Modification of Optical and Electrical Properties of PET Foils by He⁺, Ne^+ and Ar^+ Implantation

Abstract

Thin (3 µm) polyethylene terephthalate (PET) foils were irradiated with 135 keV He + , Ne + and Ar + ions with the fluences up to 5 × 10 15 cm −2 . Changes of chemical structure of the polymer were studied with the Fourier transform infrared and Raman spectroscopy -breaking of numerous chemical bonds, polymer chain cross-linking as well as formation of sp 2 hybridised carbon clusters and cluster networks were demonstrated. The increase of the implanted sample absorbance with the implantation fluence in the UV-VIS spectra as well as the decrease of optical band-gap energy (2.75 and 2.0 eV for He and Ne, respectively, at 5 × 10 15 cm −2 ) are observed. Decrease of bulk resistance of heavily treated samples by ≈ 5 orders of magnitude is determined. Measurements of the sheet resistance confirm that the sample becomes conducting also on the reverse (unimplanted) side of the foil. Both of these effects depend on the impinging ion mass -they are the strongest for Ar. The increase of both ac conductance and dielectric constant is observed in the frequency range up to 2 MHz and these changes rise with the impinging ion mass.

Modification of PET Polymer Foil by Na+ Implantation

“…It should be mentioned that a similar effect was observed for the samples irradiated with different projectiles, including noble gases [40][41][42][43], metals [44][45][46][47][48][49], and non-metals [3,50,51]. The bulk resistivity reduction due to Na implantation is stronger than that reported for the PET samples irradiated with light noble gases [54]. This may be due to the fact that metallic precipitates are known to be formed in the implanted polymers and such "conducting islands" also contribute to the change of sample resistivity [2,4,5].…”

“…The above mentioned changes were also observed in our previous paper describing modification of thin PET foil samples by He, Ne, and Ar irradiation [54]. In this paper the investigations of polymer modification induced by irradiation with light metallic projectiles, namely sodium ions are considered.…”

“…Even for the smallest fluence the destruction of chemical bonds in the subsurface layer of the polymer is visible, the peaks corresponding to C=C ring and 1727 cm −1 C=O stretching, are the only distinct ones. The peak height reduction is much stronger than that observed for PET implanted with noble gases [54]. As the fluence increases to 10 15 cm −2 the polymer characteristic peaks disappear, whilst wide bands near 1600 cm −1 and a smaller one at ≈ 1350 cm −1 appear.…”

“…The sheet resistivity on the reverse side is only ≈ 2 times higher than that of the implanted side. In the case of noble gas implantations [54] the sheet resistivity on the reverse side was more than 2 orders of magnitude higher than that on the implanted one, still noticeably lower than the pristine sample resistivity.…”

“…More details about the relations between the sample colour and its band structure could be found in [43]. For the implantation fluences larger than 10 15 cm −2 a large increase of the absorbance could be seen as well as the shift of the absorption edge towards larger wavelengths as in the case of noble gas implantation [54]. Both these effects are due to the formation of conduction carbon cluster structures related to the decrease of the optical bandgap of the modified sample which was also seen in Ref.…”