Pulsed laser deposition of thin superconducting films of Ho₁Ba₂Cu₃0_7-x and Y₁Ba₂Cu₃0_7-x

Thin films of Ho₁Ba₂Cu₃0₇_ _x and Y₁Ba₂Cu₃0₇__ _xwere deposited on SrTi0₃and A1₂0₃ substrates by pulsed laser deposition of high- T_c bulk superconductor pellets in vacuum. Following annealing in 0₂ at 800–900 °C the films were superconducting with typical T_c(50%) = 89 K and transition widths of 10 K. Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) were utilized to study the stoichiometry of the as-deposited films for laser energy densities between 0.11 and 4.5 J cm^-2. The films were deficient in holmium and yttrium for energy densities below 0.6 and 0.4 J cm^-2, respectively. The films were stoichiometric for fluences above 0.6 J cm^-2. In addition, preliminary time dependence and spectroscopic observations of the laser-produced plasma are presented. The results indicate an ablation mechanism that at high energy densities preserves stoichiometry. TEM and x-ray characterization of annealed, superconducting Ho₁Ba₂Cu₃0₇ _ _x films on (100) SrTi0₃showed mixed regions of epitaxially oriented 1:2:3 material with either the c axis or a axis oriented along the surface normal. The a-axis-oriented material grew preferentially in the films with b, c, twinning.