MATERIALS MODIFICATION WITH HIGH-ENERGY HEAVY-IONS

Fast ions moving through condensed matter produce a track of excitatio ns and ionizations that can have lasting effects depending on the prop erties of the medium. Latent tracks or columnar defects are always pro duced in insulators. These columnar defects have been used to modify t he properties of high temperature superconductors by pinning the vorti ces. The effect of pinning is also observed in the microwave frequency regime. With the use of higher energy heavy ions electronic loss indu ced effects are now observed even for metals. There seems to exist a t hreshold electronic stopping power for each material above which laten t tracks can be produced. Creation and annealing of defects due to the heavy ion energy locked into electronic excitations needs to be under stood. It is observed that below the threshold, electronic stopping po wer (S-e) can even provide annealing effects. The nuclear stopping pow er (S-e) is predominant at lower energies, i.e. towards the end of the range of the high energy ions. The extent of lattice deformation in t he spatially separated electronic and nuclear loss region has been exa mined in Si crystal with a 100 MeV Ti beam using X-ray topography. An attempt is made to study the transient behavior of the defects produce d by S-e in cuprate superconductors. The microstructure changes associ ated with 85 MeV Ni ion irradiation have been studied along with the h ydrogen concentration variations in diamond-like carbon films.