DISTRIBUTION OF FLUORINE IN YBCO THIN-FILMS PREPARED BY BAF2 TECHNIQUE

Thin YBa2Cu3O7-x superconducting films were prepared by coevaporation of Y, BaF2 and Cu components. An in-situ annealing process in dry oxygen was used to obtain high-T-c films at substrate temperatures not exceeding 600 degrees C for Al2O3, and 720 degrees C for SrTiO3. Analyses performed by X-ray diffraction, Auger electron spectroscopy (AES) and ion-scattering spectroscopy (ISS) revealed an escape of fluorine from the deposited films already during the coevaporation stage in vacuum and preannealing steps in oxygen. The ISS spectra indicate the main fluorine concentration right beneath the film surface. In addition, the AES analyses show both the presence of fluorine at the film-surface interface and rather limited diffusion of substrate constituents into the YBCO films apparently due to the low substrate temperatures used.