Growth mechanism of YBa2Cu3O7-y thin films on the metallic tapes by MOCVD

We fabricated a YBa₂Cu₃O_7-y (YBCO) thin film on an MgO single crystalline substrate and cube textured (CUTE-Ag)-tapes using metal organic chemical vapor deposition (MOCVD). It was confirmed that a c-axis oriented YBCO film grew on these substrates. The terraced surface and spiral growth pattern are clearly visible. Many Ag particles were observed on the terrace surface of the spiral steps. After heat treatment these particles concentrated at the edge of the spiral steps. The dependence of the terrace width on the substrate temperature is drastically changed at the certain temperature range between 750 and 800°C. At high temperatures, the terrace width of the films on MgO increases and reaches about 90 nm at 800°C, whereas those on CUTE-Ag tape have a terrace width of about 160 nm at the same temperature. The values of the supersaturation ratios are estimated as 50 and 15 from the terrace widths on MgO and CUTE-Ag. The results from the surface morphology and the microstructure suggest that there is a difference in the growth mechanism between the YBCO films on MgO and those on CUTE-Ag in the higher temperature region. We speculate that the quasi-liquid layer is more stable on the CUTE-Ag at higher temperatures than 750°C, and the growth mechanism of the YBCO films on the CUTE-Ag is mixed with the Vapor-Liquid-Solid (VLS) growth mode and the surface-active species (Surfactants) growth mode