Influence of substrate irradiation on critical current density and microstructure in YBCO thin films

Strontiumtitanate substrates have been irradiated in defined areas with a f ocused ion beam (FIB) of gallium ions. This leads to a change of the sur fa ce structure of the substrates. Afterwards YBCO was grown epitactically on these substrates by pulsed laser deposition. The effect of the modification on the flux density distribution in the YBCO thin films has been observed magnetooptically and the local current distribution has been determined. Th e correlation between the change in j(c) and the microstructure of the YBCO samples, investigated by transmission electron microscopy (TEM), is discus sed.