Effect of Focused Ion Beam Irradiation on Superconducting Nanowires

Recent advances in focused ion beam (FIB) technology exploit accelerated helium or neon ions, rather than gallium, for maskless fabrication of superconducting nanocomponents. We present a study of the effect of the damage induced by the accelerated ions on the superconducting transition temperature, T_c, of a patterned ~ 85-nm-wide Nb wire, demonstrating a decrease of T_c from ~ 5.5 K in the wire patterned by He ions to ~ 2.8 and 2.3 K exploiting Ne and Ga ions, respectively. In an effort to gain insight into the origin of these changes in T_c, we performed Stopping and Range of Ions in Matter (SRIM) simulations to estimate the damage induced by each type of ion. The simulations show that the lateral distribution of the ion beam and the sputtering rate in using Ne or Ga are significantly larger than those caused by He, consistent with the changes in the measured electrical properties of the nanowire.