Ion beam analysis of laser-deposited high T_c YBa₂Cu₃O₇ superconducting thin films

We have performed Rutherford backscattering spectrometry, non-Rutherford proton elastic scattering, and axial ion channeling analysis to determine the composition, the crystallinity, and the epitaxial quality of YBa₂Cu₃O₇ superconducting thin films on (100) SrTiO₃ and (100) yttria stabilized zirconia (YSZ) substrates. YBa₂Cu₃O₇ superconducting thin films were fabricated both by high and low temperature laser ablation techniques. The former method requires high temperature annealing in oxygen to recover the superconducting properties, whereas in the latter method as-deposited in situ superconducting thin films are formed at low processing temperatures (500 °C-650 °C). Helium ions in the energy range of 2.0-2.5 MeV were used to determine the relative stoichiometries of the heavier atomic number elements (Y, Ba, Cu) in the film, but are not sensitive enough to determine the relative amount of oxygen in the superconducting phase. The detection sensitivities to oxygen can be greatly enhanced by using the proton elastic scattering [¹⁶O(p, p) ¹⁶O] reaction, which was found to increase the scattering cross section by a factor of 3 to 5 relative to the Rutherford scattering cross section. The ion-channeling of YBa₂Cu₃O₇ superconducting thin films on (100) SrTiO₃ substrates showed excellent minimum channeling yields corresponding to epitaxial growth, but the presence of defects increased the channeling yields for films deposited on (100) YSZ substrates. The ion channeling yields are compared with the microstructure of the films determined by transmission electron microscopy.