EFFECTS OF SUBSTRATE TREATMENTS ON THE GROWTH OF YBCO SUPERCONDUCTING THIN-FILMS ON MGO BY PULSED-LASER ABLATION

Abstract

Different treatments on single crystalline MgO(100) substrates have been performed to study the effects of the substrate conditions on the growth mechanisms and superconducting properties of YBCO thin films deposited in-situ by pulsed laser ablation process. The nucleation and growth of YBCO thin films on these substrates during deposition have been studied by using the in-situ resistance measurement method. The characteristics of as-deposited films have also been investigated by X-ray diffraction analysis (XRD), temperature dependent resitivity measurement (R - T), temperature dependent critical current density measurement (J(c) - T), scanning electron mircoscopy (SEM), and scanning tunneling mircoscopy (STM). It has been found that, while the zero-resistance transition temperature (T(co)) and the overall crystallographic orientation of the films are only affected slightly, the surface morphology and grain structure of the films have shown strong dependencies on the substrate conditions. Recognizing that for YBCO grown on MgO, due to the large lattice mismatch between the film and substrate, the film growth is semicoherent in nature, the observed results are consistently explained by attributing to the interplays between nucleation and grain coalescence processes. The dramatic differences in superconducting transport properties exhibited by films obtained with the conditions studied are also reported to reinforce the arguments proposed.