Peter B. Mozhaev

Growth and domain structure of YBa2Cu3Ox thin films and YBa2Cu3Ox/CeO2 heterostructures on tilted NdGaO3 substrates

Abstract Growth, structure and physical properties of YBa2Cu3Ox (YBCO) thin films and YBCO/CeO2 heterostructures on tilted-axes NdGaO3 (NGO) substrates with an inclination of normal of the substrate from the [1xa01xa00] axis were investigated. It was shown that the orientation of epitaxial YBCO thin films is influenced by the deposition rate and the presence of symmetrical-equivalent directions [1xa01xa00] and [1xa0 1 xa00] in the substrate and [1xa00xa00], [0xa01xa00] and [0xa00xa01] in the CeO2 layer. Domain structure and morphology of the YBCO thin film surface change with an increase of the inclination angle. The YBCO thin films on the tilted-axes substrates are twinned of the same way as on (1xa01xa00) NGO substrates. However, formation of one or both twinning complexes is suppressed with an increase of the inclination angle.

Tilted-axes YBCO thin films: from vicinal range to step bunching

Tilted-axes YBCO thin films were deposited on NdGaO3 (NGO) substrates with surface inclination from the standard (110) crystallographic plane. All deposited films were epitaxial with the (001) YBCO plane aligned with the {110} planes of the substrate. Structural and morphological studies revealed three angular ranges of the film formation: a small-angle “vicinal” range, where the films to not differ much from films deposited on (110) NGO; a high-angle range, characterized by “step bunching” during the thin film growth; and an intermediate range, providing very smooth films with the best crystal structure. Differences in film morphology and structure are probably due to an increasing density of seeding centers on the surface of tilted-axes substrate with an increase of inclination angle. The reason for the high-quality film formation in the intermediate range is probable the matching of the density of seeding centers and the diffusion length of the atoms on the surface. This model is corroborated by differences in the intermediate range angles for different deposition techniques. The intermediate range thin films showed also the best electrical properties (Tc, Jc(77 K), Rs(77K, 10 GHz).

Orientation relations and twinning in heterostructures YBa2Cu3OxNdGaO3 and YBa2Cu3OxCeO2Al2O3

Abstract Epitaxial YBa 2 Cu 3 O 7− x (YBCO) thin films on (110) NdGaO 3 and (100) CeO 2 ue643(1 1 02)Al 2 O 3 substrates were studied with X-ray diffraction methods, orientation features of film twinning were determined. Films on both substrates were mainly c -oriented with c =11.67 A. Orthorhombic structure of NdGaO 3 results in increase of the angle between (110) and (1 1 0) twinning planes in YBCO films to 90.20° and in difference in volume of two twin domain systems. About 60% of YBCO film on CeO 2 ue643Al 2 O 3 substrates show no twinning. The lattice direction 〈1 1 02〉 of the Al 2 O 3 substrate and 〈100〉 of the CeO 2 film were inclined by 0.15°; this inclination can result from high lattice mismatch between CeO 2 film and Al 2 O 3 substrate. The 〈001〉 direction of the YBCO film was inclined to 〈1 1 02〉 Al 2 O 3 direction only by 0.06°. The spread of in-substrate-plane misorientation in CeO 2 film of 1.65° was also higher than that of the YBCO film (1.22°).

Bi-epitaxial YBa2Cu3Ox Thin Films on Tilted-axes NdGaO3 Substrates with CeO2 Seeding Layer

Bi-epitaxial YBa2Cu3Ox (YBCO) thin films with out-of-plane tilt angle in the range 18 - 27? were manufactured using pulsed laser deposition on NdGaO3 tilted-axes substrates with CeO2 seeding layers. The YBCO thin film orientation over the seeding layer depended on deposition conditions. Removal of the seeding layer from part of the substrate surface by ionbeam etching resulted in formation of a bi-epitaxial thin film with different c-axis orientation of two parts of the film. The bi-epitaxial film orientation and structure were studied using X-ray diffraction techniques, and surface morphology was observed with atomic force microscope (AFM). Photolithography and ion-beam etching techniques were used for patterning bi-epitaxial thin films. Electrical characterization of the obtained structures was performed.