I. Yamaguchi

Effect of substrate material on the crystallinity and epitaxy of Pb(Zr,Ti)O3 thin films

Abstract Pb(Zr,Ti)O3 thin films (Pb:Zr:Ti=1:0.52:0.48) were prepared on various single-crystal substrates via dipping-pyrolysis process by use of metal naphthenates as starting materials. The alignments of these films were examined by X-ray diffraction (XRD) θ–2θ scans and β scans (pole figures). The films grown on Nb-doped SrTiO3, MgO or LaAlO3 showed an epitaxial relationship with substrates after heat treatment at 750°C, while those grown on sapphire and Si wafers exhibited polycrystalline or amorphous characteristics. Epitaxial films on SrTiO3 and LaAlO3 were found to consist of a c-axis oriented tetragonal phase, to minimize the lattice misfit with the substrates. These epitaxial films exhibited very smooth surfaces by SEM and AFM observations. In addition, the fluctuation of in-plane alignment was significantly dependent on the lattice-misfit values.

Preparation of epitaxial V2O3 films on C-, A- and R-planes of α-Al2O3 substrates by coating-pyrolysis process

Abstract Epitaxial films of vanadium(III) oxide V2O3 were prepared on the C-, A-, and R-planes of α-Al2O3 substrates by a coating-pyrolysis process. The final heat treatment was carried out at 1000°C in a precisely controlled gas flow of a CO–CO2 mixture (pCO/pCO2=10−1) at ambient pressure. This condition corresponds to an oxygen partial pressure of ~10−12 atm. The X-ray diffraction θ–2θ scanning and pole-figure analysis showed that the 0.5-μm-thick V2O3 films chiefly comprise the grains grown epitaxially to the substrate surfaces and a small amount of uniaxially oriented crystallites with the c-axis perpendicular to the substrate surfaces. In the films grown on the C- and A-planes of α-Al2O3, epitaxial grains grown 60°-rotated in the basal plane relative to the substrates (or 180° domains) were also present. The occurrence of the uniaxially c-axis-oriented and 180° domains may be attributed to the crystallization from the film surface accompanying the reduction of the precursors, which contain higher-valence vanadium ions, by the CO–CO2 mixed gas, whereas the epitaxial grains grow from the film/substrate interface.

Preparation of Epitaxial YBCO Films by a Novel Excimer-Laser-Assisted MOD

Epitaxial (YBCO) films were prepared on cerium oxide-buffered (40 nm)-cut single-crystal sapphire substrates by a novel excimer-laser-assisted metalorganic deposition (ELAMOD). Laser irradiation after application of a fluorine-free ingredient solution onto the substrates revealed to have the advantages of shorter heating (prefiring and heat-treatment) time and higher superconducting current density . The in excess of 5 was measured by an inductive method at 77.3 K. The laser irradiation is considered to produce a desirable precursor, in which three metal components are well-mixed in short time. The X-ray diffraction measurement of the irradiated area clearly showed a complete -axis oriented YBCO and no impurity phase, whereas -axis oriented YBCO was also observed in the area without irradiation. The ratio of the -axis component decreased with an increase of the laser irradiation.

Preparation of CeO/sub 2/-buffer layers for large-area MOD-YBCO films (10/spl times/30 cm/sup 2/) with high-J/sub c/

Epitaxial cerium oxide (CeO/sub 2/; thickness: 40 nm) buffer layers were deposited on large area (maximum size 10/spl times/30 cm/sup 2/) R-cut single-crystal sapphire (/spl alpha/-Al/sub 2/O/sub 3/) substrates by double electron-beam guns. Substrate heater-and-holder system was modified to maintain the substrate temperature uniform over the large area during deposition. Oxygen gas of a pressure 4/spl times/10/sup -2/ Pa was introduced to keep radio frequency plasma. When the substrate temperature was controlled in the range 640/spl deg/-700/spl deg/C, the CeO/sub 2/ buffer showed a complete [001] orientation and very smooth surfaces by x-ray diffraction analysis and atomic force microscopic observations, respectively, in the whole area of the large size substrates. These buffer layers without post-deposition annealing were quite suitable for preparing YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films by a metal-organic deposition (MOD) using a metal acetylacetonate-based solution. The average critical current density of the 210-nm-thick MOD-YBCO film was in excess of 2.6 MA/cm/sup 2/ measured by an inductive method at 77.3 K.

Epitaxy of (106)-oriented SrBi2Ta2O9 and SrBi2Nb2O9 thin films

Abstract Non- c -axis oriented epitaxial films of bismuth layer-structured ferroelectrics, SrBi 2 Ta 2 O 9 (SBT) and SrBi 2 Nb 2 O 9 (SBN), were prepared on SrTiO 3 (110) by coating-pyrolysis process. These films were found to be (106)-oriented (pseudo-tetragonal indices). Interestingly, this orientation is ‘stealthy’ or unseen in the conventional XRD θ –2 θ scans due to extinction rule so that its presence was revealed by XRD pole-figure measurement and reciprocal-space mapping. The crystallographic relationship of the films and substrates was SBT, SBN (106)∥SrTiO 3 (110) and SBT, SBN [010]∥SrTiO 3 [001]. This epitaxial relationship was also discussed from the standpoint of ion arrangement.

Effects of substrate materials and annealing temperature on crystal structure and epitaxy of La0.7Sr0.3MnO3 films via dipping-pyrolysis process

Abstract Epitaxially grown La 0.7 Sr 0.3 MnO 3 (LSMO) films were prepared on SrTiO 3 (001), LaAlO 3 (001) and MgO(001) single-crystal substrates by dipping-pyrolysis process. The fluctuation of alignments (mosaicity) of the films was evaluated based on X-ray diffraction 2 θ / θ scans, β scans (pole figures) and asymmetric 2 θ / ω scans (reciprocal-space maps). Lattice types and epitaxy were examined in the films after heat treatment at 1473–1873 K; the lattice type of the films on SrTiO 3 was pseudocubic, whereas those on LaAlO 3 and MgO were pseudocubic or rhombohedral, depending on the heat-treatment temperature. A mosaic spread (Δ ω ) of the LSMO film varied with the lattice-mismatch value between film and substrate. The LSMO films on SrTiO 3 (lattice misfit ≈1%) showed high epitaxy with a low Δ ω (≈0.50°), whereas the films on MgO (misfit ≈8%) exhibited a larger Δ ω (≈2.8°). Also, surface morphology of the film was found to markedly depend on the kind of substrate materials and annealing temperature.

Dimpling in critical current density vs. magnetic field angle in YBa2Cu3O7 films irradiated with 3-MeV gold ions

Magnetic-field-angle θ dependence of critical current density Jc was measured in YBa2Cu3O7 films irradiated with 3-MeV gold ions. Such films were recently found to show large pinning force arising from point-like irradiation defects. A dimpled line-shape of Jc(θ) and its variation with magnetic field strength were revealed that could be well described by a simple model based on flux-lattice shear and Blatter scaling. Our results strongly suggest that vortex elasticity and electron-mass anisotropy coordinately produce the characteristic Jc anisotropy, called “shoulders,” in cuprate and iron-pnictide films.

Structural aspect of high-Jc MOD-YBCO films prepared on large area CeO2-buffered YSZ substrates

YBa2Cu3O7 (YBCO) film was prepared by fluorine-free metalorganic deposition (MOD) on a 2-inch-diameter CeO2-buffered yttria-stabilized zirconia (CbYSZ) substrate. The MOD-YBCO films on a flat CbYSZ prepared using a metal acetylacetonate-based coating solution demonstrated high critical current density (Jc), the average being higher than 4 MA/cm2 at 77.3 K and in a self field using an inductive method. The Jc distribution was uniform in the whole area of the MOD-YBCO films on the large size substrates. Cross sectional transmission electron microscopic images of the MOD-YBCO film exhibited a very smooth CeO2/ YSZ and CeO2 buffer layer/ YBCO film interfaces. Both the buffer and the YBCO layers were dense; however, a small amount of (100)-oriented YBCO occurred inside the matrix of (001)-oriented YBCO layers. Also, some distinct dislocations were observed at the CeO2/ YBCO interface. From around the stepped surface of the CeO2 buffer layer there seemed to grow a slightly distorted (001)-oriented YBCO domain, however, the domain restored its (001)-oriented periodicity in the region at some distance above the steps. Such growth mode is considered to correlate the high Jc of the MOD-YBCO film with very small average roughness of CeO2 buffer layer.

Solid-state epitaxy of c-axis-oriented Yb124 films prepared by coating-pyrolysis process

Abstract Epitaxially grown c -axis-oriented and nearly single phase YbBa 2 Cu 4 O 8 (Yb124) films were prepared on SrTiO 3 (001) substrates by coating-pyrolysis process. Based on X-ray diffraction θ –2 θ and β scanning, the film heat-treated at 780°C in flowing O 2 at 1 atm was found to consist of c -axis-oriented Yb124 and a trace amount of c -axis YbBa 2 Cu 3 O 7− y (Yb123). This film showed metallic behaviour in the normal state and sharp superconducting transition at T c, zero =76 K by dc-resistance measurement, and T c, onset =78 K by ac-susceptibility measurement. The Yb124 phase is considered to form through a novel solid-state epitaxy route from the Yb 2 O 3 –BaCO 3 –CuO precursor, accompanying the decomposition of BaCO 3 , at ambient pressure without melt formation.

Microstructure of Epitaxial Y123 Films on

Epitaxial YBa2Cu3O7 (Y123) films have been prepared by fluorine-free metalorganic deposition (MOD) using a metal acetylacetonate-based coating solution on cerium oxide (CeO2: 40 nm)-buffered yttria-stabilized zirconia (CbYSZ) substrates. The 210-nm-thick Y123 film demonstrated a high critical current density (Jc), the average Jc being 4.5 MA/cm2 at 77.3 K using an inductive method. However, with increasing thickness the Jc values decreased; the average Jc was 3.4 and 2.2 MA/cm2 for 400-nm- and 550-nm-thick films, respectively. In low-magnification cross sectional transmission electron microscopy (XTEM) images for the films, the stripe-like contrast due to the c-axis orientation of Y123 was clearly seen from the interface with CeO2 to the surface. The whole c-axis-oriented Y123 layers were very dense even in the 550-nm-thick film. Full width at half maximum (FWHM) of Deltaomega for the 308/038 reflections in XRD omega - 2thetas scanning decreased with increasing film thickness. High resolution XTEM images of the 550-nm-thick film showed wavy c-planes of Y123 due to the short stacking faults near the interface with CeO2 buffer and near the surface whereas the c-planes were very flat but contained long stacking faults in the middle part of the film. It is suggested that the absence of wavy stacking faults, which probably work as pinning centers, decreased Jc in the thicker films. Further decrease in Jc in the 550-nm-thick film is presumably caused by the roughness in the outer layer near the surface.