The effect of surface modification of CeO2 layers upon the properties of thin Cu3Ba2YO7 films prepared by using large-area pulsed laser deposition was evaluated with particular regard to the critical current density, Jc, and the defect microstructure. High-temperature (1050C) annealing was found to reduce the very rough (5 to 10nm rms) granular surfaces, of as-grown CeO2 layers, to atomic flatness (about 0.5nm rms). However, a quite unique characteristic of CeO2 layers deposited by large-area pulsed laser deposition was the development of pores when subjected to prolonged high-temperature annealing. For very short annealing periods (600 to 1200s), the surface morphology became atomically flat; with the appearance of a high density of nanopores that were 40 to 100nm in diameter and 3 to 5nm in depth. Extension of the annealing period to 1h or more resulted in the development of a surface with enlarged pores: 0.2 to 0.5µm in diameter. When compared with Cu3Ba2YO7 thin films deposited onto as-grown CeO2, the Cu3Ba2YO7 thin films on annealed CeO2 exhibited better homogeneity of Jc and a better crystalline texture. Among Cu3Ba2YO7 thin films deposited onto annealed CeO2, higher self-field and in-field Jc were obtained for Cu3Ba2YO7 thin films deposited onto CeO2 with smooth surfaces, but interspersed with nanopores. Investigation of the defect microstructure by using etch-pit methods in conjunction with atomic force microscopy of Cu3Ba2YO7 thin films revealed a high density of linear defects in the form of screw and edge dislocations. These correlated well with a high density of nanopores on annealed CeO2. Transmission electron microscopy further confirmed the presence of threading dislocations which clearly emanated from nanopore sites. The angular dependence of Jc revealed enhanced flux pinning in Cu3Ba2YO7 thin films deposited onto CeO2 which contained a high density of nanopores.

Effect of Surface Modification of CeO2 Buffer Layers on Jc and Defect Microstructures of Large-Area YBCO Thin Films. K.Develos-Bagarinao, H.Yamasaki, Y.Nakagawa: Superconducting Science and Technology, 2006, 19[8] 873-82