SUBSTRATE-TEMPERATURE EFFECTS ON THE PREPARATION OF YBA2CU3O7-X SUPERCONDUCTING FILMS ON (100) SRTIO3 BY LASER ABLATION

In situ high-T(c) superconducting thin films of YBa2Cu3O7-x were deposited on (100) SrTiO3 substrate by laser ablation with a glancing angle geometry at different substrate temperatures in the 560-700-degrees-C range. The transition temperatures, x-ray diffraction patterns, and surface morphologies of the films were substantially different from one another. The critical temperatures of the films deposited at below 600-degrees-C were 72-84 K, while the films deposited at above 650-degrees-C showed T(c0) of 85-91 K. The x-ray diffraction patterns and surface morphologies of the films showed that the orientations of the deposited films depended on the substrate temperature. The films deposited at 700-degrees-C showed an exclusive orientation of "c" axis perpendicualr to the (100) SrTiO3 substrate surface, but those deposited at below 600-degrees-C exhibited random but a preferential orientation of c axis parallel to the (100) SrTiO3 surface. The dependence of the film orientations versus substrate temperature is explained in terms of lattice misfits as well as the surface mobility of the adatoms or molecules at the deposition temperature. Also, the deposition rates were found to be a function of the substrate temperature, and the activation energy of surface migration of adatoms was measured to be 0.21 +/- 0.03 eV.