Effects Of Nitrogen Ion Irradiation On Properties And Structures Of PI And TiO₂/PI Materials

As target materials of polyimide sheet(PI) and nano-Ti O2-film deposited PI(Ti O2/PI), the property changes of PI and Ti O2/PI after nitrogen ion irradiation were measured by UV/Vis and four-probe tester while their structures and irradiated defects were investigated using electron paramagnetic resonant spectroscopy(EPR), scanning eletron microscopy(SEM), Raman spectroscopy(Raman) and x-ray photo-electron spectroscopy(XPS), etc. In this case, it was exposed the effect rules and the corresponding mechanisms of nitrogen ion implantation on the materials properties in this paper.The results indicate that the optical and electrical properties will be changed drastically for 100 ke V nitrogen ion irradiated PI. After nitrogen ion irradiations, the material would be colored as the optical transmittance decreases drastically with increasing nitrogen ion fluence. As the nitrogen ion fluence is more than 5E15cm-2, the irradiated PI becomes almost opaque to appear black color and lustrous, and its reflectance increase obviously. Meanwhile, the surface resistivity of irradiated PI decrease rapidly with nitrogen ion fluence. As the nitrogen ion fluence is more than 5E15cm-2, the surface resistivity decreases down to the order of 103Ω·cm and lower, implying that PI was “metallized” by nitrogen ion implantation. Compared to 100 ke V nitrogen ion irradiation, 150 ke V nitrogen ion irradiation would result in more serious change on the properties and structures of PI.EPR results and structural characterizations indicate that, carbonyl and amide group were dissociated rapidly from PI chains during nitrogen ion irradiation. However, nitrogen concentration in the irradiated PI could not be increased but inversely decreased down to about 2at.% due to the nitrogen implantation. In the meantime, the materials shows carbonized tendency. The EPR measurement results present that during the nitrogen ion irradiation, free radical population increases increase with the ion fluence, and the full with at half peak-maximum(FWHM) decreases drastically as the nitrogen ion fluence is more than 5E15cm-2, implying that electronic states was change in the whole irradiation zone. Thus the comprehensive analysis of the above-mentioned results presents a conclusion that it occurs an insulator-to-metal(semiconductor) transformation as the displacement damage dose reaches about 3E10 rad(regardless of the energy of nitrogen ions). Finally, the paper proposed a mechanism of irradiation-induced carbonization. As to the case of PI materials protected with surface nano-Ti O2 film, nitrogen ion irradiation shows similar damage effects on PI substrate such as detected carbonization and free radicals, thus there presents similar change features of optical and electronic properties of the Ti O2/PI to that of pure PI. However, compared with the bare PI, much larger irradiation-induced resistivity could be detected due to surface oxide Ti O2, while the surface chemical states will also different from those on PI. On the other hand, obvious surface-sputtering was detected in Ti O2 film during nitrogen ion irradiation, and Ti content in the Ti O2/PI decreases from about 7.0at.% in its as-deposited state down to about 0.3 % as the nitrogen ion fluence is more than 1E16cm-2.This study implies that nitrogen ion irradiation will path a new way to surface modification and functionalization to PI materials.