Superconducting properties of YBa2Cu3O7-δ films deposited on commercial tape substrates, decorated with Pd or Ta nano-islands

To obtain an engineered surface for deposition of high-T_c superconductors, nanoscale modulations of the surface of the underlying LaMnO₃ (LMO) cap layer is a potential source for generating microstructural defects in YBa₂Cu₃O_7-δ (YBCO) films. These defects may improve the flux pinning and consequently increase the critical current density, J_c. To provide such nanoscale modulation via a practical and scalable process, palladium (Pd) or tantalum (Ta) nano-islands were deposited using dc-magnetron sputtering on the surface of the cap layer of commercial metal tape templates for second-generation wires. The size and density of these nano-islands can be controlled by changing sputtering conditions such as the power and deposition time. Compared to the reference sample grown on an untreated LMO cap layer, the YBCO films grown on the LMO cap layers with Pd or Ta nano-islands exhibited improved in-field J_c performance. Atomic force microscopy and transmission electron microscopy were used to assess the evolving size and density of the nano-islands.