Transmission electron microscopy on interface engineered superconducting thin films

Transmission electron microscopy is used to evaluate different deposition techniques, which optimize the microstructure and physical properties of superconducting thin films. High-resolution electron microscopy proves that the use of an YBa₂Cu₂O_x buffer layer can avoid a variable interface configuration in YBa₂Cu₃O_7-δ thin films grown on SrTiO₃. The growth can also be controlled at an atomic level by using sub-unit cell layer epitaxy, which results in films with high quality and few structural defects. Epitaxial strain in Sr_0.85La_0.15CuO₂ infinite layer thin films influences the critical temperature of these films, as well as the microstructure. Compressive stress is released by a modulated or a twinned microstructure, which eliminates superconductivity. On the other hand, also tensile strain seems to lower the critical temperature of the infinite layer.