Electron Microscopic Investigation of Superconducting Fe- and Cu-based Thin Films

Superconducting materials enable lossless current transport, bringing them into focus for technical applications. Particularly relevant are epitaxially grown thin films of high-temperature superconductors, like the Fe- and Cu-based materials Ba(Fe$_{0.92}$Co$_{0.08}$)$_{2}$As$_{2}$ (Ba122) and REBa$_{2}$Cu$_{3}$O$_{7-δ}$ (REBCO, with rare-earth elements, REs, such as Y, Sm, Gd, ..., and the O non-stoichiometry δ). A central goal of current research is to improve the current-carrying capacity of superconducting thin films for improved coated-conductor technology. Non-superconducting defects of suitable shape and size (typically a few nanometers) play an essential role in superconductivity, as they prevent the unwanted movement of magnetic flux lines (“flux pinning”). However, the controlled fabrication of such defects is difficult since several fabrication parameters influence defect formation. In this work, scanning (transmission) electron microscopy (S(T)EM) in combination with energy dispersive x-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS) was applied for a better understanding of the film growth and defect formation.