Growth mechanisms and surface morphology of YBCO based high-T_c thin films and heterostructures for SnS junctions

摘要

We have controlled the nanoscale growth mechanism and surface morphology of Ybs_2Cu_3O_7(YBCO) based high-T_c thin films and heterostructures, using miscut SrTiO_3 substrates. On exact (001) SrTiO_3 substrates, the YBCO films grow in a screw dislocation growth mode. The barrier layers (La_6.4Sr_1.6Cu_8O_20 and PrBa_2Cu_3O_7) grown on top of such a YBCO film also show spiral growth features, indicating pseudomorphic growth. On miscut substrates (with miscut angle >= 4 deg toward [010]) the YBCO films grow by step-flow. However, the La_6.4Sr_1.6Cu_8O_20 layers grown on such YBCO bottom electrodes, show a high degree of step bunching with rough surface. In contrast, the PrBa_2Cu_3O_7 layers show clear step-terrace surface morphology similar to the underlying YBCO bottom electrode, suggesting the existence of periodic nanoscale steps at the S-N interface. These heterostructures can be used for the fabrication of SNS Josephson junctions to take advantage of the proximity effect coupling at the nanoscale steps at the interface.