M.A. Bodea

Modification and nano-patterning of high-Tc superconducting thin films by masked ion beam irradiation

Ion irradiation of the high-temperature superconductor (HTS) YBa2Cu3O7 (Y-123) creates different types of defects depending on ion mass, energy and dose. Irradiation with helium ions of moderate energy (75 keV) primarily creates point defects. We measure in situ the modification of electrical transport properties of Y-123 thin films (thickness 310 nm) during ion irradiation. The He ions penetrate thin films and produce collision cascades with small lateral straggle that allow for patterning of nanostructures in the HTS layer. We present features smaller than 100 nm in size produced by masked ion beam irradiation of Y-123 films. Computer simulations indicate that nano-patterning of Y-123 thin films with 10 nm lateral resolution is achievable.

Ion beam irradiation of high-temperature superconductors: From nano-size defects to the fabrication of nanodevices

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. On the other hand, He⁺ ions with energy of about 75 keV 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 straggle of the collision cascades allow for the patterning of nanostructures by directing a low divergence beam of He⁺ ions onto a thin film of YBa₂Cu₃O₇ through a mask. Features with about 60 nm size have been produced and observed by transmission electron microscopy.