X-ray diffraction analyses using symmetrical and asymmetrical reflections were performed on YBa2Cu3O7−x films grown in situ by pulsed laser deposition. Monocrystalline (100) oriented SrTiO3, MgO and YSZ were used as substrates. The measurements allowed the calculation of the film lattice parameters and the determination of the film-substrate epitaxial relationships. The in-plane and out-plane film textures were also studied. The critical current density between 17 K and 87 K was measured in narrow strips patterned by a direct writing laser system. A comparative discussion of the results obtained for the transport properties and the structural characteristics was carried out for films grown on MgO.
YBaCuO superconducting thin films have been prepared by sequential evaporation of copper, Y2O3 and BaF2 layers on Si[100] and polycrystalline Al2O3 substrates. Such sequences were evaporated 1, 10 or 30 times on Si[100] with a 0.5 μm ZrO2 buffer layer. The effects of different buffer layers were studied for Al2O3 substrates by means of the deposition of ZrO2, copper, silver and BaTiO3 layers with thicknesses of 20, 100 and 500 nm. The film properties were studied using electrical measurements, scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectrometry and secondary ion mass spectrometry. The best properties were obtained for the obtained on ZrO2/Si[100] with a single evaporation sequence. The studies of the different buffers reveal a strong dependence of the film properties on the nature and thickness of the buffer, with the best results for films deposited on a silver layer.
The microstructure of superconducting YBaCuO thin films grown in situ by magnetron sputtering on mechanically polished (001)MgO was studied by transmission electron microscopy. The main microstructural feature of the films investigated is a number of grain boundaries formed by 90°-misoriented epitaxial domains. The films also contain mirror twins, planar stacking defects, misfit dislocationsand c0 lattice parameter variations. Domains with a and c normal orientations have a rather different microstructure owing to differences in growth mechanisms.
Superconductive YBaCuO films (10–40 μm thick), have been screen-printed on SiO2/Si (obtained by wet and dry methods) and Si3N4SSi from different powders obtained via the auomization method. Experimettal sintering conditions of the powders were adjusted to optimize the physical properties of the films. The resistivity measurements, the X-ray diffraction spectra and the mechanical and microstructural properties of the samples were found to be sensitive to the initial morphology of the powders. However the samples present a zero resistivity, and in most cases above 77 K, with a Tc onset of 95–96 K and a ΔTc varying 3rom 3 to 14. . Analysis of the results shows the good quality of the screen printed films on both SiO2 and Si3N4SSi substrates; the superconducting character is not affected by silicon.
Superconductive multilayered thin films have been deposited by excimer laser ablation and d.c. magnetron sputtering. The laser deposited films were grown on (100) SrTiO3 substrates and consisted of alternating layers of La2−xSrxCuO4 (LSCO) and YBa2Cu3O7−δ (YBCO) while the sputtered films, deposited on (100) MgO substrates, consist of a 3 nm MgO layer sandwiched in 100 nm YBCO layers. Cross-sectional transmission electron microscopy (TEM) specimens have been prepared so as to investigate the different interfaces and the local structure of the films. The results show that the laser deposited films are epitaxially grown with the c-axis normal to the surface. The interfaces are rather sharp but some roughness of the YBCO over LSCO interface, possibly related to the presence of shear defects in the LSCO layers, is evidenced. The observations of the sputtered films reveal the presence of some a-axis oriented YBCO grains and the partial crystallization of the amorphous deposited MgO layer. Some a-axis oriented grains are also observed in the laser deposited films but only in the upper layers. The different types of structural defects as well as the different interfaces, characterized by high resolution electron microscopy (HREM), will be reported.
Y Ba Cu oxide thin films were grown epitaxially on single cryst. yttria-stabilized zirconia substrates by laser deposition. [on SciFinder(R)]
YBCO films were prepared on various single-crystalline substrates, (100)-oriented LaAlO 3 , SrTiO 3 , MgO, randomly oriented Zr(Y)O 2 and r-plane sapphire, by Inverted Cylindrical Magnetron Sputtering (ICMS). The surface morphology was investigated by scanning electron microscopy (SEM). The inductively measured T c values of the films “as prepared” ranged from 87 to 90K. The j c values at 77K of films on (100) LaAlO 3 and SrTiO 3 were 5 · 10 6 and 4 · 10 6 A/cm 2 , respectively. j c of films on r-plane sapphire was 5 · 10 4 A/cm 2 . The surface resistance R s was measured using a 67 GHz resonator made of copper. R s of a 0.4μm thick YBCO film on LaAlO 3 was 17mω at 77K. All the films were highly c-axis textured with small admixtures of a-axis oriented grains. Microstrips of a width down to 2μm were patterned by means of conventional UV-photolithography. The etch step was performed in diluted phosphoric acid or EDTA. Measuring T c of the microstrips as a function of their width, we found that the T c -degradation starts at 8μm using phosphoric acid but not above 2μm using EDTA.
The YBaCuO compound contains two conductive subsystems and as a result displays a two-gap structure. Oxygen ordering affects the value of the smaller gap. Charge transfer leads to an induced superconducting state in the chains. The short coherence length, anisotropy and the presence of different structural units lead to peculiar microwave properties of high T c films. In this paper the authors describe their approach to the theory of high T c films and then focus on the microwave properties of the films.
Epitaxial thin films of YBa2Cu3O7 were grown by evaporation of the metals from electron-guns in the presence of atomic oxygen. The films were characterized structurally by X-ray diffraction and electrically by measurements of d.c. magnetization and flux creep. The progress in device technology is discussed. Results are presented on Josephson junctions, and a superconducting microwave filter with the ground plane grown on the back.
Resistive measurements of the I-V characteristics are carried out on patterned thin films of epitaxially grown, c-axis oriented YBa2Cu3O7. The I-V curve is roughly described by ln(V) proportional to ln(I). The determination of the volume pinning force is based upon different voltage criteria. Although the absolute values of the volume pinning force change with the value of the criteria, the field and temperature dependences are not affected. They agree with a flux-flow mechanism dominated by flux-line shear. Model calculations on the basis of a modified flux-line shear mechanism are carried out, which are in good agreement with the experimentally measured I-V characteristics and the observed field and temperature dependences of the volume pinning force.
(Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ (2223-Bi) thin films, were fabricated on [100] oriented MgO single crystal substrates using the pulsed laser deposition technique. For preparing the films, two different routes were followed. First, insulating amorphous films of Bi-2223 were deposited on the substrates at room temperature. After the annealing procedure of these films at 865 °C, they showed a T c,zero as high as 105K. Second, films were prepared at substrate's heater temperature about 835 °C. The SEM and XRD results indicated the c-axis oriented films. The resistivity results showed the T c,zero between 60K to 70 K on these films, after annealing at 865 C C, the onset of superconducting transition increased to 117 K and T c,zero to 105 K. The annealing procedure and the effect of annealing on the surface quality of the films are discussed.
We have used laser deposition to make two types of NdGaO 3 /YBa 2 Cu 3 O 7-δ multilayer structures. The growth of NdGaO 3 thin films on different substrates was studied and it was shown that the films grow epitaxially only on well lattice matched substrates, such as SrTiO 3 (100) and c-axis oriented YBa 2 Cu 3 O 7-δ films. YBa 2 Cu 3 O 7-δ /NdGaO 3 /YBa 2 Cu 3 O 7-δ trilayers were epitaxially grown and a T c of 86 K was measured for the top and bottom layers. The resistivity of a 300 nm thick NdGaO 3 interlayer was as high as 10 8 ωcm at 300 K. NdGaO 3 /YBa 2 Cu 3 O 7-δ double layers were grown and tested as a complex buffer layer for the YBa 2 Cu 3 O 7-δ growth on sapphire.
YBaCuO (YBCO) based multilayers have been deposited independently by three techniques: laser ablation, inverted cylindrical target sputtering and on-axis planar d.c. magnetron sputtering. The last technique is used to cover uniformly R-plane sapphire and LaAlO3 2 in wafers with YBCO or multilayers to produce optoelectronic devices such as IR detectors. Very thin (about 3 nm) yttria-stabilized zirconia and MgO dielectric films have been studied as tunnel barriers for making such high Tc tunnel junctions.
Defects in superconducting YBaCuO thin films deposited by laser ablation are investigated by high resolution transmission electron microscopy. Micrographs reveal numerous defects in the YBaCuO film, falling into four basic classes. One of these is an interesting, non-stoichiometric helical defect structure which possibly corresponds to a growth-related screw dislocation. In general, defects in the YBaCuO film are associated both with growth geometry and with local deviations in stoichiometry. Substrate surface geometry is seen to have a profound effect on the number and type of defects produced. Simulation of annealing transformations using a static lattice, three dimensional, Monte Carlo technique is carried out to gain further insight into specific defect formation mechanisms. The results of these studies suggest preparation conditions that are expected to lead to films with improved critical current densities. 17 refs., 6 figs.
Li doped Bi-Sr-Ca-Cu-O thin films were deposited on MgO(100) substrates at room temperature using a Nd:YAG laser (λ=1064 nm). The target materials had compositions near Bi 2 Sr 2 Ca 1 Cu 2-x L ix O y (x 2 Sr 2 Ca 1 Cu 2 LiO y and Bi 2 Sr 2 Ca 2 Cu 3 Li 1.5 O y . The structure of the films was studied by x-ray diffraction and SEM/EDS. After annealing at 840 °C — 850 °C, the films consisted mainly of the 2212 phase. These films had T c0 at 83 K — 86 K, 3 to 6 K higher than undoped films prepared under similar conditions. Large amounts of the 2212 phase were obtained even at 740 °C, but these films had T c0 below 80 K. The best films had critical currents exceeding 10 4 A/cm 2 at 77 K. The superconducting phases in the annealed films were strongly oriented with the Cu-O planes parallel with the substrate surface but with no in-plane epitaxy.
