THE MULTI-ASPECTS OF ION-BEAM MODIFICATION OF INSULATORS

The complexity of the phenomena observed when insulators are bombarded with energetic ions is due to many different aspects. On the one hand ''insulators'' are generally polyatomic materials having a wide range of structure and bonding and thus different behaviors under electroni c excitations or elastic atomic collisions. On the other hand, the str ong localization of the defect creation by electronic or nuclear proce sses surrounding the particle trajectories leads to specific aspects, as the yield for defect creation can be very different in the anion or cation sublattices. In addition, the doping process by ion implantati on occurs out of thermodynamic equilibrium, and then chemical bonds or charge states of the implanted species depend on their site location, local concentration, temperature and on the defects created in their vicinity. Current examples of these multi-aspects will be discussed wi th particular emphasis on the effects of electronic excitations at hig h density, leading to: (a) defect creation and defect diffusion at low temperature in refractory oxides well known as insensible to radiolys is; (b) abrupt changes of polymer properties illustrated by the sol-ge l transition in polystyrene or the insulator-metal transition in polyi mide, which can be interpreted by a simple model of percolation.