Radiation-induced change of polyimide properties under high-fluence and high ion current density implantation
Polyimide (PI) films were implanted with 40-keV Ar+ and 80-keV Ar2+ ions in a fluence range of 5.0×1014-1.5×1017 cm-2 at ion-current densities of 1-16 μA/cm2. It is shown that the conductivity of the samples rises with the ion-current density at a fixed fluence. Electrophysical parameters of the polyimide change stepwise with the implantation fluence when it exceeds a certain value. The change of electrical parameters of the implanted PI correlates with that of the optical and paramagnetic characteristics. The phenomenon of complete volatilisation of argon implanted with an energy of 40 keV due to surface heating and disordering under the high-power beam is found. It is shown that the change of ion charge and energy at constant beam-power density causes only a quantitative change in the polymer characteristics. A model of PI alteration and carbonised phase formation, taking into account the action of the high-power ion beam and the peculiarities of PI chemical structure, is developed to explain the observed effects. Implantation at high ion-current density can be suggested as an efficient practical means to control polymer conductivity and other parameters.