Assessment of the Irradiation Exposure of PET Film with Swift Heavy Ions Using the Interference-Free Transmission UV-Vis Transmission Spectra

This paper presents the results of a study of polyethylene terephthalate (PET) films irradiated with Ar and Kr ions at both normal orientation and an angle of 40 degrees to the normal. Normal irradiation was performed using Ar8+ and Kr15+ ions with an energy of 1.75 MeV/au and fluences in the range (2-500) x 10(10) cm(-2) for Ar8+ ions and (1.6 - 6.5) x 10(10) cm(-2) for Kr15+ ions. Kr ions with an energy of 1.2 MeV/au and charges of 13(+), 14(+), and 15(+) were used for angled irradiation. For each Kr ion charge value, three fluence values were used: 5 x 10(10), 1 x 10(11), and 2.5 x 10(11) cm(-2). It is well known that irradiation of PET films by swift heavy ions results in a red shift of the UV-vis transmission spectra absorption edge. The experimental transmission spectra exhibit well-defined interference fringes, which obscure the underlying transmission response. Using an existing technique to obtain interference-free transmission curves T-alpha(lambda) for both pristine and irradiated PET film samples, we found that S, the total radiation-induced absorption of light by the PET film, is proportional to the logarithm of the fluence F. In addition to this dependence on the irradiating fluence, we also found that the charge of the irradiating ion has a significant influence on the position of the absorption edge in the UV-vis spectra. This provides experimentally independent evidence to confirm our previous results showing that ion charge has an effect on the post-irradiation state of PET films. We present a physical interpretation of the observed absorption edge red shift in irradiated PET films as being due to the growth of extended conjugated systems via the formation of intermolecular helical structures. Our investigations into the stability of irradiation-induced effects in PET films show that comparison of UV-vis transmission spectra before and after annealing can provide information about the structure of deep traps in PET.

Automated summary

This study investigated the effects of irradiation on PET films by different ions, showing that the radiation fluence impacts light absorption by PET films and the charge of irradiating ions influences the position of the absorption edge in UV-vis spectra.