A Cu(100) surface has been investigated by means of time-of-flight low-energy ion scattering using 4 He + ions.Polar and azimuth scans have been performed. The evaluation of the obtained spectra demonstrates the influence of background contributions to the overall yield. Selection of single scattering processes was achieved by background subtraction. This allows for high surface sensitivity even for neutral scattering spectra.
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 2 Cu 3 O 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 2 Cu 3 O 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 + , He + , Ne + , and Pb + ions of moderate energy. He + 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 2 Cu 3 O 7 but primarily create point defects by displacement of the oxygen atoms. Such defects are very small and distributed homogeneously in YBa 2 Cu 3 O 7. The small lateral spread of the collision cascades allows for the patterning of nanostructures by directing a low-divergence beam of He + ions onto a thin film of YBa 2 Cu 3 O 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 2 Cu 3 O 7 thin film and observed by scanning electron microscopy.
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