Abstract
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° 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) × 1010 cm−2 for Ar8+ ions and (1.6 − 6.5) × 1010 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 × 1010, 1 × 1011, and 2.5 × 1011 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 Tα(λ) 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.
Highlights
Experimental studies of the properties of polymer films irradiated with swift heavy ions are of interest to a large number of research groups: for reviews see for example [1,2]
By conducting a series of experiments irradiating polyethylene terephthalate (PET) films with different fluences and ion charges, we have shown that the total UV-vis optical response of irradiated PET films has a logarithmic dependence on the fluence
This offers a new method of determining the irradiation exposure of PET films to swift heavy ions, which currently poses a technical challenge at high fluences
Summary
Experimental studies of the properties of polymer films irradiated with swift heavy ions are of interest to a large number of research groups: for reviews see for example [1,2]. I.e., the value of Tα(λ) is defined as the geometric mean of TM(λ) and Tm(λ) It has been shown in [27] that in pristine and irradiated PET films, interference fringes occur in the experimental transmission curve T(λ) in a similar region of weak/medium transparency (up to about 15% reduction from maximum transmission). The observed red shift reflects changes in the state of electrons in the film after irradiation, and the comparison of the smooth transmission curves Tα(λ) for pristine and irradiated films over the entire wavelength range should provide quantitative information about the total irradiation fluence that the polymer film has been exposed to. We consider the physical interpretation of these experimental results
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