Masked ion beam irradiation of high-temperature superconductors: patterning of nano-size regions with high point-defect density

Ion-beam irradiation of high-temperature superconductors creates different types of defects depending on ion mass, energy and dose. Computer simulations reveal the diversity of the ion-target interactions with YBa₂Cu₃O₇ and are compared to previous experimental results from transmission electron microscopy and electrical transport properties. While protons have a very low efficiency to create defects in YBa₂Cu₃O₇, significantly heavier ions produce defect clusters and inhomogeneous damage in the target material. The situation is exemplarily illustrated by a computer simulation study of the defect cascades produced by H⁺, He⁺, Ne⁺, and Pb⁺ ions of moderate energy. He⁺ ions with energy of about 75 keV were found useful for a systematic modification of the electrical properties of high-temperature superconductors, since they do not implant into 100-nm thick films of YBa₂Cu₃O₇ but primarily create point defects by displacement of the oxygen atoms. Such defects are very small and distributed homogeneously in YBa₂Cu₃O₇. The small lateral spread of the collision cascades allows for the patterning of nanostructures by directing a low-divergence beam of He+ ions onto a thin film of YBa₂Cu₃O₇ through a mask. Simulations indicate that the resolution can be about 10 nm. An experimental test with a masked ion beam irradiation confirmed that features with about 200 nm size could be produced in a YBa₂Cu₃O₇ thin film and observed by scanning electron microscopy.