PROCESSING DEPENDENCE OF THE INTERFACIAL MICROSTRUCTURE OF AG CONTACTS TO YBA2CU3O7-DELTA THIN-FILMS

The interfacial microstructure of three differently prepared silver contacts on c-axis oriented YBa2Cu3O7-delta (YBCO) thin films was examined using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintained at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomically sharp YBCO(001)/Ag interfaces were observed. In contrast, the cross-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 angstrom thick. Scattered Y2O3 precipitates are found at the YBCO surface of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interface layer for in situ contacts to cold films must be ascribed to reactions with gaseous impurities in the sputter chamber ambient. In conclusion, we strongly emphasize the importance of using ultrahigh purity process gases in order to avoid formation of a resistive interfacial barrier.