| In this paper, the optical degradations and the corresponding post-irradiated recovery processes of the SiO2 film modified polyimide (SiO2/Kapton) were investigated under 100keV proton irradiation compared with its countpart polyimide (Kapton) as a reference. Using electron paramagnetic resonance spectroscopy (EPR) analysis, the correlation of optical degradation and free radicals evolution of the samples after irradiation was exposed. Furthermore, the permanent damage mechanisms of SiO2/Kapton were also studied using complementary techniques such as x-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).The results indicate that, similar to Kapton, the optical transmittance of 100keV proton irradiated SiO2/Kapton decreases significantly with increasing proton fluence in the wavelength range of 400-800nm. Moreover, the irradiated SiO2/Kapton shows more decrease in the optical transmittance, especially under low proton fluence. It should be noted that the degraded optical transmittance can recover to some degree during the room-temperature storage after irradiation for both Kapton and SiO2/Kapton, implying that the optical degradation is composed of the recovered damage and the permanent one. Through the continuous measurements, it was found that during the storage, the optical recovery of the irradiated proton evolutes in a exponent mode to the storage time,After EPR analysis, it is found that large amount free radicals are prodiced during the proton irradiation for both Kapton and SiO2/Kapton. During the post-irradiated storage in ambient, the free radical populations for two kinds of materials present similar recovery rules to those evolutions of optical transmittances, the corresponding time constants are exact the same characteristics. These results imply that the optical recoveries are determined physically by the irradiated radicals. On the other hand, the boundary damage between SiO2 and Kapton is the main reason for more serious optical degradation in SiO2/Kapton material.The analysis of morphologies and structures indicate that proton irradiation-induced permanent damage in Kapton is originated from the chain break at the bonds of amine, carbonyl and aether groups, resulting in carbonization and evaporation of low molecular and surface roughnening. Correspondingly, the Kapton substrate in SiO2/Kapton material shows similar permanent damage to that of it countpar pristine one, but there is no micro hole formed on the surface. However, it is important to be noted that the nitrogen content increases within the interface between SiO2 and Kapton substrate, and then the Si-N bond forms. This is due to that free-radical-induced reactions occur at the interface between SiO2 and evaporated amine. |
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