Substrate influence on low energy electron beam processing of YBa₂Cu₃O_7−δ thin films

The influence of substrate material on electron writing (EW) procedures directed at fabrication of artificial channels for easy vortex motion in YBa₂Cu₃O_7−δ (YBCO) epitaxial thin films has been investigated. Films deposited on two types of substrates providing epitaxial growth, magnesium oxide (MgO) and La_0.18Sr_0.82Al_0.59Ta_0.41O₃ (LSAT) substrates, have been irradiated in a standard electron transmission microscope with low and high fluency 30 keV electrons. The effects of irradiation have been assessed by the measurements of the superconducting transition temperature and the critical current, completed by the micro-Raman spectroscopy and transmission electron microscopy structural investigations. The irradiation effects were found to depend on the type of substrate on which films were deposited. Differences have been attributed to distinct structural properties of the films, resulting from different matching of substrates lattices to the YBCO crystalline lattice. A stronger mismatch of MgO substrates causes the formation of in-plane disoriented epitaxial grains and significant heat confinement during EW procedures. Heat confinement mechanism, together with differences in the thermal properties of the substrates enables understanding the performance of different YBCO films in electron writing procedures.