Effect of the CeO2 buffer layer thickness on the microwave properties of YBCO thin films

We have examined the effect of varying the CeO2 buffer layer thickness on t he microwave surface resistance R-s and surface morphology of YBCO films de posited by pulsed laser deposition. Above the critical thickness value d(c) of CeO2 at similar to 90 nm, the surface roughness and areal density of ou tgrowths of the film increased significantly. The YBCO films grown on CeO2 with thickness less than d(c) were completely c-axis oriented and had lower c-axis lengths than those grown on CeO2 with thickness greater than d(c). R-s measured via the sapphire dielectric resonator technique was significan tly lower for the YBCO film grown on CeO2 with thickness less than d(c). Th e increase in the R-s value when the buffer layer thickness is greater than d(c) is considered to be due to the increased surface outgrowths and prese nce of a-axis domains in the YBCO film. Changes in the microstructure and o rientation of the YBCO films were found to be strongly influenced by the un derlying CeO2 layer.