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

摘要

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 YBa{sub}2Cu{sub}3O{sub}7 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 YBa{sub}2Cu{sub}3O{sub}7, 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{sup}+, He{sup}+, Ne{sup}+, and Pb{sup}+ ions of moderate energy. He{sup}+ 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 YBa{sub}2Cu{sub}3O{sub}7 but primarily create point defects by displacement of the oxygen atoms. Such defects are very small and distributed homogeneously in YBa{sub}2Cu{sub}3O{sub}7. The small lateral spread of the collision cascades allows for the patterning of nanostractures by directing a low-divergence beam of He{sup}+ ions onto a thin film of YBa{sub}2Cu{sub}3O{sub}7 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 YBa{sub}2Cu{sub}3O{sub}7 thin film and observed by scanning electron microscopy.