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

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.

Effect of irradiation with heavy Xe22+ ions with energies of 165–230 MeV on change in optical characteristics of ZrO2 ceramic

“…At the same time, an increase in the energy of incident ions and the irradiation fluence leads to both an increase in the overlapping degree and an increase in the electron density distribution anisotropy. As previously shown, for dielectric materials, including polymers and ceramics, high-dose irradiation leads to the formation of crystal and electron anisotropy in the structure, which are expressed in a change in the diffraction maxima intensity with a circular scan of φ=0-360° [48,49], as well as the appearance of additional induced absorption bands, indicating a change in the electron density in the material [50]. Also, changes in the electron density can be associated with induced phase transformations of the t-ZrO 2 → c-ZrO 2 type in the structure of ZrO 2 ceramic under the action of irradiation with heavy ions [43].…”

Urbach Rule in the Red-Shifted Absorption Edge of PET Films Irradiated with Swift Heavy Ions

“…For high fluences, the broadening of the absorption edge can increase by over an order of magnitude (for example, for PET films, the width of the pristine absorption edge is less than 0.1 eV, but is ~2 eV at high fluences). The absorption edge red shift has been extensively studied [ 5 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], and both differential [ 5 , 8 , 9 , 10 , 11 , 14 , 15 , 16 , 17 ] and integral [ 12 ] relationships have been established between the irradiating fluence and the optical transmission/absorption spectra. It is generally agreed that the shift is associated with the formation and subsequent growth of extended π -conjugated systems, but there are differing views as to exactly how this growth occurs.…”

“…However, SHI irradiation also excites slow electrons of energies below typical ionisation energies [ 20 ]. In [ 12 , 21 , 22 , 23 , 24 , 25 ], we used optical and X-ray methods to show that the effects of SHI irradiation on PET films depend not only on the energy and fluence of the SHI ions, but also their charge. This charge dependence can only be understood by the consideration of slow electrons.…”

“…Electret properties of PET films contribute to the retention of the electron enrichment in the central core of the latent track. A study of the optical spectra of irradiated PET film after thermally stimulated discharge (annealing) showed that electrons were released from the deepest traps (benzene-carboxyl complexes) during thermal relaxation from the irradiation-induced ordered state to a more thermodynamically stable disordered state [ 12 , 21 ].…”

Effect of Cu Ions Implantation on Structural, Electronic, Optical and Dielectric Properties of Polymethyl Methacrylate (PMMA)

“…To avoid the channeling effect, implantation was performed at a low angle with respect to the ion beam direction. The electronic energy loss (S e ) and nuclear energy loss (S n ) for PMMA samples was calculated using the Stopping and Range of Ions in Matter (SRIM) simulation program [32].…”