Atomic-scale analysis of the interface structure and lattice mismatch relaxation of Bi2Sr2CaCu2O8+δ/SrTiO3 heterostructure

Abstract

With the increasing research on heterojunctions, it is gradually been realized that interface structure and strain have a huge impact on film properties. However, the research on Bi-based superconducting heterojunctions is still lacking and needs to be explored at the atomic-scale. In this article, the interface structure, element diffusion, and lattice mismatch relaxation of the Bi2Sr2CaCu2O8+δ(Bi-2212)/SrTiO3 heterojunction have been investigated by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (Cs-HAADF STEM), energy-dispersive X-ray spectroscopy (EDX), and geometric phase analysis (GPA). The experiment results reveal the interfacial atomic sequence as SrTiO3(TiO2-terminated)-SrO-Cu/TiO2–Ca–BiO-(Bi-2212)n, where the SrO layer is the nucleation layer and Ti atoms diffuse into the CuO2 layer. The Bi-2212/SrTiO3 heterointerface is found to be semi-coherent and accompanied by the non-ideally periodic arrangement of stand-off misfit dislocations. Moreover, lattice distortion and stacking fault have also been revealed to release part of the in-plane lattice mismatch. Through the combined effect of the above several lattice mismatch relaxation methods, the final Bi-2212 film experiences an average in-plane tensile strain (εxx ~ +0.414%) compared with bulk Bi-2212.