High-quality off-stoichiometric YBa2Cu3O7−δ films produced by diffusion-assisted preferential laser ablation

The fluence dependence of the composition of pulsed-laser deposited YBa2Cu3O7−δ films is investigated and interpreted in terms of laser-induced target modification. Both target degradation (at fluence J<1.0 J/cm2) and diffusion-assisted preferential ablation (1.0<J<1.3 J/cm2) are found to be responsible for nonstoichiometric transfer. A one-dimensional, moving-boundary diffusion model is developed to describe diffusion-assisted preferential ablation. This model predicts stoichiometric transfer at large ablation rates. Indeed, for J≫1.3 J/cm2 stoichiometric deposition is found, resulting in precipitate-free films. However, slightly off-stoichiometric films, deposited in the diffusion-assisted preferential ablation regime, exhibit the best superconducting properties (Tc=91.0 K, ΔTc=0.4 K) and can be produced with a remarkably high reproducibility.