IMPLANTATION OF POLYMERS AT MEDIUM ION FLUENCES - A SPATIAL HETEROGENEITY OF RADIATION-DAMAGE DUE TO DOMINANT ELECTRONIC STOPPING

When low energy light ions are implanted into polymers it has been shown (1984) that at room temperature they have a final distribution in space which parallels that of the initial deposition of energy to the electrons. This suggests that such ions might be used as tracers in order to probe the detailed distribution of damage due to excited electrons. Experiments are described in which the full, three-dimensional, spatial redistribution of some such typical light ions were studied. Specifically due to application of a recently developed and modified tomographic reconstruction procedure. A 5 MeV Li6 ion beam was chosen in order both to optimise the tomographic evaluation procedure, and also to facilitate comparison with the results of other previous low energy ion implantations. It is assumed that transverse mobility of the implanted ions in the polymer is only achieved above a certain threshold of polymeric destruction, and that this most likely corresponds to achieving a certain excited-electron energy transfer turning-point, due to track overlap. In these experiments, and for these doses, the electronically damaged polymer zones around the ion trajectories are indeed expected to begin to overlap each other. However, a substantial undamaged volume of polymer between latent tracks still remains. Because of this the ion mobility parallel to the tracks still dominates, and broader three-dimensional ion distributions are therefore not observed.