Film thickness dependence of microwave surface resistance and microstructure in YBa2Cu3O7ÿd thin ®lms

Film thickness dependence of microwave surface resistance, morphology and microstructures of YBa2Cu3O7ÿd thin ®lms were studied by X-ray di€raction (XRD), AFM and transmission electron microscopy (TEM). There was no direct correlation between the microwave surface resistance and ®lm thickness, although full width at half maximum of XRD rocking curve of (0 0 5) peak increased with increase in ®lm thickness. AFM morphology investigation showed no signi®cant di€erence on ®lm surface roughness and particulate density. Through the TEM cross-section microstructure analysis, it was found that the c-axis ®lm became more regular from the bottom to the top, which could explain the abnormal phenomenon observed. It was very interesting to note that the c-axis ®lms contained few stacking faults and tilting c-axis grains with a-axis grains occurring immediately. We have proposed that the occurrence of small volume fractional a-axis grains with high-angle grain boundary might bene®t microwave dissipation loss. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 74.76.Bz; 74.25.Nf; 74.62.Dh