Microstructure of epitaxial superconductive YBa2Cu3O7 thin films prepared at different deposition rates

A study is reported on the growth mechanism of YBa₂Cu₃O₇ with different growth speeds by high resolution transmission microscopy (HRTEM) and analysis of the interface and thin film microstructure. Two thin films were synthesized by pulse laser deposition on [100], miscut 5°, SrTiO₃ substrate at 820 °C, one with a pulse laser frequency of 1 Hz and one with 6 Hz. Cross-sections were studied by an H-9000 NAR HRTEM along the [010] direction. The growth process of the sample made at 1 Hz was as follows. First, distorted step flow growth occurred on a step-mediated substrate surface of 3–4 cells thickness. Second, about a 15 nm thickness of island shape growth becomes superimposed on the area of the step flow layer. Finally, thin film growth occurred but with growth fluctuation. The sample made at 6 Hz showed the characteristics of island growth; the growth area of island or ball shape was of small size and dense distribution, and seemed to be a confused mosaic stack. The influence of growth speed on YBCO epitaxial film microstructure was studied explicitly by HRTEM.     

YBCO films buffered by pyrochlore Nd2Mo2O7 layer on YSZ substrates by chemical solution deposition

A chemical solution deposition process was used to grow epitaxial Nd₂Mo₂O₇ (NMO) buffer layers on YSZ substrates to produce YBa₂Cu₃O_7?δ (YBCO) coated conductors. The NMO precursor solution prepared using metal acetylacetonates was spin-coated onto single crystal YSZ substrate of 10 mm × 10 mm in size at 3000 rpm for 30 s and heat-treated at 1000 °C for 2 h in Ar after calcinated at 550 °C for 1 h. The YBCO film was deposited by TFA-MOD route on top of the NMO/YSZ architecture. The phase purity and the crystalline orientation of NMO and YBCO films were evaluated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to observe their microstructure and their surface roughness. The critical current density (J_c) of YBCO film on NMO/YSZ is 1.8 MA/cm² at 77 K in self-field, which indicates that the Nd₂Mo₂O₇ is a potential buffer for YBCO coated conductor.     

Smectic vortex phase in optimally doped YBa2Cu3O7 thin films

Angular dependent resistivity measurements of optimally doped YBa2Cu3O7 films in fields H pulsed to 50 T are presented. Up to the highest H, the vortex melting field Hm increases and vortex motion is reduced for H aligned with the correlated pinning centers along the main crystalline axes, otherwise 3D anisotropic scaling describes the vortex dynamics. For H parallel ab, the rapid increase in Hm at low temperatures and a critical exponent analysis near Hm confirm the presence of the liquid-crystalline smectic phase predicted for layered superconductors.     

Femtosecond-excimer-laser patterning of YBa2Cu3O7 films

Projection patterning of Y-Ba-Cu-O films on (100) SrTiO₃ and (100) MgO substrates using femtosecond KrF-excimer-laser pulses is reported     

Magnetoresistance of epitaxial SrRuO3 thin films on a flexible CoFe2O4-buffered mica substrate

We have investigated the magnetoresistance of epitaxial SrRuO₃ (SRO) thin films on a flexible CoFe₂O₄ (CFO)-buffered mica substrate. High-resolution X-ray diffraction and transmission electron microscopy revealed that the SRO film could be epitaxially grown on a mica substrate with a 22-nm-thick CFO buffer layer. The epitaxial relationships were SRO [1–10] || CFO [1–10] || mica [010] and SRO [111] || CFO [111] || mica [001]. Epitaxial SRO thin films exhibited two magnetoresistance (MR) peaks; one peak occurred at a Curie temperature of 160 K (HT-MR) and the other at a low temperature of 40 K (LT-MR). The LT-MR increased more rapidly with an increase of the buffer layer thickness than the HT-MR. The LT-MR was similar for the two orthogonal current directions with respect to the magnetic field. We explained the HT-MR and LT-MR in terms of the suppression of spin fluctuations and the magnetic rotation of crystallographic domains, respectively.     

Effect of YBa2Cu3O7-x thin films on the textures and orientational properties of liquid crystals

In the present work, the effect of thin films of YBa₂Cu₃O_7-x complex compound on the mesomorphic and orientational properties of thermotropic nematic liquid crystals has been studied. Homogeneous, stable and reproducible homeotropic and tilted oriented textures of nematic liquid crystals were obtained. The effect of YBa₂Cu₃O_7-x thin films on the morphologic, orientational and optical properties of thermotropic nematic liquid crystals are discussed.