Influence of sequential etching on YBCO films deposited by PLD from a nanostructured target

Thin YBa₂Cu₃O_6+x (YBCO) films with T_c = 90 K and high critical current in the order of 10⁷ A/cm² at 77 K are prepared with pulsed laser deposition from a nanostructured target. Changes in the superconducting and structural properties of the films are investigated after repeated thinning by Ar-ion sputtering or by electrochemical etching. As shown by Auger depth profiling, the chemical composition is preserved through the film during Ar-ion sputtering while electrochemical etching changes the atomic concentrations and surface structures. Investigations by SQUID magnetometry and by conventional resistivity measurements give evidence that the dependence of T_c on the film thickness is similar to as-prepared ultrathin films. The thickness dependence of J_c indicates an excess of pinning centers on the surface of the as-deposited film.