Micro-Raman studies of substrate temperature effects on pulsed laser deposition fabricated YBa₂Cu₃O_7-x epitaxial thin films

Micro-Raman spectroscopy has been used to analyse the substrate temperature effects on high temperature superconducting YBa₂Cu₃O_7-x thin films grown by the in situ pulsed laser deposition method. In particular, the dependence of the epitaxy quality on substrate temperature T_s is studied. Our results reveal that films with the highest epitaxy degree are grown with substrate temperature T_s between 680 and 720°C, in good agreement with previous superconducting transition temperature measurements and x-ray diffraction analyses. In addition, the formation and distribution of impurities produced during growth are identified by Raman spectra and Raman imaging, and they are found to be more pronounced at higher substrate temperatures. Finally, localized Raman analysis has been performed to investigate the orientation of the single crystal grains in films grown at substrate temperature T_s > 760°C. It is confirmed that, within the experimental error of 3°, the crystal a/b-axes of these single crystal grains have a strong tendency to orient themselves along the crystal axis of the substrate, independent of their size, shape and orientation of the domain boundaries.