High resolution electron microscopy of heavy-ion induced defects in superconducting Bi-2212 thin films in relation to their effect on J(c)

Bi2Sr2CaCu2O8+delta thin films were irradiated with 200 MeV Ca-40, 1162 MeV and 2640 MeV Au-197 and 1404 MeV U-238 ions. The radiation-induced defects in the films were investigated with high resolution electron microscopy (HREM) both in cross-section and in-plane view, The HREM study shows that swift heavy ions produce well defined latent columnar tracks consisting of totally amorphized material divided by a sharp transition from the surrounding crystalline material. In-situ measurements of the transport critical current density J(c) on a single sample irradiated first with Ca then with Au ions were performed, Correlations of the transport measurements with HREM data show clearly that continuous columnar defects (Au-197, U-238) are more efficient pinning centers than scattered defect cascades (Ca-40).