Microstructure studies of epitaxial YBa2Cu3O7–δ films

Abstract

Thin films of YBaCuO were prepared as a superlattice of three constituents on SrTiO₃ (100) substrates from three electron guns using a dedicated, computer‐controlled evaporator. The results indicate that the as‐deposited thin films grow as a superlattice of the three constituents, with a mixture of amorphous and polycrystalline regions. After annealing, however, the multilayer films are converted to the homogeneous superconducting phase; the morphology, studied with transmission electron microscopy, consisted of an array of orthogonal interconnecting rectangular bars. The better films had T_c(R=0)=90 K and J_c=2.9×10⁶ A/cm² at 4.2 K. The selected area electron diffraction pattern, and the high‐resolution electron microscopy images show that the interconnecting bars are single crystals of the 1‐2‐3 phase. During annealing, the growth rate along the a and b directions is faster than along the c direction. For the films with the a axis oriented perpendicular to the substrate, the grains nucleated directly on the (100) surface of the SrTiO₃ and grow through to the <named-content xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:oasis="http://www.niso.org/standards/z39-96/ns/oasis-exchange/table" content-type="sem:AIPTh1.2"...