increase in Jc observed in YBCO films prepared by the addition of nano HfO2, BaHfO3 and YBa2HfO5.5, attributed to the formation of a non-reacting 'derived secondary phase' YBa2HfO5.5 (YBHO) in the YBCO matrix. YBCO-YBa2HfO5.5 composite thick films have showed eightfold increases in Jc (3.29 MA/cm2) at 77 K and 0.4 T compared to pure YBa2Cu3O7-δ film (0.37 MA/cm2), while maintaining a high transition temperature (Tc). The development of effective pinning centers in nano particle added YBCO thick film have enhanced the flux pinning force from 1.8 GN/m3 for pure YBCO to a maximum value of 13.15 GN/m3 for YBCO-YBa2HfO5.5. X-ray diffraction and energy dispersive spectroscopic analysis confirmed the presence of secondary phase, derived in the matrix.

  15. The coherent gradient sensor for film curvature measurements at cryogenic temperature.

    PubMed

    Liu, Cong; Zhang, Xingyi; Zhou, Jun; Zhou, Youhe; Feng, Xue

    2013-11-01

    Coherent Gradient Sensor (CGS) system is presented for measurement of curvatures and nonuniform curvatures changes in film-substrate systems at cryogenic temperature. The influences of the interface of refrigerator and itself on the interferograms which are accounting for the temperature effect are successfully eliminated. Based on the measurement technique, the thermal stresses (including the radial stress, circumferential stress and shear stress) of superconducting YBCO thin-film are obtained by the extended Stoney's formula during the heating process from 30K to 150K. Take the superconducting YBCO thin film as an example, the thermal stresses of which are gained successfully.

  16. Properties of large-scale melt-processed YBCO samples

    NASA Astrophysics Data System (ADS)

    Gauss, S.; Elschner, S.; Bestgen, H.

    Magnetic bearings and superconducting permanent magnets are some of the first possible applications of bulk high Tc superconductors. Large samples were prepared by a new melt process starting from reacted YBCO 123 and 211 powders. The addition of PtO 2 to the mixture led to reduced 211 inclusion size and better homogeneity. Simultaneously the density of microcracks dividing the a- b basal plane was reduced. For testing the overall magnetic properties of these samples magnetization and levitation force measurements were performed. In comparison to samples without PtO 2 addition a strong increase in the magnetization M and the repulsion force from a magnet were observed. The maximum in the field dependence of M increased to more than 1000 G. According to the time dependence of the trapped field after a field cooling experiment an acceptable flux creep at 77 K for a long-term application was achieved.

  17. Magnetic coupling by using levitation characteristics of YBCO superconductors

    NASA Astrophysics Data System (ADS)

    Ishigaki, H.; Ito, H.; Itoh, M.; Hida, A.; Takahata, R.

    1993-03-01

    A mechanical system which uses high lateral restoring forces of high-Tc materials as the driving force for a magnetic coupling is proposed. As the basic study of the superconducting magnetic coupling, the relationship between the lateral restoring force and levitation force, transmitted torque characteristics as a function of a twisting angle and clearance, and damping characteristics of the coupling were examined. Superiorities of the coupling such as high damping coefficients and high stability against time and twisting angle were revealed. A magnetic force sensor system was used to evaluate the superconducting characteristics of materials, and nonuniform distribution of repulsive force was observed for the YBCO pellet fabricated by the melt-powder-melt-growth process. The improvement of the homogeneity was achieved by compensating for the composition rate which had changed during the quenching process.

  18. Texture analysis of melt-textured YBCO superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Simon, P.; Ogasawara, K.; Murakami, M.

    2003-10-01

    We compare the results of an X-ray based pole figure texture analysis with the local texture analysis by means of electron-backscatter diffraction (EBSD) analysis. As samples, we employ two different melt-textured YBCO samples; one fully processed and one without oxygen treatment. To enable the direct comparison of the two techniques, we employ the [1 0 3] pole figures. We find a clear coincidence between the results obtained by the two measurement techniques on our samples, however, the EBSD results are much more detailed, yielding the local grain orientation distribution and quantitative results of the grain or subgrain misorientation angles. Therefore, the EBSD measurements give information not accessible to the X-ray pole figure analysis. The surface preparation procedure is essential to enable the automated EBSD mapping as high image quality Kikuchi patterns are required. The polishing procedures are discussed in detail.

  19. Superconducting properties of experimental YBCO coils for FFAG accelerator magnets

    NASA Astrophysics Data System (ADS)

    Takayama, S.; Koyanagi, K.; Tosaka, T.; Tasaki, K.; Kurusu, T.; Ishii, Y.; Amemiya, N.; Ogitsu, T.

    2014-05-01

    A project to develop fundamental technologies for accelerator magnets using high-Tc coated conductors is currently in progress. The primary applications of this project are fixed field alternating gradient (FFAG) accelerators for carbon cancer therapy systems and accelerator-driven subcritical reactors. Several types of superconducting coils for FFAG accelerators have been conceptually designed. These coils have complicated shapes, including a negative-bend part or a three-dimensional bent part. One of the aims of the project is to establish winding technologies for complicated coil shapes using coated conductors. To demonstrate winding technologies for YBa2Cu3O7-x (YBCO) coils, small test coils having a negative-bend part or a three-dimensional bent part were designed and fabricated according to the present design of the FFAG magnet. The outside dimensions of the negative-bend test coil were 460 mm long and 190 mm wide, and the radius of curvature of the negative-bend part was 442 mm. The outside dimensions of the three-dimensional test coil were 380 mm long and 280 mm wide, and the radius of curvature of the mandrel of the three-dimensional coil was 700 mm. The test coils were wound using YBCO coated conductors with a length of about 100 m and were then impregnated with epoxy resin. The coils were placed in liquid nitrogen and excited to measure their V-I characteristics. From the V-I characteristics throughout a voltage range down to 10-9 V/cm, the V-I characteristics before and after impregnation were approximately the same, demonstrating that the superconducting properties were not degraded.

  20. Photoreflectance for in-situ characterization of MOCVD growth of semiconductors under micro-gravity conditions

    NASA Technical Reports Server (NTRS)

    Pollak, Fred H.

    1990-01-01

    A contactless electromodulation technique of photoreflectance (PR) was developed for in-situ monitoring of metal-organic chemical vapor deposition (MOCVD) semiconductor growth for micro-gravity applications. PR can be employed in a real MOCVD reactor including rotating substrate (approximately 500 rev/min) in flowing gases and through a diffuser plate. Measurements on GaAs and Ga(0.82)Al(0.18)As were made up to 690 C. The direct band gaps of In(x)Ga(1-x)As (x = 0.07 and 0.16) were evaluated up to 600 C. In order to address the question of real time measurement, the spectra of the direct gap of GaAs at 650 C was obtained in 30 seconds and 15 seconds seems feasible.

  1. In-situ estimation of MOCVD growth rate via a modified Kalman filter

    SciTech Connect

    Woo, W.W.; Svoronos, S.A.; Sankur, H.O.; Bajaj, J.; Irvine, S.J.C.

    1996-05-01

    In-situ laser reflectance monitoring of metal-organic chemical vapor deposition (MOCVD) is an effective way to monitor growth rate and epitaxial layer thickness of a variety of III-V and II-VI semiconductors. Materials with low optical extinction coefficients, such as ZnTe/GaAs and AlAs/GaAs for a 6,328 {angstrom} HeNe laser, are ideal for such an application. An extended Kalman filter modified to include a variable forgetting factor was applied to the MOCVD systems. The filter was able to accurately estimate thickness and growth rate while filtering out process noise and cope with sudden changes in growth rate, reflectance drift, and bias. Due to the forgetting factor, the Kalman filter was successful, even when based on very simple process models.

  2. Radiation effects on p+n InP junctions grown by MOCVD

    NASA Technical Reports Server (NTRS)

    Messenger, Scott R.; Walters, Robert J.; Panunto, M. J.; Summers, Geoffrey P.

    1994-01-01

    The superior radiation resistance of InP over other solar cell materials such as Si or GaAs has prompted the development of InP cells for space applications. The early research on radiation effects in InP was performed by Yamaguchi and co-workers who showed that, in diffused p-InP junctions, radiation-induced defects were readily annealed both thermally and by injection, which was accompanied by significant cell recovery. More recent research efforts have been made using p-InP grown by metalorganic chemical vapor deposition (MOCVD). While similar deep level transient spectroscopy (DLTS) results were found for radiation induced defects in these cells and in diffused junctions, significant differences existed in the annealing characteristics. After injection annealing at room temperature, Yamaguchi noticed an almost complete recovery of the photovoltaic parameters, while the MOCVD samples showed only minimal annealing. In searching for an explanation of the different annealing behavior of diffused junctions and those grown by MOCVD, several possibilities have been considered. One possibility is the difference in the emitter structure. The diffused junctions have S-doped graded emitters with widths of approximately 0.3 micrometers, while the MOCVD emitters are often doped with Si and have widths of approximately 300A (0.03 micrometers). The difference in the emitter thickness can have important effects, e.g. a larger fraction of the total photocurrent is generated in the n-type material for thicker emitters. Therefore the properties of the n-InP material may explain the difference in the observed overall annealing behavior of the cells.

  3. Final report on LDRD project : outstanding challenges for AlGaInN MOCVD.

    SciTech Connect

    Mitchell, Christine Charlotte; Follstaedt, David Martin; Russell, Michael J.; Cross, Karen Charlene; Wang, George T.; Creighton, James Randall; Allerman, Andrew Alan; Koleske, Daniel David; Lee, Stephen Roger; Coltrin, Michael Elliott

    2005-03-01

    The AlGaInN material system is used for virtually all advanced solid state lighting and short wavelength optoelectronic devices. Although metal-organic chemical vapor deposition (MOCVD) has proven to be the workhorse deposition technique, several outstanding scientific and technical challenges remain, which hinder progress and keep RD&A costs high. The three most significant MOCVD challenges are: (1) Accurate temperature measurement; (2) Reliable and reproducible p-doping (Mg); and (3) Low dislocation density GaN material. To address challenge (1) we designed and tested (on reactor mockup) a multiwafer, dual wavelength, emissivity-correcting pyrometer (ECP) for AlGaInN MOCVD. This system simultaneously measures the reflectance (at 405 and 550 nm) and emissivity-corrected temperature for each individual wafer, with the platen signal entirely rejected. To address challenge (2) we measured the MgCp{sub 2} + NH{sub 3} adduct condensation phase diagram from 65-115 C, at typical MOCVD concentrations. Results indicate that it requires temperatures of 80-100 C in order to prevent MgCp{sub 2} + NH{sub 3} adduct condensation. Modification and testing of our research reactor will not be complete until FY2005. A new commercial Veeco reactor was installed in early FY2004, and after qualification growth experiments were conducted to improve the GaN quality using a delayed recovery technique, which addresses challenge (3). Using a delayed recovery technique, the dislocation densities determined from x-ray diffraction were reduced from 2 x 10{sup 9} cm{sup -2} to 4 x 10{sup 8} cm{sup -2}. We have also developed a model to simulate reflectance waveforms for GaN growth on sapphire.

  4. Progress in MOCVD growth of HgCdTe epilayers for HOT infrared detectors

    NASA Astrophysics Data System (ADS)

    Kebłowski, A.; Gawron, W.; Martyniuk, P.; Stepień, D.; Kolwas, K.; Piotrowski, J.; Madejczyk, P.; Kopytko, M.; Piotrowski, A.; Rogalski, A.

    2016-05-01

    In this paper we present progress in MOCVD growth of (100) HgCdTe epilayers achieved recently at the Institute of Applied Physics, Military University of Technology and Vigo System S.A. It is shown that MOCVD technology is an excellent tool in fabrication of different HgCdTe detector structures with a wide range of composition, donor/acceptor doping and without post grown annealing. Particular progress has been achieved in the growth of (100) HgCdTe epilayers for long wavelength infrared photoconductors operated in HOT conditions. The (100) HgCdTe photoconductor optimized for 13-μm attain detectivity equal to 6.5x109 Jones and therefore outperform its (111) counterpart. The paper also presents technological progress in fabrication of MOCVD-grown (111) HgCdTe barrier detectors. The barrier device performance is comparable with state-of-the-art of HgCdTe photodiodes. The detectivity of HgCdTe detectors is close to the value marked HgCdTe photodiodes. Dark current densities are close to the values given by "Rule 07".

  5. The growth of the complex oxide YBCO by pulsed organo-metallic beam epitaxy

    NASA Astrophysics Data System (ADS)

    Buchholz, Donald Bruce

    To address the problems associated with the thin film heteroepitaxial growth of complex oxides a deposition technique, called pulsed organo-metallic beam epitaxy (POMBE), is developed. POMBE is designed to grow films layer-by-layer. Organo-metallics are delivered to the substrate as a series of discrete pulses via a set of computer-controlled valves. The precursor sequence and the amount of precursor in each pulse is programmed as the computer. Quartz crystal microbalances monitor the precursor transport rates. Computer feedback control maintains the precursor pulses at their programmed values. The ability to grow films layer-by-layer and to control the amount of material in each layer is demonstrated by the growth of YBasb2CUsb3Osb{7-delta}/PrBasb2CUsb3Osb{7-delta} superlattices. This is the first report of a high temperature superconductor superlattice grown by a chemical vapor deposition technique. The ability to grow films layer-by-layer is used to investigate the effect of changing the type and amount of precursor used to start the film growth. The correct choice of these parameters allows the growth of (001) YBasb2Cusb3Osb{7-delta} with a single in-plane orientation and Jsb{c}(77 K,0T) = 1-2× 10sp6amp/cmsp2 on (100) LaAlOsb3, (100) NdGaOsb3, (100) MgO, and (100) YSZ. The ability to control the initial film layer provides a means to control the in-plane orientation of (001) YBasb2Cusb3Osb{7-delta} (YBCO) grown on (100) MgO. Depositions started with thin BaO layers ({}{≈}1.1× 10sp{15}Ba/cmsp2) grow lbrack 100rbrack YBCOVertlbrack 100rbrack MgO. A mechanism that relates the change of in-plane orientation to a structural change of the initial BaO layer is described. The in-plane orientation of (001) YBasb2Cusb3Osb{7-delta} grown on (100) MgO can also be controlled by the ex situ, low energy Arsp+ sputtering of the MgO surface prior to film growth. To simultaneously grow lbrack 110rbrack YBCOVertlbrack 100rbrack MgO on non-sputtered MgO and lbrack 100rbrack

  6. The distribution of Ag in Ag-doped YBa2Cu3O7-δ thin film prepared by dual-beam pulsed-laser deposition

    NASA Astrophysics Data System (ADS)

    Zhou, W. Z.; Chua, D. H. C.; Xu, S. Y.; Ong, C. K.; Feng, Y. P.; Osipowicz, T.; Chen, M. S.

    1999-06-01

    The Ag distribution in Ag-doped YBa2Cu3O7-δ (YBCO) thin films fabricated by dual-beam pulsed-laser deposition on SrTiO3 (100) substrates has been studied by Auger electron spectroscopy, microproton-induced x-ray emission, atomic force microscopy and scanning electron microscopy. All the results consistently show that Ag aggregated in the bar-like structures observed in the film. These bars are aligned along the a-b-axis or at 45° to the a-b-axis of the YBCO thin film. The main body of the long bars aligned with the a-b-axes of the film was found to be a combination of metallic Ag with other precipitates of YBCO film that may grow from the substrate surface to the YBCO film surface. There were other precipitates aggregating as well at the surface of these bars, such as oxides of Cu and Ba. The short bars that aligned along 45° to the a-b-axes of the film were found to be deficient in Ag but rich in Cu, Ba and O, which could be oxide precipitates of YBCO. The growth mechanisms of the two types of bars seem quite different.

  7. Stable preparation process of superconductor insulator multilayer films for HTS devices by off-axis magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Adachi, S.; Wakana, H.; Kamitani, Ai; Tanabe, K.

    2006-10-01

    The preparation process for epitaxial multilayer films consisting of Y0.9La0.2Ba1.9Cu3Oy (La-YBCO) and SrSnO3 (SSO) for high-Tc superconductor (HTS) electronic devices was developed. Four-layer films of SSO/La-YBCO/SSO/La-YBCO were deposited on BaZrO3-buffered MgO(1 0 0) substrates by off-axis magnetron sputtering. During deposition, the substrates were directly heated from backside by thermal radiation of a heater. No adhesive paste, such as Ag, for fixing the substrate was used in order to avoid contamination. Deposition conditions, especially the heater temperature profiles and atmosphere during elevating the temperature, were carefully controlled. The multilayer films with the average surface roughness Ra around 2.0 nm were prepared with high reproducibility. Continuous production of the high-quality films throughout one year proved excellent stability of the preparation process.

  8. Thin film cadmium telluride, zinc telluride, and mercury zinc telluride solar cells. Final subcontract report, 1 July 1988--31 December 1991

    SciTech Connect

    Chu, T.L.

    1992-04-01

    This report describes research to demonstrate (1) thin film cadmium telluride solar cells with a quantum efficiency of 75% or higher at 0. 44 {mu}m and a photovoltaic efficiency of 11.5% or greater, and (2) thin film zinc telluride and mercury zinc telluride solar cells with a transparency to sub-band-gap radiation of 65% and a photovoltaic conversion efficiency of 5% and 8%, respectively. Work was directed at (1) depositing transparent conducting semiconductor films by solution growth and metal-organic chemical vapor deposition (MOCVD) technique, (2) depositing CdTe films by close-spaced sublimation (CSS) and MOCVD techniques, (3) preparing and evaluating thin film CdTe solar cells, and (4) preparing and characterizing thin film ZnTe, CD{sub 1-x}Zn{sub 1-x}Te, and Hg{sub 1-x}Zn{sub x}Te solar cells. The deposition of CdS films from aqueous solutions was investigated in detail, and their crystallographic, optical, and electrical properties were characterized. CdTe films were deposited from DMCd and DIPTe at 400{degrees}C using TEGa and AsH{sub 3} as dopants. CdTe films deposited by CSS had significantly better microstructures than those deposited by MOCVD. Deep energy states in CdTe films deposited by CSS and MOCVD were investigated. Thin films of ZnTe, Cd{sub 1- x}Zn{sub x}Te, and Hg{sub 1-x}Zn{sub x}Te were deposited by MOCVD, and their crystallographic, optical, and electrical properties were characterized. 67 refs.

  9. High-quality reproducible PLD Y-Ba-Cu-O:Ag thin films up to 4 inch diameter for microwave applications

    NASA Astrophysics Data System (ADS)

    Lorenz, Michael; Hochmuth, Holger; Natusch, Dieter; Grundmann, Marius

    2002-08-01

    Large-area pulsed laser deposition (PLD) has reached a state in terms of film quality and reproducibility which makes possible now real applications of PLD-YBa 2Cu 3O 7- δ (YBCO) thin films on both sides of R-plane sapphire substrates as HTSC devices in mobile communication systems. Bandpass filters optimized from PLD-YBCO thin films presently fulfill the requirements of the main national companies which are active in future communication techniques. A relatively simple PLD arrangement with fixed laser plume and rotating substrate, with an offset between the laser plume and the center of the substrate is employed to deposit laterally homogeneous 4 inch diameter Ag-doped YBCO thin films. With the experience of more than 1000 double-sided 3 inch diameter films a high degree of homogeneity and reproducibility of jc and Rs is reached. The extension up to 8 inch substrate diameter will increase the productivity of the flexible PLD technique considerably.

  10. Applications of HTSC films in hybrid optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor

    1992-03-01

    An overview is given of potential applications of high-Tc superconductors (HTSC) in the context of hybrid optoelectronic technology. The main requirements are described for the in situ growth of epitaxial YBa2Cu3O(7-delta) (YBCO) films on SrTiO3 and discuss the properties of YBCO layers grown on Si and GaAs substrates with intermediate, conducting indium-tin-oxide buffer layers. The performances of the microbridge and the meander type of HTSC bolometer are compared, and several concepts are discussed that may become relevant for future hybrid optoelectronic technology.

  11. Effect of YBa2Cu3O7-δ film thickness on the dielectric properties of Ba0.1Sr0.9TiO3 in Ag /Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ/LaAlO3 multilayer structures

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaohong; Peng, Wei; Li, Jie; Chen, Yingfei; Tian, Haiyan; Xu, Xiaoping; Zheng, Dongning

    2005-01-01

    Ferroelectric and superconductor bilayers of Ba0.1Sr0.9TiO3 (BSTO)/YBa2Cu3O7-δ (YBCO), with different YBCO film thicknesses, have been fabricated in situ by pulsed-laser deposition on 1.2° vicinal LaAlO3 substrates. The dielectric properties of BSTO thin films were measured with a parallel-plate capacitor configuration in the temperature range of 77-300K. We observed a strong dependence of the dielectric properties of BSTO thin films on the thickness of the YBCO layer. As the YBCO-film thickness increases, the temperature of the dielectric permittivity maximum of BSTO thin films shifts to higher values, and the leakage current and dielectric loss increase drastically, while the dielectric constant and dielectric tunability decrease remarkably. The results are explained in terms of the transformation in the growth mode of the YBCO layer from two-dimensional step flow to three-dimensional island that leads to significant deterioration in the dielectric properties of BSTO thin films. We propose that improved dielectric properties could be obtained by reasonably manipulating the growth mode of the YBCO layer in the multilayer structures.

  12. Use of Ion Beam Analysis to Study in Situ the Oxygen Diffusion and Interfacial Transfer Coefficients in Y1Ba2Cu 3O7-x Thin Films

    NASA Astrophysics Data System (ADS)

    García López, J.; Siejka, J.; Lemaitre, Y.; Mage, J. C.; Marcilhac, B.

    An experimental chamber was connected to the 2.5 MV Van de Graaff accelerator allowing in situ sample annealing at T ≤ 700°C and under pO2 ranging from 10-8 to 1 bar. For the first time to our knowledge the 16O(3He,α)15O nuclear reaction has been employed to monitor in situ the oxygen loss and uptake in Y1Ba2Cu3 O7-x (YBCO) thin films as a function of oxygen pressure and temperature (T ≤ 500°C). The role played by the presence of carbon contamination on YBCO surface was elucidated. Using the 12C(d,p)13C nuclear reaction the carbon loss was observed for T ≥ 250°C and it was associated with the oxygen loss enhancement in YBCO. It is found that in absence of carbon contamination, oxygen in-diffusion rate in YBCO is much faster than the out-diffusion rate, the later being surface reaction limited. The oxygen diffusion coefficients and the surface exchange coefficients of YBCO films have been evaluated. These results will be discussed in relation with the mechanism of high temperature YBCO thin film growth by cathodic sputtering and with the mechanism of the oxygen loss and/or uptake during the sample cooling.

  13. Visible influence of substrate-surface defects on YBa 2Cu 3O 7-x film nucleation and growth on polycrystalline silver

    NASA Astrophysics Data System (ADS)

    Huang, D. X.; Yamada, Y.; Hirabayashi, I.

    2001-06-01

    YBa 2Cu 3O 7-x (YBCO) thin films were grown on the polycrystalline-silver substrates by pulsed laser deposition. The influences of various substrate-surface defects on the film nucleation and growth have been systematically analyzed using transmission electron microscopy (TEM). The obtained results show that the YBCO film usually nucleates and grows on the flat area of the substrate-surface with its a-b plane simply parallel to the substrate-surface plane, no matter the substrate-surface plane is a low-index or a high-index crystal plane. A small angle change of the substrate-surface plane will cause the same angle change of the c-axis orientation of the grown YBCO film. On the defective surface with valleys, however, the YBCO film cannot directly grow, instead, there is an intermediate layer with some other oxide phases previously grown on the substrate surface. Concerning the surface steps and hills, the TEM observation indicates that they can be simply covered by the lateral overgrowth of the YBCO crystals surrounding them. From the viewpoints of energy and kinetics, a detailed discussion has been given for the forming mechanism of various film microstructures on the substrate-surface areas with different surface defects.

  14. ME-μSR study in YBCO vortex states.

    NASA Astrophysics Data System (ADS)

    Le, T. H.; Boekema, C.

    2007-03-01

    We are analyzing μSR vortex data of YBa2Cu3O7-δ (Tc = 91 K). The average superconducting grain size is ˜20 μm. The μSR data are recorded in a transverse 1 kOe field and at temperatures below 10 K. The μSR technique is used to probe the magnetic fields in the cuprate vortex state. The μSR signals show an oscillatory time dependence. To determine the frequency-dependent signals, we use the Maximum Entropy (ME) transform technique. [2] The ME-Burg algorithm removes noise, and does not suffer from Fourier-like truncation effects. The frequency signals are better fit with Lorentzians than static Gaussians. This Lorentzian behavior indicates the existence of dynamic magnetism in and around the vortex cores. This is consistent with earlier YBCO vortex ME-μSR results [3] and the SO(5) modeling [4] of cuprate superconductivity, predicting the existence of antiferromagnetism in the vortex states. Research is supported by NSF-REU and WiSE at SJSU. [1] C. Boekema et al, Physica C282-287 (1997) 2069. [2] J Lee et al, J Appl Phys 95 (2004) 6906 and ref therein; AIP www: Virtual J Appl of Superconductivity 2004 V6 Iss11. [3] C. Boekema et al, 8th Int M2S-HTSC Conf, Physica C in press. [4] H-D Chen et al, Phys Rev B70 (2004) 024516; SC Zhang, Science 275 (1997) 1089.

  15. AC Loss Measurements on a 2G YBCO Coil

    SciTech Connect

    Rey, Christopher M; Duckworth, Robert C; Schwenterly, S W

    2011-01-01

    The Oak Ridge National Laboratory (ORNL) is collaborating with Waukesha Electric Systems (WES) to continue development of HTS power transformers. For compatibility with the existing power grid, a commercially viable HTS transformer will have to operate at high voltages in the range of 138 kV and above, and will have to withstand 550-kV impulse voltages as well. Second-generation (2G) YBCO coated conductors will be required for an economically-competitive design. In order to adequately size the refrigeration system for these transformers, the ac loss of these HTS coils must be characterized. Electrical AC loss measurements were conducted on a prototype high voltage (HV) coil with co-wound stainless steel at 60 Hz in a liquid nitrogen bath using a lock-in amplifier technique. The prototype HV coil consisted of 26 continuous (without splice) single pancake coils concentrically centered on a stainless steel former. For ac loss measurement purposes, voltage tap pairs were soldered across each set of two single pancake coils so that a total of 13 separate voltage measurements could be made across the entire length of the coil. AC loss measurements were taken as a function of ac excitation current. Results show that the loss is primarily concentrated at the ends of the coil where the operating fraction of critical current is the highest and show a distinct difference in current scaling of the losses between low current and high current regimes.

  16. Nanoscale inhomogeneities in yttrium-barium-copper-oxide (YBCO) superconductors

    NASA Astrophysics Data System (ADS)

    Islam, Zahirul; Sinha, S. K.; Lang, J. C.; Liu, X.; Haskel, D.; Moss, S. C.; Srajer, G.; Veal, B. W.; Wermeille, D.; Lee, D. R.; Haeffner, D. R.; Welp, U.; Wochner, P.

    2004-03-01

    X-ray diffraction studies at the Advanced Photon Source reveal that nanoscale inhomogeneities, electronic or structural in origin, form in yttrium-barium-copper-oxide (YBa_2Cu_3O_6+x) superconductors and coexist with the superconducting (SC) state. Diffuse scattering from these inhomogeneous superstructures is due to atomic displacements with respect to equilibrium lattice sites (Z. Islam et al. Phys. Rev. B 66, 92501 (2002)), that are characterized by a wavevector of the form q=(q_x,0,0), where qx varies with hole doping from 2 unit cells (along shorter Cu-O-Cu direction) for very low doping to 4 unit cells at optimal doping. Interestingly, while these superstructures are 3-dimensionally ordered when the SC state is weakened (e.g., at x=0.4), as the doping increases, they become quasi 1D with correlation lengths comparable to SC coherence lengths in these cuprates. Recent first-principles calculations (D. de Fontaine et al., to be published) for the x=0.63 compound show that atomic displacements consistent with experimental data can be the result of ordering of O vacancies in YBCO. Models for various superstructures and their role in the phase diagram will be discussed.

  17. Planar transmission line resonators from YBa2Cu3O(7-x) thin films and epitaxial SIS multilayers

    NASA Astrophysics Data System (ADS)

    Rauch, W.; Gornik, E.; Valenzuela, A. A.; Soelkner, G.; Fox, F.; Behner, H.; Gieres, G.; Russer, P.

    1993-03-01

    The authors have grown c-axis-oriented YBa2Cu3O(7-x) (YBCO) thin films and epitaxial YBCO/NdAlO3/YBCO trilayers by sputtering. From the YBCO films, coplanar half-wavelength transmission line resonators were patterned. At 77 K the unloaded quality factors of coplanar stripline resonators were up to 2570 at 5.6 GHz. The attenuation constant of such a line was evaluated to be 0.6 dB/m at 77 K and at 5.6 GHz. Coplanar waveguide resonators yielded quality factors up to 1200 at 77 K and at 6.2 GHz resulting in an attenuation constant of 1.8 dB/m. From these measurements the surface resistance values Rs of the films were determined. The lowest Rs was 105 micro-ohms at 77 K and at 6.2 GHz. Trilayer structures with a dielectric as thick as 800 nm were patterned into microstrip resonators. At 50 K the authors measured a quality factor of 85 at 4.7 GHz, resulting in an attenuation of 26 dB/m and a surface resistance of 340 micro-ohms. For thick dielectrics the upper YBCO film already contains significant portions of polycrystalline material.

  18. Thermal behavior of MOCVD-grown Cu-clusters on ZnO(1010).

    PubMed

    Kroll, Martin; Löber, Thomas; Schott, Vadim; Wöll, Christof; Köhler, Ulrich

    2012-02-01

    Scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS, AES) were used to study MOCVD of Cu-clusters on the mixed terminated ZnO(1010) surface in comparison to MBE Cu-deposition. Both deposition methods result in the same Cu cluster morphology. After annealing to 670 K the amount of Cu visible above the oxide surface is found to decrease substantially, indicating a substantial diffusion of Cu atoms inside the ZnO-bulk. The spectroscopic data do not show any evidence for changes in the Cu oxidation state during thermal treatment up to 770 K.

  19. Investigation of GaP/Si Heteroepitaxy on MOCVD Prepared Si(100) Surfaces

    SciTech Connect

    Warren, Emily L.; Kibbler, Alan E.; France, Ryan M.; Norman, Andrew G.; Olson, Jerry M.; McMahon, William E.

    2015-06-14

    Antiphase-domain (APD) free growth of GaP on Si has been achieved on Si surfaces prepared in situ by etching with AsH3. The pre-nucleation AsH3 etching removes O and C contaminants at a relatively low temperature, and creates a single-domain arsenic-terminated Si surface. The As-As dimer rows are all parallel to the step edges, and subsequent GaP growth by MOCVD retains this dimerization orientation. Both LEED and TEM indicate that the resulting epilayer is APD-free, and could thereby serve as a template for III-V/Si multijunction solar cells.

  20. High critical current density YBa 2Cu 3O 7- δ films on surface-oxidized metallic substrates

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kaname; Kim, SeokBeom; Yamagiwa, Katsuya; Koike, Yoshihiro; Hirabayashi, Izumi; Watanabe, Tomonori; Uno, Naoki; Ikeda, Masaru

    2000-06-01

    YBa 2Cu 3O 7-δ (YBCO) films with high critical current density ( Jc) were fabricated on nickel tapes buffered with bi-axially textured NiO prepared by surface-oxidation epitaxy (SOE). The effects of oxide cap layers, such as YSZ, CeO 2 and MgO, on the SOE-grown NiO were investigated to improve the superconducting properties of the YBCO films on NiO. By inserting a thin MgO cap layer between NiO layer and YBCO film, a Jc of 3×10 5 A/cm 2 (77 K, 0 T) was achieved. This result indicates the potentiality of the SOE method. In this paper, the application of the NiO/Ni substrate to non-vacuum processings, such as metal-organic deposition (MOD) and liquid phase epitaxy (LPE) will be also introduced.

  1. Levitation forces of a bulk YBCO superconductor in gradient varying magnetic fields

    NASA Astrophysics Data System (ADS)

    Jiang, J.; Gong, Y. M.; Wang, G.; Zhou, D. J.; Zhao, L. F.; Zhang, Y.; Zhao, Y.

    2015-09-01

    The levitation forces of a bulk YBCO superconductor in gradient varying high and low magnetic fields generated from a superconducting magnet were investigated. The magnetic field intensity of the superconducting magnet was measured when the exciting current was 90 A. The magnetic field gradient and magnetic force field were both calculated. The YBCO bulk was cooled by liquid nitrogen in field-cooling (FC) and zero-field-cooling (ZFC) condition. The results showed that the levitation forces increased with increasing the magnetic field intensity. Moreover, the levitation forces were more dependent on magnetic field gradient and magnetic force field than magnetic field intensity.

  2. Compound semiconductor native oxide-based technologies for optical and electrical devices grown on gallium arsenide substrates using MOCVD

    NASA Astrophysics Data System (ADS)

    Holmes, Adrian Lawrence

    1999-11-01

    The beginning of the modern microelectronics industry can be traced back to an invention made in 1947 when Bardeen and Brattain created the first semiconductor switch, called a transistor. Several other important discoveries followed; however, two of the more significant were (i) the development of the first planar process using silicon dioxide (SiO2) as a mask for diffusions into silicon by Frosch in 1955, and (ii) the subsequent integration of several transistors in tiny circuits by Kilby in 1958. Due to the superior quality of the SiO2-silicon interface, Si-based metal-oxide-semiconductor (MOS) transistors have primarily been used in integrated circuits. Until recently, compound semiconductors did not have a native oxide of sufficient quality to create similar MOS transistors. In 1990, research performed by Professor Holonyak and his group at the University of Illinois at Urbana-Champaign has led to a high-quality, stable, and insulating native oxide created from aluminum-containing compound semiconductor alloys. This study investigates native oxide films that are formed by the thermal oxidation of AlAs and InAlP epitaxial layers grown lattice-matched on GaAs substrates using metalorganic chemical vapor deposition (MOCVD). The primary goal is to evaluate how these native oxides can help form novel device structures and transistors. To qualify the material properties of these native oxide films, we have used several characterization techniques including photoluminescence, cross-sectional scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Additionally, we have performed leakage current and capacitance-voltage measurements to evaluate the electrical characteristics of the native oxide-semiconductor interface. The kinetics of the thermal oxidation process for both the surface oxidation of InAlP and lateral oxidation of AlAs are studied and contrasted. Aided by this knowledge, we have created a sealed

  3. Solderability Study of RABiTS-Based YBCO Coated Conductors

    SciTech Connect

    Zhang, Yifei; Duckworth, Robert C; Ha, Tam T; Gouge, Michael J

    2011-01-01

    The solderability of commercially available YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) coated conductors that were made from Rolling Assisted Biaxially Textured Substrates (RABiTS)-based templates was studied. The coated conductors, also known as second-generation (2G) high temperature superconductor (HTS) wires (in the geometry of flat tapes about 4 mm wide), were laminated with copper, brass, or stainless steel strips as stabilizers. To understand the factors that influence their solderability, surface profilometry and scanning electron microscopy were used to characterize the wire surfaces. The solderability of three solders, 52In48Sn, 67Bi33In, and 100In (wt.%), was evaluated using a standard test (IPC/ECA J-STD-002) and with two different commercial fluxes. It was found that the solderability varied with the solder and flux but the three different wires showed similar solderability for a fixed combination of solder and flux. Solder joints of the 2G wires were fabricated using the tools and the procedures recommended by the HTS wire manufacturer. The solder joints were made in a lap-joint geometry and with the superconducting sides of the two wires face-to-face. The electrical resistances of the solder joints were measured at 77 K, and the results were analyzed to qualify the soldering materials and evaluate the soldering process. It was concluded that although the selection of soldering materials affected the resistance of a solder joint, the resistivity of the stabilizer was the dominant factor.

  4. Superconductivity in the surface of YBa 2Cu 3O 7-δ films. Role of the charge reservoir block on the occurence of the superconductivity in one-unit-cell thick YBa 2Cu 3O 7-δ

    NASA Astrophysics Data System (ADS)

    Shimura, Ken-ichi; Daitoh, Yoshihiro; Yano, Yoshihiko; Terashima, Takahito; Bando, Yoshichika; Matsuda, Yuji; Komiyama, Susumu

    1994-07-01

    We have studied the superconductivity in the surface of c-axis oriented ultrathin films of YBa 2Cu 3O 7-δ (YBCO) using a heterostructure of cap oxide/one-unit-cell thick (1-UCT) YBCO/PrBa 2Cu 3O 7-δ buffer layer/SrTiO 3. Atomic force microscope images of the film have revealed multi-terraces with a height of a unit cell of YBCO, indicating two-dimensional nucleation and growth. From cross-sectional transmission electron microscope observation, it has been revealed that the terminating layer of the film is a CuO layer. Cap oxides of BaO and SrO with NaCl-type structure and BaTiO 3, SrTiO 3, CaTiO 3, PbTiO 3, and CdTiO 3 with perovskite-type structure have the ability to produce superconductivity in 1-UCT YBCO. These cap oxides contain an MO ‘rocksalt’-type layer which is needed to form an MO-CuO-BaO charge reservoir block. It is required for making the superconductivity in 1-UCT YBCO that the lattice mismatch between the cap oxide and YBCO is sufficiently small (⩽6%) and the valence of M is 2+.

  5. Investigation for surface resistance of yttrium-barium-copper-oxide thin films on various substrates for microwave applications

    NASA Astrophysics Data System (ADS)

    Yao, Hongjun

    High temperature superconducting (HTS) materials such as YBCO (Yttrium-Barium-Copper-Oxide) are very attractive in microwave applications because of their extremely low surface resistance. In the proposed all-HTS tunable filter, a layer of HTS thin film on a very thin substrate (100 mum) is needed to act as the toractor that can be rotated to tune the frequency. In order to provide more substrate candidates that meet both electrical and mechanical requirements for this special application, surface resistance of YBCO thin films on various substrates was measured using microstrip ring resonator method. For alumina polycrystalline substrate, a layer of YSZ (Yttrium stabilized Zirconia) was deposited using IBAD (ion beam assisted deposition) method prior to YBCO deposition. The surface resistance of the YBCO thin film on alumina was found to be 22 mO due to high-angle grain boundary problem caused by the mixed in-plane orientations and large FWHM (full width at half maximum) of the thin film. For YBCO thin films on a YSZ single crystal substrate, the surface resistance showed even higher value of 30 mO because of the mixed in-plane orientation problem. However, by annealing the substrate in 200 Torr oxygen at 730°C prior to deposition, the in-plane orientation of YBCO thin films can be greatly improved. Therefore, the surface resistance decreased to 1.4 mO, which is still more than an order higher than the reported best value. The YBCO thin films grown on LaAlO3 single crystal substrate showed perfect in-plane orientation with FWHM less 1°. The surface resistance was as low as 0.032 mO. A tunable spiral resonator made of YBCO thin film on LaAlO3 single crystal substrate demonstrated that the resonant frequency can be tuned in a rang as large as 500 MHz by changing the gap between toractor and substrate. The Q-factor was more than 12,000, which ensured the extraordinarily high sensitivity for the proposed all-HTS tunable filter.

  6. Effect of Interim Annealing on Mechanical Strength of TFA-MOD Derived YBCO Coated Conductors

    NASA Astrophysics Data System (ADS)

    Takagi, Y.; Nakaoka, K.; Nakamura, T.; Yoshizumi, M.; Kiss, T.; Izumi, T.; Shiohara, Y.

    TFA-MOD derived YBCO tapes are expected for many applications due to cost-efficiency. In some applications, uniformity and mechanical strength are required for tapes. A 205 m-long YBCO tape was fabricated with high and uniform Ic performance throughout the tape by adopting the interim annealing before the conversion process. The effect of the interim annealing on the crystal growth mechanism of YBCO has been studied focusing on the relationship between the interim annealing conditions and delamination, in this work. Delamination strength was evaluated in the samples prepared with and without interim annealing by the stud pull method. Measurements were carried out on 50 different points for each sample and the results were analyzed statistically. The difference between the two samples was remarkably seen in the delamination strength below 60 MPa. The conventionally annealed sample had more points with low delamination strength below 60 MPa than the interim annealed one. The cross sectional images of both samples observed by SEM showed that there were few pores within the interim annealed superconducting layer, although conventional superconducting layer had many pores. These results suggest that the pores within YBCO layer might be origins to be propagated for delamination at low strength.

  7. New method for introducing nanometer flux pinning centers into single domain YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yang, W. M.; Wang, Miao

    2013-10-01

    Single domain YBCO superconductors with different additions of Bi2O3 have been fabricated by top seeded infiltration and growth process (TSIG). The effect of Bi2O3 additions on the growth morphology, microstructure and levitation force of the YBCO bulk superconductor has been investigated. The results indicate that single domain YBCO superconductors can be fabricated with the additions of Bi2O3 less than 2 wt%; Bi2O3 can be reacted with Y2BaCuO5 and liquid phase and finally form Y2Ba4CuBiOx(YBi2411) nanoscale particles; the size of the YBi2411 particles is about 100 nm, which can act as effective flux pinning centers. It is also found that the levitation force of single domain YBCO bulks is increasing from 13 N to 34 N and decreasing to 11 N with the increasing of Bi2O3 addition from 0.1 wt% to 0.7 wt% and 2 wt%. This result is helpful for us to improve the physical properties of REBCO bulk superconductors.

  8. Experimental studies of helical solenoid model based on YBCO tape-bridge joints

    SciTech Connect

    Yu, M.; Lombardo, V.; Turrioni, D.; Zlobin, A.V.; Flangan, G.; Lopes, M.L.; Johnson, R.P.; /Fermilab

    2011-06-01

    Helical solenoids that provide solenoid, helical dipole and helical gradient field components are designed for a helical cooling channel (HCC) proposed for cooling of muon beams in a muon collider. The high temperature superconductor (HTS), 12 mm wide and 0.1 mm thick YBCO tape, is used as the conductor for the highest-field section of HCC due to certain advantages, such as its electrical and mechanical properties. To study and address the design, and technological and performance issues related to magnets based on YBCO tapes, a short helical solenoid model based on double-pancake coils was designed, fabricated and tested at Fermilab. Splicing joints were made with Sn-Pb solder as the power leads and the connection between coils, which is the most critical element in the magnet that can limit the performance significantly. This paper summarizes the test results of YBCO tape and double-pancake coils in liquid nitrogen and liquid helium, and then focuses on the study of YBCO splices, including the soldering temperatures and pressures, and splice bending test.

  9. Thermal stability of YBCO coated conductor with different Cu stabilizer thickness

    NASA Astrophysics Data System (ADS)

    Bae, J. H.; Park, H. Y.; Eom, B. Y.; Seong, K. C.; Baik, S. K.

    2010-11-01

    The studies on the conduction-cooled superconducting magnets are actively underway with rapid advancement in refrigeration technology recently. YBCO coated conductor (CC) is one of the promising conductors for a conduction-cooled superconducting magnet because of increasing the operation temperature of magnets and being able to have cost collectiveness with conventional copper conductor in the future. However, it is known that quench propagation velocity in high-temperature superconductor (HTS) is two or three orders of magnitude slower than that in low-temperature superconductor because of its large heat capacity and the high operating temperature. The hot spot will emerge in local region if a critical current is non-uniform along the length of HTS tape and eventually, it causes permanent destroy for the whole HTS tape. Based on the protection of YBCO CC, it is necessary to determine a suitable stabilizer thickness for YBCO CC so that the temperature of hot spot in local area does not exceed the permissible temperature. In this study, we have established a suitable thermal analysis model, and analyzed minimum quench energy and thermal properties for three kinds of YBCO CC samples with different stabilizer thickness, which are fabricated by Superpower Incorporated, using finite element method.

  10. Microstructural studies of K 2CO 3 and Rb 2CO 3 doped YBCO HTSC

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.

    2003-10-01

    The influence of Me 2CO 3 (Me=K or Rb) additions on the microstructural morphology of YBa 2Cu 3O x (YBCO) HTSC with nominal composition Y (1-0.2 x) Ba (2-0.2 x) M xCu 3O y ( x=0-2.0) were investigated by means of orientation imaging microscopy which provides a method for measuring a large number of individual grain orientations and relating them directly to the microstructural features by means of evaluating electron backscatter Kikuchi patterns in scanning electron microscopy. We investigated the influence of the alkali additions on the grain orientation distributions of YBCO. The samples are characterized by grain orientation maps, and pole and inverse pole figures. Finally, the grain orientation distribution functions are obtained from the measured data. Within a certain range of doping (up to 5 wt.% in the initial batch), the grain sizes are found to increase as compared to pure YBCO, accompanied by an improvement of the superconducting properties ( Tc). It is shown that the additions of alkali carbonates do not introduce any preferred grain orientations in YBCO HTSC in the entire doping range.

  11. Method of forming superconducting Tl-Ba-Ca-Cu-O films

    DOEpatents

    Wessels, Bruce W.; Marks, Tobin J.; Richeson, Darrin S.; Tonge, Lauren M.; Zhang, Jiming

    1993-01-01

    A method of forming a superconducting Tl-Ba-Ca-Cu-O film is disclosed, which comprises depositing a Ba-Ca-Cu-O film on a substrate by MOCVD, annealing the deposited film and heat-treating the annealed film in a closed circular vessel with TlBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x and cooling to form said superconducting film of TlO.sub.m Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2, wherein m=1,2 and n=1,2,3.

  12. MOCVD growth of N-polar GaN on on-axis sapphire substrate: Impact of AlN nucleation layer on GaN surface hillock density

    NASA Astrophysics Data System (ADS)

    Marini, Jonathan; Leathersich, Jeffrey; Mahaboob, Isra; Bulmer, John; Newman, Neil; (Shadi) Shahedipour-Sandvik, F.

    2016-05-01

    We report on the impact of growth conditions on surface hillock density of N-polar GaN grown on nominally on-axis (0001) sapphire substrate by metal organic chemical vapor deposition (MOCVD). Large reduction in hillock density was achieved by implementation of an optimized high temperature AlN nucleation layer and use of indium surfactant in GaN overgrowth. A reduction by more than a factor of five in hillock density from 1000 to 170 hillocks/cm-2 was achieved as a result. Crystal quality and surface morphology of the resultant GaN films were characterized by high resolution x-ray diffraction and atomic force microscopy and found to be relatively unaffected by the buffer conditions. It is also shown that the density of smaller surface features is unaffected by AlN buffer conditions.

  13. High efficiency thin film cadmium telluride solar cells

    NASA Astrophysics Data System (ADS)

    Chu, T. L.; Chu, Shirley S.; Britt, J.; Chen, G.; Ferekides, C.; Schultz, N.; Wang, C.; Wu, C. Q.

    1992-12-01

    Cadmium sulfide (CdS), grown from an aqueous solution, and zinc oxide (ZnO), cadmium zinc sulfide (Cd1-xZnxS), and zinc selenide (ZnSe), deposited by metalorganic chemical vapor deposition (MOCVD), have been used as the window for thin film cadmium telluride (CdTe) solar cells. Thin film solar cells were prepared by the successive deposition of the window and p-CdTe (by MOCVD and close-spaced sublimation, CSS) on SnO2:F/glass substrates. CdS/CdTe(CSS) solar cells show considerably better characteristics than CdS/CdTe(MOCVD) solar cells because of the better microstructure of CSS CdTe films. Total area conversion efficiency of 14.6%, verified by the National Renewable Energy Laboratory, has been achieved for solar cells of about 1 cm2 area. Solar cell prepared by using ZnO, ZnSe, or Cd1-xZnxS as window have significantly lower photovoltage than CdS/CdTe solar cells.

  14. Chemical vapor deposition of high T(sub c) superconducting films in a microgravity environment

    NASA Technical Reports Server (NTRS)

    Levy, Moises; Sarma, Bimal K.

    1994-01-01

    Since the discovery of the YBaCuO bulk materials in 1987, Metalorganic Chemical Vapor Deposition (MOCVD) has been proposed for preparing HTSC high T(sub c) films. This technique is now capable of producing high-T(sub c) superconducting thin films comparable in quality to those prepared by any other methods. The MOCVD technique has demonstrated its superior advantage in making large area high quality HTSC thin films and will play a major role in the advance of device applications of HTSC thin films. The organometallic precursors used in the MOCVD preparation of HTSC oxide thin films are most frequently metal beta-diketonates. High T(sub c) superconductors are multi-component oxides which require more than one component source, with each source, containing one kind of precursor. Because the volatility and stability of the precursors are strongly dependent on temperature, system pressure, and carrier gas flow rate, it has been difficult to control the gas phase composition, and hence film stoichiometry. In order circumvent these problems we have built and tested a single source MOCVD reactor in which a specially designed vaporizer was employed. This vaporizer can be used to volatilize a stoichiometric mixture of diketonates of yttrium, barium and copper to produce a mixed vapor in a 1:2:3 ratio respectively of the organometellics. This is accomplished even though the three compounds have significantly different volatilities. We have developed a model which provides insight into the process of vaporizing mixed precursors to produce high quality thin films of Y1Ba2Cu3O7. It shows that under steady state conditions the mixed organometallic vapor must have a stoichiometric ratio of the individual organometallics identical to that in the solid mixture.

  15. Photoeffects in cobalt doped pyrite (FeS 2) films

    NASA Astrophysics Data System (ADS)

    Thomas, B.; Ellmer, K.; Bohne, W.; Röhrich, J.; Kunst, M.; Tributsch, H.

    1999-07-01

    By indiffusion of a thin metallic cobalt layer into a pyrite film deposited by metal organic chemical vapour deposition (MOCVD), cobalt doped pyrite (FeS 2) films have been prepared. The cobalt in these films acts as a donor and transforms the originally p-type into n-type conductivity. To our knowledge this is the first time that n-type pyrite films have been prepared. Compared to the undoped p-type pyrite films, the cobalt-diffused films exhibit a much higher photoconductivity, as revealed by time resolved microwave conductivity analysis. From Hall and conductivity measurements a charge carrier concentration of about 10 20 cm -3 and a Hall mobility of about 1.5 cm 2/(V s) was calculated. This has to be compared with p-type pyrite films which do not show a Hall mobility above 0.1 cm 2/(V s), the detection limit of our Hall system. By analytical techniques (Rutherford backscattering and photoelectron spectroscopy) it was confirmed that the increase of the photoactivity is a bulk property of the pyrite films and not merely due to a surface passivation (for instance, due to metallic CoS 2). The presented results stimulate further experiments on in-situ-doping of pyrite by MOCVD and open the opportunity for the preparation of pn-junctions and pn-solar cells with pyrite.

  16. Large-area YBa2Cu3O(7-delta) thin films on sapphire for microwave applications

    NASA Technical Reports Server (NTRS)

    Cole, B. F.; Liang, G.-C.; Newman, N.; Char, K.; Zaharchuk, G.; Martens, J. S.

    1992-01-01

    We have deposited YBa2Cu3O(7-delta) (YBCO) films with low microwave surface resistance (Rs) on 5-cm-diam, oxide-buffered sapphire substrates by planar magnetron sputtering. MgO buffer layers are used on M-plane (1 0 -1 0) sapphire, and R-plane (1 -1 0 2) sapphire is buffered by CeO2. Rs values of 450-620 microhms at 77 K and 10 GHz were measured across an entire 5-cm diam YBCO film on M-plane sapphire. For YBCO on R-plane sapphire, Rs values at 77 K and 10 GHz were 950 microohms for a 5-cm-diam wafer and 700 microohms for 1 x 1 sq cm samples.

  17. Effect of silver doping on the transport properties of epitaxial YBa 2Cu 3O 7-x thin films

    NASA Astrophysics Data System (ADS)

    Bolaños, G.; Prieto, P.; Arias, D.; Sefrioui, Z.; Santamaría, J.

    Epitaxial YBa 2Cu 3O 7 (YBCO) thin films doped with 5-20 wt % Ag have been grown “ in situ” at high oxygen pressure by a dc sputtering technique on (001) SrTiO 3 substrates. Critical current densities, J c, were measured in 5 wt % Ag-doped YBCO films in magnetic fields up to 6 T, and were found to be greater than the values obtained for undoped samples. Current-voltage (I-V) characteristics were used to investigate the vortex phase transition, in magnetic field of 6 T applied parallel to the c-axis. The ϱ-j curves scale according to the 3D vortex-glass (VG) model with values of the critical exponents similar to those found for undoped YBCO samples (ν=1.4 and z=4.87).

  18. Pulsed laser deposition of hexagonal GaN-on-Si(100) template for MOCVD applications.

    PubMed

    Shen, Kun-Ching; Jiang, Ming-Chien; Liu, Hong-Ru; Hsueh, Hsu-Hung; Kao, Yu-Cheng; Horng, Ray-Hua; Wuu, Dong-Sing

    2013-11-01

    Growth of hexagonal GaN on Si(100) templates via pulsed laser deposition (PLD) was investigated for the further development of GaN-on-Si technology. The evolution of the GaN growth mechanism at various growth times was monitored by SEM and TEM, which indicated that the GaN growth mode changes gradually from island growth to layer growth as the growth time increases up to 2 hours. Moreover, the high-temperature operation (1000 °C) of the PLD meant no significant GaN meltback occurred on the GaN template surface. The completed GaN templates were subjected to MOCVD treatment to regrow a GaN layer. The results of X-ray diffraction analysis and photoluminescence measurements show not only the reliability of the GaN template, but also the promise of the PLD technique for the development of GaN-on-Si technology.

  19. Three-dimensional modelling of horizontal chemical vapor deposition. I - MOCVD at atmospheric pressure

    NASA Technical Reports Server (NTRS)

    Ouazzani, Jalil; Rosenberger, Franz

    1990-01-01

    A systematic numerical study of the MOCVD of GaAs from trimethylgallium and arsine in hydrogen or nitrogen carrier gas at atmospheric pressure is reported. Three-dimensional effects are explored for CVD reactors with large and small cross-sectional aspect ratios, and the effects on growth rate uniformity of tilting the susceptor are investigated for various input flow rates. It is found that, for light carrier gases, thermal diffusion must be included in the model. Buoyancy-driven three-dimensional flow effects can greatly influence the growth rate distribution through the reactor. The importance of the proper design of the lateral thermal boundary conditions for obtaining layers of uniform thickness is emphasized.

  20. Microstructure of GaN Grown on (111) Si by MOCVD

    SciTech Connect

    Fleming, J.G.; Follstaedt, D.M.; Han, J.; Provencio, P.

    1998-12-17

    Gallium nitride was grown on (111) Si by MOCVD by depositing an AIN buffer at 108O"C and then GaN at 1060 {degrees}C. The 2.2pm layer cracked along {1-100} planes upon cooling to room temperature, but remained adherent. We were able to examine the microstructure of material between cracks with TEM. The character and arrangement of dislocation are much like those of GaN grown on Al{sub 2}O{sub 3}: -2/3 pure edge and - 1/3 mixed (edge + screw), arranged in boundaries around domains of GaN that are slightly disoriented with respect to neighboring material. The 30 nm AIN buffer is continuous, indicating that AIN wets the Si, in contrast to GaN on Al{sub 2}O{sub 3}.

  1. Free-standing GaAs nanowires growth on ITO glass by MOCVD

    NASA Astrophysics Data System (ADS)

    Wu, D.; Tang, X. H.; Olivier, A.; Li, X. Q.

    2015-04-01

    GaAs nanowires (NWs) are directly grown on indium tin oxide (ITO) glass substrate by metalorganic chemical vapour deposition (MOCVD), using Au nanoparticles (NPs) as catalyst. By functionalization of the ITO glass and optimization of the Au NPs deposition time, the Au NPs area density deposited on the ITO glass reaches 92 NP μm-2. Uniform and free-standing GaAs NWs without kinking or worm-shape defects have been grown at 430 °C. More than 96% of the NWs have tilt angles larger than 45° with respect of the substrate. The effects of the growth temperature and the Au NPs size on the GaAs NWs growth rate, the NW diameter, and tapering effect are investigated. These results of GaAs NWs growth are the essential step for understanding III-V NWs integration on transparent conductive oxide coated low cost substrate and developing high efficiencyhybrid solar cells.

  2. Low ohmic contact AlN/GaN HEMTs grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Guodong, Gu; Shaobo, Dun; Yuanjie, Lü; Tingting, Han; Peng, Xu; Jiayun, Yin; Zhihong, Feng

    2013-11-01

    AlN/GaN high-electron-mobility transistors (HEMTs) on SiC substrates were fabricated by metal-organic chemical vapor deposition (MOCVD) and then characterized. An Si/Ti/Al/Ni/Au stack was used to reduce ohmic contact resistance (0.33 Ω·mm) at a low annealing temperature. The fabricated devices exhibited a maximum drain current density of 1.07 A/mm (VGS = 1 V) and a maximum peak extrinsic transconductance of 340 mS/mm. The off-state breakdown voltage of the device was 64 V with a gate—drain distance of 1.9 μm. The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 36 and 80 GHz with a 0.25 μm gate length, respectively.

  3. Growth of AlN nanostructure on GaN using MOCVD

    SciTech Connect

    Loganathan, R.; Ramesh, R.; Jayasakthi, M.; Prabakaran, K.; Kuppulingam, B.; Sankaranarayanan, M.; Balaji, M.; Arivazhagan, P.; Singh, Subra; Baskar, K.

    2015-06-24

    Aluminum nitride (AlN) nanowalls have been epitaxially grown on dislocation assisted GaN/Al{sub 2}O{sub 3} template by metal organic chemical vapor deposition (MOCVD) without any help of metal catalysts. A large number of nanowalls with thicknesses of 1.5-2.0 µm and height 400 nm have been deposited. The AlN nanowalls were found to have a preferred c-axis oriented with a hexagonal crystal structure. The AlN nanowalls and GaN/Al{sub 2}O{sub 3} template have been characterize at room temperature photoluminescence (PL) and high resolution X-ray diffraction (HRXRD)

  4. Monitoring and Controlling of Strain During MOCVD of AlGaN for UV Optoelectronics

    SciTech Connect

    Han, J.; Crawford, M.H.; Shul, R.J.; Hearne, S.J.; Chason, E.; Figiel, J.J.; Banas, M.

    1999-01-14

    The grown-in tensile strain, due to a lattice mismatch between AlGaN and GaN, is responsible for the observed cracking that seriously limits the feasibility of nitride-based ultraviolet (UV) emitters. We report in-situ monitoring of strain/stress during MOCVD of AlGaN based on a wafer-curvature measurement technique. The strain/stress measurement confirms the presence of tensile strain during growth of AlGaN pseudomorphically on a thick GaN layer. Further growth leads to the onset of stress relief through crack generation. We find that the growth of AlGaN directly on low-temperature (LT) GaN or AlN buffer layers results in a reduced and possibly controllable strain.

  5. Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Nouhi, Akbar (Inventor); Stirn, Richard J. (Inventor)

    1990-01-01

    A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, wherein a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd.sub.1-x Mn.sub.x Te, wherein 0.ltoreq..times..ltoreq.0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) maganese (TCPMn) is employed. To prevent TCPMn condensation during the introduction thereof int the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, wherein the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

  6. Study of GaP single crystal layers grown on GaN by MOCVD

    SciTech Connect

    Li, Shuti; Liu, Chao; Ye, Guoguang; Xiao, Guowei; Zhou, Yugang; Su, Jun; Fan, Guanghan; Zhang, Yong; Liang, Fubo; Zheng, Shuwen

    2011-11-15

    Highlights: {yields} We investigated the growth of GaP layers on GaN by MOCVD. {yields} A single crystal GaP layer could be grown on GaN. {yields} The V/III ratio played an important role to improve GaP layer quality. {yields} The GaP:Mg layer with hole concentration of 4.2 x 10{sup 18} cm{sup -3} was obtained. -- Abstract: The performance of GaN based devices could possibly be improved by utilizing the good p-type properties of GaP layer and it provides the possibility of the integration of InAlGaN and AlGaInP materials to produce new devices, if high quality GaP compounds can be grown on III-nitride compounds. In this paper, the growth of GaP layers on GaN by metalorganic chemical vapor deposition (MOCVD) has been investigated. The results show that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature GaP growth. Using a 40 nm thick GaP buffer layer, a single crystal GaP layer, whose full-width at half-maximum of the (1 1 1) plane measured by double crystal X-ray diffraction is 580'', can be grown on GaN. The V/III ratio plays an important role in the GaP layer growth and an appropriate V/III ratio can improve the quality of GaP layer. The GaP:Mg layer with hole carrier concentration of 4.2 x 10{sup 18} cm{sup -3} has been obtained.

  7. High efficiency cadmium and zinc telluride-based thin film solar cells

    SciTech Connect

    Rohatgi, A.; Summers, C.J.; Erbil, A.; Sudharsanan, R.; Ringel, S. . School of Electrical Engineering)

    1990-10-01

    Polycrystalline Cd{sub 1-x}Zn{sub x}Te and Cd{sub 1-x}Mn{sub x}Te films with a band gap of 1.7 eV were successfully grown on glass/SnO{sub 2}/CdS substrates by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. Polycrystalline Cd{sub 1-x}Zn{sub x}Te films grown by MBE resulted in uniform composition and sharp interfaces. However, polycrystalline Cd{sub 1-x}Mn{sub x}Te films grown by MOCVD showed nonuniform compositions and evidence of manganese accumulation at the Cd{sub 1-x}Mn{sub x}Te/CdS interface. We found that manganese interdiffuses and replaces cadmium in the CdS film. By improving the CdTe/CdS interface and, thus, reducing the collection function effects, the efficiency of the MOCVD CdTe cell can be improved to about 13.5%. MBE-grown CdTe cells also produced 8%--9% efficiencies. The standard CdTe process was not optimum for ternary films and resulted in a decrease in the band gap. Recent results indicate that CdCl{sub 2} + ZnCl{sub 2} chemical treatment may prevent the band-gap reduction, and that chromate etch (rather than bromine etch) may provide the solution to contact resistance in the ternary cells.

  8. The mechanism of thermal runaway due to continuous local disturbances in the YBCO-coated conductor coil winding

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Y.; Okuyama, E.; Nakagome, H.; Takematsu, T.; Takao, T.; Hamada, M.; Matsumoto, S.; Kiyoshi, T.; Takizawa, A.; Takahashi, M.; Maeda, H.

    2012-07-01

    Though YBCO coils are stable against transient disturbances such as conductor motion, they suffer from thermal runaway at a current below the coil critical current due to continuous local disturbances attributed to partial degradation of the conductor in the coil winding. Continuous heat generation in the degraded layer induces thermal runaway in adjacent layers; thermal runaway does not occur in the degraded layer spontaneously due to the small n index of the degraded YBCO-coated conductor. The thermal runaway current depends on the cooling conditions of the winding. For a paraffin-impregnated YBCO coil under quasi-adiabatic conditions, the thermal runaway current is far below the coil critical current, while it is close to the coil critical current in the case of a dry-wound coil. The permissible temperature rise following a thermal runaway for YBCO conductors in the degraded layer is demonstrated to be 340 K. If the YBCO coils are operated at a temperature below 20 K, the current density, typically 600-800 A mm-2, is much higher than that at 77 K. Therefore, the time interval between thermal runaway initiation and the melting temperature becomes less than 0.5 s, posing a difficult problem for protection; i.e., thermal runaway due to continuous local disturbances is hazardous to the safe operation of high current density YBCO coils.

  9. Recovery of superconductivity and recrystallization of ion-damaged YBa 2Cu 3O 7- x films after thermal annealing treatment

    NASA Astrophysics Data System (ADS)

    Li, Yijie; Linzen, S.; Machalett, F.; Schmidl, F.; Seidel, P.

    1995-02-01

    We have systematically studied the annealing effects of high-quality epitaxial YBa 2Cu 3O 7- x (YBCO) films on (100) SrTiO 3 substrates implanted with 100 keV Ar ions at different fluences. The mechanisms for Tc degradation induced by ion implantation have been discussed. After annealing in oxygen atmosphere in a temperature range from 450 to 950°C, R( T) curve measurements show a partial or complete recovery of superconductivity. The recrystallization of ion-implanted YBCO films have been investigated using X-ray diffraction (XRD) and Rutherford backscattering spectrometry with channeling. It is found that the annealing at 450°C indeed results in the movement of oxygen defects and ordering of the oxygen sublattice in the sample implanted with low to moderate fluences, however, only a small partial recovery of superconductivity is observed. The results suggest that ion implantation induced Tc degradation is mainly caused by disordering of the cation sublattice not the oxygen sublattice. After annealing at 850°C, the recovery of superconductivity and recrystallization of implanted YBCO films are related to the fluence. For YBCO films implanted with low to moderate fluences (1 × 10 11-1 × 10 14/cm 2), the superconductivity can be nearly completely recovered, and the pure c-axis orientation of the samples is observed in the XRD spectra. However, recrystallization of amorphous YBCO films implanted with high fluences (1 × 10 15-1 × 10 16/cm 2) is quite different. The orientation of the samples depends on the annealing temperature. With the increasing of the annealing temperature from 750 to 950°C, the regrowth orientation gradually changes from a- to c-axis orientation. After annealing at temperatures of 750 and 800°C, the samples have the nearly pure a-axis orientation. At 850°C, the sample has a mixed a- and c-axis oriented structure but the a-axis orientation is still dominant. Above 900°C the structure of the annealed sample has the pure c

  10. Second harmonic generation in ZnO thin films fabricated by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Liu, C. Y.; Zhang, B. P.; Binh, N. T.; Segawa, Y.

    2004-07-01

    Second harmonic generation (SHG) from ZnO thin films fabricated by metalorganic chemical vapor deposition (MOCVD) technique was carried out. By comparing the second harmonic signal generated in a series of ZnO films with different deposition temperatures, we conclude that a significant part of second harmonic signal is generated at the film deposited with appropriate temperature. The second-order susceptibility tensor χ(2)zzz=9.2 pm/V was deduced for a film deposited at 250 °C.

  11. Temperature coefficients and radiation induced DLTS spectra of MOCVD grown n(+)p InP solar cells

    NASA Technical Reports Server (NTRS)

    Walters, Robert J.; Statler, Richard L.; Summers, Geoffrey P.

    1991-01-01

    The effects of temperature and radiation on n(+)p InP solar cells and mesa diodes grown by metallorganic chemical vapor deposition (MOCVD) were studied. It was shown that MOCVD is capable of consistently producing good quality InP solar cells with Eff greater than 19 percent which display excellent radiation resistance due to minority carrier injection and thermal annealing. It was also shown that universal predictions of InP device performance based on measurements of a small group of test samples can be expected to be quite accurate, and that the degradation of an InP device due to any incident particle spectrum should be predictable from a measurement following a single low energy proton irradiation.

  12. Study of microstructure and electrical properties of bulk YBCO prepared by melt textured growth technique

    SciTech Connect

    Gonal, M. R.; Krishnan, Madangopal; Tewari, R.; Tyagi, A. K.; Gyore, A.; Vajda, I.

    2015-06-24

    Bulk YBCO components were prepared using Melt Texture Growth (MTG) technique. Components were fabricated using MTG by addition of Y{sub 2}BaCuO{sub 5} (Y211) and Ag to YBCO, which leads to improved grain size without affecting superconducting properties. Green compacts prepared by cold isostatic pressing were pre-sintered at 930°C before subjecting melt texturing. Cooling rates lower than 1 °C.h{sup −1} was used, in between (peritectic) temperature of about 995 and 1025°C, to obtain large grained components. Microstructure studies in details were carried out by Scanning Electron Microscope (SEM), Electron Probe Micro Analysis (EPMA), Orientation Imaging Microscope (OIM) and TEM correlated with electrical properties like Critical current density (J{sub c})

  13. Static Test for a Gravitational Force Coupled to Type 2 YBCO Superconductors

    NASA Technical Reports Server (NTRS)

    Li, Ning; Noever, David; Robertson, Tony; Koczor, Ron; Brantley, Whitt

    1997-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cc. Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating type II, YBCO superconductor, with the percentage change (0.05 - 2.1 %) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10' was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field. Changes in acceleration were measured to be less than 2 parts in 108 of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between static superconductors and gravity.

  14. T /B scaling without quasiparticle mass divergence: YbCo2Ge4

    NASA Astrophysics Data System (ADS)

    Sakai, Akito; Kitagawa, Kentaro; Matsubayashi, Kazuyuki; Iwatani, Makoto; Gegenwart, Philipp

    2016-07-01

    YbCo2Ge4 is a clean paramagnetic Kondo lattice which displays non-Fermi-liquid behavior. We report a detailed investigation of the specific heat, magnetic Grüneisen parameter (Γmag), and temperature derivative of the magnetization (M ) on a high-quality single crystal at temperatures down to 0.1 K and magnetic fields up to 7 T. Γmag and d M /d T display a divergence upon cooling and obey T /B scaling. Similar behavior has previously been found in several other Yb-based Kondo lattices and related to a zero-field quantum critical point without fine tuning of pressure or composition. However, in the approach of B →0 the electronic heat capacity coefficient of YbCo2Ge4 saturates at low T , excluding ferromagnetic quantum criticality. This indicates that T /B scaling is insufficient to prove a zero-field quantum critical point.

  15. Pinning features of the magnetic flux trapped by YBCO single crystals in weak constant magnetic fields

    NASA Astrophysics Data System (ADS)

    Monarkha, V. Yu.; Paschenko, V. A.; Timofeev, V. P.

    2013-02-01

    The dynamics of Abrikosov vortices and their bundles was experimentally investigated in weak constant magnetic fields, in the range of Earth's magnetic field. Characteristics of the isothermal magnetization relaxation in YBCO single-crystal samples with strong pinning centers were studied for different sample-field orientation. The obtained values of normalized relaxation rate S allowed us to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results of similar measurements in significantly higher magnetic fields was performed. To compare different techniques for evaluation of Jc, the magnetization loop measurements M(H), which relate the loop width to the critical current, were carried out. These measurements provided important parameters of the samples under study (penetration field Hp and first critical field Hc1), which involve the geometrical configuration of the samples.

  16. Proximity effect induced by Kondo interaction in a network composed of YBCO and spin density wave

    NASA Astrophysics Data System (ADS)

    Maity, S.; Ghosh, Ajay Kumar

    2015-10-01

    The possibility of the proximity effect mediated by Kondo interaction in YBCO embedded in system of diluted magnetic spin ordering has been studied. An YBCO sample is selected in which both metal to insulator transition and superconducting state exist in the different ranges of temperature. The intergranular network of the bulk Y-123 has been modified by the inclusion of YMnO3 which has a well defined magnetic structure depending on temperature. The current-voltage measurements have been carried out in pure Y-123 at several temperatures. At the same set of temperatures the current-voltage curves in presence of YMnO3 have been studied. The role of the diluted spin magnetic ordering in tuning proximity effect and conduction property in binary systems is associated with reduced coherence length in the normal region.

  17. ZnO Films with Very High Haze Value for Use as Front Transparent Conductive Oxide Films in Thin-Film Silicon Solar Cells

    NASA Astrophysics Data System (ADS)

    Hongsingthong, Aswin; Krajangsang, Taweewat; Afdi Yunaz, Ihsanul; Miyajima, Shinsuke; Konagai, Makoto

    2010-05-01

    We successfully increased the haze value of zinc oxide (ZnO) films fabricated using metal-organic chemical vapor deposition (MOCVD) by conducting glass-substrate etching before film deposition. It was found that with increasing the glass treatment time, the surface morphology of ZnO films changed from conventional pyramid-like single texture to greater cauliflower-like multi texture. Further, the rms roughness and the haze value of the films increased remarkably. Using ZnO films with a high haze value as front transparent conductive oxide (TCO) films in hydrogenated microcrystalline silicon (µc-Si:H) solar cells, we improved the quantum efficiency of these cells particularly in the long-wavelength region.

  18. Flux pinning effect in a melt textured YBCO bulk evaluated by using tension measurements

    NASA Astrophysics Data System (ADS)

    Lee, Joon Ho; Ahmad, Dawood; Kim, Byoung Joo; Cha, Myoungsik; Yang, Ho Soon; Kim, Young Cheol; Ko, Rock Kil; Jeong, Dae Young

    2013-01-01

    Research on the flux pinning effect in type-II superconductors has usually been focused on microor nanosize pinning centers, and mm-sized pinning centers have been relatively less studied. In order to investigate the flux pinning effect caused by mm-sized pinning centers, we introduce a tension measurement method in this research. A cm-sized melt-textured YBCO bulk, in which holes with a 2 mm diameter are made, is prepared. The YBCO bulk is field-cooled by using a strong magnet in liquid nitrogen, and the bulk and the magnet are separated from each other. Then, an attractive force ( f a ) between them is generated, and f a is detected by using a tension measuring device. As the distance ( d) between them is increased, f a increases at short distance and decreases at long distance, showing a maximum value, f am , at a specific distance. The measurement of f a is stopped when d reaches a value defined as the breaking distance ( d bk ), as if a `string' between the magnet and the YBCO bulk is broken. As the number of holes ( n) made in the YBCO bulk increases from 1 to 6, f am and d bk increase, in spite of the superconducting volume loss. f am and d bk for n ≥ 7 converge to nearly constant values, which are smaller than the values for n = 6. This means that the critical current density can be calculated by using f am or d bk for a sufficient number of holes.

  19. CHEMICAL SOLUTION DEPOSITION BASED OXIDE BUFFERS AND YBCO COATED CONDUCTORS

    SciTech Connect

    Paranthaman, Mariappan Parans

    2011-01-01

    We have reviewed briefly the growth of buffer and high temperature superconducting oxide thin films using a chemical solution deposition (CSD) method. In the Rolling-Assisted Biaxially Textured Substrates (RABiTS) process, developed at Oak Ridge National Laboratory, utilizes the thermo mechanical processing to obtain the flexible, biaxially oriented copper, nickel or nickel-alloy substrates. Buffers and Rare Earth Barium Copper Oxide (REBCO) superconductors have been deposited epitaxially on the textured nickel alloy substrates. The starting substrate serves as a template for the REBCO layer, which has substantially fewer weak links. Buffer layers play a major role in fabricating the second generation REBCO wire technology. The main purpose of the buffer layers is to provide a smooth, continuous and chemically inert surface for the growth of the REBCO film, while transferring the texture from the substrate to the superconductor layer. To achieve this, the buffer layers need to be epitaxial to the substrate, i.e. they have to nucleate and grow in the same bi-axial texture provided by the textured metal foil. The most commonly used RABiTS multi-layer architectures consist of a starting template of biaxially textured Ni-5 at.% W (Ni-W) substrate with a seed (first) layer of Yttrium Oxide (Y2O3), a barrier (second) layer of Yttria Stabilized Zirconia (YSZ), and a Cerium Oxide (CeO2) cap (third) layer. These three buffer layers are generally deposited using physical vapor deposition (PVD) techniques such as reactive sputtering. On top of the PVD template, REBCO film is then grown by a chemical solution deposition. This article reviews in detail about the list of oxide buffers and superconductor REBCO films grown epitaxially on single crystal and/or biaxially textured Ni-W substrates using a CSD method.

  20. On detection of the Fermi edge in in situ grown thin films of high- Tc oxides

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, D.; Saleh, S. A.; Rast, S.; Margaritondo, G.; Onellion, M.; Pavuna, D.

    2001-11-01

    We discuss our systematic series of experiments on the photoelectric detection of the Fermi edge using a cylindrical mirror analyser on films of high- Tc oxides, grown in situ by pulsed laser ablation. The Fermi edge (comparable to the edge of the reference Ag) is very easily observed even in the two-phase BSCCO-2212 film that exhibits onsets of superconducting transitions, at 85 and 45 K. In contrast, the Fermi edge is weaker and more difficult to observe even in the state-of-the-art, highly epitaxial, monophase YBa 2Cu 3O 7- y (YBCO) and NdBa 2Cu 3O 7- y (NBCO-123) films (both with Tc=92 K). So far we could not detect the Fermi edge in the films of the double-`chain' YBCO-124.

  1. Effect of Au nano-particles doping on polycrystalline YBCO high temperature superconductor

    NASA Astrophysics Data System (ADS)

    Dadras, Sedigheh; Gharehgazloo, Zahra

    2016-07-01

    In this research, we prepared different Au nanoparticles (0.1-2 wt%) doped YBCO high temperature superconductor samples by sol-gel method. To characterize the samples, we used X-Ray diffraction (XRD) and scanning electron microscope (SEM) analysis. Results show the formation of orthorhombic phase of superconductivity for all prepared samples. We observed that by adding Au nanoparticles, the grains' size of the samples reduces from 76 nm to 47 nm as well. The critical current density (Jc) and transition temperature (Tc) were determined using current versus voltage (I-V) and resistivity versus temperature (ρ-T) measurements, respectively. We found that by increasing Au nanoparticles in the compound, in comparison to the pure YBCO sample, the transition temperature, pinning energy and critical current density will increase. Also, the highest Jc is for 1 wt% Au doped YBCO compound that its critical current density is about 8 times more than the Jc of pure one in 0.7 T magnetic field.

  2. Bulk YBCO seeded with 45°-45° bridge-seeds of different lengths

    NASA Astrophysics Data System (ADS)

    Shi, Y.-H.; Durrell, J. H.; Dennis, A. R.; Cardwell, D. A.

    2013-01-01

    Single grain, (RE)BCO (rare earth-barium-copper oxide) bulk superconductors in large or complicated geometries are required for a variety of potential applications, such as in motors and generators and magnetic shielding devices. As a result, top, multi-seeded, melt growth has been investigated over the past 15 years in an attempt to enlarge the size of (RE)BCO single grains specifically for such applications. Of these multi-seeding techniques, so-called bridge-seeding provides the best alignment of two seeds in a single grain growth process. Here we report, for the first time, the successful growth of YBCO (yttrium-barium-copper oxide) using a special, 45°-45°, arrangement of bridge-seeds. The superconducting properties, including trapped field, of the multi-seeded YBCO grains have been measured for different bridge lengths of the 45°-45° bridge-seeds. The boundaries at the impinging growth front and the growth features of the top, multi-seeded surface and cross-section of the multi-seeded, samples have been analysed using optical microscopy. The results suggest that an impurity-free boundary between the two seeds of each leg of the bridge-seed can form when 45°-45° bridge-seeds are used to enlarge the size of YBCO grains.

  3. Application of HTSC-thin films in microwave integrated delay lines

    NASA Astrophysics Data System (ADS)

    Jha, A. R.

    This paper reveals unique capabilities of High-Temperature Superconducting Thin Films (HTSTF) for possible application in microwave integrated delay lines. HTSTF can be characterized as Thin Film Microstrip (TFMS) lines operating at superconducting temperatures. Low insertion loss, minimum signal delay, and small power dissipation are possible with HTSTF delay lines. The conductor loss, dielectric loss, signal distortion, signal delay, and instantaneous bandwidth are dependent on the film thickness, superconducting film material, and substrate properties. Thin films of Yttrium Barium Copper Oxide (YBCO), Bismuth Strontium Calcium Copper Oxide (BSCCO), and Thallium Calcium Barium Copper Oxide (TCBCO) appear to be most suitable for microwave integrated delay lines.

  4. Nucleation and mesostrain influence on percolating critical currents of solution derived YBa2Cu3O7 superconducting thin films

    NASA Astrophysics Data System (ADS)

    Obradors, X.; Martínez-Julián, F.; Zalamova, K.; Vlad, V. R.; Pomar, A.; Palau, A.; Llordés, A.; Chen, H.; Coll, M.; Ricart, S.; Mestres, N.; Granados, X.; Puig, T.; Rikel, M.

    2012-11-01

    After briefly reviewing the present understanding of the nucleation process of YBCO films, a new approach is presented to enhance the stability of c-axis nucleation in epitaxial chemical solution deposited YBCO thin films derived from TFA precursors. We show that with silver addition to the TFA precursor c-axis nucleation can be reached in a wide range of temperature thus keeping high percolating Jc. We argue that silver reduces supersaturation and makes more stable the c-axis nuclei without modifying Tc. Additional advantages of silver addition are an enhanced surface smootheness and a reduced porosity of the YBCO films. The second reported topic relates to the discovery of an adverse relationship between percolating Jc and YBCO films mesostrain, as determined through X-ray diffraction line broadening. We show that mesostrain is enhanced in processes leading to inefficient strain healing at grain boundaries, for instance annealing times too short or growth temperatures too low. It is suggested that the strained regions at the low angle grain boundaries lead to a weak link behavior which can be microscopically understood on the basis of pair formation prevention, as proposed by the bond contraction pairing model.

  5. Strongly enhanced flux pinning in the YBa2Cu3O7 -x films with the co-doping of BaTiO3 nanorod and Y2O3 nanoparticles at 65 K

    NASA Astrophysics Data System (ADS)

    Wang, Hong-Yan; Ding, Fa-Zhu; Gu, Hong-Wei; Zhang, Teng

    2015-09-01

    YBa2Cu3O7 - x (YBCO) films with co-doping BaTiO3 (BTO) and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates (TFA-MOD). The properties of the BTO/Y2O3 co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM). The optimized content of yttrium excess in the BTO/Y2O3 co-doped YBCO films is 10 mol.%, and the critical current density is as high as ˜17 mA/cm2 (self-field, 65 K) by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density (JC) not only at the self-magnetic field, but also in the applied magnetic field. Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Natural Science Foundation of Beijing, China (Grant No. 2152035).

  6. Synthesis of novel barium precursors and their use to deposit thin films by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Studebaker, Daniel Bliss

    A new class of volatile compounds of barium were synthesized. These 'capsule' compounds were prepared to saturate the coordination sphere of barium with one ligand. The covalent bonding of the polyglyme ligand to the 2,2,6,6-tetramethyl-3,5-heptanedione or similar ligand also increased the chelate effect, making loss of the glyme ligand on sublimation less likely. Single crystal X-ray crystal diffraction studies were done on these complexes. One of the complexes was used to grow BaTiO3 thin films to display the ability for these complexes to be used as metal organic chemical vapor deposition (MOCVD) precursors. Thin films of the superconducting material YBa2Cu3O 7-x were deposited on silver substrates by MOCVD. These films were analyzed by microscopy, and the electrical properties are discussed. The first reported growth of beta-BaBLO4 thin films by MOCVD is given. These films were grown on platinum, fused silica, sapphire, and silicon. Second harmonic generation of light from a Nd:YAG laser is observed in optical measurements.

  7. Effect of deposition conditions on YBa 2Cu 3O 7- δ thin films by inverted cylindrical magnetron sputtering and substrate effects

    NASA Astrophysics Data System (ADS)

    Avci, İlbeyi; Tepe, Mustafa; Abukay, Doğan

    2004-05-01

    The dependence of YBCO thin film properties on the deposition conditions was studied for different substrates. The deposition conditions were optimized for the epitaxial growth of high quality YBCO thin films of 1500 Å thickness onto single crystal (100-oriented) SrTiO 3 (STO), MgO and LaAlO 3 (LAO) substrates by DC Inverted Cylindrical Magnetron Sputtering (ICMS). The samples were investigated in detail by means of X-ray diffraction analysis (XRD), EDX, AFM, ρ- T, magnetic susceptibility and current-voltage ( I- V) characterizations. The samples show strong diamagnetic behavior and sharp transition temperatures of 89-91 K with Δ T<0.5 K. XRD of the samples exhibited highly c-axis orientation. The full width at half maximum (FWHM) values of the rocking curves were ranging typically from 0.22 to 0.28°. The samples have smooth surfaces as shown from AFM micrographs. The surface roughness, Ra, changed between 5-7 nm. I- V characteristics were obtained from the 20 μm-wide microbridges, which were patterned by a laser writing technique. The critical current densities ( Jc, 1.06×10 6 for LAO-based YBCO, 1.39×10 6 for MgO-based YBCO, 1.67×10 6 A/cm 2 for STO based YBCO) of the microbridges were evaluated from I- V curves at 77 K.

  8. Growth of hexagonal and cubic InN nanowires using MOCVD with different growth temperatures

    NASA Astrophysics Data System (ADS)

    Yun, Seok-Hyo; Ra, Yong-Ho; Lee, Young-Min; Song, Ki-Young; Cha, Jun-Ho; Lim, Hong-Chul; Kim, Dong-Wook; Suthan Kissinger, N. J.; Lee, Cheul-Ro

    2010-07-01

    We have performed a detailed investigation of the metal-organic chemical vapor deposition (MOCVD) growth and characterization of InN nanowires formed on Si(1 1 1) substrates under nitrogen rich conditions. The growth of InN nanowires has been demonstrated by using an ion beam sputtered (˜10 nm) Au seeding layer prior to the initiation of growth. We tried to vary the growth temperature and pressure in order to obtain an optimum growth condition for InN nanowires. The InN nanowires were grown on the Au+In solid solution droplets caused by annealing in a nitrogen ambient at 700 °C. By applying this technique, we have achieved the formation of InN nanowires that are relatively free of dislocations and stacking faults. Scanning electron microscopy (SEM) showed wires with diameters of 90-200 nm and lengths varying between 3 and 5 μm. Hexagonal and cubic structure is verified by high resolution X-ray diffraction (HR-XRD) spectrum. Raman measurements show that these wurtzite InN nanowires have sharp peaks E2 (high) at 491 cm -1 and A 1 (LO) at 591 cm -1.

  9. Influence of AlN thickness on AlGaN epilayer grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Jayasakthi, M.; Juillaguet, S.; Peyre, H.; Konczewicz, L.; Baskar, K.; Contreras, S.

    2016-10-01

    AlGaN/AlN layers were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The AlN buffer thickness was varied from 400 nm to 800 nm. The AlGaN layer thickness was 1000 nm. The crystalline quality, thickness and composition of AlGaN were determined using high resolution X-ray diffraction (HRXRD). The threading dislocation density (TDD) was found to decrease with increase of AlN layer thickness. Reciprocal space mapping (RSM) was used to estimate the strain and relaxation between AlGaN and AlN. The optical properties of AlGaN layers were investigated by temperature dependent photoluminescence (PL). PL intensities of AlGaN layers increases with increasing the AlN thickness. The surface morphology of AlGaN was studied by atomic force microscopy (AFM). Root mean square (RMS) roughness values were found to be decreased while increase of AlN thickness.

  10. Original GaN-based LED structure on ZnO template by MOCVD

    NASA Astrophysics Data System (ADS)

    Lin, Ray-Ming; Yu, Sheng-Fu; Chen, Miin-Jang; Hsu, Wen-Ching

    2010-03-01

    In this study, we have successfully grown blue LED structure on ZnO template (deposited on sapphire substrate by atomic layer deposition, ALD) by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD). Although GaN semiconductor material is very similar to ZnO in many ways, i.e. relatively small lattice mismatch ~1.8 % compared with traditional sapphire substrate~16 %, it still has a big challenge when GaN-based LEDs grow on ZnO template at usually growth temperature near 1100°C. With too high a temperature and a long deposited time, it would cause reaction at GaN/ZnO interface which is a vital reason that degrades the GaN crystalline quality. In view of this, we introduced an optimized thin AlN cover layer on ZnO template protecting the underneath ZnO layer and then obtained a real work LED structure. Meanwhile, the TEM measurement characterized the epilayer crystalline structure. The optical properties also were carried out by photoluminescence and electroluminescence analysis. Finally, with a suitable fabrication of LED processing, the ZnO template may has the potential as a sacrificial layer by chemical etching technical instead of conventional laser lifted-off.

  11. Wurtzite InP nanowire arrays grown by selective area MOCVD

    SciTech Connect

    Chu, Hyung-Joon; Yeh, Ting-Wei; Stewart, Lawrence; Dapkus, P. Daniel

    2010-06-22

    InP nanowires are a unique material phase because this normally zincblende material forms in the wurtzite crystal structure below a critical diameter owing to the contribution of sidewalls to the total formation energy. This may allow control of the carrier transport and optical properties of InP nanowires for applications such as nano scale transistors, lasers and detectors. In this work, we describe the fabrication of InP nanowire arrays by selective area growth using MOCVD in the diameter range where the wurtzite structure is formed. The spatial growth rate in selective area growth is modeled by a diffusion model for the precursors. The proposed model achieves an average error of 9%. Electron microscopy shows that the grown InP nanowires are in the wurtzite crystal phase with many stacking faults. The threshold diameter of the crystal phase transition of InP nanowires is larger than the thermodynamic estimation. In order to explain this tendency, we propose a surface kinetics model based on a 2×2 reconstruction. This model can explain the increased tendency for wurtzite nanowire formation on InP (111)A substrates and the preferred growth direction of binary III-V compound semiconductor nanowires.

  12. [The influential factors of MOCVD growth of InP in opals].

    PubMed

    Tan, Chun-hua; Fan, Guang-han; Huang, Xu-guang

    2008-12-01

    The key problem of fabricating the 3-D InP inverse opal photonic crystal is to increase the loading of InP in opals. In the present paper, low-pressure metal-organic chemical-vapour deposition (MOCVD) was used to infill the voids within synthetic opals with InP. The morphologies and optical properties of SiO2-InP photonic crystal were characterized by scanning electron microscopy and ultraviolet-visible spectrophotometry (UV-Vis). Several series of experiments were carried out in order to analyze the factors that influence the loading of InP in opals and determine the optimal InP growth conditions. The results of optical experiments are in good agreement with those derived from the theoretical considerations: By increasing the extent of InP infilling within the voids, the extent of refractive index contrast between the silica spheres and the void as well as the extent of natural optical properties change of the photonic crystal were increased. Cycle growth, low-pressure growth, and using the match substrate and the same configuration character between SiOi and InP are beneficial to increaseing the extent of InP infilling within the opal voids. The process has been optimized to achieve SiO2-InP photonic crystal with higher loading of InP. The study provides a scientific basis for manufacturing three-dimensional InP inverse opal photonic crystals.

  13. Effects of Au on the Growth of ZnO Nanostructures on Si by MOCVD

    NASA Astrophysics Data System (ADS)

    Cong, Chen; Fan, Lu Yang; Ping, He Hai; Wei, Wu Ke; Zhen, Ye Zhi

    2013-08-01

    The effects of Au on the growth of ZnO nanostructures on Si by metal organic chemical vapor deposition (MOCVD) at a relatively low temperature (450°C) were investigated. The experimental results showed that Au nanoparticles played a critical role during the growth of the ZnO nanostructures and affected their morphology and optical properties. It was found that Au nanoparticles particularly affected the nucleation of ZnO nanostructures during the growth process and the Au-assisted growth mechanism of ZnO nanostructures should be ascribed to the vapor-solid (VS) mechanism. The formation of a nanoneedle may be attributed to a more reactive interface between Au and ZnO, which leads to more zinc gaseous species absorbed near the interface. Different nucleation sites on ZnO nuclei resulted in the disorder of ZnO nanoneedles. Moreover, the crystalline quality of nano-ZnO was improved due to the presence of Au, according to the smaller full width at half maximum (FWHM) of the low-temperature exciton emission. We confirmed that ZnO nanoneedles showed better crystalline quality than ZnO nanorods through the HRTEM images and the SAED patterns. The reason for the improvement of the crystalline quality of nano-ZnO may be due to the less lattice mismatch.

  14. Process control of MOCVD growth for LEDs by in-situ photoluminescence

    NASA Astrophysics Data System (ADS)

    Prall, C.; Haberland, K.; Kaspari, C.; Brunner, F.; Weyers, M.; Rueter, D.

    2016-03-01

    Development and manufacturing of LED structures is still driven by production cost reduction and performance improvements. Therefore, in-situ monitoring during the epitaxial process plays a key role in view of further yield improvement and process optimization. With the continuing trend towards larger wafers, stronger bow and increased aspherical curvature are additional challenges the growers have to face, leading to non-uniform LED-emission. Compared to traditional in-situ metrology like curvature measurement and near UV pyrometry, in-situ photoluminescence measurements can provide a more direct access to the quantum well emission already during growth. In this paper we show how in-situ photoluminescence measurements can be used in a production type multi-wafer MOCVD system to characterize the quantum well emission already during growth. We also demonstrate how deviations from the desired wavelength can be detected and corrected in the same growth run. Since the method is providing spatially resolved line-scans across the wafer, also the uniformity of the emission wavelength can be characterized already during growth. Comparison of in-situ and ex-situ photoluminescence data show excellent agreement with respect to wavelength uniformity on 4 inch wafers.

  15. Effect of inductors to mitigate the hot-spot problem in parallel-connected superconducting thin-film fault current limiting elements

    NASA Astrophysics Data System (ADS)

    Yamasaki, H.; Furuse, M.; Kaiho, K.

    2015-06-01

    We have been developing superconducting thin-film fault current limiter (FCL) elements, in which high-resistivity Au-Ag alloy shunt layers are used to protect YBa2Cu3O7 (YBCO) thin films deposited on CeO2-buffered sapphire substrates. The high resistance of the thin films enables the element to withstand high electric fields of more than 40 Vpeak cm-1 during the current-limiting period after quenching, thus greatly reducing the amount of YBCO thin film needed and, consequently, the cost of an FCL. We have succeeded in fabricating and testing 500 V/200 A FCL modules using two 20 cm long YBCO films connected in parallel. In the present study, we performed extensive switching experiments on FCL elements, in which two YBCO films are connected in parallel to achieve higher rated currents, and confirmed the previously observed phenomenon that the hot-spot problem causing film damage just after quench initiation becomes more severe when the total critical current of the thin films is higher. We have investigated the origin of this phenomenon and found that a rapid current transfer from the first-quenched film with lower critical current to the other film causes higher current in the secondly-quenched film that sometimes leads to hot spots. It is demonstrated that the serious hot-spot problem can be mitigated by the use of inductors when the high-resistance FCL elements are connected in parallel. Based on these findings we propose an appropriate architecture of a high electric-field superconducting thin-film FCL that can be used in a real power grid.

  16. Epitaxial Growth Of Y2O3 On Biaxially Textured Ni Tapes Using A Sol-Gel Process For YBCO Coated Conductors

    NASA Astrophysics Data System (ADS)

    Ciontea, L.; Ristoiu, T.; Suciu, R.-C.; Petrisor, T.

    2007-04-01

    A solution processing technique was used to deposit an epitaxial Y2O3 film on (001)[100] cube textured Ni tapes for YBa2Cu3Ox (YBCO) coated conductors manufacturing. The cube texture was developed in Ni by a conventional thermo-mechanical process. A precursor solution of yttrium 2-methoxyethoxide in 2-methoxyethanol was spin-coated on the Ni substrate. The as-deposited amorphous film was thermally treated at 1100°C in a flowing Ar+4%H2 gas mixture. The θ-2θ X-ray spectra revealed predominantly (001) reflections, indicating a high degree of out-of-plane orientation. Pole figures for the (222) Y2O3 reflections demonstrate a single in-plane texture. The out-of-plane and in-plane epitaxial relationship is [400]Y2O3//[200] Ni and [110]Y2O3//[100] Ni, respectively. The full-width-half-maximum (FWHM) of the ω-scans and φ-scans is 6° and 11°, respectively.

  17. Thin films of InP for photovoltaic energy conversion. Final report, July 5, 1979-July 4, 1980

    SciTech Connect

    Manasevit, H. M.; Ruth, R. P.; Moudy, L. A.; Yang, J. J.J.; Johnson, R. E.

    1980-08-01

    Research to develop a low-cost high-efficiency thin-film InP heterojunction solar cell, using the metalorganic chemical vapor deposition (MO-CVD) technique for InP film growth on suitable substrates is reported. Heterostructure devices of CdS/InP, using InP films prepared by CO-CVD, were prepared and characterized. The research effort involved three major technical tasks: (1) materials growth; (2) materials characterization; and (3) device fabrication and characterization. The principal results achieved in the investigations are as follows: (1) temperature-activated orientation-dependent background donor doping was observed in undoped epitaxial InP films; (2) p-type epitaxial InP films were prepared by Zn and by Cd doping during growth; (3) the efficacy of Cd doping was found to vary exponentially with the reciprocal of the deposition temperature in the range 650 to 730/sup 0/C; (4) Cd doping appeared to offer no clear advantages over Zn doping for preparation of p-type InP by the MO-CVD process; (5) GaP grown by MO-CVD was investigated as a possible intermediate-layer material for growth of InP films on low-cost substrates; (6) p/sup +/GaAs polycrystalline layers (p > /sup 19/ cm/sup -3/) were successfully prepared by Zn doping during MO-CVD growth on various low-cost substrates and used as surfaces for growth of p-type polycrystalline InP:Zn layers; (7) nCdS/pInP heterojunction solar cells were prepared by vacuum deposition of CdS onto p-type InP films grown by MO-CVD as well as on InP single-crystal wafers; (8) the best polycrystalline CdS/InP cells were obtained in structures on P/sup +/GaAs:Zn layers on both Mo sheet and Corning Code 0317 Glass; and (9) structure analyses of the Cds films used in the heterojunction cells indicated the presence of polycrystalline hexagonal CdS even in films grown on single-crystal InP films or bulk-wafer substrates. (WHK)

  18. Orientations of Y 2BaCuO 5 and YBCO within melt-textured and directional solidified samples studied by EBSD

    NASA Astrophysics Data System (ADS)

    Koblischka, M. R.; Koblischka-Veneva, A.; Reddy, E. S.; Schmitz, G. J.; Ogasawara, K.; Murakami, M.

    2003-10-01

    By means of automated electron backscatter diffraction (EBSD) analysis, we studied the local orientations of embedded Y 2BaCuO 5 (2 1 1) particles within melt-textured YBCO samples, and also the orientations of embedded YBCO particles in directional solidified 211 samples. On both systems, we obtained high-quality Kikuchi patterns, allowing the automated mapping of the crystal orientations and a multi-phase analysis. In melt-textured YBCO with (0 0 1) orientation, we find that the embedded 211 particles do not have any preferred orientation, but the maps also reveal that at certain orientations of the 211 particles the YBCO growth is not altered. In directional solidified 211 samples, where the 211 is mainly oriented in (0 0 1) direction, the embedded YBCO particles show only some specific orientations.

  19. Protection of high temperature superconducting thin-films in a semiconductor processing environment

    SciTech Connect

    Xu, Yizi; Fiske, R.; Sanders, S.C.; Ekin, J.W.

    1996-12-31

    Annealing studies have been carried out for high temperature superconductor YBaCuO{sub 7{minus}{delta}} in a reducing ambient, in order to identify insulator layer(s) that will effectively protect the superconducting film in the hostile environment. While a layer of magnesium oxide (MgO) sputter deposited directly on YBaCuO{sub 7{minus}{delta}} film provides some degree of protection, the authors found that a composite structure of YBCO/SrTiO{sub 3}/MgO, where the SrTiO{sub 3} was grown by laser ablation immediately following YBCO deposition (in-situ process), was much more effective. They also address the need for a buffer layer between YBCO and aluminum (Al) during annealing. Al is most commenly used for semiconductor metalization, but is known to react readily with YBCO at elevated temperatures. The authors found that the most effective buffer layers are platinum (Pt) and gold/platinum (Au/Pt).

  20. Critical current behavior of Ag-coated YBa2Cu3O(7-x) thin films

    NASA Astrophysics Data System (ADS)

    Ono, R. H.; Beall, J. A.; Harvey, T. E.; Reintsema, C. D.; Johansson, M.

    1991-03-01

    The authors studied the behavior of high-quality YBa2Cu3O(7-x) (YBCO) thin films with Ag overlayers. The authors chose to study Ag in detail because of its widespread use as contact metallization and because of their earlier studies of proximity effects in YBCO. The details of transport critical current measurements are presented. It is shown that the Ag coatings can reduce normal state resistance while not degrading the critical current density. The key technological result is that the various thicknesses of Ag that were used did not reduce Jc or Jc(H). Critical current densities in excess of 106 A/sq cm have been achieved at temperatures greater than 76 K. An unusual effect was seen in Jc(H) when the field was oriented perpendicular to the c axis of the film. The Jc at 1 T was higher in samples with 10-nm coatings of Ag than in similar uncoated samples. It was also shown that the composite resistance of Ag-YBCO bilayers can be much lower than the resistance of uncoated YBCO.

  1. Micro-machined thin film hydrogen gas sensor, and method of making and using the same

    NASA Technical Reports Server (NTRS)

    DiMeo, Jr., Frank (Inventor); Bhandari, Gautam (Inventor)

    2001-01-01

    A hydrogen sensor including a thin film sensor element formed, e.g., by metalorganic chemical vapor deposition (MOCVD) or physical vapor deposition (PVD), on a microhotplate structure. The thin film sensor element includes a film of a hydrogen-interactive metal film that reversibly interacts with hydrogen to provide a correspondingly altered response characteristic, such as optical transmissivity, electrical conductance, electrical resistance, electrical capacitance, magnetoresistance, photoconductivity, etc., relative to the response characteristic of the film in the absence of hydrogen. The hydrogen-interactive metal film may be overcoated with a thin film hydrogen-permeable barrier layer to protect the hydrogen-interactive film from deleterious interaction with non-hydrogen species. The hydrogen sensor of the invention may be usefully employed for the detection of hydrogen in an environment susceptible to the incursion or generation of hydrogen and may be conveniently configured as a hand-held apparatus.

  2. Metal-organic chemical vapour deposition of polycrystalline tetragonal indium sulphide (InS) thin films

    NASA Technical Reports Server (NTRS)

    Macinnes, Andrew N.; Cleaver, William M.; Barron, Andrew R.; Power, Michael B.; Hepp, Aloysius F.

    1992-01-01

    The dimeric indium thiolate /(t Bu)2In(mu-S sup t Bu)/2 has been used as a single-source precursor for the MOCVD of InS thin films. The dimeric In2S2 core is proposed to account for the formation of the nonequilibrium high-pressure tetragonal phase in the deposited films. Analysis of the deposited films has been obtained by TEM, with associated energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy.

  3. Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films

    PubMed Central

    2011-01-01

    The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated. PMID:21711646

  4. Superconducting YBa 2Cu 3O 7-δ films on SrTiO 3 by electrodeposition process

    NASA Astrophysics Data System (ADS)

    Machado, A. J. S.; Moehlecke, S.; Kopelevich, Y.; Robin, A.; dos Santos, C. A. M.

    An ac electrodeposition (ED) process to obtain good quality YBa 2Cu 3O 7-δ (YBCO) high-temperature superconductor (HTS) films was developed. These films were deposited on SrTiO 3 (100) single crystal substrates previously coated with a thin silver layer (800 Å) that was deposited by chemical reduction. A small amount of Ag (0.7% in weight) added to the electrolyte bath was shown to improve the quality of the deposited films. YBCO films after an appropriate heat treatment present single phase material with an onset T c ∼ 90 K, ΔT c ∼ 2 K, homogeneous grain morphology and strong biaxial texture. Transport measurements show a metallic behavior in the normal state and a self-field critical current densities ∼ 10 5 A/cm 2 at 4.2 K and ∼ 10 4 A/cm 2 at 77K.

  5. The mechanism of the growth of InP by MOCVD: A flow-tube investigation of the pyrolysis of the indium precursor

    NASA Astrophysics Data System (ADS)

    Haigh, J.; O'Brien, S.

    1984-09-01

    A flow-tube method has been used to investigate the pyrolysis of indium trimethyl and indium trimethyl-phosphorus triethyl adduct, as part of an investigation of the MOCVD process for epitaxial deposition of InP and related semiconductors. At partial pressures close to those used in MOCVD the rate of pyrolysis of indium trimethyl was found to be dependent on the nature of the reactor surface, being faster on glass than on (100) InP. At higher pressures this difference was not observed. The pyrolysis of the adduct proceeds via gas-phase dissociation to the two constituents followed by decomposition of indium trimethyl. The implications for MOCVD are discussed.

  6. Thin films of InP for photovoltaic energy conversion. Third quarterly technical progress report, December 29, 1979-March 28, 1980

    SciTech Connect

    Manasevit, H M; Ruth, R P; Moudy, L A; Yang, J J.J.; Johnson, R E

    1980-04-01

    A research study is being conducted for the purpose of developing a low-cost high-efficiency thin-film InP heterojunction solar cell based on InP films grown by the metalorganic chemical vapor deposition (MO-CVD) process on suitable substrates. Heterostructure devices of CdS/InP (and possibly indium tin oxide/InP) are to be prepared at Stanford University under subcontract, using the MO-CVD InP films grown at Rockwell. The work of the third quarter of the program is summarized. Experiments continued on evaluation of GaP as an intermediate layer material for subsequent growth of InP films on various substrate materials, and Cd (obtained from dimethylcadmium) was evaluated as a p-type dopant (an alternative to Zn obtained from diethylzinc) for InP films made by the MO-CVD process. A preliminary x-ray diffraction analysis was conducted of the crystallographic structure of the vacuum-deposited CdS films prepared at Stanford as part of the process of fabricating CdS/InP heterojunction solar cells. A group of CdS/InP heterostructure cells involving vacuum-deposited CdS and p-type epitaxial InP films grown by MO-CVD was prepared and evaluated. High J/sub 0/ values and low fill factors were observed in all of the cells, resulting in AM1.5 efficiencies in the 2 to 5 percent range. (WHK)

  7. Centre seeded infiltration and growth process for fabrication of large grain bulk YBCO/Ag superconducting composites

    NASA Astrophysics Data System (ADS)

    Parthasarathy, R.; Seshubai, V.

    2012-06-01

    We report the fabrication of a large grain bulk YBCO/Ag superconductor using a novel technique which we call Centre Seeded Infiltration and Growth Process (CSIGP). Using this technique, it has been made possible to get bulk YBCO/Ag composite sample with uniform grain growth textured along the c-axis. The resulting large grain sample has been found to have high critical current densities up to large magnetic fields. We correlate the improved superconducting and magnetic properties to the modified grain growth conditions employed in this fabrication technique.

  8. The peculiarities of local structure of YbNi2 and YbCo2 intermetallics synthesized at high pressure.

    NASA Astrophysics Data System (ADS)

    Chernysheva, O. V.; Menushenkov, A. P.; Tsvyashchenko, A. V.; Fomicheva, L. N.; Ivanov, A. A.; Kuznetsov, A. V.

    2016-09-01

    Local structure of YbCo2 and YbNi2 was investigated by EXAFS and XANES spectroscopy. It was found that the bond Yb-Co(Ni) has the highest static disorder and its length increases with temperature decrease, while all other bonds remain almost unchanged. This phenomenon may be caused by short-range magnetic ordering at temperatures above the phase transition. XANES measurements above ZIII-Yb absorption edge in YbCo2 and YbNi2 revealed that both compounds have almost the same density of free 5d-states

  9. Modeling of electrical properties in the fabrication of layered superconducting thin films

    NASA Astrophysics Data System (ADS)

    Din, Fasih Ud; Shaari, Abdul Halim; Kien, Chen Soo; Yar, Asfand; Talib, Zainal Abidin; Pah, Lim Kean

    2015-05-01

    The Pulse laser deposition (PLD) is a sole tool that is used to develop fine quality superconducting (YBCO) epitaxial films. The description and devices application aspect of the PLD on high temperature superconducting epitaxial films have an important role in the field of superconductivity. In the present study, thin films fabrication by PLD, buffer layers and electrical properties have been probed numerically with computer simulations. The electrical transport properties are discussed in term of thermally-activated flux motion model. The present study concludes that the plume dynamics is important in fabricating high quality epitaxial films thus improving the superconducting electrical transport properties.

  10. HTS current lead units prepared by the TFA-MOD processed YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Shiohara, K.; Sakai, S.; Ishii, Y.; Yamada, Y.; Tachikawa, K.; Koizumi, T.; Aoki, Y.; Hasegawa, T.; Tamura, H.; Mito, T.

    2010-11-01

    Two superconducting current lead units have been prepared using ten coated conductors of the Tri-Fluoro-Acetate - Metal Organic Deposition (TFA-MOD) processed Y 1Ba 2Cu 3O 7-δ (YBCO) coated conductors with critical current ( Ic) of about 170 A at 77 K in self-field. The coated conductors are 5 mm in width, 190 mm in length and about 120 μm in overall thickness. The 1.5 μm thick superconducting YBCO layer was synthesized through the TFA-MOD process on Hastelloy™ C-276 substrate tape with two buffer oxide layers of Gd 2Zr 2O 7 and CeO 2. The five YBCO coated conductors are attached on a 1 mm thick Glass Fiber Reinforced Plastics (GFRP) board and soldered to Cu caps at the both ends. We prepared two 500 A-class current lead units. The DC transport current of 800 A was stably applied at 77 K without any voltage generation in all coated conductors. The voltage between both Cu caps linearly increased with increasing the applied current, and was about 350 μV at 500 A in both current lead units. According to the estimated values of the heat leakage from 77 K to 4.2 K, the heat leakage for the current lead unit was 46.5 mW. We successfully attained reduction of the heat leakage because of improvement of the transport current performance ( I c), a thinner Ag layer of YBCO coated conductor and usage of the GFRP board for reinforcement instead of a stainless steel board used in the previous study. The DC transport current of 1400 A was stably applied when the two current lead units were joined in parallel. The sum of the heat leakages from 77 K to 4.2 K for the combined the current lead units was 93 mW. In comparison with the conventional Cu current leads by gas-cooling, it could be noted that the heat leakage of the current lead is about one order of magnitude smaller than that of the Cu current lead.

  11. Study on Quench Protection of Coil Wound of Copper or Silver Stabilized YBCO Conductors

    NASA Astrophysics Data System (ADS)

    Tsukamoto, O.; Fu, Y.; Yoshida, H.; Furuse, M.

    2004-06-01

    We investigated necessary amount of copper or silver stabilizer added to YBCO conductor by numerical calculation to protect the conductor in a coil of dry windings from damages caused by quenches. The coil is assumed to be operated at 20K, 40K and 77K and hot-spot temperature of the conductor during energy dump sequence is calculated. The necessary amount of the stabilizer and overall conductor current density of the conductor including the stabilizer were calculated to suppress the hot spot temperature below a certain threshold depending on the operation temperature.

  12. Fabrication and test of short helical solenoid model based on YBCO tape

    SciTech Connect

    Yu, M.; Lombardo, V.; Lopes, M.L.; Turrioni, D.; Zlobin, A.V.; Flanagan, G.; Johnson, R.P.; /MUONS Inc., Batavia

    2011-03-01

    A helical cooling channel (HCC) is a new technique proposed for six-dimensional (6D) cooling of muon beams. To achieve the optimal cooling rate, the high field section of HCC need to be developed, which suggests using High Temperature Superconductors (HTS). This paper updates the parameters of a YBCO based helical solenoid (HS) model, describes the fabrication of HS segments (double-pancake units) and the assembly of six-coil short HS model with two dummy cavity insertions. Three HS segments and the six-coil short model were tested. The results are presented and discussed.

  13. Fabrication of low-density GaN/AlN quantum dots via GaN thermal decomposition in MOCVD.

    PubMed

    Zhang, Jin; Li, Senlin; Xiong, Hui; Tian, Wu; Li, Yang; Fang, Yanyan; Wu, Zhihao; Dai, Jiangnan; Xu, Jintong; Li, Xiangyang; Chen, Changqing

    2014-01-01

    With an appropriate high anneal temperature under H2 atmosphere, GaN quantum dots (QDs) have been fabricated via GaN thermal decomposition in metal organic chemical vapor deposition (MOCVD). Based on the characterization of atomic force microscopy (AFM), the obtained GaN QDs show good size distribution and have a low density of 2.4 × 10(8) cm(-2). X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the GaN QDs were formed without Ga droplets by thermal decomposition of GaN.

  14. Characterization of Defects on MOCVD Grown Gallium Nitride Using Transient Analysis Techniques

    NASA Astrophysics Data System (ADS)

    Kasani, Sujan Phani Kumar

    Since the invention of the first visible spectrum (red) LED by Holonyak in 1962, there has been a need for more efficient, more reliable and less expensive LEDs. The III-nitrides revolutionized semiconductor technology with their applications in the blue LED's. However the internal quantum efficiency of LED's are limited by the deep level traps in GaN substrate. Traps are defects in the crystal lattice, which depends on growth parameters. These traps act as non-radiative centers where non-radiative recombination occurs without conversion of available energy into light. Characterization of these traps in a material is necessary for better understanding of the material growth quality and resulting device performance. In this work Capacitance-Voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) are conducted which provide electronic properties of trap centers like activation energy, doping concentration and capture cross-section. In n-GaN grown by Metalorganic Chemical Vapor Deposition (MOCVD) on Sapphire two defects types are detected and are characterized by Capacitance-Voltage and Deep Level Transient Spectroscopy. Two deep levels E1 and E2 are typically observed in n-GaN with the activation energies of 0.21eV and 0.53eV at 125°K and 325°K, respectively. The deep level E1 is caused by linear line defects along dislocation cores while deep level E2 is related to point defects. The characterization techniques, experimental systems and preliminary characterization results are discussed in detail.

  15. Study of carrier recombination transient characteristics in MOCVD grown GaN dependent on layer thickness

    SciTech Connect

    Gaubas, E. Čeponis, T.; Jasiunas, A.; Jelmakas, E.; Juršėnas, S.; Kadys, A.; Malinauskas, T.; Tekorius, A.; Vitta, P.

    2013-11-15

    The MOCVD grown GaN epi-layers of different thickness have been examined in order to clarify a role of surface recombination, to separate an impact of radiative and non-radiative recombination and disorder factors. The microwave probed –photoconductivity (MW-PC) and spectrally resolved photo-luminescence (PL) transients were simultaneously recorded under ultraviolet (UV) light 354 nm pulsed 500 ps excitation. The MW-PC transients exhibited the carrier decay components associated with carrier decay within micro-crystals and the disordered structure on the periphery areas surrounding crystalline columns. Three PL bands were resolved within PL spectrum, namely, the exciton ascribed UV-PL band edge for hν>3.3 eV, blue B-PL band for 2.5 < hν < 3.0 eV and yellow Y-PL band with hν < 2.4 eV. It has been obtained that intensity of UV-PL band increases with excitation density, while intensity of B-PL band is nearly invariant. However, intensity of the Y-PL increases with reduction of the excitation density. The Y-PL can be associated with trapping centers. A reduction of UV excitation density leads to a decrease of the relative amplitude of the asymptotic component within the MW-PC transients and to an increase of the amplitude as well as duration of the yellow spectral band (Y-PL) asymptotic component. Fractional index α with values 0.5 < α < 0.8 was evaluated for the stretched-exponent component which fits the experimental transients determined by the disordered structure ascribed to the periphery areas surrounding the crystalline columns.

  16. 500 V/200 A fault current limiter modules made of large-area MOD-YBa2Cu3O7 thin films with high-resistivity Au-Ag alloy shunt layers

    NASA Astrophysics Data System (ADS)

    Yamasaki, H.; Arai, K.; Kaiho, K.; Nakagawa, Y.; Sohma, M.; Kondo, W.; Yamaguchi, I.; Matsui, H.; Kumagai, T.; Natori, N.; Higuchi, N.

    2009-12-01

    We developed 500 Vrms/ 200 Arms superconducting thin-film fault current limiter (FCL) modules that can withstand high electric fields (E>30 Vrms cm-1) by using large-area YBa2Cu3O7 (YBCO) thin films with high-resistivity Au-Ag alloy shunt layers. Au-Ag alloy films about 60 nm thick were sputter-deposited on YBCO/CeO2/sapphire films (2.7 cm × 20 cm) prepared using a fluorine-free MOD method. Each 20 cm long Au-Ag/YBCO film was then divided into three segments (each ~5.7 cm long) by four Ag electrodes deposited on the Au-Ag layer, resulting in an effective length of 17 cm. The 500 V/200 A FCL modules were then fabricated by first connecting two of the segmented films in parallel using Ag-sheathed Bi-2223 superconducting tapes and then connecting in parallel an external resistor and a capacitor for each segment to protect the Au-Ag/YBCO film from hot spots. Switching tests using a short-circuit generator revealed that all the modules carried a superconducting ac current of >=237 Arms and that modules prepared with YBCO films having a relatively homogeneous critical current Ic distribution successfully withstood >=515 Vrms for five cycles without any damage. These results demonstrate that (a) the FCL modules fabricated here successfully achieved the rated current of 200 Arms and rated voltage of 500 Vrms and (b) total area of the YBCO films on sapphire substrates required for the 500 V/200 A (100 kV A) module was less than one-third that for conventional thin-film FCL modules that use gold shunt layers, leading to the significantly reduced cost of thin-film FCLs. Film damage due to hot spots depended on the difference in Ic between the two parallel-connected films and on the inhomogeneity of the Ic distribution in the film, and is most probably due to nonlinear current flows at the moment of quenching that cause local overheating.

  17. Effect of bulk growth temperature on antiphase domain boundary annihilation rate in MOCVD-grown GaAs on Si(001)

    NASA Astrophysics Data System (ADS)

    Barrett, C. S. C.; Martin, T. P.; Bao, X.-Y.; Kennon, E. L.; Gutierrez, L.; Martin, P.; Sanchez, E.; Jones, K. S.

    2016-09-01

    GaAs is a material of interest as a potential buffer layer in future III-V semiconductor-based transistor technologies integrated on Si wafers. The goal of this study was to investigate the effect of growth temperature on the propagation and annihilation of antiphase domain boundaries (APBs) in GaAs films grown on Si(001) by metal-organic chemical vapor deposition (MOCVD). No intentional wafer off-cuts or high temperature pre-growth anneals (>1000 °C) were employed as both of these practices complicate integration with other devices. To evaluate the role of growth temperature on the APB evolution, a 200 nm thick layer of GaAs was grown on the Si at a fixed temperature of 530 °C so that all samples started with the same approximate APB density. Subsequently, 600 nm of GaAs was grown at temperatures varying between 530 °C and 650 °C. Chemical etching combined with scanning electron microscopy (SEM) was used to profile the density of the APBs in each sample as a function of depth. The APB annihilation rate, i.e. the exponential decay rate of APB density with respect to film thickness, increases from 2.6 μm-1 to 10.7 μm-1 as the growth temperature increases from 530 °C to 610 °C and then saturates. The increase in annihilation rate with increasing temperatures suggests that the higher temperatures remove kinetic barriers to the reduction of the overall APB interfacial area. An activation energy of 1.1 eV was extracted using an Arrhenius relationship and likely corresponds to the energy needed for APBs to kink from {110} to higher-index planes, e.g. {112}. Dark field transmission electron microscopy showed that at higher growth temperatures the APBs can shift from vertical {110} habit planes to {112} planes leading to self-annihilation with sufficient thickness.

  18. Thin films of InP for photovoltaic energy conversion. Second quarterly technical progress report, September 29, 1979-December 28, 1979

    SciTech Connect

    Manasevit, H M; Ruth, R P; Moudy, L A; Yang, J J.J.; Johnson, R E

    1980-01-01

    A research study is being conducted for the purpose of developing a low-cost high-efficiency thin-film InP heterojunction solar cell based on InP films grown by the metalorganic chemical vapor deposition (MO-CVD) process on suitable substrates. Heterostructure devices of CdS/InP (and possibly indium-tin oxide/InP) are to be prepared at Stanford University using the MO-CVD InP films grown at Rockwell. The work of the second quarter of the program is summarized. Growth parameters have been established using new triethylindium, diethylzinc (DEZn), and PH/sub 3/ sources for the formation of Zn-doped p-type InP films in the modified MO-CVD reactor system. Appropriately doped films have been prepared and sent to Stanford for use in deposition of CdS layers. An investigation of the properties of grains and grain boundaries in polycrystalline InP films was begun using several polycrystalline film/substrate combinations, including tungsten (W) layers produced by roller coating and screen-printing on polycrystalline alumina, and mechanically abraded surfaces of single-crystal bulk InP:Fe wafers. An investigation was also undertaken into the use of GaP as an alternative intermediate-layer material to GaAs on low-cost substrates for subsequent growth of InP films. Auger electron spectroscopy analysis done on a group of specially prepared Zn-treated films of polycrystalline InP indicated the presence of Zn at surfaces of InP:Zn films grown on Al and/or heat-treated in high concentrations of DEZn at approx. 600/sup 0/C. However, no Zn was detected in polycrystalline films grown under deposition conditions that would be expected to produce highly doped p-type epitaxial films if single-crystal substrates were used.

  19. Preparation of YBCO single-crystal surfaces for angularly resolved planar tunneling studies

    NASA Astrophysics Data System (ADS)

    Lussier, Benoit; Charalambous, M.; Guillou, H.; Chaussy, J.; Lejay, P.; Pissas, M.

    1998-03-01

    For BCS superconductors, tunneling has proven to be a valuable tool. Indeed, using multiple recrystallisation techniques, planar junctions could be prepared along various crystalline directions enabling a direct mapping of the superconducting gap. For various reasons, such techniques are difficult (if not impossible) to apply to high-Tc materials. Furthermore, due to the small thickness of the single crystals, very few planar tunneling results into the basal plane are availlable. We present a new sample preparation technique which enables us to prepare surfaces for planar tunneling in any direction in the basal plane. After proper orientation of the high-Tc single crystal, the surface is mechanically polished using fine diamond paste. Such process routinely yields samples with rms surface roughness as low as 15ÅThe sample is then ion-polished with normal incidence xenon atoms and the tunneling barrier and counter-electrode are evaporated in-situ. Preliminary tunneling results for Au/YBCO and Nb/YBCO will be presented for twinned single crystals with tunneling in the (100) and (110) directions.

  20. Transport AC loss characteristics of a nine strand YBCO Roebel cable

    NASA Astrophysics Data System (ADS)

    Jiang, Zhenan; Badcock, R. A.; Long, N. J.; Staines, Mike; Thakur, K. P.; Lakshmi, L. S.; Wright, A.; Hamilton, K.; Sidorov, G. N.; Buckley, R. G.; Amemiya, Naoyuki; Caplin, A. D.

    2010-02-01

    Transport AC loss in a short length of 9/2 YBCO Roebel cable (nine 2 mm wide strands) is measured. The AC loss data are compared with those in a 5/2 YBCO Roebel cable (five 2 mm wide strands) as well as that in a single strand. All the strands composing the cables and the single strand are insulated and cut from the same stock material. The validity of the measurement method was reconfirmed by results at a range of frequencies. At a wide range of It/Ic, the normalized AC losses in the Roebel cable were around 6.2-6.7 times of those in the single strand. This is less than the nine times predicted for a tight bundle of nine conductors. The normalized transport AC losses in the 5/2 Roebel cable are much smaller than those in the 9/2 Roebel. This should be due to larger superposition of magnetic field in the 9/2 Roebel. The Ic of the 9/2 and 5/2 Roebel cables is determined by serial connection of the strands. This eliminates the effect where differing resistances in the current terminations cause uneven current sharing between strands when the strands are connected in parallel.

  1. VOLTAGE DISTRIBUTION AND MECHANICAL STRENGTH IN SPLICE JOINTS MADE FROM AS-MANUFACTURED YBCO COATED CONDUCTORS

    SciTech Connect

    Duckworth, Robert C; Zhang, Yifei; Gouge, Michael J; Rey, Christopher M; Van der Laan, Danko; Clickner, Cam

    2010-01-01

    With recommendations from wire manufacturers as a starting point, a series of solder joints were fabricated and characterized to determine the best method to produce repeatable, low-resistance and high-mechanical-strength splices in as-manufactured, stabilized YBCO coated conductors. From the 2.54 cm long splice joints that were fabricated, parameters such as solder material, stabilization material, fabrication method, and conductor geometry were varied to determine the impact of each on splice joint properties. Results indicate that the lowest resistance splice joints were influenced primarily by the tape orientation in the joint and the stabilization material. The lowest resistances were between 2 10-8 and 1.0 10-7 in 4-mm wide tapes and were obtained from pure copper stabilized tapes oriented with the YBCO layers in closest proximity. The voltage drop along the splice length indicated that only a fraction of the splice length contributes to the splice joint resistance. Mechanical characterization of splice joints showed that the joint resistance remained unchanged under axial stress up to a stress level at which the critical current of the tapes forming the joint degrades irreversibly.

  2. Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

    NASA Technical Reports Server (NTRS)

    Noever, David; Li, Ning; Robertson, Tony; Koczor, Ron; Brantley, Whitt

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

  3. Position-dependent texture analysis of melt-textured YBCO by means of electron backscatter diffraction

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Ogasawara, K.; Murakami, M.

    2003-10-01

    The texture and phase distribution of melt-textured YBa 2Cu 3O x (YBCO) was studied by means of automated electron backscatter diffraction (EBSD) analysis as a function of the position in the bulk pellet of 4 cm diameter. A total of five samples was cut from the pellet; four samples from the surface of the bulk with different distances to the seed crystal, and one cut in vertical direction in the middle of the pellet. The melt-textured YBCO samples require a two-phase analysis to be performed, so a high surface quality is necessary to enable an automated EBSD scan. Good quality Kikuchi patterns are obtained from both the 1 2 3 and 2 1 1 phases. We found an inhomogeneous distribution of the 2 1 1 particles. Whereas the samples cut from the surface contain a large amount of 2 1 1 particles, in the samples of the vertical direction only traces of 2 1 1 particles are found. Furthermore, we measured the misorientation angle distribution of all samples. The data are presented in form of phase mappings, misorientation distribution functions and pole figures.

  4. The influence of magnetic nano metal oxides doping on structure and electrical properties of YBCO superconductor

    NASA Astrophysics Data System (ADS)

    Salama, A. H.; El-Hofy, M.; Rammah, Y. S.; Elkhatib, M.

    2016-03-01

    Superconductor samples of YBa2Cu3O7-δ (YBCO) + x where x = 0.1, 0.2, 0.3, 0.4 and 0.5 wt% of nano metal oxides namely Cr2O3, Co3O4 and Mn3O4 namely are synthesized by the solid-state reaction route. Both x-ray diffraction and electron microscopy have been employed to study the phase identification and the microstructure of these samples. Transition temperature of the samples has been determined by four probe resistivity measurements. The x-ray diffraction patterns indicate that the gross structure of YBCO does not change with the substitution of three types of nano metal oxides with different doping level. The critical transition temperature (Tc) is found to decrease with the increases of doping level. Mn3O4 has highest Tc value which may be due to flux pinning from some defects and the rapid suppression in Tc with increasing concentration of Mn3O4 may be due to the cooper pair breaking and the hole filling in the CuO2 planes.

  5. Inkjet printing of multifilamentary YBCO for low AC loss coated conductors

    NASA Astrophysics Data System (ADS)

    Hopkins, S. C.; Joseph, D.; Mitchell-Williams, T. B.; Calleja, A.; Vlad, V. R.; Vilardell, M.; Ricart, S.; Granados, X.; Puig, T.; Obradors, X.; Usoskin, A.; Falter, M.; Bäcker, M.; Glowacki, B. A.

    2014-05-01

    Considerable progress has been made with the development of REBCO coated conductors in recent years, and high performance conductors are available commercially. For many applications, however, the cost remains prohibitive, and AC losses discourage their selection for higher frequency applications. Chemical solution deposition (CSD) methods are attractive for low-cost, scalable preparation of buffer and superconductor layers, and in many respects inkjet printing is the method of choice, permitting non-contact deposition with minimal materials wastage and excellent control of coating thickness. Highly textured coatings of YBCO and Gd-doped CeO2 have previously been reported on buffered metal substrates. Inkjet printing also introduces the possibility of patterning - directly depositing two and three dimensional structures without subtractive processing - offering a low-cost route to coated conductors with reduced AC losses. In this contribution, the inkjet deposition of superconducting YBCO tracks is reported on industrially relevant buffered metal substrates both by direct printing and an inverse patterning approach. In the latter approach, ceria tracks were printed reported, which are a candidate both for resistive filament spacers and buffer layers. TFA-based precursor solutions have been printed on SS/ABAD-YSZ/CeO2 and Ni-W/LZO/CeO2 RABiTS substrates, and the resulting multifilamentary samples characterised by microscopy and scanning Hall probe measurements. The prospects for future inkjet-printed low AC loss coated conductors are discussed, including control of interfilamentary resistivity and bridging, transposed filamentary structures and stabilisation material.

  6. Estimation of magnetic relaxation property for CVD processed YBCO-coated conductors

    NASA Astrophysics Data System (ADS)

    Takahashi, Y.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Shikimachi, K.; Watanabe, T.; Kashima, N.; Nagaya, S.

    2010-11-01

    Ion Beam Assist Deposition/Chemical Vapor Deposition(IBAD/CVD)-processed YBCO-coated conductors with high critical current density Jc at high magnetic fields are expected to be applied to superconducting equipments such as superconducting magnetic energy storage (SMES). For application to superconducting magnet in SMES one of the most important properties for superconductors is the relaxation property of superconducting current. In this paper, the relaxation property is investigated for IBAD/CVD-processed YBCO-coated conductors of the superconducting layer in the range of 0.18-0.90 μm. This property can be quantitatively characterized by the apparent pinning potential, U0∗. It is found that U0∗ takes a smaller value due to the two-dimensional pinning mechanism at high magnetic fields for conductor with thinner superconducting layer. Although U0∗ decreases with increasing thickness at low magnetic fields at 20 K, it increases at high magnetic fields. The results are theoretically explained by the model of the flux creep and flow based on the dimensionality of flux pinning. Scaling analysis is examined for the dependence of U0∗ on the magnetic field, temperature and the layer thickness.

  7. Status of HgCdTe Barrier Infrared Detectors Grown by MOCVD in Military University of Technology

    NASA Astrophysics Data System (ADS)

    Kopytko, M.; Jóźwikowski, K.; Martyniuk, P.; Gawron, W.; Madejczyk, P.; Kowalewski, A.; Markowska, O.; Rogalski, A.; Rutkowski, J.

    2016-09-01

    In this paper we present the status of HgCdTe barrier detectors with an emphasis on technological progress in metalorganic chemical vapor deposition (MOCVD) growth achieved recently at the Institute of Applied Physics, Military University of Technology. It is shown that MOCVD technology is an excellent tool for HgCdTe barrier architecture growth with a wide range of composition, donor /acceptor doping, and without post-grown annealing. The device concept of a specific barrier bandgap architecture integrated with Auger-suppression is as a good solution for high-operating temperature infrared detectors. Analyzed devices show a high performance comparable with the state-of-the-art of HgCdTe photodiodes. Dark current densities are close to the values given by "Rule 07" and detectivities of non-immersed detectors are close to the value marked for HgCdTe photodiodes. Experimental data of long-wavelength infrared detector structures were confirmed by numerical simulations obtained by a commercially available software APSYS platform. A detailed analysis applied to explain dark current plots was made, taking into account Shockley-Read-Hall, Auger, and tunneling currents.

  8. A high-speed high-sensitivity acoustic cell for in-line continuous monitoring of MOCVD precursor gases

    NASA Astrophysics Data System (ADS)

    Wajid, A.; Gogol, C.; Hurd, C.; Hetzel, M.; Spina, A.; Lum, R.; McDonald, M.; Capik, R. J.

    1997-01-01

    We describe a continuous wave resonant acoustic sensor that has been optimized as a very sensitive in-line monitor for measuring the composition of precursor gases used in MOCVD processes. The precursor/carrier gas mixtures flow through a compact stainless steel acoustic chamber that is isolated from the acoustic transducers by a set of metallic diaphragms. The sensor has been successfully operated at supply line pressures from atmosphere down to 50 Torr with gas flow rates of up to 1600 sccm. The accuracy of the speed of sound measurement for hydrogen gas is better than 0.005%, even in a high noise and low pressure environment. Hydrogen, as well as nitrogen or argon carrier gases, are accommodated within the instrument's 1-5 kHz working frequency range. The instrument's sensitivity and stability are demonstrated with the laboratory data. Measurements of the dynamic response characteristics of the metalorganic bubbler lines at low pressure are also be presented. Application of the cell is general, encompassing any of the metalorganic and hydride materials typically used in MOCVD processes.

  9. Correlation between incoherent phase fluctuations and disorder in Y1-xPrxBa2Cu3O7-δ epitaxial films from Nernst effect measurements

    NASA Astrophysics Data System (ADS)

    Li, Pengcheng; Mandal, Soumen; Budhani, R. C.; Greene, R. L.

    2007-05-01

    Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ (Pr-YBCO, 0⩽x⩽0.4 ) are reported over a broad range of temperature and magnetic-field strength. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature (Tc) . This effect is attributed to vortexlike excitations in the phase incoherent condensate existing above Tc . A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc≈110K for disorder-free YBa2Cu3O7-δ .

  10. Mesoscopic inhomogeneity creation in YBa2Cu3O7-y thin film by swift heavy ion irradiation at low temperature

    NASA Astrophysics Data System (ADS)

    Biswal, R.; John, J.; Raychaudhuri, P.; Behera, D.; Mohanty, T.; Avasthi, D. K.; Kanjilal, D.; Mishra, N. C.

    2011-09-01

    In the present study, we report the modification of pulsed laser deposited c-axis oriented thin films of YBa2Cu3O7-y (YBCO) in a cylindrical region around the path of swift heavy ions (SHIs). Our in situ temperature-dependent resistivity measurement and in situ low-temperature X-ray diffraction (XRD) study on YBCO irradiated at liquid nitrogen temperature with 200 MeV Ag ions shows that the SHI-induced secondary electrons selectively create point defects at CuO basal chains of YBCO. Beyond a critical fluence (∼1012 ions/cm2), the radially strained region around the amorphous latent tracks estimated from full width at half-maximum of (00l) XRD peaks tends to overlap, and a two-step superconducting transition evolves instead of a single transition in the in situ resistivity measurement.

  11. Self-heating technique of metallic substrate for reel-to-reel and double-sided deposition of YBa2Cu3O7- δ films

    NASA Astrophysics Data System (ADS)

    Zhang, Fei; Zhao, Ruipeng; Xue, Yan; Wang, Hui; He, Yuanying; Zhang, Pan; Tao, Bowan; Xiong, Jie; Li, Yanrong

    2016-02-01

    A new, simple, and highly efficient heating technology for metal tape substrates is proposed and applied to reel-to-reel and double-sided film deposition. In this technology, direct electrical current ( I DC) is conducted into the metal layer of oxide-buffered metal substrate to induce heat. Different substrate surface temperatures were achieved by varying I DC from 22 to 25 A. At these temperatures, a series of 1-μm-thick and 5-cm-long YBa2Cu3O7- δ (YBCO) films were fabricated on ion-beam-assisted deposition (IBAD) templates through metal organic chemical vapor deposition. X-ray diffraction analysis on the samples revealed that the YBCO film changed its growth mode from mixed a-axis and c-axis to purely c-axis with increasing I DC. The optimal out-of-plane and in-plane texture reached ~1.4° and 3.5°, respectively. A 30-m-long and 500-nm-thick single-sided YBCO-coated conductor was also prepared through reel-to-reel deposition using the proposed heating method. The fabricated conductor presented homogeneous crystallization and texture and exhibited a critical current density at self-field and 77 K ( J c 77K, 0T ) of 2.8-3.2 MA/cm2. Moreover, 500-nm-thick YBCO films were fabricated simultaneously on both sides of the double-sided IBAD template. The two sides of films demonstrated uniform texture and J c 77K, 0T of 3.2 MA/cm2. Results demonstrated that the proposed substrate heating technology can be used for reel-to-reel and double-sided deposition of YBCO-coated conductors.

  12. Influence of Both Cooling Rate and TeO2 Addition on the Properties of YBCO Superconductor

    NASA Astrophysics Data System (ADS)

    Ahmed, Yasser Momtaz Zaki; Hassan, Mervat Said; Abd-Elatif, Hassan

    2016-08-01

    Composite of superconducting system YBCO-TeO2 was synthesized utilizing solid-state reaction technique. Different weight percentages of TeO2 were mixed with a basic mixture [YBCO] for the synthesis of [YBa2Cu3O7-y ]1-x (TeO2) x composites. These mixtures were sintered at 1213 K (940 °C) for 24 hours and the samples cooled down by two different ways. The first way carried out via slowly cooling in furnace with the rate of 274 K/min to 275 K/min (1 °C/min to 2 °C/min) and the second one is quenching in oxygen gas. The XRD analysis showed that YBCO orthorhombic phase is the major phase appeared in all samples with different TeO2 content regardless of the cooling way. Additionally, minor unknown secondary phases appeared and enlarged with increasing TeO2 addition. Although quenched samples showed a phase difference between the sample's outer surface (orthorhombic) and its interior (tetragonal), the slowly cooled one did not clearly show such distinction. Moreover, doping YBCO with TeO2 leads to increase in the sample bulk density and reduction in their degradation degree in the wet atmosphere.

  13. Enhanced critical currents by silver sheeting of YBa2Cu3O7-δ thin films

    NASA Astrophysics Data System (ADS)

    Kienzle, M.; Albrecht, J.; Warthmann, R.; Kronmüller, H.; Leonhardt, S.; Jooss, Ch.

    2002-08-01

    Magneto-optical investigation of flux penetration into high-temperature superconducting thin films allows the determination of the local critical current density jc by an inversion scheme of Biot-Savart's law. This method is used to examine the influence of silver sheeting on jc in thin films of YBa2Cu3O7-δ (YBCO) quantitatively. It can be found that a feasible silver covering layer on top of a YBCO thin film can enhance the critical current density by up to 50%. Spatially resolved measurements of the magnetic-flux density distribution in partly silver covered YBCO films show the influence of the cover layer on the current pattern in the superconductor. The measured enhancement of the critical current density, that is induced by the silver layer, has its origin in a spatially varying proximity effect between superconductor and silver layer which leads to a strong variation of the flux-line energies on a small length scale. This variation is directly related to an additional pinning force density on the flux lines. A detailed model is developed that can explain the measured enhancement of the critical current density by considering this additional pinning.

  14. Feasibility studies of the growth of 3-5 compounds of boron by MOCVD

    NASA Technical Reports Server (NTRS)

    Manasevit, H. M.

    1988-01-01

    Boron-arsenic and boron-phosphorus films have been grown on Si sapphire and silicon-on-sapphire (SOS) by pyrolyzing Group 3 alkyls of boron, i.e., trimethylborane (TMB) and triethylborane (TEB), in the presence of AsH3 and PH3, respectively, in an H2 atmosphere. No evidence for reaction between the alkyls and the hydrides on mixing at room temperature was found. However, the films were predominantly amorphous. The film growth rate was found to depend on the concentration of alkyl boron compound and was essentially constant when TEB and AsH3 were pyrolyzed over the temperature range 550 C to 900 C. The films were found to contain mainly carbon impurities (the amount varying with growth temperature), some oxygen, and were highly stressed and bowed on Si substrates, with some crazing evident in thin (2 micron) B-P and thick (5 micron) B-As films. The carbon level was generally higher in films grown using TEB as the boron source. Films grown from PH3 and TMB showed a higher carbon content than those grown from AsH3 and TMB. Based on their B/As and B/P ratios, films with nominal compositions B sub12-16 As2 and B sub1.1-1.3 P were grown using TMB as the boron source.

  15. Carrier decay and luminescence characteristics in hadron irradiated MOCVD GaN

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Ceponis, T.; Pavlov, J.; Jasiunas, A.; Jonkus, V.; Meskauskaite, D.; Tekorius, A.

    2014-12-01

    Crystalline GaN is a promising material for producing of the radiation hard particle detectors of different types capable to operate in harsh areas of particle accelerators. Moreover, GaN crystals show rather efficient luminescence properties in several spectral bands under excitation by high energy radiation. Thereby, GaN material can be employed for fabrication of a combined device which is able to operate both as scintillating and charge collecting detector. However, the efficiency of such detectors and their functionality has insufficiently been investigated. This work is addressed to study the evolution of the efficiency of photon and hadron induced luminescence. To evaluate the density of excess carriers induced by the high energy protons, a correlation between the microwave probed photoconductivity transients and the proton induced luminescence intensity has been examined using 1.6 MeV protons to produce a nearly homogeneous and rather strong excitation in 2.6 μm thick MOCVD grown GaN epi-layers. To estimate the radiation hardness of such material, the evolution of the photoconductivity transients and of the proton induced photoluminescence characteristics has been studied by in situ measurements of the changes of luminescence intensity and photoconductivity decay rate during the exposure to a proton beam reaching fluences up to 1015 cm-2. The production rate of radiation defects, determined from in situ and post-irradiation examination of the changes of radiative and non-radiative recombination have been examined by combining penetrative hadron (nuclear reactor neutrons and 24 GeV/c protons) irradiations with those of the 1.6 MeV protons. The parameters of the efficiency κP of carrier pair generation by a single proton of κP = nP/NP cong 1.3 × 107 cm-3 per proton and κPApr = 40 carrier pairs per a micrometer of layer depth per proton have been estimated. The production rate of radiation defects is estimated to be KP cong 0.6 cm-1 for both penetrative

  16. Characterization of epitaxial YBa2Cu3O7-δ films deposited by metal propionate precursor solution

    NASA Astrophysics Data System (ADS)

    Angrisani Armenio, A.; Augieri, A.; Ciontea, L.; Contini, G.; Davoli, I.; Galluzzi, V.; Mancini, A.; Rufoloni, A.; Petrisor, T.; Vannozzi, A.; Celentano, G.

    2008-12-01

    YBa2Cu3O7-δ(YBCO) films were deposited with a low-fluorine modified trifluoroacetate metalorganic deposition (TFA-MOD) method on SrTiO3 single crystals and buffered Ni-W metallic tape with a thickness ranging from 450 to 600 nm. The method consists in the substitution of yttrium and copper trifluoroacetates with Cu and Y acetates dispersed in propionic acid. A reduced pyrolysis time with respect to the usual TFA method is obtained. Apart from CuO, no traces of second phases are revealed by x-ray measurements. The films are compact without cracks, and exhibit a slight superficial porosity, but they still remain well connected, and therefore the observed porosity does not affect either the critical current density or the normal state resistivity values, which are indicative of high-quality YBCO films. Moreover, YBCO films were also obtained on Pd-buffered Ni-W, with a CeO2/YSZ/CeO2 buffer layer architecture. These films show good morphological, structural, and superconductive properties with high critical temperature (higher than 91 K) and critical current density higher than 1 MA cm-2 at 77 K in self-field.

  17. Thin films of gallium arsenide on low-cost substrates. Final technical report, July 5, 1976-December 5, 1978

    SciTech Connect

    Ruth, R.P.; Dapkus, P.D.; Dupuis, R.D.; Johnson, R.E.; Moudy, L.A.; Yang, J.J.; Yingling, R.D.

    1980-03-01

    The MO-CVD technique was applied to the growth of thin films of GaAs and GaAl As on inexpensive polycrystalline or amorphous substrate materials (primarily glasses and metals) for use in fabrication of large-area low-cost photovoltaic device structures. Trimethylgallium, arsine, and trimethylaluminum are mixed in appropriate concentrations at room temperature in the gaseous state and pyrolyzed at the substrate, which is heated in a vertical reactor chamber to temperatures of 700 to 750/sup 0/C, to produce the desired film composition and properties. Studies of the properties of grain boundaries in polycrystalline GaAs films by the use of transport measurements as a function of temperature indicated that the grain boundary regions are depleted of majority carriers by a large density of neutral traps at the grain boundary interface, causing a barrier to majority carrier flow in the material. Schottky-barrier solar cells of approx. 3 percent efficiency (simulated AM0 illumination, no AR coating) were demonstrated on thin-film polycrystalline GaAs n/n/sup +/ structures on Mo sheet, Mo film/glass, and graphite substrates. Substantial enhancement of average grain size in polycrystalline MO-CVD GaAs films on Mo sheet was obtained by the addition of HCl to the growth atmosphere during deposition. Extensive investigation of polycrystalline thin-film p-n junctions indicated that the forward voltage of such devices is apparently limited to 0.5 to 0.6V. A laboratory-type deposition apparatus for the formation of TiO/sub 2/ antireflection (AR) coatings by pyrolysis of titanium isopropoxide was assembled and tested. Detailed analyses were made of the materials and labor costs involved in the laboratory-scale fabrication of MO-CVD thin-film GaAs solar cells. Details are presented. (WHK)

  18. Structural and flux-pinning properties of laser ablated YBa 2Cu 3O 7-δ thin films: Effects of self-assembled CeO 2 nanodots on LaAlO 3 substrates

    NASA Astrophysics Data System (ADS)

    Haywood, Talisha; Oh, Sang Ho; Kebede, Abebe; Pai, Devdas M.; Sankar, Jag; Christen, David K.; Pennycook, Stephen J.; Kumar, Dhananjay

    2008-12-01

    Self-assembled nanodots of CeO 2 on (1 0 0) LaAlO 3 substrates, generated in situ by means of a pulsed laser deposition method prior to the deposition of YBa 2Cu 3O 7-δ (YBCO) films, have been used to modify the superconducting properties of resulting YBCO films. Structural characterization has indicated that CeO 2 layers grow via van der Merwe three-dimensional mode and the islands eventually acquire a pancake type of structure with lateral dimension several times larger than vertical dimension. The three-dimensional growth of CeO 2 islands with (1 0 0) preferred orientation is believed to be associated with its surface energy anisotropy. The magnetization versus temperature and magnetization versus field measurements and analysis have suggested that CeO 2 can affect the superconducting properties of YBCO films favorably or adversely depending on the density of CeO 2 nanodots on the substrate surfaces prior to the deposition of YBCO films.

  19. Process for forming epitaxial perovskite thin film layers using halide precursors

    DOEpatents

    Clem, Paul G.; Rodriguez, Mark A.; Voigt, James A.; Ashley, Carol S.

    2001-01-01

    A process for forming an epitaxial perovskite-phase thin film on a substrate. This thin film can act as a buffer layer between a Ni substrate and a YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor layer. The process utilizes alkali or alkaline metal acetates dissolved in halogenated organic acid along with titanium isopropoxide to dip or spin-coat the substrate which is then heated to about 700.degree. C. in an inert gas atmosphere to form the epitaxial film on the substrate. The YBCO superconductor can then be deposited on the layer formed by this invention.

  20. Factors associated with biaxial texturing of Cu tapes for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Sung, T. H.; Han, S. C.; Han, Y. H.; Jeong, N. H.; Kim, C. J.; Jun, B. H.; Oh, S. S.; Kim, H. S.; Kim, T. H.; No, K. S.

    2007-10-01

    A biaxially textured Cu(2 0 0) tape was used as a substrate for YBCO coated conductors by cold rolling followed by recrystallization heat treatment. In this work, we studied the influence of annealing conditions and final tape thickness on the recrystallization process. Phi (ϕ) scan and omega (ω) scan XRD revealed that the best in-plane and out-of-plane alignment of the Cu tape (thickness 100 μm), measured in terms of full width half maximum (FWHM) values of 6.64° and 4.49°, were obtained by annealing at 800 °C for 30 min. The texture of CeO2 buffer layer thermally-evaporated on the Cu tape was also analyzed.

  1. Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

    NASA Astrophysics Data System (ADS)

    Zhu, Yunpeng; Wang, Gang; Liu, Liyuan; Yang, Xinsheng; Zhao, Yong

    2015-12-01

    HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate.

  2. 2D SQIF arrays using 20 000 YBCO high R n Josephson junctions

    NASA Astrophysics Data System (ADS)

    Mitchell, E. E.; Hannam, K. E.; Lazar, J.; Leslie, K. E.; Lewis, C. J.; Grancea, A.; Keenan, S. T.; Lam, S. K. H.; Foley, C. P.

    2016-06-01

    Superconducting quantum interference filters (SQIFs) have been created using two dimensional arrays of YBCO step-edge Josephson junctions connected together in series and parallel configurations via superconducting loops with a range of loop areas and loop inductances. A SQIF response, as evidenced by a single large anti-peak at zero applied flux, is reported at 77 K for step-edge junction arrays with the junction number N = 1 000 up to 20 000. The SQIF sensitivity (slope of peak) increased linearly with N up to a maximum of 1530 V T-1. Array parameters related to geometry and average junction characteristics are investigated in order to understand and improve the SQIF performance in high temperature superconducting arrays. Initial investigations also focus on the effect of the SQUID inductance factor on the SQIF sensitivity by varying both the mean critical current and the mean inductance of the loops in the array. The RF response to a 30 MHz signal is demonstrated.

  3. Experimental and numerical study of a YBCO pancake coil with a magnetic substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Kvitkovic, J.; Pamidi, S. V.; Coombs, T. A.

    2012-12-01

    A finite element model for a YBCO pancake coil with a magnetic substrate is developed in this paper. An axial symmetrical H formulation and the E-J power law are used to construct the model, with the magnetic substrate considered by introducing an extra time-dependent term in the formula. A pancake coil is made and tested. The measurement of critical current and transport loss is compared to the model result, showing good consistency. The influence of magnetic substrate in the condition of AC and DC current is studied. The AC loss decreases without a magnetic substrate. It is observed that when the applied DC current approaches the critical current the coil turn loss profile changes completely in the presence of magnetic substrate due to the change of magnetic field distribution.

  4. 2D SQIF arrays using 20 000 YBCO high R n Josephson junctions

    NASA Astrophysics Data System (ADS)

    Mitchell, E. E.; Hannam, K. E.; Lazar, J.; Leslie, K. E.; Lewis, C. J.; Grancea, A.; Keenan, S. T.; Lam, S. K. H.; Foley, C. P.

    2016-06-01

    Superconducting quantum interference filters (SQIFs) have been created using two dimensional arrays of YBCO step-edge Josephson junctions connected together in series and parallel configurations via superconducting loops with a range of loop areas and loop inductances. A SQIF response, as evidenced by a single large anti-peak at zero applied flux, is reported at 77 K for step-edge junction arrays with the junction number N = 1 000 up to 20 000. The SQIF sensitivity (slope of peak) increased linearly with N up to a maximum of 1530 V T‑1. Array parameters related to geometry and average junction characteristics are investigated in order to understand and improve the SQIF performance in high temperature superconducting arrays. Initial investigations also focus on the effect of the SQUID inductance factor on the SQIF sensitivity by varying both the mean critical current and the mean inductance of the loops in the array. The RF response to a 30 MHz signal is demonstrated.

  5. Critical currents of YBCO tapes and Bi-2212 wires at different temperatures and magnetic fields

    SciTech Connect

    Lombardo, V.; Barzi, e.; Turrioni, D.; Zlobin, A.V.; /Fermilab

    2010-08-01

    Design studies for the cooling channel of a Muon Collider call for straight and helical solenoids generating field well in excess of the critical fields of state of the art Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn or NbTi. Therefore, High Temperature Superconductors (HTS) will need to be used for the manufacturing of all or certain sections of such magnets to be able to generate and withstand the field levels at the cryogenic temperatures required by the new machine. In this work, two major High Temperature Superconductors - Bi2212 round wires and YBCO coated conductor tapes - are investigated to understand how critical current density of such conductors scales as a function of external field and operating temperature. This is vital information to make conductor choices depending on the application and to proceed with the design of such magnets.

  6. High-Tc Coated Conductors - Performance of Meter-Long YBCO/IBAD Flexible Tapes

    SciTech Connect

    Foltyn, S.R.; Arendt, P.N.; Dowden, P.C.; DePaula, R.F.; Groves J.R.; Coulter, J.Y.; Jia, Q.; Maley, M.P.; Peterson, D.E.

    1998-09-13

    One meter long tapes based on 50-100 {micro}m thick by 1 cm wide nickel alloy substrates have been coated in a continuous process with a textured yttria-stabilized zirconia layer by ion beam-assisted deposition, followed by a 1-2 {micro}m thick layer of YBCO by pulsed laser deposition. The best result to date is a tape with a critical current (I{sub c}) at 75 K of 96 A over an 87 cm measurement length. The overall critical current density and engineering current density are 1 MA/cm{sup 2} and 10 kA/cm{sup 2}, respectively. Using a special probe, individual I-V curves were generated for each centimeter of tape length in order to investigate longitudinal uniformity of the transport properties: the highest and lowest I{sub c} values fall within a range of {+-}25%.

  7. Magnetic levitation and its application for education devices based on YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yang, W. M.; Chao, X. X.; Guo, F. X.; Li, J. W.; Chen, S. L.

    2013-10-01

    A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN2 temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications.

  8. (abstract) All Epitaxial Edge-geometry SNS Devices with Doped PBCO and YBCO Normal Layers

    NASA Technical Reports Server (NTRS)

    Barner, J. B.; Hunt, B. D.; Foote, M. C.

    1995-01-01

    We will present our results on tapered-edge-geometry SNS weak link fabricated from c-axis oriented base-, counterelectrode and normal layers using a variety of processing conditions. To date, we have employed a variety of different normal materials (Co-doped YBCO, Y-doped PBCO, Ca-doped PBCO). We have been examining the junction fabrication process in detail and we will present our methods. In particular, we have been examining both epitaxial and non-epitaxial milling mask overlayers and we will present a comparison of both methods. These devices behave similar to the expectations of the resisively shunted junction model and conventional SNS proximity effect models but with some differences which will be discussed. We will present the detailed systematics of our junctions including device parameters versus temperature, rf and dc magnetic response for the various processing conditions.

  9. Magnetization losses in superconducting YBCO conductor-on-round-core (CORC) cables

    NASA Astrophysics Data System (ADS)

    Majoros, M.; Sumption, M. D.; Collings, E. W.; van der Laan, D. C.

    2014-12-01

    Described are the results of magnetization loss measurements made at 77 K on several YBCO conductor-on-round-core (CORC) cables in ac magnetic fields of up to 80 mT in amplitude and frequencies of 50 to 200 Hz, applied perpendicular to the cable axis. The cables contained up to 40 tapes that were wound in as many as 13 layers. Measurements on the cables with different configurations were made as functions of applied ac field amplitude and frequency to determine the effects of their layout on ac loss. In large scale devices such as e.g. Superconducting Magnetic Energy Storage (SMES) magnets, the observed ac losses represent less than 0.1% of their stored energy.

  10. XPS-nanocharacterization of organic layers electrochemically grafted on the surface of SnO2 thin films to produce a new hybrid material coating

    NASA Astrophysics Data System (ADS)

    Drevet, R.; Dragoé, D.; Barthés-Labrousse, M. G.; Chaussé, A.; Andrieux, M.

    2016-10-01

    This work presents the synthesis and the characterization of hybrid material thin films obtained by the combination of two processes. The electrochemical grafting of organic layers made of carboxyphenyl moieties is carried out from the reduction of a diazonium salt on tin dioxide (SnO2) thin films previously deposited on Si substrates by metal organic chemical vapor deposition (MOCVD). Since the MOCVD experimental parameters impact the crystal growth of the SnO2 layer (i.e. its morphology and its texturation), various electrochemical grafting models can occur, producing different hybrid materials. In order to evidence the efficiency of the electrochemical grafting of the carboxyphenyl moieties, X-ray Photoelectron Spectroscopy (XPS) is used to characterize the first nanometers in depth of the synthesized hybrid material layer. Then three electrochemical grafting models are proposed.

  11. Numerical simulation and analysis of single grain YBCO processed from graded precursor powders

    NASA Astrophysics Data System (ADS)

    Zou, J.; Ainslie, M. D.; Hu, D.; Zhai, W.; Devendra Kumar, N.; Durrell, J. H.; Shi, Y.-H.; Cardwell, D. A.

    2015-03-01

    Large single-grain bulk high-temperature superconducting materials can trap high magnetic fields in comparison with conventional permanent magnets, making them ideal candidates to develop more compact and efficient devices, such as actuators, magnetic levitation systems, flywheel energy storage systems and electric machines. However, macro-segregation of Y-211 inclusions in melt processed Y-Ba-Cu-O (YBCO) limits the macroscopic critical current density Jc of such bulk superconductors, and hence, the potential trapped field. Recently, a new fabrication technique with graded precursor powders has been developed, which results in a more uniform distribution of Y-211 particles, in order to further improve the superconducting properties of such materials. In order to develop this graded fabrication technique further, a 3D finite-element numerical simulation based on the H-formulation is performed in this paper. The trapped field characteristics of a graded YBCO sample magnetized by the field cooling method are simulated to validate the model, and the simulation results are consistent with the experimental measurements. In addition, the influence of the graded technique and various graded Jc distributions for pulsed field magnetization, recognized widely as a practical route for magnetizing samples in bulk superconductor applications, is also investigated, with respect to the trapped field and temperature profiles of graded samples. This modelling framework provides a new technique for assessing the performance of various sizes and geometries of graded bulk superconductors, and by adjusting the Y-211, and hence Jc, distribution, samples can be fabricated based on this concept to provide application-specific trapped field profiles, such as the generation of either a high magnetic field gradient or a high level of uniformity for the traditionally conical, trapped field profile.

  12. Size effects of nano-scale pinning centers on the superconducting properties of YBCO single grains

    NASA Astrophysics Data System (ADS)

    Moutalbi, Nahed; Noudem, Jacques G.; M'chirgui, Ali

    2014-08-01

    High pinning superconductors are the most promising materials for power engineering. Their superconducting properties are governed by the microstructure quality and the vortex pinning behavior. We report on a study of the vortex pinning in YBa2Cu3O7-x (YBCO) single grain with defects induced through the addition of insulating nano-particles. In order to improve the critical current density, YBCO textured bulk superconductors were elaborated using the Top Seeded Melt Texture and Growth process with different addition amounts of Al2O3 nano-particles. Serving as strong pinning centers, 0.05% excess of Al2O3 causes a significant enhancement of the critical current density Jc under self field and in magnetic fields at 77 K. The enhanced flux pinning achieved with the low level of alumina nano-particles endorses the effectiveness of insulating nano-inclusions to induce effectives pinning sites within the superconducting matrix. On the other side, we focused on the effect of the size of pinning centers on the critical current density. This work was carried out using two batches of alumina nano-particles characterized by two different particle size distributions with mean diameters PSD1 = 20 nm and PSD2 = 2.27 μm. The matching effects of the observed pinning force density have been compared. The obtained results have shown that the flux pinning is closely dependent on the size of the artificial pinning centers. Our results suggest that the optimization of the size of the artificial pinning centers is crucial to a much better understanding of the pinning mechanisms and therefore to insure high superconducting performance for the practical application of superconducting materials.

  13. Flat YBa 2Cu 3O 7- x layers for planar tunnel-device technology

    NASA Astrophysics Data System (ADS)

    Klemenz, C.; Scheel, H. J.

    1996-02-01

    The conditions for achieving extremely flat YBa 2Cu 3O 7- x (YBCO) surfaces with large interstep distances as required for a reliable planar HTSC tunnel-device technology are analyzed. Considerations of thermodynamics, kinetics and transport of the growth species show that by liquid phase epitaxy (LPE) it is possible to achieve such flat YBCO surfaces, which is experimentally proven. Specifically, in LPE the growth from relatively concentrated solutions occurs at high temperatures near thermodynamic equilibrium. The small supersaturation (of < 0.17°C) required for obtaining step distances of more than 10 μm has been calculated by using the heat of solution from the measured solubility curve and the theoretical treatment of the experimental sufface features. Jackson's α factors (roughness parameter) are derived for a- and c-oriented YBCO films and explain the different degree of polygonization of the observed growth spirals. The concentrations of YBCO in physical vapour deposition (PVD) and in metal-organic chemical vapour deposition (MOCVD) are very small and the supersaturations at least 10 2 times higher than in LPE. This, together with the thermodynamic stability limit (temperature, oxygen partial pressure), sets an inherent limit to the interstep distance in PVD and MOCVD, thus limiting the achievable flatness of vapour-grown YBCO layers.

  14. Driving Down HB-LED Costs. Implementation of Process Simulation Tools and Temperature Control Methods of High Yield MOCVD Growth

    SciTech Connect

    Quinn, William

    2012-04-30

    The overall objective of this multi-faceted program is to develop epitaxial growth systems that meet a goal of 75% (4X) cost reduction in the epitaxy phase of HB-LED manufacture. A 75% reduction in yielded epitaxy cost is necessary in order to achieve the cost goals for widespread penetration of HB-LED's into back-lighting units (BLU) for LCD panels and ultimately for solid-state lighting (SSL). To do this, the program will address significant improvements in overall equipment Cost of Ownership, or CoO. CoO is a model that includes all costs associated with the epitaxy portion of production. These aspects include cost of yield, capital cost, operational costs, and maintenance costs. We divide the program into three phases where later phases will incorporate the gains of prior phases. Phase one activities are enabling technologies. In collaboration with Sandia National Laboratories we develop a Fluent-compatible chemistry predictive model and a set of mid-infrared and near-ultraviolet pyrometer monitoring tools. Where previously the modeling of the reactor dynamics were studied within FLUENT alone, here, FLUENT and Chemkin are integrated into a comprehensive model of fluid dynamics and the most advanced transport equations developed for Chemkin. Specifically, the Chemkin model offered the key reaction terms for gas-phase nucleation, a key consideration in the optimization of the MOCVD process. This new predictive model is used to design new MOCVD reactors with optimized growth conditions and the newly developed pyrometers are used monitor and control the MOCVD process temperature to within 0.5°C run-to-run and within each wafer. This portion of the grant is in collaboration with partners at Sandia National Laboratories. Phase two activities are continuous improvement projects which extend the current reactor platform along the lines of improved operational efficiency, improved systems control for throughput, and carrier modifications for increased yield

  15. Species transport and chemical reaction in a MOCVD reactor and their influence on the GaN growth uniformity

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi; Fang, Haisheng; Yao, Qingxia; Yan, Han; Gan, Zhiyin

    2016-11-01

    Fluid flow, heat transfer, and species transport with chemical reactions have been investigated for gallium nitride (GaN) growth in a commercial metal-organic chemical vapor deposition (MOCVD) reactor. Both the growth rate and the growth uniformity are investigated zone by zone, as the wafers are divided into three zones/groups according to their distances to the susceptor center. The results show that species transport in the reactor is affected by the inlet conditions, i.e., the premixed or non-premixed inlet, the inlet temperature, the total gas flow rate, and the V/III component ratio, and reveal that the premixed inlet condition is preferred for uniform growth. Especially, a large total flow rate or a low V/III ratio results in both increase of the growth rate and improvement of the growth uniformity.

  16. The anti-surfactant effect of silane on the facets-controlled growth of GaN nanorods by MOCVD

    NASA Astrophysics Data System (ADS)

    Li, J. Z.; Chen, Z. Z.; Li, S. F.; Jiao, Q. Q.; Feng, Y. L.; Jiang, S. X.; Chen, Y. F.; Yu, T. J.; Shen, B.; Zhang, G. Y.

    2016-08-01

    N-polar GaN nanorods were selective area grown by continuous mode metalorganic chemical vapor deposition (MOCVD) under a Ga-rich and high silane flow condition. The interruption comparing with continuous supply of silane flow was performed to study the role of silane flux. High resolution scanning electron microscopy (SEM), x-ray diffraction (XRD), cathodoluminescence (CL) and x-ray photoelectron spectroscopy (XPS) measurements were performed. The enhanced vertical growth rate was achieved as 42 μm/h and sharp smooth m-plane, r-plane and c-plane facets were obtained for the nanorods with high silane flux. Sisbnd N bonds were clarified to be formed on the surface of the nanorod by XPS spectra. The silane acting as anti-surfactant was suggested to explain the diffusion and incorporation of the species on the facets of GaN nanorods.

  17. Growth model and the effect of CuO nanocrystallites on the properties of chemically derived epitaxial thin films of YBa2Cu3O7-x

    NASA Astrophysics Data System (ADS)

    Araki, Takeshi; Niwa, Toshiharu; Yamada, Yutaka; Hirabayashi, Izumi; Shibata, Junko; Ikuhara, Yuichi; Kato, Kazumi; Kato, Takeharu; Hirayama, Tsukasa

    2002-09-01

    In metalorganic deposition using trifluoroacetates (TFA-MOD), CuO nanocrystallites in calcined film, which influence the critical current density (Jc) of the resulting film, have seldom been considered before. CuO nanocrystallites ripen and grow during the calcining process at 200-250 degC and grow into large CuO grains in the YBa2Cu3O7-x (YBCO) film. The final diameter of the grains is about 0.1 mum. When highly purified coating solution is used, suppressing the creation of nanocrystallites in the precursor film is an effective way to obtain high-Jc YBCO film because the nanocrystallites consist only of CuO. We obtained the highest-Jc YBCO film on LaAlO3 single crystal with a calcining process of 9h43m at 200-250 degC. It was 141 nm thick and had a Jc of 7.5 MA/cm2 (77 K, 0 T), as measured by the four-probe method. The firing process of TFA-MOD still has several unsolved problems; why can H2O and HF gas diffuse quickly within the film? These phenomena can be explained by a model with a quasiliquid consisting of Y, Ba, Cu, O, H, and F. The H2O and HF can move quickly in the quasiliquid network within the film during the firing process. According to the model, we can get more conversion of CuO nanocrystallites into quasiliquid by increasing the amount of water vapor. Jc of the film was increased from 3.3 to 4.5 MA/cm2 (77 K, 0 T) by increasing the humidity from 4.2% to 12.1% during the long calcining profile of 66h40m at 200-250 degC. These results confirm the above model. CuO nanocrystallites in precursor films induce nonstoichiometric metal contents in the quasiliquid. Isolated CuO grains in YBCO film indirectly cause nonstoichiometric quasiliquid in other areas. Such nonstoichiometric quasiliquid leads to non-YBCO materials such as BaO, Y2O3, and Y2Cu2O5. Thus, films derived from non-highly purified coating solution and ones prepared with an inappropriate calcining process both have lower Jc values. Micrographs obtained by transmission electron microscopy and Jc

  18. MOCVD growth of group III nitrides for high power, high frequency applications

    NASA Astrophysics Data System (ADS)

    di Forte Poisson, M.-A.; Magis, M.; Tordjman, M.; Sarazin, N.; di Persio, J.

    2005-02-01

    This paper reports on the LP-MOCVD growth optimisation of bulk GaN, GaAlN materials and GaAlN/GaN heterostructures grown on Sapphire and Silicon Carbide substrates for MESFET and HEMT applications, and on the device performances obtained with these structures. High purity and high resistivity GaN grown on sapphire and Silicon Carbide has been obtained. GaN/Al2O3 MESFETs based on such high purity GaN buffer layers, have exhibited very promising static and microwave performances: high beakdown voltage 200 V, ft = 12 GHz, fmax = 25 GHz and CW output power in excess of 2.2 W/mm at 2 GHz.. They have shown the best low frequency noise performances, with the lowest Hooge's parameter as compared to previous values reported in the literature for different GaN-based FETs (HFETs and HEMTs). The main mechanisms involved in the growth of GaAlN/GaN alloys have been studied and their impact on the physical properties of these materials determined. A parasitic reaction was clearly identified to occur in the gas phase between TMA and NH3, with a strong influence on the growth rate and the aluminium incorporation. The SiC substrate surface preparation (both ex-situ and in-situ) and the nucleation layer growth conditions (growth temperature, thickness, composition and strain) have been found to be key steps of the GaAlN/GaN/SiC growth process. Static characteristics of the devices such as maximum drain current Idss or pinch-off voltage have been correlated with the nucleation layer composition of the HEMT structure and the defect density of the SiC substrate. The devices performances related to our first GaAlN/GaN HEMT structures grown on Sapphire and Silicon Carbide have confirmed the high potentiality of GaN and related alloys for high power microwave transistors. Load-Pull measurements performed at 2 GHz on devices related to GaAlN/GaN/Al2O3 HEMT structures, have shown a remarkably high output power density (4.4 W/mm) and absolute power level (3.2 W

  19. Two-step epitaxial lateral overgrowth of a-plane GaN by MOCVD

    NASA Astrophysics Data System (ADS)

    Ni, X.; Özgür, Ü.; Morkoç, H.; Baski, A. A.; Liliental-Weber, Z.; Everitt, H. O.

    2007-02-01

    We report on growth and characterization of epitaxial lateral overgrown (ELO) (11 II -0) a-plane GaN by metalorganic chemical vapor deposition (MOCVD). The ELO samples were grown using a SiO II striped mask pattern consisting of 4 μm wide open windows and 10 μm or 20 μm wide SiO II stripes. Different growth rates in Ga- and N-wings along with the wing tilt create a major obstacle for achieving a fully coalesced flat surface in ELO-GaN. To address this problem we have employed a two-step growth method that is able to provide a high height to width aspect ratio in the first growth step followed by enhanced lateral growth in the second step by controlling the growth temperature. Depending on the growth conditions, lateral growth rate of the wings with Ga-polarity were from 2 to 5 times larger than that of the N-polarity wings. We investigated the effects of growth parameters on wing tilt, which was observed to be ~0.25° from the Kikuchi lines using large angle convergent beam electron diffraction (LACBED) and accompanied by some twist (0.09°) between the two opposite wings. Transmission electron microscopy (TEM) results showed that the threading dislocation density in the resulting fully coalesced overgrown GaN was reduced from 4.2×10 10 cm -2 in the window area to 1.0×10 8 cm -2 in the wing area, and that the wing areas contained relatively high density of basal stacking faults, 1.2×10 4 cm -1. The recombination of carriers/excitons localized at stacking faults was evident in far-field near bandedge photoluminescence (PL) measured at 10 K. Moreover, atomic force microscopy (AFM) measurements revealed two orders of magnitude higher density of surface pits in window than in wing regions, which could be decorating dislocation termination on surface. Time-resolved PL measurements for the a-plane ELO-GaN samples revealed biexponential decays. The recombination times were significantly increased ( τ I =80 ps and τ II =250 ps) compared to the standard a

  20. Magnetic and magnetotransport characterization of La0.7Sr0.3MnO3/YBCO/La0.7Sr0.3MnO3/YBCO spin valve

    NASA Astrophysics Data System (ADS)

    Dybko, K.; Aleshkevych, P.; Sawicki, M.; Przyslupski, P.

    2015-01-01

    We present magnetoresistance measurements on La0.7Sr0.3MnO3/YBCO/La0.7Sr0.3MnO3/YBCO (L1/Y1/L2/Y) heterostructure. The Ll/Y1/L2/Y spin valve shows large magnetoresistance peaks in coercive field at temperatures below the onset of the superconducting transition. The rotation in parallel magnetic field demonstrates a change of magnetoresistance; simultaneously the transition temperature to superconducting state Tc0(H=450 Oe, β) exhibits nonmonotonic dependence due to change of noncolinearity of magnetic moments of LSMO layers. Nonmonotonic change of the transition temperature as a function of angle is interpreted as a signature of generation of the triplet component superconducting phase in the Ll/Y1/L2/Y heterostructure.

  1. Crystalline phase transition information induced by high temperature susceptibility transformations in bulk PMP-YBCO superconductor growth in-situ

    NASA Astrophysics Data System (ADS)

    Zhang, C. P.; Chaud, X.; Beaugnon, E.; Zhou, L.

    2015-01-01

    The dynamic susceptibility transformations of bulk HTSC PMP-YBCO growth have been investigated from 200 °C up to 1060 °C by the Faraday Balance in-situ. It revealed that the crystalline phase transitions of bulk PMP-YBCO growth in process. A new discovery of Y123 phase pre-formed then melted in heating stage has been found. It also discovered that Y123 crystal solidification started at 1004 °C in cooling stage. Before Y123 solidification the liquid phase CuO change to Cu2O reciprocally as well as the copper ion valence changed between divalent Cu2+ and trivalent Cu1+ each other. It was essential to keep quantities of CuO phase instead of the Cu2O for Y123 crystal solidification.

  2. EBSD characterisation of Y2Ba4CuUOx phase in melttextured YBCO with addition of depleted uranium oxide

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Mücklich, F.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.

    2006-06-01

    Melt-textured YBCO samples processed with added Y2O3 and depleted uranium oxide (DU) contain nano-particles, which have been identified previously as Y2Ba4CuUOx (U-411). This phase has a cubic unit cell, which is clearly distinct from the orthorhombic Y-123 and Y-211 phases within the YBCO system. In samples with a high amount of DU addition (0.8 wt-% DU), U-2411 particles have sizes between 200 nm and several µm, so identification of the Kikuchi patterns of this phase becomes possible. Together with a parallel EDX analysis, the particles embedded in the Y-123 matrix can be identified unambiguously. In this way, a three-phase EBSD scan becomes possible, allowing also the identification of nanometre-sized particles in the sample microstructure.

  3. A simple multi-seeding approach to growth of large YBCO bulk with a diameter above 53 mm

    NASA Astrophysics Data System (ADS)

    Tang, Tian-wei; Wu, Dong-jie; Wu, Xing-da; Xu, Ke-Xi

    2015-12-01

    A successful simple multi-seeding approach to growing large size Y-Ba-C-O (YBCO) bulks is reported. Compared with the common single seeding method, our multi-seeding method is more efficient. By using four SmBa2Cu3O7-δ (Sm-123) seeds cut from a large size Sm-Ba-C-O (SmBCO) single domain, large YBCO samples up to 53 mm in diameter could be produced successfully and 100 mm diameter samples can also be grown. Experimental results show that the processing time can be shortened greatly by using this new approach, and the superconducting properties can also be improved. The Hall probe mapping shows that the trapped field distribution of 53 mm diameter multi-seeded sample is homogeneous and the peak value is up to 0.53 T. The magnetic levitation force density reaches to 14.7 N/cm2 (77 K, 0.5 T).

  4. One-step graphene coating of heteroepitaxial GaN films.

    PubMed

    Choi, Jae-Kyung; Huh, Jae-Hoon; Kim, Sung-Dae; Moon, Daeyoung; Yoon, Duhee; Joo, Kisu; Kwak, Jinsung; Chu, Jae Hwan; Kim, Sung Youb; Park, Kibog; Kim, Young-Woon; Yoon, Euijoon; Cheong, Hyeonsik; Kwon, Soon-Yong

    2012-11-01

    Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as ~0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as 'pseudo-substrates' in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.

  5. Topological insulator Bi2Te3 films synthesized by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Venkatasubramanian, Rama; Liu, Chang; Pierce, Jonathan; Yang, Haoran; Zahid Hasan, M.; Wu, Yue; Chen, Yong P.

    2012-10-01

    Topological insulator (TI) materials such as Bi2Te3 and Bi2Se3 have attracted strong recent interests. Large scale, high quality TI thin films are important for developing TI-based device applications. In this work, structural and electronic properties of Bi2Te3 thin films deposited by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrates were characterized via x-ray diffraction (XRD), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and electronic transport measurements. The characteristic topological surface states with a single Dirac cone have been clearly revealed in the electronic band structure measured by ARPES, confirming the TI nature of the MOCVD Bi2Te3 films. Resistivity and Hall effect measurements have demonstrated relatively high bulk carrier mobility of ˜350 cm2/Vs at 300 K and ˜7400 cm2/Vs at 15 K. We have also measured the Seebeck coefficient of the films. Our demonstration of high quality topological insulator films grown by a simple and scalable method is of interests for both fundamental research and practical applications of thermoelectric and TI materials.

  6. Development of a 20 GHz scanned beam microstrip antenna array with a proximity coupled YBCO feed network

    SciTech Connect

    Mittleman, S.D.; Herd, J.S.; Kenny, J.P.; Poles, L.D.; Champion, M.H.; Rainville, P.J.; Silva, J.H.

    1994-12-31

    A superconducting antenna array with a proximity coupled feed network operating at 20 GHz has been developed. The antenna is a 4x4 array and its performance was measured from 18 GHz to 22 GHz. At temperatures below 80 K, there was a 15 dBi gain measured at several frequencies in this range. The design of a low loss superconducting phase shifter monolithically incorporated into the YBCO feed network is indicated.

  7. HTSC cuprate films doped with nanoparticles and their electrodynamics, determined by Abrikosov vortices

    NASA Astrophysics Data System (ADS)

    Flis, V. S.; Kalenyuk, A. A.; Kasatkin, A. L.; Moskalyuk, V. O.; Rebikov, A. I.; Svechnikov, V. L.; Tret'yachenko, K. G.; Pan, V. M.

    2010-01-01

    This paper presents the results of a comprehensive study of the relationship of the structural and electrodynamic characteristics of quasi-single-crystal films of the HTSC cuprate YBa2Cu3O7-δ (YBCO) with various concentrations (several mass percent) of nanosize inclusions of the perovskitelike phase of BaZrO3 (BZO). High-resolution electron microscopy is used to investigate the nanostructure of the fabricated films and to determine the main types of defects that cause strong pinning of Abrikosov vortices and, accordingly, large critical current densities. The results of theoretically modelling the genesis of the defect nanostructure that appears in such films and its influence on the critical current are presented. The magnetic and transport properties of HTSC films made from YBCO(BZO) have been experimentally studied. The temperature, magnetic-field, and magnetic-orientation dependences of the critical current density of the test films are found. The results of an experimental investigation of the high-frequency properties of YBZO(BZO) films—the surface microwave impedance of the films in the linear and nonlinear regimes—are also given. The experimental results are discussed, and the influence of the nanostructure of the impurity phase on the electrodynamic characteristics of the HTSC films is analyzed.

  8. Peculiarities of the current-voltage characteristics of a Josephson medium in a YBCO high-temperature superconductor

    NASA Astrophysics Data System (ADS)

    Vasyutin, M. A.

    2013-12-01

    The influence of a weak magnetic field ( H < 150 Oe) on the current-voltage ( I- U) characteristic of a YBa2Cu3O7 - x (YBCO) high-temperature superconductor (HTSC) near the superconducting transition temperature has been studied. It is established that there exist narrow (<0.2 K) temperature regions where the I- U curve exhibits sharp bending for H < 30 Oe and the ohmic behavior changes to a quadratic dependence of the voltage on current in a region of several milliamperes. At higher temperatures, the I- U curve bending exhibits smearing. This behavior is observed at a temperature below that corresponding to a zero critical current. Above a certain current, the temperature and magnetic field exhibit equivalent effects on the I- U curve of YBCO. Experimental results are explained by a sharp decrease in the critical currents of intergranular Josephson junctions under the action of magnetic field and by the current-induced formation of uncoupled (with respect to the order parameter) superconducting grains. Characteristic currents for the transition of the intergranular Josephson medium into an incoherent state are determined and the first critical fields in YBCO are evaluated.

  9. An electron backscatter diffraction investigation of crystallographic orientations of embedded nanoparticles within melt-textured YBCO high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.; Shlyk, L.; Krabbes, G.

    2006-07-01

    Microstructures of melt-textured YBCO samples with embedded nanosized particles of Y2BaCuO5 (Y-211) and Y2Ba4CuMOx (M-2411 with M = U,Zr) are analysed by means of electron backscatter diffraction (EBSD). With the recent developments of the EBSD technique, we can directly measure the crystallographic orientation of the embedded nanoparticles, employing a spatial resolution of about 40 nm. The high image quality of the Kikuchi patterns allows true three-phase (YBCO, Y-211 and M-2411) scans to be performed. The Y-211 particles do not exhibit any preferred orientation, even if their size is considerably reduced, to the 100 nm range. The size reduction reduces the negative influence of the Y-211 particles on the YBCO matrix, however. U-2411 particles, which are formed during the processing stage, do not show any orientation, and with increasing concentration, some texture develops. In contrast to this, embedded Zr-2411 particles are fully oriented in the (001) orientation according to the surrounding superconducting matrix.

  10. Field Performance of an Optimized Stack of YBCO Square “Annuli” for a Compact NMR Magnet

    PubMed Central

    Hahn, Seungyong; Voccio, John; Bermond, Stéphane; Park, Dong-Keun; Bascuñán, Juan; Kim, Seok-Beom; Masaru, Tomita; Iwasa, Yukikazu

    2011-01-01

    The spatial field homogeneity and time stability of a trapped field generated by a stack of YBCO square plates with a center hole (square “annuli”) was investigated. By optimizing stacking of magnetized square annuli, we aim to construct a compact NMR magnet. The stacked magnet consists of 750 thin YBCO plates, each 40-mm square and 80- μm thick with a 25-mm bore, and has a Ø10 mm room-temperature access for NMR measurement. To improve spatial field homogeneity of the 750-plate stack (YP750) a three-step optimization was performed: 1) statistical selection of best plates from supply plates; 2) field homogeneity measurement of multi-plate modules; and 3) optimal assembly of the modules to maximize field homogeneity. In this paper, we present analytical and experimental results of field homogeneity and temporal stability at 77 K, performed on YP750 and those of a hybrid stack, YPB750, in which two YBCO bulk annuli, each Ø46 mm and 16-mm thick with a 25-mm bore, are added to YP750, one at the top and the other at the bottom. PMID:22081753

  11. Effect of addition of BaTiO3 nano particles on the electrical transport properties of YBCO superconductor

    NASA Astrophysics Data System (ADS)

    Rejith, P. P.; Vidya, S.; Thomas, J. K.

    2015-02-01

    The flux pinning properties of YBCO bulk superconductors synthesized by conventional solid state route and are added with different weight% (x=0, 0.5, 1, 2, 3, 5) of nano BaTiO3 which are prepared by a modified combustion route are studied systematically. The phase analysis of the samples was done by using X-ray diffraction and scanning electron microscopy. Temperature-resistivity measurements, magnetic field dependence of critical current density (Jc-B Characteristics) and flux pinning force calculations were done at 77 K. From the SEM images the microstructure of the sample showed a relative uniform distribution of the nano-particles within the specimen. We found that, even though the transition temperature (Tc) does not change considerably with the BaTiO3 addition, both the critical current density (Jc) and flux pinning force (Fp) increased systematically up to 2 wt% BaTiO3 in the composite, in the presence of magnetic field ranging between 0 and 0.6 T. The Jc value in 2 wt% BaTiO3 added sample showed at least 250% larger than that of the pure YBCO. Also the flux pinning force calculated for the 2 wt% BaTiO3 added is found to be enhanced more than 9 times that of pure YBCO. These observations suggest that the BaTiO3 addition to the Y-123- compounds improve the electrical connection between superconducting grains to result in the increase in Jc.

  12. Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} thin films on polycrystalline ferrite for magnetically tunable microwave components

    SciTech Connect

    Jia, Q.X.; Findikoglu, A.T.; Arendt, P.; Foltyn, S.R.; Roper, J.M.; Groves, J.R.; Coulter, J.Y.; Li, Y.Q.; Dionne, G.F.

    1998-04-01

    Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) thin films with a surface resistance of 0.86 m{Omega} at 10 GHz and 76 K have been grown on polycrystalline ferrite yttrium iron garnet (YIG) substrates. The chemical and structural mismatches between YBCO and YIG are solved by using a double buffer layer of biaxially oriented yttria-stabilized zirconia (YSZ) and CeO{sub 2}, where YSZ is deposited by an ion-beam-assisted-deposition technique. The YBCO films are {ital c} axis oriented with an in-plane mosaic spread [full width at half maximum of an x-ray {phi}-scan on (103) reflection] of less than 8{degree}. The films have a superconductive transition temperature above 88 K with a transition width less than 0.3 K, giving a critical current density above 10{sup 6}A/cm{sup 2} in self field at 75 K. At 75 K in an external magnetic field of 1 T perpendicular to the film surface, the films maintain a critical current density over 2{times}10{sup 5}A/cm{sup 2}. {copyright} {ital 1998 American Institute of Physics.}

  13. Investigation on F R(LT) - F R(HT) phase transition and pyroelectric properties of pulsed laser deposited Pb(Zr 0.93 Ti 0.07 )O 3 thin films

    NASA Astrophysics Data System (ADS)

    Zeng, Hui; Wu, Ping; Zhang, Peng; Dong, Daxing

    2011-09-01

    The preparation process, crystallinity and electrical properties of pulse laser deposited Pb(Zr xTi 1-x)O 3 (PZT) thin films were investigated in this paper. PZT ( x = 0.93) thin film samples deposited at different substrate temperatures were prepared. Si (1 1 0) was the substrate; Ag and YBCO were the top electrode and the bottom electrode respectively. The bottom electrode YBCO was deposited on the Si substrate by pulsed laser deposition (PLD), and then PZT was epitaxially deposited on YBCO also by PLD. After annealing, the top electrode Ag was prepared on PZT by thermal evaporation, and then the Ag/PZT/YBCO/Si structured thin films were obtained. The XRD and the analysis of their electrical characters showed that, when the substrate temperature was elevated from 600 °C to 800 °C, the crystallinity and electrical properties of PZT thin films became better and better, and the FR(LT)- FR(HT) phase transition of PZT ( x = 0.93) thin films occurred at 62 °C. The PZT film deposited at 800 °C had the best pyroelectric properties, and when the FR(LT)- FR(HT) phase transition of this film occurred, the peak value of pyroelectric coefficient ( p) was obtained, with a value of 1.96 × 10 -6 C/(cm 2 K). The PZT film deposited at 800 °C had the highest remnant polarization ( Pr) and the lowest coercive field ( Ec), with the values of 34.3 μC/cm 2 and 41.7 kV/cm respectively.

  14. Thin film preparation of semiconducting iron pyrite

    NASA Astrophysics Data System (ADS)

    Smestad, Greg P.; Ennaoui, Ahmed; Fiechter, Sebastian; Hofmann, Wolfgang; Tributsch, Helmut; Kautek, Wolfgang

    1990-08-01

    Pyrite (Fe52) has been investigated as a promising new absorber material for thin film solar cell applications because of its high optical absorption coefficient of 1OL cm1, and its bandgap of 0.9 to 1.0 eV. Thin layers have been prepared by Metal Organic Chemical Vapor Deposition, MOCVD, Chemical Spray Pyrolysis, CSP, Chemical Vapor Transport, CVT, and Sulfurization of Iron Oxide films, 510. It is postulated that for the material FeS2, if x is not zero, a high point defect concentration results from replacing 2 dipoles by single S atoms. This causes the observed photovoltages and solar conversion efficiencies to be lower than expected. Using the Fe-O-S ternary phase diagram and the related activity plots, a thermodynamic understanding is formulated for the resulting composition of each of these types of films. It is found that by operating in the oxide portion of the phase diagram, the resulting oxidation state favors pyrite formation over FeS. By proper orientation of the grains relative to the film surface, and by control of pinholes and stoichiometry, an efficient thin film photovolatic solar cell material could be achieved.

  15. Flux pinning by a-axis grains in c-axis-oriented Y-Ba-Cu-O films

    NASA Astrophysics Data System (ADS)

    Fuke, H.; Yoshino, H.; Yamazaki, M.; Thanh, T. D.; Nakamura, S.; Ando, K.; Kobayashi, Y.

    1992-05-01

    The relationship between the microstructures and pinning forces is investigated by measuring the magnetic-field dependence and angular dependence of Jc in several kinds of YBCO thin films having different microstructures. A high-Jc value was kept even when the magnetic field was applied perpendicular to the film plane in the case of a c-axis-oriented film which was studded with a-axis-oriented grains. The boundaries between the a-axis-oriented grain and the c-axis-oriented grain are considered to be effective as pinning centers.

  16. MOCVD of GaAs in a horizontal reactor - Modeling and growth

    NASA Technical Reports Server (NTRS)

    Clark, Ivan O.; Fox, Bradley A.; Jesser, William A.; Black, Linda R.

    1991-01-01

    A two-dimensional model for metalorganic chemical vapor deposition of GaAs in a horizontal reactor is presented. The model is characterized by the following parameters: reactor geometry and operating pressure, thermal boundary conditions, ratio of reactants, chemical reactions, total inlet gas flow rate, as well as molecular weights, thermal conductivities, heat capacities, viscosities, and binary diffusion coefficients of the gas-phase species. Film thickness profiles predicted by the model are compared with those of GaAs thin films grown in the modeled reactor. Results obtained show a good agreement between the predictions and data over the entire length of the deposition region for the low pressure and high flow rate run. Attention is also given to the reactor design and growth conditions.

  17. Atomic layer epitaxy of superconducting oxides and heterostructures. Final report

    SciTech Connect

    Chang, R.P.; Marks, T.J.

    1998-06-30

    This project focuses on optimizing/understanding the growth and properties of YBCO, TBCCO, and lattice-matched dielectric films as well as YBCO superlattices by MOCVD and POMBE. Emphasis is on bulk film properties as well as film growth, interface evolution, and in situ studies of film growth processes. The objective of this program is to create via novel means and to understand the properties of interfacial growth regions between films of high-temperature superconducting (HTS) materials and insulating metal oxides. Improving the nature of such interfaces is a crucial barrier which must be surmounted before HTS materials can be successfully incorporated on a large scale into a myriad of advanced active and passive electronic device technologies. In addition, low melting-point advanced precursors are to be designed and synthesized for large scale HTS production. Studies of vapor transport properties and stabilities are carried out to assure that these precursors are of HTS manufacturing quality.

  18. Epitaxial YBa2Cu3O7-x nanocomposite thin films from colloidal solutions

    NASA Astrophysics Data System (ADS)

    Cayado, P.; De Keukeleere, K.; Garzón, A.; Perez-Mirabet, L.; Meledin, A.; De Roo, J.; Vallés, F.; Mundet, B.; Rijckaert, H.; Pollefeyt, G.; Coll, M.; Ricart, S.; Palau, A.; Gázquez, J.; Ros, J.; Van Tendeloo, G.; Van Driessche, I.; Puig, T.; Obradors, X.

    2015-12-01

    A methodology of general validity to prepare epitaxial nanocomposite films based on the use of colloidal solutions containing different crystalline preformed oxide nanoparticles (ex situ nanocomposites) is reported. The trifluoroacetate (TFA) metal-organic chemical solution deposition route is used with alcoholic solvents to grow epitaxial YBa2Cu3O7 (YBCO) films. For this reason stabilizing oxide nanoparticles in polar solvents is a challenging goal. We have used scalable nanoparticle synthetic methodologies such as thermal and microwave-assisted solvothermal techniques to prepare CeO2 and ZrO2 nanoparticles. We show that stable and homogeneous colloidal solutions with these nanoparticles can be reached using benzyl alcohol, triethyleneglycol, nonanoic acid, trifluoroacetic acid or decanoic acid as protecting ligands, thereby allowing subsequent mixing with alcoholic TFA solutions. An elaborate YBCO film growth analysis of these nanocomposites allows the identification of the different relevant growth phenomena, e.g. nanoparticles pushing towards the film surface, nanoparticle reactivity, coarsening and nanoparticle accumulation at the substrate interface. Upon mitigation of these effects, YBCO nanocomposite films with high self-field critical currents (J c ˜ 3-4 MA cm-2 at 77 K) were reached, indicating no current limitation effects associated with epitaxy perturbation, while smoothed magnetic field dependences of the critical currents at high magnetic fields and decreased effective anisotropic pinning behavior confirm the effectiveness of the novel developed approach to enhance vortex pinning. In conclusion, a novel low cost solution-derived route to high current nanocomposite superconducting films and coated conductors has been developed with very promising features.

  19. A K-band Frequency Agile Microstrip Bandpass Filter using a Thin Film HTS/Ferroelectric/dielectric Multilayer Configuration

    NASA Technical Reports Server (NTRS)

    Subramanyam, Guru; VanKeuls, Fred; Miranda, Felix A.

    1998-01-01

    We report on YBa2Cu3O(7-delta) (YBCO) thin film/SrTiO3 (STO) thin film K-band tunable bandpass filters on LaAlO3 (LAO) dielectric substrates. The 2 pole filter has a center frequency of 19 GHz and a 4% bandwidth. Tunability is achieved through the non-linear dc electric field dependence of the relative dielectric constant of STO(epsilon(sub rSTO). A large tunability ((Delta)f/f(sub 0) = (f(sub Vmax) - f(sub 0)/f(sub 0), where f(sub 0) is the center frequency of the filter at no bias and f(sub Vmax) is the center frequency of the filter at the maximum applied bias) of greater than 10% was obtained in YBCO/STO/LAO microstrip bandpass filters operating below 77 K. A center frequency shift of 2.3 GHz (i.e., a tunability factor of approximately 15%) was obtained at a 400 V bipolar dc bias, and 30 K, with minimal degradation in the insertion loss of the filter. This paper addresses design, fabrication and testing of tunable filters based on STO ferroelectric thin films. The performance of the YBCO/STO/LAO filters is compared to that of gold/STO/LAO counterparts.

  20. Effects of self-assembled gold nanoparticles on YBa2Cu3O7-δ thin films and devices

    NASA Astrophysics Data System (ADS)

    Michalowski, P.; Katzer, C.; Schmidl, F.; Seidel, P.

    2012-11-01

    In our work we prepared YBa2Cu3O7-δ (YBCO) thin films with self-assembled gold nanoparticles on SrTiO3 (STO) substrates. We carried out different experiments to determine the effects on the crystallographic properties of the YBCO matrix as well as of the gold nanoparticles. Furthermore, we investigated how the particles influence the superconducting parameters of the film, e.g. the critical temperature TC and the critical current density jC. To ascertain jC we employed magneto-optical Faraday microscopy. In addition, the YBCO film was deposited and structured on STO bi-crystal substrates, thus producing grain boundary Josephson junctions. We studied those junctions with respect to the normal state resistance RN, and the dependence of the critical current IC on the temperature T as well as on the magnetic flux Φ. Finally, we prepared direct current superconducting quantum interference device (dc-SQUID) gradiometers and embedded gold nanoparticles at well-defined areas such as only the antenna or the SQUID region. We measured the flux noise in a shielded environment using an ac-bias reversal technique and compared it with that of sensors without gold nanoparticles. Thus, we demonstrate a new preparation method and an innovative application of gold nanoparticles.

  1. Orientation of embedded Y2BaCuO5 particles within the YBa2Cu3Ox matrix in melt-textured YBCO superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.; Mücklich, F.; Murakami, M.

    2005-03-01

    Automated electron backscatter diffraction (EBSD) was employed to study the local orientations of embedded Y2BaCuO5 (Y-211) particles within the YBa2Cu3Ox (Y-123) superconducting matrix of large grain, melt-textured Y-Ba-Cu-O (YBCO) samples. High-quality Kikuchi patterns were obtained, enabling automated mapping of the individual crystal orientations and a two-phase analysis of the samples. Investigations were performed on a variety of melt-textured YBCO samples, including samples with different element additions. We observe from the maps that the embedded Y-211 particles do not have any preferred orientation in melt-textured YBCO with (001) orientation, and that the YBCO growth is not altered for certain orientations of the Y-211 particles. In samples with (100) orientation, on the other hand, we observe only a small misorientation within the YBCO matrix, and the embedded Y-211 particles do not exhibit any texture. We can conclude from the EBSD maps obtained that the formation of small Y-211 particles does not disturb the Y-123 matrix growth, whereas the presence of large Y-211 particles leads, significantly, to the formation of subgrains.

  2. Evaluation of the invasion heat for the HTS current lead using YBCO

    NASA Astrophysics Data System (ADS)

    Endoh, R.; Kato, H.; Izumi, T.; Shiohara, Y.

    2003-10-01

    Current leads using high- TC superconductors (HTS current leads) are one of cryogenic key devices to assemble compact superconducting magnets such as applied for maglev trains etc. It is essential to evaluate effective thermal conductance through a HTS current lead package together with evaluating Joule heat and critical current for efficient design that has high current capacity and low heat invasion. We have designed the 500 A class HTS current lead package using a YBCO rod whose size is ∅ 3 × 30 mm, and developed an apparatus to measure its heat invasion. Temperature drop as a function of heat flow between the two ends of the package was measured by a conventional steady heat flow method. The quantity of heat invasion of the package under typical practical conditions, from 80 K hot end to 20 K cold end, was 163 mW. This value was simulated to the total value of 158 mW by counting contributions of all the component materials.

  3. The effect of disorder on the critical points in the vortex phase diagram of YBCO

    SciTech Connect

    Crabtree, G. W.; Kwok, W. K.; Paulius, L. M.; Petrean, A. M.; Olsson, R. J.; Karapetrov, G.; Tobos, V.; Moulton, W. G.

    2000-01-19

    The effect of line disorder induced by heavy ion irradiation and of point disorder induced by proton and electron irradiation on the upper and lower critical points in the vortex phase diagram of YBCO is presented. The authors find that dilute line disorder induces a Bose glass transition at low fields which is replaced at the lower critical point by first order melting at higher fields. Strong pinning point defects raise the lower critical point, while weak pinning point defects have little or no effect on the lower critical point. The upper critical point is lowered by point disorder, but raised by line disorder. First order melting is suppressed by point disorder in two ways, by lowering of the upper critical point only for weak point pins, or by merging of the upper and lower critical points for strong point pins. The differing responses of the upper and lower critical points to line and point disorder can be understood in a picture of transverse and longitudinal spatial fluctuations.

  4. Voltage-ampere characteristics of YBCO coated conductor under inhomogeneous oscillating magnetic field

    NASA Astrophysics Data System (ADS)

    Geng, J.; Shen, B.; Li, C.; Zhang, H.; Matsuda, K.; Li, J.; Zhang, X.; Coombs, T. A.

    2016-06-01

    Direct current carrying type II superconductors present a dynamic resistance when subjected to an oscillating magnetic field perpendicular to the current direction. If a superconductor is under a homogeneous field with high magnitude, the dynamic resistance value is nearly independent of transport current. Hoffmann and coworkers [Hoffmann et al., IEEE Trans. Appl. Supercond. 21, 1628 (2011)] discovered, however, flux pumping effect when a superconducting tape is under an inhomogeneous field orthogonal to the tape surface generated by rotating magnets. Following their work, we report the whole Voltage-Ampere (V-I) curves of an YBCO coated conductor under permanent magnets rotating with different frequencies and directions. We discovered that the two curves under opposite rotating directions differ from each other constantly when the transport current is less than the critical current, whereas the difference gradually reduces after the transport current exceeds the critical value. We also find that for different field frequencies, the difference between the two curves decreases faster with lower field frequency. The result indicates that the transport loss is dependent on the relative direction of the transport current and field travelling, which is distinct from traditional dynamic resistance model. The work may be instructive for the design of superconducting motors.

  5. C-axis critical current density of second-generation YBCO tapes.

    SciTech Connect

    Jia, Y.; Hua, J.; Crabtree, G. W.; Kwok, W. K.; Welp, U.; Malozemoff, A. P.; Rupich, M.; Fleshler, S.; Materials Science Division; American Superconductor Corp.

    2010-10-01

    We report on measurements of the temperature and field dependence of the c-axis critical current density (J{sub c}{sup c}) obtained on mesa structures that were patterned into the YBCO layer of second-generation HTS tapes. We find the J{sub c}{sup c}-values of {approx}4 kA cm{sup -2} at 77 K and self-field, corresponding to an unexpectedly high anisotropy in the critical current density J{sub c}{sup ab}/J{sub c}{sup c} of 500-600. C-axis current flow is expected to arise in applications such as the helically wound wires in HTS cables. A simple estimate is given of the fraction of tape width for such a c-axis flow; while in our samples this fraction is approximately 5% for a typical geometry, the fraction will grow linearly with increasing current density anisotropy and could affect the current-carrying ability of the tape.

  6. Progress of 275 kV-3 kA YBCO HTS cable

    NASA Astrophysics Data System (ADS)

    Yagi, M.; Mukoyama, S.; Amemiya, N.; Ishiyama, A.; Wang, X.; Aoki, Y.; Saito, T.; Ohkuma, T.; Maruyama, O.

    2011-11-01

    A 275 kV-3 kA high temperature superconducting (HTS) cable has been developed in the Materials & Power Applications of Coated Conductors (M-PACC) project. AC loss reduction of a two-layer HTS conductor was undertaken by removing the edges of YBCO tapes with low critical current density. The HTS conductor using these tapes was fabricated, and low loss of 0.235 W/m at 3 kA rms was achieved. The 275 kV-3 kA cable was designed, and the 2 m model cables were fabricated. This cable had 325 mm 2 copper stranded former inside the HTS conductor and a 310 mm 2 copper shield layer on the HTS shield layer for over-current protection. These cables withstood an over-current of 63.0 kA for 0.6 s, which is the worst situation for 275 kV systems. The partial discharge (PD) and V- t characteristics of a liquid nitrogen (LN 2)/polypropylene (PP) laminated paper composite insulation system have been integrated into the design of the insulation for the 275 kV cable. The results revealed that the PD inception stress (PDIE) did not depend on the insulation thickness, and that lifetime indices of V- t characteristics at PD inception were as high as about 80-100.

  7. Doubling of the Critical Current Density of 2G-YBCO Coated Conductors through proton irradiation

    NASA Astrophysics Data System (ADS)

    Welp, Ulrich; Jia, Ying; Kwok, Wai-Kwong; Rupich, Marty; Fleshler, Steven; Kayani, Asfghar

    2013-03-01

    We report on magnetization and transport measurements of the critical current density of commercial 2G YBCO coated conductors before and after proton irradiation. The samples were irradiated along the c-axis with 4 MeV protons to a fluence of 1.5x1016 p/cm2. We find that at temperatures below 50 K, proton irradiation increases Jc by a factor of 2 in low fields and increases up to 2.5 in fields of 7 T. At 77 K, proton irradiation is less effective in enhancing the critical current. Doubling of Jc in fields of several Tesla and at temperatures below 50 K will be highly beneficial for applications of coated conductors in rotating machinery, generators and magnet coils. - Work supported by the US DoE-BES funded Energy Frontier Research Center (YJ), and by Department of Energy, Office of Science, Office of Basic Energy Sciences (UW, WKK), under Contract No. DE-AC02-06CH11357.

  8. Size effect of out-of-plane thermal conductivity of epitaxial YBa2Cu3O7-δ thin films at room temperature measured by photothermal radiometry

    NASA Astrophysics Data System (ADS)

    Ikeda, Tatsuya; Ando, Tetsu; Taguchi, Yoshihiro; Nagasaka, Yuji

    2013-05-01

    The out-of-plane (c-axis) thermal conductivities of high-temperature superconducting thin films (YBa2Cu3O7-δ: YBCO) have been measured by photothermal radiometry (PTR) at room temperature. The YBCO samples are in c-axis-aligned epitaxially grown thin films with thicknesses of 250, 500, and 1000 nm. PTR is a noncontact measurement technique for the thermal conductivity and is based on the detection of infrared radiation emitted from a sample heated by a frequency-modulated laser beam. By changing the modulation frequency up to about 1 MHz, the thermal conductivity of thin film can be determined by a curve-fitting analysis of phase-lag data in the frequency domain. The uncertainty of measured thermal conductivity is estimated to be better than ±7%. The experimental results for thermal conductivity exhibit apparently positive film thickness dependence, and their absolute values are less than half of those for single crystal at the smallest thickness. The results indicate a size effect that cannot be explained by the very short phonon mean free path that the kinetic theory predicts. By employing a simple model taking into account phonon boundary scattering, the possible mean free path to interpret the present results is substantially larger than the prediction. The conclusion supports the validity of quite broad spectral distribution of phonons responsible for the thermal conductivity of YBCO.

  9. Cobalt(I) Olefin Complexes: Precursors for Metal-Organic Chemical Vapor Deposition of High Purity Cobalt Metal Thin Films.

    PubMed

    Hamilton, Jeff A; Pugh, Thomas; Johnson, Andrew L; Kingsley, Andrew J; Richards, Stephen P

    2016-07-18

    We report the synthesis and characterization of a family of organometallic cobalt(I) metal precursors based around cyclopentadienyl and diene ligands. The molecular structures of the complexes cyclopentadienyl-cobalt(I) diolefin complexes are described, as determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis and thermal stability studies of the complexes highlighted the isoprene, dimethyl butadiene, and cyclohexadiene derivatives [(C5H5)Co(η(4)-CH2CHC(Me)CH2)] (1), [(C5H5)Co(η(4)-CH2C(Me)C(Me)CH2)] (2), and [(C5H5)Co(η(4)-C6H8)] (4) as possible cobalt metal organic chemical vapor deposition (MOCVD) precursors. Atmospheric pressure MOCVD was employed using precursor 1, to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere (760 torr) of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 325, 350, 375, and 400 °C, respectively, by scanning electron microscopy and atomic force microscopy reveal temperature-dependent growth features. Films grown at these temperatures are continuous, pinhole-free, and can be seen to be composed of hexagonal particles clearly visible in the electron micrograph. Powder X-ray diffraction and X-ray photoelectron spectroscopy all show the films to be highly crystalline, high-purity metallic cobalt. Raman spectroscopy was unable to detect the presence of cobalt silicides at the substrate/thin film interface. PMID:27348614

  10. Optical and X-ray studies of MOCVD-grown InGaN epilayers with low indium concentration

    NASA Astrophysics Data System (ADS)

    Park, Gil; Hwang, Seon-Ju; Shee, Sang-Kee; Sugahara, Tomoya; Lam, Jack; Gainer, Gordon; Song, Jin-Joo; Sakai, S.

    2001-03-01

    Optical and X-ray studies of MOCVD-grown InGaN epilayers with low indium concentration G. H. Park, S. J. Hwang, S. K. Shee, T. Sugahara, J. B. Lam, G. H. Gainer and J. J. Song, Center for Laser and Photonics Research and Department of Physics, Oklahoma State University, Stillwater, OK 74078, USA; S. Sakai, Electrical and Electronic Department, University of Tokushima, Tokushima, Japan. In_xGa_1-xN epilayers with low indium concentration (x < 5%) were grown by low pressure metalorganic chemical vapor deposition on (0001) sapphire. These samples were characterized by optical techniques and high-resolution X-ray diffraction. Photoluminescence (PL) and stimulated emission (SE) were measured. The PL intensity of the InGaN epilayers is much higher than that of GaN, even for very small indium concentrations. The PL peaks show the S-shaped temperature dependence, and the stimulated emission threshold is also temperature dependent. The PL and SE also vary greatly with indium concentration. These observations indicate that the way indium incorporates into GaN varies with In concentration. The structural characteristics will be discussed in light of their possible relation to the optical characteristics. This work is supported by ONR, BMDO, and AFOSR.

  11. Optimization of structural and growth parameters of metamorphic InGaAs/GaAs photoconverters grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Rybalchenko, D. V.; Mintairov, S. A.; Shvarts, M. Z.; Kalyuzhnyy, N. A.

    2016-08-01

    Metamorphic Ga0.76In0.24As heterostructures for PV converters of 1064 nm laser radiation have been grown by the MOCVD. Parameters of the GaInAs metamorphic buffer layer with a stepwise profile of In composition variation were calculated. Its epitaxial growth conditions have been optimized, which allowed improving collection of charge carriers from the n-GaInAs base region and obtaining the photo-response quantum yield of 83% at 1064 nm wavelength. It has been found that, due to discontinuity of valence bands at the In0.24Al0.76As- p/Ga0.76In0.24As-p heterointerface (window/emitter) a potential barrier for holes arises as a result of low carrier concentration in the wide-band-gap material. The use of InAlGaAs solid solution with Al concentration of < 40% has allowed raising the holes concentration in the wide-band-gap window, eliminating completely the potential barrier and reducing the device series resistance. Optimization of the PV converter metamorphic heterostructure has resulted in obtaining 1064 nm laser radiation conversion efficiency at the level of 38.5%.

  12. Monolithic integration of MQW wavelength tunable DBR lasers with external cavity electroabsorption modulators by selective-area MOCVD

    NASA Astrophysics Data System (ADS)

    Lammert, Robert M.; Smith, Gary M.; Hughes, J. S.; Osowski, Mark L.; Jones, A. M.; Coleman, James J.

    1997-01-01

    The design and operation of multiple-quantum well (MQW) wavelength tunable distributed Bragg reflector (DBR) lasers with nonabsorbing gratings and monolithically integrated external cavity electroabsorption modulators fabricated by selective-area metal-organic chemical vapor deposition (MOCVD) are presented. Uncoated devices exhibit cw threshold currents as low as 10.5 mA with slope efficiencies of 0.21 W/A from the laser facet and 0.06 W/A from the modulator facet. After the application of facet coatings, slope efficiencies from the modulator facet increase to 0.14 W/A. Wavelength tuning of 7 nm is obtained by injection current heating of the DBR section. These devices exhibit extinction ratios of 18 dB from the modulator facet at a low modulator bias of 1 V, when measured with a broad-area detector. When coupled to a singlemode fiber, these devices exhibit high extinction ratios of 40 dB at a modulator bias of 1.25 V. Photo-generated current versus optical power plots indicate that the extinction ratios are not limited by carrier build- up in the modulator quantum wells.

  13. Vertically p-n-junctioned GaN nano-wire array diode fabricated on Si(111) using MOCVD.

    PubMed

    Park, Ji-Hyeon; Kim, Min-Hee; Kissinger, Suthan; Lee, Cheul-Ro

    2013-04-01

    We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 10(7) cm(-2). The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute).

  14. Au-catalyzed synthesis and characterisation of phase change Ge-doped Sb-Te nanowires by MOCVD

    NASA Astrophysics Data System (ADS)

    Longo, M.; Stoycheva, T.; Fallica, R.; Wiemer, C.; Lazzarini, L.; Rotunno, E.

    2013-05-01

    The interest in the Ge doped Sb-Te chalcogenide alloy is mainly related to phase change memory applications. In view of phase change device scaling and reduction of programming energy, Sb-Te nanowires (NWs) become an attractive option. In this work, in order to investigate their potential transferability to industrial implementation, the self-assembly of Sb2Te3 NWs and Ge-Sb-Te NWs with Ge content in the range of 1-13% (Ge doping) was studied by coupling the advantages of MOCVD and the Vapour-Liquid-Solid (VLS) mechanism. The results show the structural and compositional gradual changes occurring from pure Sb2Te3 NWs to the previously reported, stoichiometric Ge1Sb2Te4 NWs [[12] M. Longo et al., Nano Lett., 12 (2012) 1509]. The typical diameter of the obtained NWs resulted to be 50 nm, with lengths up to 3 μm. The typology of Au catalyst nanoislands influenced both the NW morphology and the Ge incorporation during the VLS self-assembly; the Ge metalorganic precursor partial pressure affected the NW morphology and their structure. Finally, TEM observations revealed that defect-free, monocrystalline Sb2Te3 and Ge-doped Sb-Te phase change NWs could be obtained.

  15. MOCVD Growth and Optical Characterization of Strain-Induced Quantum Dots with InP Island Stressors

    SciTech Connect

    Hanna, M. C.; Lu, Z. H.; Cahill, A. F.; Heben, M. J.; Nozik, A. J.

    1997-01-01

    Coherent InP islands, grown by low pressure metal organic chemical vapor deposition (MOCVD), were used to produce quantum dots by strain confinement. Lateral confinement of carriers in a GaAs/AlGaAs quantum well located near the surface was obtained from the inhomogeneous strain produced by the InP islands. The evolution of the InP islands on Al0.3Ga0.7As surfaces with increasing InP coverage at different growth temperatures and substrate orientations was studied using atomic force microscopy. Under certain growth conditions, a fairly uniform distribution of coherent InP islands was obtained which had an average apparent diameter of 140 nm with a standard deviation of 12.2 nm and height of 19.5 {+-} 1.1 nm. Lateral confinement depths up to 100 meV were obtained when using the islands as stressors. Photoluminescence from ensembles of the strain-induced dots exhibit peaks, narrow line widths (16 meV) and high efficiency up to room temperature.

  16. Oxygen ion irradiation on AlGaN/GaN heterostructure grown on silicon substrate by MOCVD method

    SciTech Connect

    Ramesh, R.; Arivazhagan, P.; Balaji, M.; Baskar, K.; Asokan, K.

    2015-06-24

    In the present work, we have reported 100 MeV O{sup 7+} ion irradiation with 1×10{sup 12} and 5×10{sup 12} ions/cm{sup 2} fluence on AlGaN/GaN heterostructures grown on silicon substrate by Metal Organic Chemical Vapour Deposition (MOCVD). The Irradiated samples were characterized by High Resolution X-Ray Diffraction (HRXRD), Atomic Force Microscope (AFM) and Photoluminescence (PL). Crystalline quality has been analysed before and after irradiation using HRXRD. Different kinds of morphology are attributed to specific type of dislocations using the existing models available in the literature. A sharp band-edge emission in the as grown samples was observed at ∼3.4 eV in GaN and 3.82 for AlGaN. The band-edge absorption intensity reduced due to irradiation and these results have been discussed in view of the damage created by the incident ions. In general the effect of irradiation induced-damages were analysed as a function of material properties. A possible mechanism responsible for the observations has been discussed.

  17. Reconciling results of MOCVD of a CNT composite with equilibrium thermodynamics

    NASA Astrophysics Data System (ADS)

    Dhar, Sukanya; Arod, Pallavi; Shivashankar, S. A.

    2016-05-01

    Composition and microstructure of the composite films can be tailored by controlling the CVD process parameters if an appropriate model can be suggested for quantitative prediction of growth. This is possible by applying equilibrium thermodynamics. A modification of such standard modeling procedure was required to account for the deposition of a hybrid film comprised of carbon nanotubes (CNTs), metallic iron (Fe0), and magnetite (Fe3O4), a composite useful for energy storage. In contrast with such composite nature of the deposits obtained by inert-ambient CVD using Fe(acac)3 as precursor, equilibrium thermodynamic modeling with standard procedure predicts the deposition of only Fe3C and carbon, without any co-deposition of Fe and Fe3O4. A modification of the procedure comprising chemical reasoning is therefore proposed herein, which predicts simultaneous deposition of FeO1-x, Fe3C, Fe3O4 and C. At high temperatures and in a carbon-rich atmosphere, these convert to Fe3O4, Fe and C, in agreement with experimental CVD. Close quantitative agreement between the modified thermodynamic modeling and experiment validates the reliability of the modified procedure. Understanding of the chemical process through thermodynamic modeling provides potential for control of CVD process parameters to achieve desired hybrid growth.

  18. A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

    NASA Technical Reports Server (NTRS)

    Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor); Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor)

    2004-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  19. High J{sub c} YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} Films via Rapid, Low pO{sub 2} Pyrolysis

    SciTech Connect

    DAWLEY,JEFFREY T.; CLEM,PAUL G.; SIEGAL,MICHAEL P.; OVERMYER,DONALD L.

    2000-09-21

    In this investigation, YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) films were fabricated via a metal acetate, trifluoroacetic acid based sol-gel route, and spin-coat deposited on (100) LaAlO{sub 3} with a focus on maximizing J{sub c}, while minimizing processing time. We demonstrate that the use of a low pO{sub 2} atmosphere during the pyrolysis stage can lead to at least a tetiold reduction in pyrolysis time, compared to a 1 atm. O{sub 2} ambient. High-quality YBCO films on LaAlO{sub 3}, with J{sub c} values up to 3 MA/cm{sup 2} at 77 K, can be routinely crystallized from these rapidly pyrolyzed films.

  20. 1 Tbit/in.2 Very-High-Density Recording in Mass-Productive Polycrystalline Ferroelectric Thin Film Media

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kenjiro; Kawano, Takahiro; Onoe, Atsushi; Tamura, Masahiro; Umeda, Masaru; Toda, Masayuki

    2009-07-01

    We demonstrate very-high-density ferroelectric recording experiments of 1 Tbit/in.2 in polycrystalline Pb(Zr,Ti)O3 (PZT) thin film for the first time. A high-quality polycrystalline PZT thin film was successfully deposited on a silicon substrate with a SrRuO3 (SRO) electrode by metal-organic chemical vapor deposition (MOCVD). The roughness of the PZT film was reduced to less than 1 nm by chemical mechanical polishing (CMP). The PZT film has very high controllability for domain inversion. Our fabrication process also enables high productivity. Therefore, our PZT film has potential to be a mass-productive ferroelectric recording medium for high-density storage systems.

  1. In-plane texturing control of Y-Ba-Cu-O thin films on polycrystalline substrates by ion-beam-modified intermediate buffer layers

    NASA Astrophysics Data System (ADS)

    Iijima, Y.; Onabe, K.; Futaki, N.; Tanabe, N.; Sadakata, N.; Kohno, O.; Ikeno, Y.

    1993-03-01

    Biaxially aligned YBCO thin films were successfully formed on polycrystalline Ni-based alloy by using ion-beam-modified yttria-stabilized-zirconia (YSZ) intermediate layers. YSZ layers were deposited by ion-beam-assisted deposition (IBAD) with concurrent off-axis ion beam bombardment. The YSZ 100-line axis was oriented normal to the substrate, and a YSZ 111-line axis was aligned to the bombarding ion beam axis. Explicit in-plane ordering was achieved on polycrystalline metallic substrates without epitaxial relationships. C-axis-oriented YBCO thin films were grown on those buffer layers, with controlled in-plane a- and b-axes, by pulsed laser deposition. At 77 K, 0 T and at 77 K, 0.6 T, 4.3 x 10 exp 5 A/sq cm and 1.1 x 10 exp 5 A/sq cm were achieved, respectively.

  2. Noise measurements in a composite niobium/YBCO SQUID and determination of the magnetic noise by direct measurement

    SciTech Connect

    Harrop, S.P.; Keene, M.N.; Muirhead, C.M.; Gough, C.E. )

    1991-03-01

    We have measured the noise performance of a composite niobium/YBCO point contact 2-hole SQUID, at 4.2 K in both rf and dc bias modes. The noise was measured by a technique which allowed the component which was flux noise to be measured. The flux noise was found to be the same in both bias modes. A direct measurement of the noise in a single hole in the same sample was made as a function of temperature and was found to display two peaks. Possible causes are discussed in this paper.

  3. Magnetism in EuBCO and YBCO vortex states near and below Tc

    NASA Astrophysics Data System (ADS)

    Schwartz, R.; Browne, M. C.; Boekema, C.

    2012-02-01

    By means of MaxEnt-μSR [1] analysis, we investigate transverse field μSR data [2] of EuBa2Cu3O7-δgEuBCO; Tc = 93 K). Our focus is on a temperature interval near Tc to search for precursor effects, [3] and for predicted [4a] pseudogap loop currents above and below Tc, already observed [4b] above Tc for GdBCO. Further, we continue to study the field-direction dependence of the predicted [5a] and observed [5b] antiferromagnetism (AF) below 0.5Tc for the vortex states in c-axis-oriented YBCO. This AF in and near the vortex cores is likely three-dimensional. In sum, magnetic roots of cuprate superconductivity are well plausible. Research is supported by LANL-DOE, REU-NSF and AFC. [4pt] [1] C Boekema and MC Browne, AIP Conf Proc #1073 (2008) 260.[0pt] [2] DW Cooke et al, Phys Rev B 39 (1989) 2748.[0pt] [3] B Aguilar, C Boekema et al, Bull Am Phys Soc 37 (1992).[0pt] [4a] CM Varma, Phys Rev Lett 83 (1999) 3538.[0pt] [4b] T Songatikamas et al, J Supercond & Novel Magn 23 (2010) 793.[0pt] [5a] S-C Zhang, Science 275 (1997) 1089; H-D Chen et al, Phys Rev B70 (2004) 024516.[0pt] [5b] C. Boekema et al, J Phys Conf Series, 150 (2009) 052022. http://jpcs.iop.org/LT25

  4. Onset of Superconductivity in YBCO in Very High Fields from ^17O and ^63Cu NMR

    NASA Astrophysics Data System (ADS)

    Halperin, William

    2000-03-01

    We have used NMR to study the onset of superconductivity in near optimally doped YBCO in fields from 1 to 27 T. We have compared Knight shift(^17O), spin-spin relaxation measurements(^17O), and spin lattice relaxation measurements (^63Cu and ^17O). The measurements have been performed as a function of temperature above and below the transition region. The Knight shift can be measured with considerable precision directly giving the Pauli spin susceptibility. We show that the onset of superconductivity in a magnetic field is really a crossover region from normal state behavior to a vortex liquid for which we determine a H-T phase diagram up to high field. The relaxation measurements show clear evidence for the opening of a pseudo gap near 100 K in the transition region. The different NMR experiments are sensitive to the susceptibility dependence on wave vector from different regions of the Brillouin zone indicating possible origins of such a gap including superconducting fluctuations or a gap in the spin excitation spectrum. Magnetic field dependence of the data allows discrimination. Intercomparison between samples near optimal doping as well as the work from other laboratories will be made. This work was performed in collaboration with V. F. Mitović, H. N. Bachman, E. E. Sigmund, M. Eschrig, J. A. Sauls, A. P. Reyes, P. Kuhns, and W. G. Moulton. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity. The NHMFL is supported through the NSF and the state of Florida.

  5. 3d xy scaling of the resistivity and the effect of disorder in YBa 2Cu 3O 7-δ thin films

    NASA Astrophysics Data System (ADS)

    Wooldridge, Ian; Howson, Mark A.; Gauzzi, Andrea; Pavuna, Davor; Walker, Daron J. C.

    1994-12-01

    We present measurements for the resistivity of ‘c’ axis oriented YBa 2Cu 3O 7-δ (YBCO) films grown on (100) SrTiO 3 substrates by both Laser Ablation and ion beam sputtering. The effect of the magnetic field on the resistivity is investigated with the field parallel to the ‘c’ axis. The zero field transition widths vary from 1K to 4K in different films. However the data exhibits 3d XY critical scaling having introduced an ‘effective’ magnetic field, characteristic of the length scale of the disorder in the film.

  6. Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Nouhi, Akbar (Inventor); Stirn, Richard J. (Inventor)

    1988-01-01

    A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, in which a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd(sub 1-x)Mn(sub x)Te, in which 0 is less than or equal to x less than or equal to 0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) manganese (TCPMn) is employed. To prevent TCPMn condensation during its introduction into the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, in which the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

  7. Electrodeposited Biaxially Textured CeO2 and CeO2:Sm Buffer Layer for YBCO Superconductor Oxide Films

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Raghu; Phok, Sovannary; Spagnol, Priscila; Chaudhuri, Tapas

    2006-03-01

    Nonvacuum electrodeposition was used to prepare biaxially textured CeO2 and Sm-doped CeO2 coatings on Ni-W substrates. The samples were characterized by X-ray diffraction (including θ/2θ, pole figures, omega scans, and phi scans), atomic force microscopy (AFM), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Full-width at half-maximum values of the ω scan and φ scan of the electrodeposited layers were better than those of the Ni-W base substrates, indicating improved biaxial texturing of the electrodeposited layers.

  8. Mononuclear barium diketonate polyamine adducts. Synthesis, structures, and use in MOCVD of barium titanate

    SciTech Connect

    Gardiner, R.A.; Gordon, D.C.; Stauf, G.T.; Vaartstra, B.A.; Ostrander, R.L.; Rheingold, A.L.

    1994-11-01

    Mononuclear barium {beta}-diketonate Lewis base adducts have been synthesized by reaction of Ba(thd){sub 2} (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) with polyamines 1,1,4,7,7-pentamethyldiethylenetriamine (pmdt) and 1,1,4,7,10,10-hexamethyltriethylenetetramine (hmtt). The adducts [Ba(thd){sub 2}(pmdt)] (I) and [Ba(thd){sub 2}(hmtt)] (II) have been characterized by NMR spectroscopy, elemental analyses and single-crystal X-ray diffraction. Compound I crystallizes in the space group P2{sub 1}/c with a = 10.577(3) {angstrom}, b = 23.547(7) {angstrom}, c = 15.963(5) {angstrom}, {beta} = 105.21(2){degrees}, and Z = 4. Compound II crystallizes in the space group P2{sub 1}/c with a = 10.833(6) {angstrom}, b = 20.442(12) {angstrom}, c = 19.404(9) {angstrom}, {beta} = 104.35(4){degrees}, and Z = 4. The adducts are seven- and eight-coordinate, respectively, with all nitrogen atoms of the polyamine bound to a single barium center. Compound I has been used for thin-film growth of BaTiO{sub 3} which has revealed that, compared to Ba(thd){sub 2}(tetraglyme), the polyamine adduct allows a larger temperature window for effective vapor transport. 10 refs., 2 figs., 2 tabs.

  9. Quantum cascade laser based on GaAs/Al0.45Ga0.55As heteropair grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Zasavitskii, I. I.; Zubov, A. N.; Andreev, A. Yu; Bagaev, T. A.; Gorlachuk, P. V.; Ladugin, M. A.; Padalitsa, A. A.; Lobintsov, A. V.; Sapozhnikov, S. M.; Marmalyuk, A. A.

    2016-05-01

    A pulsed quantum cascade laser emitting in the wavelength range 9.5-9.7 μm at 77.4 K is developed based on the GaAs/Al0.45Ga0.55As heteropair. The laser heterostructure was grown by MOCVD. The threshold current density was 1.8 kA cm-2. The maximum output power of the laser with dimensions of 30 μm × 3 mm and with cleaved mirrors exceeded 200 mW.

  10. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Analysis and finite element simulation of electromagnetic heating in the nitride MOCVD reactor

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Ming; Hao, Yue; Zhang, Jin-Cheng; Xu, Sheng-Rui; Ni, Jin-Yu; Zhou, Xiao-Wei

    2009-11-01

    Electromagnetic field distribution in the vertical metal organic chemical vapour deposition (MOCVD) reactor is simulated by using the finite element method (FEM). The effects of alternating current frequency, intensity, coil turn number and the distance between the coil turns on the distribution of the Joule heat are analysed separately, and their relations to the value of Joule heat are also investigated. The temperature distribution on the susceptor is also obtained. It is observed that the results of the simulation are in good agreement with previous measurements.

  11. Growth and characterization of In{sub X}Ga{sub 1-X}N/GaN single quantum well prepared by MOCVD

    SciTech Connect

    Prabakaran, K.; Ramesh, R.; Jayasakthi, M.; Loganathan, R.; Arivazhagan, P.; Baskar, K.

    2015-06-24

    The InGaN/GaN SQW structures were grown on c-plane sapphire substrate using metal-organic chemical vapor deposition (MOCVD). The thickness and indium composition of the InGaN was determined by HRXRD. From simulation fit the composition of indium was found to be 10% and thickness was around 5nm and 10nm. The Photoluminescence emission was found to be shifited towards lower wavelength as 479nm, 440nm on increasing the thickness. The photoluminescence intensity was degrades with increases of InGaN thickness. Atomic force microscopy studies were also carried out and the results are discussed in detail.

  12. Study of critical current density in superconducting magnesium diboride films grown by ex situ annealing of CVD boron films

    NASA Astrophysics Data System (ADS)

    Hanna, Mina

    MgB2 films have been processed by different techniques, the most successful of which include the hybrid physical-chemical vapor deposition (HPCVD) as well as the ex situ high temperature annealing of boron films in Mg vapor. The advantage of the ex situ method is that it allows the coating of MgB2 on large and complex surfaces, such as superconducting radio frequency (RF) cavities. However, it has always been realized that HPCVD films can carry higher J c than the ex situ annealed films. In this research, we succeeded in fabricating high quality MgB2 films by the ex situ annealing technique that produced a Jc value as high as 1.8 x 106 A/cm 2 for 1 mum thick film at 20 K and self-field. This high Jc value is, however, considerably reduced at higher thicknesses similar to that observed in YBCO coated conductors. In order to understand the mechanisms responsible for J c decrease with increasing film thickness, we studied the Jc behavior as a function of thickness in MgB2 films fabricated by ex situ annealing at 840°C of boron films, grown by chemical vapor deposition, in Mg vapor. The film thickness ranged between 300 nm and 10 mum. The values of Jc for these films ranged from 1.2 x 107 A/cm2 for 300 nm to 1.9 x 105 A/cm2 for 10 mum film thickness at 20 K and self-field. In addition, the results show that critical current (Ic) reaches a maximum value of 728 A/cm width at ˜1 mum thick MgB2 film at 20 K and self-field. These results of Jc and Ic behaviors with higher thickness are interpreted in terms of impurity diffusion during annealing and microstructural degradation for thicker films.

  13. Design of a cryogenic system for a 20m direct current superconducting MgB2 and YBCO power cable

    NASA Astrophysics Data System (ADS)

    Cheadle, Michael J.; Bromberg, Leslie; Jiang, Xiaohua; Glowacki, Bartek; Zeng, Rong; Minervini, Joseph; Brisson, John

    2014-01-01

    The Massachusetts Institute of Technology, the University of Cambridge in the United Kingdom, and Tsinghua University in Beijing, China, are collaborating to design, construct, and test a 20 m, direct current, superconducting MgB2 and YBCO power cable. The cable will be installed in the State Key Laboratory of Power Systems at Tsinghua University in Beijing beginning in 2013. In a previous paper [1], the cryogenic system was briefly discussed, focusing on the cryogenic issues for the superconducting cable. The current paper provides a detailed discussion of the design, construction, and assembly of the cryogenic system and its components. The two-stage system operates at nominally 80 K and 20 K with the primary cryogen being helium gas. The secondary cryogen, liquid nitrogen, is used to cool the warm stage of binary current leads. The helium gas provides cooling to both warm and cold stages of the rigid cryostat housing the MgB2 and YBCO conductors, as well as the terminations of the superconductors at the end of the current leads. A single cryofan drives the helium gas in both stages, which are thermally isolated with a high effectiveness recuperator. Refrigeration for the helium circuit is provided by a Sumitomo RDK415 cryocooler. This paper focuses on the design, construction, and assembly of the cryostat, the recuperator, and the current leads with associated superconducting cable terminations.

  14. Effect of magnetic and nonmagnetic nano metal oxides doping on the critical temperature of a YBCO superconductor

    NASA Astrophysics Data System (ADS)

    Salama, A. H.; El-Hofy, M.; Rammah, Y. S.; Elkhatib, M.

    2015-12-01

    Bulk superconductor samples of YBa2Cu3O7-δ (YBCO) doped with nano metal oxides of Mn3O4, Co3O4, Cr2O3, CuO and SnO2 respectively with 0.2 wt% are synthesized by a solid-state reaction route. The structural characterization of all samples has been carried out by x-ray diffraction (XRD) and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The XRD patterns indicate that the magnetic doping of nano metal oxides ≤ft({{{Mn}}}{{3}}{{{O}}}{{4}}, {{{Co}}}{{3}}{{{O}}}{{4}}, {{{Cr}}}{{2}}{{{O}}}{{3}}\\right) gives a high value of orthorhombicity of the YBCO samples which is the result of high oxygen content, and consequently could give better superconducting properties contrary to the non magnetic nano oxides (CuO, SnO2). The critical temperature (Tc) of the studied samples was found to improve by nano magnetic doping and lower with nano nonmagnetic doping. The superconducting transition temperature Tc determined from electrical resistivity measurements was found to increase for Mn3O4 (5.27 μB) doping and decrease for other metal oxides doping.

  15. X-ray diffraction study of A- plane non-polar InN epilayer grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Moret, Matthieu; Briot, Olivier; Gil, Bernard

    2015-03-01

    Strong polarisation-induced electric fields in C-plane oriented nitrides semiconductor layers reduce the performance of devices. Eliminating the polarization fields can be achieved by growing nitrides along non polar direction. We have grown non polar A-plane oriented InN on R-plane (1‾102) nitridated sapphire substrate by MOCVD. We have studied the structural anisotropy observed in these layers by analyzing High Resolution XRay Diffraction rocking curve (RC) experiments as a function of the in-plane beam orientation. A-plane InN epilayer have a unique epitaxial relationship on R-Plane sapphire and show a strong structural anisotropy. Full width at half maximum (FWHM) of the InN(11‾20) XRD RC values are contained between 44 and 81 Arcmin. FWHM is smaller when the diffraction occurs along the [0001] and the largest FWHM values, of the (11‾20) RC, are obtained when the diffraction occurs along the [1‾100] in-plane direction. Atomic Force Microscopy imaging revealed morphologies with well organized crystallites. The grains are structured along a unique crystallographic orientation of InN, leading to larger domains in this direction. This structural anisotropy can be, in first approximation, attributed to the difference in the domain sizes observed. XRD reciprocal space mappings (RSM) were performed in asymmetrical configuration on (13‾40) and (2‾202) diffraction plane. RSM are measured with a beam orientation corresponding to a maximal and a minimal width of the (11‾20) Rocking curves, respectively. A simple theoretical model is exposed to interpret the RSM. We concluded that the dominant contribution to the anisotropy is due to the scattering coherence length anisotropy present in our samples.

  16. High and low energy proton radiation damage in p/n InP MOCVD solar cells

    NASA Technical Reports Server (NTRS)

    Rybicki, George; Weinberg, Irving; Scheiman, Dave; Vargas-Aburto, Carlos

    1995-01-01

    InP p(+)nn(+) MOCVD solar cells were irradiated with 0.2 MeV and 10 MeV protons to a fluence of 10(exp 13)/sq cm. The degradation of power output, IV behavior, carrier concentration and defect concentration were observed at intermediate points throughout the irradiations. The 0.2 MeV proton irradiated solar cells suffered much greater and more rapid degradation in power output than those irradiated with 10 meV protons. The efficiency losses were accompanied by larger increases in the recombination currents in the 0.2 MeV proton irradiated solar cells. The low energy proton irradiations also had a larger impact on the series resistance of the solar cells. Despite the radiation induced damage, the carrier concentration in the base of the solar cells showed no reduction after 10 MeV or 0.2 MeV proton irradiations and even increased during irradiation with 0.2 MeV protons. In a DLTS study of the irradiated samples, the minority carrier defects H4 and H5 at E(v) + 0.33 and E(v) + 0.52 eV and the majority carrier defects E7 and E10 at E(c)- 0.39 and E(c)-0.74 eV, were observed. The defect introduction rates for the 0.2 MeV proton irradiations were about 20 times higher than for the 10 MeV proton irradiations. The defect E10, observed here after irradiation, has been shown to act as a donor in irradiated n-type InP and may be responsible for obscuring carrier removal. The results of this study are consistent with the much greater damage produced by low energy protons whose limited range causes them to stop in the active region of the solar cell.

  17. Ferroelectric properties of (Ba,Sr)TiO3 thin films grown on YBa2Cu3O7 layers

    NASA Astrophysics Data System (ADS)

    Tao, K.; Hao, Z.; Xu, B.; Chen, B.; Miao, J.; Yang, H.; Zhao, B. R.

    2003-09-01

    Ferroelectric and superconductor bilayers of Ba1-xSrxTiO3(BST)/YBa2Cu3 O7 (YBCO) are grown on (001) SrTiO3 substrates by magnetron sputtering and pulsed laser deposition. The BST thin films exhibit typical ferroelectric behavior in their hysteresis loops. Capacitance-voltage curves are measured. From the capacitance, a dielectric constant of 1250 is obtained. The current-voltage curve is fitted to investigate the mechanism of leakage. The Schottky barrier height at the Ag/BST interface is calculated to be 0.521 eV. The trapped level Et in BST is estimated to be 0.335 eV below the conduction-band edge. An energy band diagram of the Ag/BST/YBCO structure is proposed to explain the experimental results.

  18. Thin films of barium fluoride scintillator deposited by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kirlin, P. S.; Binder, R.; Winn, D. R.; O'Hare, J.; LaPierre, C.; Whitmore, M.

    1990-04-01

    We have used metal-organic chemical vapor deposition (MOCVD) technology to coat optical substrates with thin (˜1-10 μm thick) films of inorganic BaF 2 scintillator. Scanning electron microscope (SEM) photographs indicate that high-quality epitaxial crystalline film growth was achieved, with surface defects typically smaller than optical wavelengths. The scintillation light created by the deposition of ionizing radiation in the scintillating films was measured with a photomultiplier and shown to be similar to bulk melt-grown crystals. The results demonstrate the potential of these composite optical materials for planar and fiber scintillation radiation detectors in high energy and nuclear physics, synchrotron radiation research, and in radiation and X-ray imaging and monitoring.

  19. The effect of Ag diffusion on properties of YBa 2Cu 3O 7- x thin films produced by electron beam deposition techniques

    NASA Astrophysics Data System (ADS)

    Görür, O.; Küçükömeroğlu, T.; Terzioğlu, C.; Varilci, A.; Altunbaş, M.

    2005-01-01

    Superconducting YBa 2Cu 3O 7- x thin films were prepared on pure MgO and Ag/MgO substrates (without and with Ag buffer layer) using an electron beam evaporation technique. The effects of isothermal annealing temperature and Ag diffusion on the crystalline structure and some superconducting properties were investigated by X-ray diffraction, scanning electron microscopy, critical temperature, critical current density and room temperature resistivity measurements. The optimum annealing conditions causing a high degree of preferential orientation with the c-axis perpendicular to the substrates were found to be the isothermal annealing at 930 °C for 5 h. Annealing of films on Ag/MgO substrates is accompanied by Ag diffusion from the buffer layer into YBCO films. The higher rate of crystallization of the YBCO films, the higher degree of c-axis orientation, the higher dense surface morphology, the increased lattice parameter c (by ≈0.1%), the reduced room temperature resistivity (2-3 times), the slightly enchanced critical temperature ( Tc = 92 K at R = 0) and the critical current density ( Jc = 4.2 × 10 5 A/cm 2 at 77 K) were observed for the Ag-doped films (on Ag/MgO substrates) in comparison with those for the undoped films (on MgO substrates). The temperature dependence of the Ag diffusion coefficient in YBCO films in the range 600-800 °C was described by the relation D = 1.9 × 10 -6 exp(-0.73 eV/kT).

  20. Optical and crystal quality improvement in green emitting InxGa1-xN multi-quantum wells through optimization of MOCVD growth

    NASA Astrophysics Data System (ADS)

    Berkman, Erkan A.; Lee, Soo Min; Ramos, Frank; Tucker, Eric; Arif, Ronald A.; Armour, Eric A.; Papasouliotis, George D.

    2016-02-01

    We report on green-emitting In0.18Ga0.82N/GaN multi-quantum well (MQW) structures over a variety of metalorganic chemical vapor deposition (MOCVD) growth conditions to examine the morphology, optical quality, and micron-scale emission properties. The MOCVD growth parameter space was analyzed utilizing two orthogonal metrics which allows comparing and optimizing growth conditions over a wide range of process parameters: effective gas speed, S*, and effective V/III ratio, V/III*. Optimized growth conditions with high V/III, low gas speed, and slow growth rates resulted in improved crystal quality, PL emission efficiency, and micron-scale wavelength uniformity. One of the main challenges in green MQWs with high Indium content is the formation of Indium inclusion type defects due to the large lattice mismatch combined with the miscibility gap between GaN and InN. An effective way of eliminating Indium inclusions was demonstrated by introducing a small fraction of H2 (2.7%) in the gas composition during the growth of high temperature GaN quantum barriers. In addition, the positive effects of employing an InGaN/GaN superlattice (SL) underlayer to crystal quality and micron-scale emission uniformity was demonstrated, which is of special interest for applications such as micro-LEDs.

  1. Hafnium carbamates and ureates: new class of precursors for low-temperature growth of HfO2 thin films.

    PubMed

    Pothiraja, Ramasamy; Milanov, Andrian P; Barreca, Davide; Gasparotto, Alberto; Becker, Hans-Werner; Winter, Manuela; Fischer, Roland A; Devi, Anjana

    2009-04-21

    Novel volatile compounds of hafnium, namely tetrakis-N,O-dialkylcarbamato hafnium(iv) [Hf((i)PrNC(O)O(i)Pr)(4)] () and tetrakis-N,N,N'-trialkylureato hafnium(iv) [Hf((i)PrNC(O)N-(Me)Et)(4)] (), have been synthesized through the simple insertion reaction of isopropyl isocyanate into hafnium isopropoxide and hafnium ethylmethylamide, respectively; based on the promising thermal properties, compound has been evaluated as a precursor for metalorganic chemical vapor deposition (MOCVD) of HfO(2) thin films, which resulted in the growth of stoichiometric and crystalline layers with a uniform morphology at temperature as low as 250 degrees C.

  2. Preparation of YBa2Cu3O7 - x films and YBa2Cu3O7 - x/Y2O3 multilayers using coevaporation and atomic oxygen

    NASA Astrophysics Data System (ADS)

    Hudner, J.; Östling, M.; Ohlsén, H.; Stolt, L.; Nordblad, P.; Ottosson, M.; Villegier, J.-C.; Moriceau, H.; Weiss, F.; Thomas, O.

    1993-03-01

    Thin layers of YBa2Cu3O7-x (YBCO) deposited on LaAlO3 substrates have been prepared in situ by coevaporation of Y, Ba, and Cu. Incorporation of oxygen was accomplished by an atomic oxygen beam source with high cracking efficiency. The total oxygen flow at the substrate could be kept low enough to permit the use of a quadrupole mass spectrometer for evaporation rate monitoring. Films were strongly c-axis oriented with rocking curve full width at half-maximum values of 0.6°. Transport measurements on patterned films yielded critical current densities of 6×106 A/cm2 at 77 K. The deposition method was demonstrated to be feasible for preparation of Y2O3/YBCO heterostructures.

  3. Processing and properties of lead zirconate titanate thin films on gallium nitride and ruthenium by sol-gel and chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cao, Wei

    The Pb(ZrxTi1-x)O3 (PZT) thin films are potential candidates for ferroelectric random access memory (FeRAM) devices and components for microelectromechanical systems (MEMS). For example, the PZT/GaN system is being explored as RF MEMS devices for insertion in RF communication systems. A reproducible sol-gel process was developed for the deposition of PZT films on wurtzite (0001) GaN/sapphire substrates. The composition, crystallography, and interfacial nanochemistry were evaluated by various characterization techniques. The PZT/GaN heterostructure exhibited a chemically sharp interface with insignificant interdiffusion between PZT and GaN layers. However, PZT in metal -ferroelectric -semiconductor (MFS) configuration showed lower capacitance and asymmetrical polarization hysteresis compared to PZT in metal-ferroelectric-metal configuration. Such a deviation was attributed to the high depolarization field (Edepol) within PZT. To mitigate this issue, a two-pronged approach was used. First, the calculated spatial distribution of the electric field and potential, which stem from all the charge densities within the MFS configuration, demonstrated that by adjusting controllable parameters, one can minimize Edepol and maximize polarization. Second, a robust metal-organic chemical vapor deposition (MOCVD) process was developed to fabricate high quality PZT thin films on GaN. In this experimental approach, phase-pure and highly (111) oriented PZT films were deposited on GaN/sapphire substrates by MOCVD. The orientation relationships of PZT/GaN system were determined using x-ray pole figure and high-resolution transmission electron microscopy (TEM). The nanochemistry of the PZT/GaN interface, studied using analytical TEM, indicated a chemically sharp interface with interdiffusion limited to a region below 5 nm. The properties of MOCVD-PZT on GaN are briefly compared with PZT by sol-gel processing, rf sputtering, and pulsed laser deposition. Additionally, a preliminary study

  4. A new RE + 011 TSIG method for the fabrication of high quality and large size single domain YBCO bulk superconductors

    NASA Astrophysics Data System (ADS)

    Yang, W. M.; Chen, L. P.; Wang, X. J.

    2016-02-01

    High quality single domain YBCO bulk superconductors, 20 mm in diameter, have been fabricated using a new top seeded infiltration and growth method (called the RE + 011 TSIG method), with a new solid phase (Y2O3 + xBaCuO2) instead of the conventional Y2BaCuO5 solid phase, x = 0, 0.5, 1.0, 1.2, 1.5, 1.8, 2.0, 2.5, 3.0. The effects of different BaCuO2 contents x on the growth morphology, microstructure, and levitation force have been investigated. The results show that the levitation force of the YBCO bulks first increases and then decreases with increasing x, and reaches maximum levitation forces of about 49.2 N (77 K, 0.5 T, with the traditional liquid phase of YBa2Cu3O y + 3 BaCuO2 + 2 CuO) and 47 N (77.3 K, 0.5 T, with the new liquid phase of Y2O3 + 10 BaCuO2 + 6 CuO) when x = 1.2, which is much higher than that of the samples fabricated with the conventional solid phases (23 N). The average Y2BaCuO5 particle size is about 1 μm, which is much smaller than the 3.4 μm in the samples prepared with the conventional Y2BaCuO5 solid phase; this means that the flux pinning force of the sample can be improved by using the new solid phase. Based on this method, single domain YBCO bulks 40 mm, 59 mm, and 93 mm in diameter have also been fabricated using the TSIG process with the new solid phases (Y2O3 + 1.2BaCuO2). These results indicate that the new TSIG process developed by our lab is a very important and practical method for the fabrication of low cost, large size, and high quality single domain REBCO bulk superconductors.

  5. A study on the nonlinear microwave electrodynamic response of e-beam evaporated MgB2 superconducting thin films

    NASA Astrophysics Data System (ADS)

    Andreone, A.; Di Gennaro, E.; Lamura, G.; Salluzzo, M.; Purnell, A.; Cohen, L. F.; Hao, L.; Gallop, J.; Cantoni, C.; Paranthaman, M.

    2003-02-01

    We present a study on the temperature and field dependence of the microwave surface impedance Zs in thin films of the superconducting MgB2 compound. Samples were prepared by e-beam evaporation of boron on r-plane sapphire followed by an ex situ annealing in Mg vapour. Critical temperature values range between 26 and 38 K. Surface impedance measurements (Zs = Rs + iXs) were performed from 2 K close to Tc in the microwave region up to 20 GHz via parallel plate or dielectrically loaded resonators in 'symmetric' (two MgB2 films) and asymmetric (an MgB2 film and a commercial YBCO control film) configurations. At high microwave power, frequency domain measurements show a characteristic signature associated with weak links and this appears to be the limiting factor governing the performance of these films.

  6. Structural properties of strained YBa2Cu3O6+x superconducting films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Ariosa, Daniel; Abrecht, M.; Pavuna, Davor; Onellion, Marshall

    2000-09-01

    In YBa2Cu3O6+x compound the tetragonal to orthorhombic transition occurs around x equals 0.3, followed by a continuum variation of lattice parameters. Hence both, the structural and superconducting properties, depend upon the oxygen content in CuO chains. Conversely, the epitaxial stress, exerted by the substrate on YBCO films, modified the lattice parameters influencing the oxygen stability in the chains. The understanding of this mechanism is essential when growing epitaxial films for in- situ photoemission studies as well as for tunneling experiments, since the oxygen stability up to the top surface unit-cell is a central issue. We have studied this effect on c-axis oriented YBCO films grown by laser ablation on (001) STO single crystals. Accurate x-ray diffraction analysis of thick films (t GRT 500 angstrom) indicates the presence of two distinct layers, one strained and the other relaxed. Detailed analysis shows that the relaxed layer is as well oxidized as bulk samples, while the strained one is oxygen deficient. Furthermore, despite an oxygen content of about x equals 0.65, the strained layer is in the tetragonal phase (in bulk, the tetragonal phase exists for x < 0.3). We discuss these results in terms of competition between the chemical pressure induced by oxygen inclusion in the chains, and the uniaxial stress within the film.

  7. Film Reviews.

    ERIC Educational Resources Information Center

    Lance, Larry M.; Atwater, Lynn

    1987-01-01

    Reviews four Human Sexuality films and videos. These are: "Personal Decisions" (Planned Parenthood Federation of America, 1985); "The Touch Film" (Sterling Production, 1986); "Rethinking Rape" (Film Distribution Center, 1985); "Not A Love Story" (National Film Board of Canada, 1981). (AEM)

  8. High and Low Energy Proton Radiation Damage in p/n InP MOCVD Solar Cells

    NASA Technical Reports Server (NTRS)

    Rybicki, George; Weinberg, Irv; Scheiman, Dave; Vargas-Aburto, Carlos; Uribe, Roberto

    1995-01-01

    InP p(+)/n/n(+) solar cells, fabricated by metal organic chemical vapor deposition, (MOCVD) were irradiated with 0.2 MeV and 10 MeV protons to a fluence of 10(exp 13)/sq cm. The power output degradation, IV behavior, carrier concentration and defect concentration were observed at intermediate points throughout the irradiations. The 0.2 MeV proton-irradiated solar cells suffered much greater and more rapid degradation in power output than those irradiated with 10 MeV protons. The efficiency losses were accompanied by larger increases in the recombination currents in the 0.2 MeV proton-irradiated solar cells. The low energy proton irradiations also had a larger impact on the series resistance of the solar cells. Despite the radiation induced damage, the carrier concentration in the base of the solar cells showed no reduction after 10 MeV or 0.2 MeV proton irradiations and even increased during irradiation with 0.2 MeV protons. In a deep level transient spectroscopy (DLTS) study of the irradiated samples, the minority carrier defects H4 and H5 at E(sub v) + 0.33 and E(sub v) + 0.52 eV and the majority carrier defects E7 and El0 at E(sub c) - 0.39 and E(sub c) - 0.74 eV, were observed. The defect introduction rates for the 0.2 MeV proton irradiations were about 20 times higher than for the 10 MeV proton irradiations. The defect El0, observed here after irradiation, has been shown to act as a donor in irradiated n-type InP and may be responsible for obscuring carrier removal. The results of this study are consistent with the much greater damage produced by low energy protons whose limited range causes them to stop in the active region of the solar cell.

  9. A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

    NASA Technical Reports Server (NTRS)

    Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor); Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor)

    2001-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  10. Dependence of levitation force on frequency of an oscillating magnetic levitation field in a bulk YBCO superconductor

    NASA Astrophysics Data System (ADS)

    Carter, Hamilton; Pate, Stephen; Goedecke, George

    2013-02-01

    The dependence of the magnetic field strength required for levitation of a melt textured, single domain YBCO superconductor disk on the frequency of the current generating the levitating magnetic field has been investigated. The magnetic field strength is found to be independent of frequency between 10 and 300 Hz. This required field strength is found to be in good experimental and theoretical agreement with the field strength required to levitate the same superconductor with a non-oscillating magnetic field. Hysteretic losses within the superconductor predicted by Bean’s critical-state model were also calculated. The measured data rules out any significant Bean’s model effects on the required levitation field strength within the measured frequency range.

  11. Isotropic and anisotropic pinning in TFA-grown YBa2Cu3O7 - x films with BaZrO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Palau, A.; Bartolomé, E.; Llordés, A.; Puig, T.; Obradors, X.

    2011-12-01

    YBCO films grown by the trifluoroacetate (TFA) method with increasing number of BaZrO3 (BZO) nanoparticles have been measured by in-field angular transport measurements to investigate changes in the pinning landscape. The isotropic and anisotropic contributions to the critical current density, Jc(H), with the magnetic field applied in H\\parallel c and H\\parallel ab orientation have been determined, allowing us to characterize the population of isotropic and correlated defects along the c axis and ab planes. First, the influence of the YBCO oxygenation process on the formation of different sorts of anisotropic defects in standard films is demonstrated. Next, we show that the addition of non-coherent BZO nanoparticles to the YBCO matrix produces an expansion of the single-vortex pinning regime toward higher fields, due to the presence of isotropic pinning centers. Moreover, by increasing the amount of isotropic defects in the BZO nanocomposites it is possible to extend the region dominated by strong isotropic pinning centers to large magnetic fields and thus enhance the irreversibility line.

  12. Influence of superconductor film composition on adhesion strength of coated conductors

    SciTech Connect

    Kesgin, Ibrahim; Khatri, Narayan; Liu, Yuhao; Delgado, Louis; Galstyan, Eduard; Selvamanickam, Venkat

    2015-11-20

    The effect of high temperature superconductor (HTS) film composition on the adhesion strength of rare- earth barium copper oxide coated conductors (CCs) has been studied. It has been found that the mechanical integrity of the superconductor layer is very susceptible to the defects especially those along the ab plane, probably due to the weak interfaces between the defects and the matrix. Gd and Y in the standard composition were substituted with Sm and the number of in-plane defects was drastically reduced. Consequently, a four-fold increase in adhesion or peeling strength in Sm-based CCs was achieved compared to the standard GdYBCO samples.

  13. Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7-δ coated conductors by RF magnetron sputtering.

    PubMed

    Xu, Da; Liu, Linfei; Xiao, Guina; Li, Yijie

    2013-02-27

    La2Zr2O7 (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa2Cu3O7-x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO2), yttria-stabilized zirconia (YSZ)/CeO2, and CeO2/YSZ/CeO2. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks. The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

  14. The role of thermally and chemically stable composite Y2O3:Al2O3 in the development of YBa2Cu3O7-x films on metal substrates

    NASA Astrophysics Data System (ADS)

    Stan, L.; Tao, B. W.; Holesinger, T. G.; Yang, H.; Feldmann, D. M.; Maiorov, B.; Baily, S. A.; Civale, L.; DePaula, R. F.; Li, Y. R.; Jia, Q. X.

    2010-04-01

    We have developed Y2O3:Al2O3 (YAlO) composites to simplify the architecture of superconducting YBa2Cu3O7-x (YBCO) thick films on polycrystalline metal substrates. By implementing the use of YAlO, we have reduced the total number of non-superconducting layers between the polycrystalline metal substrate and the YBCO film from five (as in the standard architecture used by industry) to three. The YBCO films grown on this simplified platform exhibited an in-plane mosaic spread of less than 4° in full width at half-maximum, correlated pinning centered at \\mathbf {H}\\parallel c , and an α value (the proportionality factor of the critical current density H - α) of around 0.38 over the field range of 0.1-1.0 T. We believe that the excellent structural stability at high temperatures and the exceptional chemical inertness in an oxidizing environment make YAlO a good choice for use in the growth of biaxially oriented MgO and subsequent buffer and superconducting layers.

  15. All chemical solution deposition of textured YBa2Cu3O7-x/Y0.2Ce0.8O2/La2Zr2O7 multilayer films on biaxially textured NiW tape

    NASA Astrophysics Data System (ADS)

    Chen, Yuanqing; Tang, Xinni; Bian, Weibai; Li, Mengjuan; Jiang, Ping; Zhao, Gaoyang

    2015-07-01

    Biaxially textured La2Zr2O7 (LZO) single buffer layer, Y0.2Ce0.8O2 (YCO) single buffer layer, and YCO/LZO bilayer buffer layer are prepared on NiW tapes using chemical solution deposition technique. All the buffer layers are of good in-plane and out-of-plane texture. The introduction of a YCO cap layer on the LZO buffer layer improves the surface quality of the films. YBa2Cu3O7-x (YBCO) films are then prepared on these buffer layers using our recently developed low-fluorine solution route. Purely c-oriented YBCO films with good in-plane and out-of-plane texture are obtained on the YCO/LZO bilayer buffer layers. The YBCO/YCO/LZO/Ni stack prepared using all chemical solution routes shows a high Tc over 90 K, a sharp transition temperature ΔT = 0.8 K, and a Jc of 0.7 MA cm-2(at 77 K, 0T).

  16. Large pinning forces and matching effects in YBa2Cu3O(7-δ) thin films with Ba2Y(Nb/Ta)O6 nano-precipitates.

    PubMed

    Opherden, Lars; Sieger, Max; Pahlke, Patrick; Hühne, Ruben; Schultz, Ludwig; Meledin, Alexander; Van Tendeloo, Gustaaf; Nast, Rainer; Holzapfel, Bernhard; Bianchetti, Marco; MacManus-Driscoll, Judith L; Hänisch, Jens

    2016-02-18

    The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O(7-δ) (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m(3) at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.

  17. Electric-pulse-induced resistive memory effect of PZT buffered perovskite thin film

    NASA Astrophysics Data System (ADS)

    Xing, Zhongwen; Wu, Naijuan; Ignatiev, Alex

    2006-10-01

    A large electric-pulse-induced resistance (EPIR) switching effect has been observed in the lead zirconate titanate (PZT) buffered perovskite thin films, such as Pr0.7Ca0.3MnO3 (PCMO). Such a resistive memory device is comprised of a PCMO epitaxial layer on a c-oriented YBCO bottom electrode layer and a thin PZT buffer layer grown on top of the PCMO layer. A silver top electrode was deposited on the PZT/PCMO/YBCO heterostructure to complete the resistive device fabrication. There are two advantages for the memory properties comparing the PZT buffered device with a non-buffered thin film device. First, the EPIR resistance ratio [defined as (Rmax-RMin)/ RMin] is significantly increased. The other is that the pulse voltage needed to switch the resistive device is reduced from ±10 V to ±3 V in magnitude. These results suggest that PZT-buffered perovskite thin film resistive devices are very promising for memory applications. In addition, an effective tunneling model is developed to explain the EPIR effect. It is found that the tunneling at interfaces plays an important role in the charge transport, which is in good agreement with existing experiments.

  18. Thin Film Multilayer Conductor/Ferroelectric Tunable Microwave Components for Communication Applications

    NASA Technical Reports Server (NTRS)

    Miranda, Felix A.; Romanofsky, Robert R.; VanKeuls, Frederick W.; Mueller, Carl H.; Treece, Randolph E.; Rivkin, Tania V.

    1997-01-01

    High Temperature Superconductor/Ferroelectric (HTS/FE ) thin film multilayered structures deposited onto dielectric substrates are currently being investigated for use in low loss, tunable microwave components for satellite and ground based communications. The main goal for this technology is to achieve maximum tunability while keeping the microwave losses as low as possible, so as to avoid performance degradation when replacing conventional technology (e.g., filters and oscillators) with HTS/FE components. Therefore, for HTS/FE components to be successfully integrated into current working systems, full optimization of the material and electrical properties of the ferroelectric films, without degrading those of the HTS film; is required. Hence, aspects such as the appropriate type of ferroelectric and optimization of the deposition conditions (e.g., deposition temperature) should be carefully considered. The tunability range as well as the microwave losses of the desired varactor (i.e., tunable component) are also dependent on the geometry chosen (e.g., parallel plate capacitor, interdigital capacitor, coplanar waveguide, etc.). In addition, the performance of the circuit is dependent on the location of the varactor in the circuit and the biasing circuitry. In this paper, we will present our results on the study of the SrTiO3/YBa2Cu3O(7-delta)/LaAl03 (STO/YBCO/LAO) and the Ba(x)Sr(1-x)TiO3/YBa2Cu3O(7-delta)/LaAl03(BSTO/YBCO/ILAO) HTS/FE multilayered structures. We have observed that the amount of variation of the dielectric constant upon the application of a dc electric field is closely related to the microstructure of the film. The largest tuning of the STO/YBCO/LAO structure corresponded to single-phased, epitaxial STO films deposited at 800 C and with a thickness of 500 nm. Higher temperatures resulted in interfacial degradation and poor film quality, while lower deposition temperatures resulted in films with lower dielectric constants, lower tunabilities, and

  19. Terahertz emission from YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films via bulk electric quadrupole optical rectification

    SciTech Connect

    Siders, J.L.W.; Trugman, S.A.; Houlton, R.J.; Garzon, F.H.; Taylor, A.J.

    1998-03-01

    The authors describe here the first observation of terahertz emission from unbiased YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) thin films. These films are excited by 150 fs, 1.5 eV and 3.0 eV, optical pulses for a range of temperatures, T, 4 K < T < 300 K and for a range of oxygen doping from optimally-doped ({delta} = 0) to insulating ({delta} = 0.8). They demonstrate that this emission is generated by optical rectification due to the bulk electric quadrupole source term, comprising the first observation of such a source term in terahertz emission.

  20. Orientation-dependent critical currents in Y sub 1 Ba sub 2 Cu sub 3 O sub 7-x epitaxial thin films: Evidence for intrinsic flux pinning

    SciTech Connect

    Christen, D.K.; Klabunde, C.E.; Feenstra, R.; Lowndes, D.H.; Norton, D.P.; Budai, J.D.; Kerchner, H.R.; Thompson, J.R.; Zhu, S. ); Marwick, A.D. )

    1990-01-01

    For YBCO epitaxial thin films the basal plane transport critical current density J{sub c}, flowing perpendicular to an applied magnetic field H, depends sensitively on the orientation of the crystal with respect to H. In particular, J{sub c} is sharply peaked and greatly enhanced when H is precisely parallel to the copper-oxygen planes. Experiments on a series of epitaxial monolithic and superconductor-insulator multilayer thin films provide clear evidence that the enhancement is a bulk, rather than surface or thin sample, phenomenon. Measurements of the orientation dependence are presented and compared with a model of intrinsic flux pinning'' by the layered crystal structure.

  1. High-resolution emission spectroscopy of random lasing in GaN films pumped by UV-pulsed laser

    NASA Astrophysics Data System (ADS)

    Cachoncinlle, C.; Millon, E.; Petit, A.

    2016-06-01

    We report on room temperature photoluminescence on GaN films grown by metal organic chemical vapor deposition (MOCVD). A NdYAG pulsed-laser at 266 nm illuminates the films. Two components, at 363 nm and 370 nm, are identified in the near band edge structure on the spectra. A laser threshold of 700±150 kW cm-2 is evidenced and corresponds to random lasing in the GaN film. A drastic narrowing of the spectral bandwidth from 5.2 to 1.8 nm is observed at 370 nm. High-resolution spectroscopy measurements show laser mode widths thinner than 50 pm leading to a high quality factor Q=7750. Low-resolution measurements show redshift from 370.0 to 373.1 nm for one component and from 363.1 nm to 363.9 nm for the other. Interpretation of this redshift is discussed.

  2. Grain orientations and distribution of Y2Ba4CuUOx phase in melt-textured YBCO with addition of depleted uranium oxide studied by EBSD

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Mücklich, F.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.; Murakami, M.

    2006-07-01

    The local grain orientations and the distribution of Y2Ba4CuUOx (U-2411) phase are measured within melt-textured YBCO samples by means of electron backscatter diffraction (EBSD). In this work, several samples with varying addition (0.1-0.8 wt%) of depleted uranium oxide (DU) were analysed by means of EBSD. The embedded U-2411 particles were found to have sizes around 200 nm, some large particles being present in the samples with a high DU concentration. Combined EBSD and EDX analysis enabled the identification of the Kikuchi patterns of the U-2411 phase, so that a true three-phase EBSD scan (YBCO, Y2BaCuO5 and U-2411) becomes possible.

  3. Magnetic and structural characteristics of multiferroic Fe3O4/(Bi3.25Nd0.65Eu0.10)Ti3O12 composite thin films deposited by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kobune, Masafumi; Furotani, Ryosuke; Fujita, Satoshi; Kikuchi, Kazuki; Kikuchi, Takeyuki; Fujisawa, Hironori; Shimizu, Masaru; Fukumuro, Naoki

    2016-10-01

    Ferromagnetic magnetite (Fe3O4) thin films for magnetoelectric multiferroic applications were deposited on (200) (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT)/(101) Nb:TiO2 substrates by metalorganic chemical vapor deposition (MOCVD) using an iron(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) precursor as the iron source. The BNEuT film utilized as a ferroelectric template material was in the form of freestanding nanoplates with narrow spaces between them. The effects of deposition conditions such as the deposition time and substrate temperature on the magnetic and structural characteristics of the Fe3O4/BNEuT composite films were investigated. All the films consisted of mostly single-phase Fe3O4 with a cubic inverse-spinel structure. When deposition was carried out at temperatures of 400-420 °C, the filling rates of particles introduced into the narrow spaces between the BNEuT nanoplates exhibited high values of 76-89% including the amorphous phase. This suggested that the deposition in this temperature range made progress according to the growth mechanism of MOCVD in the surface reaction rate determining state. Room-temperature magnetic moment-magnetic field curves for Fe3O4 thin films deposited at 400-500 °C for 60 min exhibited narrow rectangular hysteresis loops, indicating typical soft magnetic characteristics.

  4. Modified pulse growth and misfit strain release of an AlN heteroepilayer with a Mg-Si codoping pair by MOCVD

    NASA Astrophysics Data System (ADS)

    Majid Soomro, Abdul; Wu, Chenping; Lin, Na; Zheng, Tongchang; Wang, Huachun; Chen, Hangyang; Li, Jinchai; Li, Shuping; Cai, Duanjun; Kang, Junyong

    2016-03-01

    We report the modified pulse growth method together with an alternating introduction of larger-radius impurity (Mg) for the quality improvement and misfit strain release of an AlN epitaxial layer by the metal-organic chemical vapour deposition (MOCVD) method. Various pulse growth methods were employed to control the migration of Al atoms on the substrate surface. The results showed that the pulse time and overlapping of V/III flux is closely related with the enhancement of the 2D and 3D growth mode. In order to reduce the misfit strain between AlN and sapphire, an impurity of larger atomic radius (e.g. Mg) was doped into the AlN lattice to minimize the rigidity of the AlN epilayer. It was found that the codoping of Mg-Si ultrathin layers could significantly minimize the residual strain as well as the density of threading dislocations.

  5. Effect of Al-mole fraction in Al{sub x}Ga{sub 1−x}N grown by MOCVD

    SciTech Connect

    Jayasakthi, M. Ramesh, R. Prabakaran, K. Loganathan, R. Kuppulingam, B. Balaji, M. Arivazhagan, P. Sankaranarayanan, S. Singh, Shubra Baskar, K.

    2014-04-24

    AlGaN/AlN layers were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The Al{sub x}Ga{sub 1−x}N layer composition was varied from 15% to 25%. The crystalline quality, thickness and aluminum (Al) composition of AlGaN were determined using high resolution X-ray diffraction (HRXRD). The growth rate decreases on increasing Al composition. Reciprocal space mapping (RSM) was used to estimate the strain and relaxation between AlGaN and AlN. The optical properties of AlGaN layers were investigated by room temperature Photoluminescence (PL). The AlGaN peak shifts towards lower wavelength with Al composition. The surface morphology of AlGaN was studied by atomic force microscopy (AFM). Root mean square (RMS) roughness values were found to be increased in AlGaN layers with composition.

  6. Effect of particle size on the flux pinning properties of YBa2Cu3O7–δ thin films containing fine Y2O3 nanoprecipitates

    NASA Astrophysics Data System (ADS)

    Yamasaki, H.

    2016-06-01

    The magnetic-field angle dependence of the critical current density, J c(H, θ), was measured at various temperatures in co-evaporated YBa2Cu3O7–δ (YBCO) thin films. The YBCO films showed volcano-shaped J c(θ) peaks around H//ab, and J c(θ) peaks around H//c were not observed. Film A, deposited at a lower temperature than the commercial standard film B, showed lower J c values at high temperatures (T ≥ 60 K) compared with film B, although film A showed higher J c at T = 20 K. Plan-view transmission electron microscope observations revealed that films A and B contained a high density of fine Y2O3 nanoprecipitates. The modes in the distribution of their cross-sectional areas are 10–20 nm2 in film A and 20–30 nm2 in film B. Because of the smaller particle size, film A showed lower J c at high temperatures owing to the smaller elementary pinning force, f p, but showed higher J c at 20 K where the temperature-dependent coherence length ξ ab (T) was short (∼2 nm) and comparable with the radius of Y2O3 nanoparticles. Film A showed anisotropic scaling behavior at T = 70–80 K, and the T dependence of J c followed ∼(1 ‑ T/T c) m (1 + T/T c)2 (m ≈ 2.5), which was expected from a simple flux-pinning model.

  7. The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

    NASA Technical Reports Server (NTRS)

    Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

    1990-01-01

    The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding.

  8. A 5.9 tesla conduction-cooled coil composed of a stack of four single pancakes wound with YBCO wide tapes

    NASA Astrophysics Data System (ADS)

    Iwai, Sadanori; Miyazaki, Hiroshi; Tosaka, Taizo; Tasaki, Kenji; Urata, Masami; Ioka, Shigeru; Ishii, Yusuke

    2013-11-01

    We have been developing a conduction-cooled coil wound with YBCO-coated conductors for HTS applications. Previously, we have fabricated a coil composed of a stack of 12 single pancakes wound with 4 mm-wide YBCO tapes. This coil had a central magnetic field as high as 5.1 T at 10 K under conduction-cooled conditions. In the present study, we fabricated and tested a coil composed of a stack of four single pancakes wound with 12 mm-wide YBCO tapes. The total size of the coil and the Jc value of the tapes were almost the same as those of the former coil. At 77 K, the voltage-current characteristics showed a high n-value of 24, confirming that the coil had no degradation. Furthermore, in a conduction-cooled configuration at 20 K to 60 K, the coil showed a high n-value of over 20. At 20 K, the central magnetic field reached 5.9 T at 903 A, which is 1.3-times higher than that of the former coil.

  9. Aspects of the SrO-CuO-TiO2 Ternary System Related to the Deposition of SrTiO3 and Copper-Doped SrTiO3 Thin-Film Buffer Layers

    SciTech Connect

    A. Ayala

    2004-12-20

    YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) coated conductors are promising materials for large-scale superconductivity applications. One version of a YBCO coated conductor is based on ion beam assisted deposition (IBAD) of magnesium oxide (MgO) onto polycrystalline metal substrates. SrTiO{sub 3} (STO) is often deposited by physical vapor deposition (PVD) methods as a buffer layer between the YBCO and IBAD MgO due to its chemical stability and lattice mismatch of only {approx}1.5% with YBCO. In this work, some aspects of the stability of STO with respect to copper (Cu) and chemical solution deposition of STO on IBAD MgO templates were examined. Solubility limits of Cu in STO were established by processing Cu-doped STO powders by conventional bulk preparation techniques. The maximum solubility of Cu in STO was {approx}1% as determined by transmission electron microscopy (TEM) and Rietveld refinements of x-ray diffraction (XRD) data. XRD analysis, performed in collaboration with NIST, on powder compositions on the STO/SrCuO{sub 2} tie line did not identify any ternary phases. SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer layers were prepared by pulsed laser deposition (PLD) and CSD on IBAD MgO flexible metallic textured tapes. TEM analysis of a {approx}100 nm thick SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. A {approx}600 nm thick YBCO film, deposited onto the SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer by PLD, exhibited a T{sub c} of 87 K and critical current density (J{sub c}) of {approx}1 MA/cm{sup 2}. STO and Cu-doped STO thin films by CSD were {approx}30 nm thick. The in plane alignment (FWHM) after deposition of the STO improved by {approx}1{sup o} while it degraded by {approx}2{sup o} with the SrCu{sub 0.05}TiO{sub y} buffer. YBCO was deposited by PLD on the STO and SrCu{sub 0.05}TiO{sub y} buffers. The in plane alignment (FWHM) of the YBCO with the STO buffer layer slightly improved while that of the

  10. Surface Optimization of RBa2Cu3O7-δ (R=Y, Nd) Epitaxial High Tc Films for In Situ Photoemission Studies

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Schmauder, T.; Ariosa, D.; Touzelet, O.; Rast, S.; Onellion, M.; Pavuna, D.

    One of the intrinsic difficulties for in situ photoemission studies of high Tc oxide films is the surface volatility, especially the oxygen loss. In order to solve this problem, we have constructed a dedicated system for high Tc film surface studies, in particular for ARPES measurements. Here we briefly describe our pulsed laser deposition (PLD) system that is linked to the photoemission chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, and discuss crystallographic and electronic properties measured on epitaxial YBa2Cu3O7-δ (YBCO) and NdBa2Cu3O7-δ (NBCO) films. Resistivity and XRD studies show that the best c axis epitaxial films, with Tc (onset)=92 K (Tc0=90.5 K), are monophase and single crystalline with crystal coherence up to almost 1 µm. Initial core level photoemission study indicates that, for YBCO on SrTiO3 (without any buffer layer), the Ba oxide layer tends to be the dominant surface layer. Further experiments are underway to reproducibly detect sharp Fermi edge and perform ARPES study on optimally doped film surfaces.

  11. A Novel K-Band Tunable Microstrip Bandpass Filter Using a Thin Film HTS/Ferroelectric/ Dielectric Configuration

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; VanKeuls, F.; Miranda, F. A.

    1998-01-01

    We report on YBCO/strontium titanate (STO) thin film K-band tunable bandpass filters on lanthanum aluminate substrates. The 2 pole filters were designed for a center frequency of 19 GHz and 4% bandwidth. Tunability is achieved through the non-linear dc electric field dependence of the relative dielectric constant of STO (epsilon-rSTO). Center frequency shifts greater than 2 GHz were obtained at a 400V bipolar dc bias at temperatures below 77K, with minimum degradation in the insertion loss of the filters.

  12. Growth and properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7−δ}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} epitaxial trilayer films

    SciTech Connect

    Sharma, Minaxi Kumar, Arvind; Sharma, K. K.; Kumar, Ravi; Choudhary, R. J.

    2015-08-28

    We report the growth and properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7−δ}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} LSMO/YBCO/LSMO epitaxial trilayer films, fabricated on SrTiO{sub 3} substrate using pulsed laser deposition technique. From x-ray diffraction and high resolution x-ray diffraction measurements, it is confirmed that the grown trilayered films are single phase and epitaxial in nature. Magneto-transport and magnetic properties are found to be dependent on the thickness of YBCO spacer layer. We infer that for fixed thickness of top and bottom LSMO layers, superconductivity is completely suppressed. At 100 K, the hysteresis loops reveal the ferromagnetic signature of trilayered film. At room temperature, we obtain a butterfly type scenario, signifies the co-existence of ferromagnetic and antiferromagnetic interaction. In addition, at room temperature, the YBCO spacer layer allowing the top and bottom LSMO layers to interact antiferromagnetically.

  13. Characterization of photoluminescent (Y{sub 1{minus}x}Eu{sub x}){sub 2}O{sub 3} thin-films prepared by metallorganic chemical vapor deposition

    SciTech Connect

    McKittrick, J.; Bacalski, C.F.; Hirata, G.A.; Hubbard, K.M.; Pattillo, S.G.; Salazar, K.V.; Trkula, M.

    1998-12-01

    Europium doped yttrium oxide, (Y{sub 1{minus}x}Eu{sub x}){sub 2}O{sub 3}, thin-films were deposited on silicon and sapphire substrates by metallorganic chemical vapor deposition (MOCVD). The films were grown in a MOCVD chamber reacting yttrium and europium tris(2,2,6,6-tetramethyl-3,5,-heptanedionates) precursors in an oxygen atmosphere at low pressures (5 Torr) and low substrate temperatures (500--700 C). The films deposited at 500 C were flat and composed of nanocrystalline regions of cubic Y{sub 2}O{sub 3}, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600 C developed from the flat, nanocrystalline morphology into a plate-like growth morphology oriented in the [111] with increasing deposition time. Monoclinic Y{sub 2}O{sub 3}:Eu{sup 3+} was observed in x-ray diffraction for deposition temperatures {ge}600 C on both (111) Si and (001) sapphire substrates. This was also confirmed by the photoluminescent emission spectra.

  14. Vortex trapping and expulsion in thin-film YBa2Cu3O7-δ strips

    NASA Astrophysics Data System (ADS)

    Kuit, K. H.; Kirtley, J. R.; van der Veur, W.; Molenaar, C. G.; Roesthuis, F. J. G.; Troeman, A. G. P.; Clem, J. R.; Hilgenkamp, H.; Rogalla, H.; Flokstra, J.

    2008-04-01

    A scanning superconducting quantum interference device microscope was used to image vortex trapping as a function of the magnetic induction during cooling in thin-film YBa2Cu3O7-δ (YBCO) strips for strip widths W from 2 to 50μm . We found that vortices were excluded from the strips when the induction Ba was below a critical induction Bc . We present a simple model for the vortex exclusion process which takes into account the vortex-antivortex pair production energy as well as the vortex Meissner and self-energies. This model predicts that the real density n of trapped vortices is given by n=(Ba-BK)/Φ0 with BK=1.65Φ0/W2 and Φ0=h/2e the superconducting flux quantum. This prediction is in good agreement with our experiments on YBCO, as well as with previous experiments on thin-film strips of niobium. We also report on the positions of the trapped vortices. We found that at low densities the vortices were trapped in a single row near the centers of the strips, with the relative intervortex spacing distribution width decreasing as the vortex density increased, a sign of longitudinal ordering. The critical induction for two rows forming in the 35μm wide strip was (2.89+1.91-0.93)Bc , consistent with a numerical prediction.

  15. Superconductor-Mediated Modification of Gravity? AC Motor Experiments with Bulk YBCO Disks in Rotating Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Noever, David A.; Koczor, Ronald J.; Roberson, Rick

    1998-01-01

    We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.

  16. Change in fatigue property and its relation to critical current for YBCO coated conductor with additional Cu layer

    NASA Astrophysics Data System (ADS)

    Yoshida, Y.; Hojo, M.; Sugano, M.; Adachi, T.; Inoue, Y.; Shikimachi, K.; Hirano, N.; Nagaya, S.

    2009-10-01

    YBa 2Cu 3O 7-δ, (YBCO) coated conductors with an additional Cu layer are expected to be applied as coils used in superconducting magnetic energy storage, SMES. In the operation of SMES, large cyclic hoop stress is applied to the coated conductor in the longitudinal direction. In the present study, we carried out fatigue tests in liquid nitrogen, LN 2, and measured the critical current, I c, after a specific number of fatigue cycles to clarify its fatigue fracture mechanism. All fatigue tests were carried out under a stress ratio (the ratio of the minimum to maximum load) of 0.5. The frequency of stress cycling was 30 Hz. Our results showed that the addition of a Cu layer increased the fatigue strength after 10 6 cycles, F, by about 19%. Decrease of I c was more than 30% of the initial critical current, I c0, without loading at the point of final overall fracture when the maximum load in the stress cycles was close to that corresponding to irreversible strain. Furthermore, microscopic observation and the change in I c showed that fatigue fracture mainly initiated from the Hastelloy C-276 substrate. Fatigue fracture also initiated from the Cu layer, but only when the maximum load was approximately F.

  17. Improvement of thermal stability of nickel silicide film using NH3 plasma treatment

    NASA Astrophysics Data System (ADS)

    Park, Jingyu; Jeon, Heeyoung; Kim, Hyunjung; Jang, Woochool; Kim, Jinho; Kang, Chunho; Yuh, Junhan; Jeon, Hyeongtag

    2014-09-01

    In this study, the effects of NH3 plasma pre-treatment on the characteristics of NiSi films were investigated. Nickel film was deposited on a Si(100) substrate by meal-organic chemical vapor deposition (MOCVD) using Ni(iPr-DAD)2 as a Ni precursor and NH3 gas as a reactant. Before the Ni deposition, silicon substrate was treated by NH3 plasma with various flow rates to adjust the amount of inserted hydrogen and nitrogen atoms. The Ni films showed a considerable low sheet resistance around 12 Ω/□, irrespective of the NH3 plasma pre-treatment conditions. The sheet resistance of the all Ni films was decreased after annealing at 500 °C due to formation of a low resistive NiSi phase. NiSi films with a high flow rate of NH3 plasma pre-treatment exhibited a lower sheet resistance and smoother interface between NiSi and the Si substrate than the low flow rate of the NH3 plasma pre-treated NiSi films because lots of nitrogen atoms incorporated at grain boundary of NiSi which result in reduce total surface/interface energy of NiSi and enhancement interface characteristics.

  18. Method for the preparation of protective coatings by low-temperature metal--organic chemical vapor deposition (MOCVD)

    SciTech Connect

    Kaloyeros, A.E.; Williams, W.S.; Constant, G.

    1988-07-01

    A simple and effective method is reported for the deposition of protective coatings of titanium carbide using low-temperature (as low as 150 /sup 0/C) metal--organic chemical vapor deposition. This method is based on the thermolysis of metal--organic molecules containing titanium and does not require the high temperature (<1100 /sup 0/C) involved in the standard TiC--CVD technique. Furthermore, the structure of the films produced (crystalline or amorphous) and their purity (inclusion of organic clusters or hydrogen) can be tailored easily by simple variations in the deposition parameters. This technique permits the coating of polymers and low-melting metals that are thermally too fragile for other deposition techniques. The process could be applied to produce films of other materials, e.g., niobium carbide, silicon carbide, titanium diboride, and gallium arsenide.

  19. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Curvature Correction of FWHM in the X-Ray Rocking Curve of Bent Heteroepitaxial Films

    NASA Astrophysics Data System (ADS)

    Wang, Liang-Ji; Zhang, Shu-Ming; Wang, Yu-Tian; Jiang, De-Sheng; Zhu, Jian-Jun; Zhao, De-Gang; Liu, Zong-Shun; Wang, Hui; Shi, Yong-Sheng; Wang, Hai; Liu, Su-Ying; Yang, Hui

    2009-07-01

    A method for accurate determination of the curvature radius of semiconductor thin films is proposed. The curvature-induced broadening of the x-ray rocking curve (XRC) of a heteroepitaxially grown layer can be determined if the dependence of the full width at half maximum (FWHM) of XRC is measured as a function of the width of incident x-ray beam. It is found that the curvature radii of two GaN films grown on a sapphire wafer are different when they are grown under similar MOCVD conditions but have different values of layer thickness. At the same time, the dislocation-induced broadening of XRC and thus the dislocation density of the epitaxial film can be well calculated after the curvature correction.

  20. Epitaxial Deposition of Low-Defect Aluminum Nitride and Aluminum Gallium Nitride Films

    NASA Astrophysics Data System (ADS)

    Jain, Rakesh

    The bjective of my research was to develop low-defect AlN and AlGaN templates to enable pseudo-homoepitaxial deposition of UV-LEDs. Two approaches have been used to achieve this objective. Firstly, hydride vapor phase epitaxy (HVPE) process was used to prepare thick AlN films with lower defect density. Interactions of dislocations in thicker films result in their annihilation. Secondly, since thick films grown on sapphire tend to crack beyond a critical thickness (3-5 mum), epitaxial lateral overgrowth (ELOG) approach was employed to eliminate cracking and to further reduce the defect density. The growth technique was switched from HVPE to Metalorganic chemical vapor deposition (MOCVD) due to much improved material quality with the later method. An HVPE growth system was first designed and constructed from ground up [1]. It is a vertical system with a quartz chamber and a resistively heated furnace. AlCl3 and NH3 were used as the precursors. AlCl3 was generated by passing HCl gas (diluted with H2) through Al metal source. A linear relationship between growth rate and HCl flow rate indicated that the growth rate is limited by mass transportation. Growth parameters including temperature, chamber pressure and V/III ratio were optimized to improve the film quality. Thick films of AlN with thicknesses exceeding 25 mum were grown with growth rates as high as 20 mum/hr [2]. AFM study revealed that surface roughness of HVPE grown AlN films strongly depends on the growth rate. The lowest RMS roughness for HVPE grown film was 1.9 nm. These films had typical (002) full-width at half maximum (FWHM) values ranging from 24 -- 400 arcsec, depending on the growth rate of the respective films. The crystalline quality of the films was also found to be deteriorating as the growth rate increased. It is inferred that the growth mode changes from two dimensional to three dimensional at higher growth rates due to reduced adatom migration length. PL spectrum exhibited near-band-edge (NBE