Ion-beam modification of high-temperature superconductor thin films for the fabrication of superconductive nanodevices

Ion-beam irradiation allows for a direct modification of the electric properties of high-temperature superconductors (HTS). Computer simulations of the ion-target interactions reveal that He+ions at energies above 60 keV do not implant into 100-nm thick films of YBa2Cu3O7but can create about one defect per unit cell at technically feasible ion doses of a few 10¹⁵cm^-2. These point defects are primarily displacements of the oxygen atoms of YBa2Cu3O7. X-ray analysis and measurements of the electrical resistivity after cumulative ion irradiation confirm that the main building blocks of the crystal structure remain intact although the superconductor is converted to an insulator. Superconductive nanodevices can be fabricated with this method by directing a low-divergence beam of light ions at a thin film of HTS through a mask placed at a distance from the surface of the material. The illuminated areas of the film are converted from superconducting to semiconducting and even insulating in a single-step process.