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

Abstract

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.