Surface morphology evolution of CeO2/YSZ (001) buffer layers fabricated via magnetron sputtering

Cerium dioxide (CeO2)/yttria-stabilized zirconia (YSZ) has long been proven to be an effective buffer layer architecture for high-temperature superconducting coated conductors. In this study, CeO2 films were deposited on YSZ (001) single crystal substrates via reactive unbalanced magnetron sputtering with varying substrate temperature, sputtering pressure, radio frequency sputtering power, and film thickness. High-quality texture was achieved even at ambient temperature, and deposition parameters were optimized to achieve the best degree of in-plane alignment with (111) ϕ scan full width at half maximum around 1.3°. Atomic force microscopy was utilized to investigate film surface morphology and roughness. At a low sputtering pressure, a flat and uniform film surface comprising nano-sized isotropic islands was observed. The surface islands transited to an anisotropic spindle-like shape at pressure higher than 1.0 Pa. The spindle-shaped islands elongated along the CeO2 [110] or [1image 0] directions, constructing an interwoven surface morphology. The distinct surface morphology evolution was correlated with the change in the film strain state attributed to varying sputtering pressure. A possible mechanism for this morphology evolution was discussed.