FORMATION OF OUTGROWTHS AT THE INITIAL GROWING STAGE OF YBA2CU3OX ULTRATHIN FILMS ON ZRO2 SUBSTRATES

Ultrathin films of YBa2Cu3Ox with good crystallinity and superconducti vity were prepared by a modified off-axis sputtering. The microstructu re, with emphasis on surface morphology and formation of outgrowths, w as studied by using atomic force microscopy and electron microscopy, I t was found that many outgrowths were formed at the initial growing st age. Therefore it is important to suppress the nucleation of outgrowth s at a very early growing step to obtain a smooth film. The nucleation of outgrowths is significantly influenced by surface defects on the s ubstrate. Discussion is also made in correlation with the occurrence o f an intermediate layer commonly observed on ZrO2. From our observatio n, YBa2Cu3Ox might be grown directly on the surface of ZrO2 without fo rming any intermediate layer, if the film thickness is very small. (C) 1995 American Institute of Physics.