Ion beam irradiation of cuprate high-temperature superconductors: Systematic modification of the electrical properties and fabrication of nanopatterns

Irradiation of thin films of the cuprate high-temperature superconductor YBa₂Cu₃O_7-δ (YBCO) with 75 keV He⁺ ions leads to an exponential increase of the resistivity and a non-linear decrease of the critical temperature. At a fluence above 3 x 10¹⁵ cm^-2 the material becomes semiconducting. Calculations of ion-target interactions using the MARLOWE code indicated that these effects are due to the creation of point defects, primarily by displacing oxygen atoms, and that the lateral broadening of the ion's collision cascades is smaller than 10 nm in a 100 nm thick YBCO film. Irradiating a YBCO film through a silicon stencil mask with minimum aperture of 125 nm placed on top of the sample results in a local modification of its electrical properties. We demonstrate that this technique can be used to produce patterns of sub-100 nm size, visualized by scanning electron microscopy and conductive atomic force microscopy. This simple one-step process does not require the removal of target material and avoids the contamination problems associated with chemical etching and focused ion beam techniques.