Modification of PET Polymer Foil by Na⁺ Implantation

Abstract

Very thin (3 µm) polyethylene terephthalate (PET) foils were irradiated with 150 keV Na + ions with the fluences in the range from 1 × 10 14 cm −2 up to 1 × 10 16 cm −2. Modification of chemical structure of the implanted polymer was studied with the Fourier transform infrared and Raman spectroscopies. Destruction of numerous chemical bonds as well as formation of carbon clusters made of sp 2 hybridised C atoms and conducting cluster networks were demonstrated. The increasing presence of chain structures in the graphite-like carbonised layer is pointed out as the G band shift and decrease of D band could be seen as irradiation fluence rises. The large increase of the modified sample absorbance with the implantation fluence in the UV-VIS region was observed. The decrease of optical band-gap energy from 3.95 eV for the pristine sample down to 0.7 eV for the most heavily treated sample was estimated using the Tauc plot. Reduction of bulk resistivity by more than 8 orders of magnitude is shown in the case of the sample implanted with the fluence 1 × 10 16 cm −2. The sheet resistivity of the sample was also reduced by 5 orders of magnitude. The effect was observed on both sides of the sample, probably as the result of chemical transformations due to local increase of the polymer foil temperature. The moderate increase (15-200%) of the dielectric constant is observed in the frequency range up to 1 MHz and the change rises with the implantation fluence.

Modification of Optical, Electronic and Microstructural Properties of PET by 150 keV Cs+ Irradiation

“…The resistivity decreases with fluence due to the formation of conducting carbon structures at the polymer surface. This effect is comparable to that observed for Na + irradiations [31] -the resistivity of sample implanted with the fluence 10 16 Cs + /cm -2 is almost 8 orders of magnitude smaller than that of the pristine sample. One deals with strong carbonization effect in the topmost layer of the polymer due to short projected range and the domination of the nuclear stopping in the case of the very heavy projectile.…”

“…As it has been already mentioned the modification of the PET polymer by Cs bombardment seems less intense than in previously considered cases of lighter alkali metal ions. One can see the darkening of irradiated samples but the intensity of that transformation is smaller than in [31]. Changes of the sample transparency was tested quantitatively using UV-Vis spectroscopy.…”

“…The ion average range was only ~100 nm with the 20 nm strangling. However one may expect that real Cs range could be at least 2 times larger having in mind results presented in [31] for Na implanted PET and then investigated with SIMS-TOF spectroscopy. In other words, one should be rather suspicious to the SRIM predictions in the case of polymer target bombardment.…”

“…It can be also a good base for high strength polymer blends [28] However, its large resistivity may e.g limit its application in electronics industry. One of the most popular ways to make it more conductive is ion implantation-formation of carbon cluster in the near-surface layer due to ion bombardment leads to dramatic decrease of resistivity by several orders of magnitude [29][30][31][32]. This structural change could be also easily seen as a darkening of the initially transparent polymer, due to modification of the band structure leading also to the bandwidth reduction to values typical for semiconductors.…”

“…Hence, it is not possible to induce changes of the polymer structure that lead e.g. to the changes of resistivity also on the reverse side, as it was seen in the case of very thin foil (3 micrometers) and lighter projectiles [30,31]. One may expect that the sample characterized by the thickness larger by more than two orders of magnitude is more resistant to changes induced by radiothermolysis occurring during ion bombardment.…”