The crystalline and superconducting properties of sputtered a-axis oriented thin films of Y~ Ba2CusO7-x on SrTiOs (100) and MgO(100) substrates are compared using X-ray diffraction (XRD), high-resolution electron microscopy (HREM), atomic force microscopy, critical current (J c) and surface resistance (R,) measurements. A two step self-template method was used for deposition, and HREM measurements revealed that the bulk film beyond the template was pure a-axis oriented on SrTiO3 and also on lattice-mismatched MgO. However, the nature of the template layer on the two substrates was completely different and the crystallinity of the film was found to be dependent on the crystallinity of the template. The Jc and/~ measurements indicated that the superconducting properties of the film on MgO owing to its poor crystallinity, were dominated by weak links in contrast to well-coupled grains for the film on SrTiOs. * Corresponding author. mismatched substrate MgO (100) using the selftemplate method [ 2 ]. However, their films had (110) oriented domains co-existing with the a-axis grains. We recently reported [4] on the growth of a-axis oriented YBC films by DC-sputtering on STO and MgO substrates by the self-template method. The fdms were found to have excellent crystallinity, smooth surface and high Tc(Tc(R=O)=84 K).
Here, we report on further characterization of these films by high-resolution electron microscopy (HREM), atomic force microscopy (AFM), critical current (Jc) and microwave surface resistance (R,) measurements. From HREM observations it was found that the bulk film beyond the template was pure a-axis oriented on both the substrates. The film on lattice-matched STO substrate had a smooth morphology, while the film on MgO had many grain