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 (YBaCu3O7)-Cu-2. 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.