Transmission electron microscopic characterization of metal-organic chemical vapor deposition-derived superconducting Tl₂Ba₂Ca₁Cu₂O_χ thin films on Au substrates. Evidence for Au-Cu alloy formation and texturing on a nonplanar metal substrate

The microstructure of superconducting Tl₂Ba₂Ca₁Cu₂O_χ thin films grown on Au substrates by metal-organic chemical vapor deposition (MOCVD) has been investigated. Characterization techniques included X-ray diffraction, variable temperature magnetization, scanning and transmission electron microscopy (SEM and TEM, respectively) and energy dispersive X-ray spectroscopy (EDX) measurements. The films exhibit a magnetically derived T_c≈80 K and a high degree of texturing with the crystallite c-axis oriented perpendicular to the Au substrate surface as evidenced by enhanced (00l) X-ray diffraction reflections. SEM/ EDX and TEM/EDX provide evidence of Au-Cu alloy formation but no Au diffusion into the film. The superconducting grains exhibit good compositional uniformity and excellent alignment with the substrate, even though the Au substrates were not smooth and exhibited a moderate density of steps.