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-delta films is investigated and interpreted in terms of laser-induced target modification. Both target degradation (at fluence J < 1.0 J/cm(2)) and diffusion-assisted preferential ablation (1.0 < J < 1.3 J/cm(2)) 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 much greater than 1.3 J/cm(2) 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 (T-c = 91.0 K, Delta T-c = 0.4 K) and can be produced with a remarkably high reproducibility. (C) 1999 American Institute of Physics. [S0021-8979(99)08523-0].