Effect of nano-SiO2 films on the evolution of proton-irradiated free radicals in Kapton

The free radical behaviors were investigated on the 170 keV proton-irradiated nano-SiO2 deposited polyimide, using electron paramagnetic resonance (EPR) measurement. The results indicate that, compared with the case of nude polyimide, the population of free radicals is much higher and increase faster with the irradiation fluence and the nona-SiO2 film thickness, but the g value of irradiated free radicals keeps at a constant of 2.0025. Theoretical analysis demonstrates that large quantities of the free radicals could be formed in the interface region, thus, the film coverage and thickness show significant influence on the population of the radicals in the interface. Due to the distribution heterogeneity of the free radical, the free radical evolution during the post-storage follows a sum of two exponential modes. The interface characteristic takes great effects during the evolution process. The mechanisms of the free radical formation and evolution are discussed detailedly in this paper.

► The shielding effect of the ultrathin SiO2 films induce the increase of the free radical population. ► The free radical distribution make the difference of the evolution processes during the post-storage. ► The coverage of the nano-SiO2 film and the interface state both affect the free radical formation and evolution processes.