Fabrication and Characterization of Superconducting Nano Layer by Pulsed Laser Deposition

Abstract:

Pulsed laser deposition (PLD) technique based on femtosecond (f.s.) provide with 2 amplifiers was usedto fabricate nano layer of YBCO thin superconducting films on a quartz substrate. A femtosecond laser contains toTi: sapphire crystal is pumped by 2nd harmonic of Nd:YLF laser at 523 nm. The femtosecond laser was focused on arotating target and was made incident on the target surface at an angle of 45°. The substrate temperature was kept at400°C and the films were deposited in vacuum and in the presence of pure oxygen at a pressure (PO2) of 5.5×10-5Torr using turbo molecular pump. In the present study, we have varied the distance from the target to the substrate(dT-S) in order to improve the film quality. As a result, we have achieved both of high quality films and the

uniformity in deposition rate under the optimized condition of dT-S = 70 mm. Nano-layer of superconducting filmsare identified as Y2Ba5Cu7Ox and Y2Ba4Cu8O20-x, respectively, as revealed by XRD and EDX measurements.Thickness of the films was measured by Fizeau interference (FI) technique at reflection and found to be~150 nmwith a deposition time of 10 min. Atomic force microscope scans, recorded in a tapping mode, of Y2Ba4Cu8O20-xthin film surface shows that the film start to have some atomic arrangements after laser ablation treatment with grainsize of 100-300 nm. Resistivity measurements for the target superconductor Y1Ba2Cu3O6.96 revealed a transition

temperatureTconset = 90 K with a transition width ΔTc= 2.0 K and the zero resistance is achieved at Tc(0) = 88 K.The Raman spectra of YBCO indicate that the five z-polarized Raman phonons exist. The electrical and structuralstudies of the polycrystalline and PLD-YBCO nano-superconducting layer films were determined in details byemploying structural x-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-rayspectroscopy (EDX), atomic-force microscope (AFM), as well as the electrical resistance R(T) measurements.Additionally, Raman spectroscopy was used to obtain more information about texture, in particular oxygen content,

the detection of foreign phases, and orientation of YBCO superconducting material. Finally, we have investigatedthe fluorescence of the films using an ultraviolet light source. By using PLD technique, we can fabricate films of

nano superconducting layers with the same chemical structure as the target material. This information would beuseful particularly in the fabrication of high Tc-device.