Ion velocity dependent secondary electron induced point defects in SHI irradiated solids

Swift Heavy Ion (SHI) mostly dissipates its energy in electron excitations rather than nuclear collisions inside a target material. It is known that about half of the energy deposited into the electron excitation contributes to track formation; the remaining energy is transported far away by the energetic secondary electrons. A certain fraction of the secondary electrons are finally ejected from the surface. We report the effect of the remaining fraction left behind in the target in modifying the target properties. We show that the energy of these secondary electrons is too low to induce defects by elastic scattering process. We therefore consider the inelastic interaction of the low energy electrons in YBa2Cu3O7-y (YBCO). As a consequence, the secondary electrons induce dissociative recombination in YBCO by breaking some of the Cu-O bonds. We estimate the maximum energy of the emanated secondary electrons from the ion tracks and their corresponding ranges in YBCO for different initial ion energies. In contrast to the velocity effect that leads to smaller diameter tracks for ions with higher energies, we show that the diameter of the defected zone due to ion induced secondary electrons increases with increasing energy of the ion. (author)