Surface outgrowth problem in c-axis oriented Y-Ba-Cu-O superconducting thin films

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Abstract
The origin of surface outgrowths in c‐axis oriented superconducting Y‐Ba‐Cu‐O thin films has been identified. We find that a,b‐axis regions nucleate heterogeneously at second phase regions and rapidly grow outward, leading to the formation of lenticular‐shaped outgrowths. The second phase has been identified by electron diffraction and high‐resolution electron microscopy to be the Y1Ba3Cu2O7−x phase that forms as microscopic platelet‐shaped precipitates on the a‐b plane. The heterogeneous nucleation of such outgrowths is general and has been observed in both in situ sputtered and laser‐deposited films. It is probably related to the ledge growth mechanism of the c‐axis oriented Y‐Ba‐Cu‐O thin film and to the precise overall composition of the film and needs to be studied in detail in order to produce films with smooth surfaces.