XTEM/SAED AND SNMS STUDY OF FILM SUBSTRATE REACTIONS IN BI2SR2CACU2OY FILMS ON SI(100) WITH SI3N4 BUFFER LAYER

We have performed cross-sectional TEM/SAED and SNMS studies of film/substrate interactions in Bi2Sr2CaCu2Oy (''2212'') films on Si(100) substrates using Au, SiO2, and Si3N4 buffer layers. The 2212 films were prepared by electron beam evaporation of stoichiometric targets in O2 of 2 x 10(-4) mbar and post-annealed in air at 800/850-degrees-C. SNMS depth profiles indicated Si3N4 layers to be most effective of the buffers studied; they enabled us to grow c-axis oriented 2212 films. These, however, were not superconductive. XTEM and SAED revealed a strong attack on the Si3N4 buffer layer by solid state reactions resulting in a severe roughness of the initially plane interface. The induced roughness of the interface obviously is responsible for the observed deviations (up to 20-degrees) of the c-axis of the 2212 grains from the substrate normal, which in turn lead to weak links. The latter then probably inhibit superconductivity.