ESR study of the insulator-conductor transition in polyimide kapton induced by swift heavy ion irradiations

Abstract

Abstract Kapton-H thin films have been irradiated with heavy ions in the MeV/u range, in the electronic stopping power (Se) regime. Effective ion track radii are extrapolated from spin density measurements and are consistent with simulations of the radial distribution of the energy density deposited by secondary electrons. This yields an apparent quadratic dependence of the data versus Se. We postulate that the paramagnetic defects are dangling bonds on aromatic condensed structures, and that conductivity appears by overlap of these structures. The final product is a highly amorphous carbonaceous substance with a conductivity (104 Ω−1.m−1) and a spin density (5 × 1019 g−1) near that of ion implanted or pyrolysed Kapton.