Modification of PET Foil by 150 keV Li+ Ion Implantation

Abstract

Very thin (3 µm in thickness) polyethylene terephthalate polymer foils were implanted with 150 keV Li⁺ with fluences  in the range from  1 x 10¹⁴ cm^-2 up to 2 x 10¹⁶ cm^-2. Modification of the irradiated polymer microstructure was studied with the Fourier transform infrared spectroscopy and Raman spectroscopy. Breaking of a variety of chemical bonds followed by the formation of carbon clusters made of sp² C was proved. The dominance of the rings in the carbonized, graphite-like subsurface layer is demonstrated based on the fact that the G band prevails in the Raman spectra for larger Li⁺ fluences. The rise of the absorbance within 200–800 nm is observed. Tauc's plots analysis enables the estimation of optical bandgap values that decrease from 3.95 eV (pristine polyethylene terephthalate) down to 1.4 eV (fluence of 2 x 10¹⁶ cm^-2). This change is not as dramatic as in the case of heavier projectiles like K⁺ or Na⁺. Reduction of surface resistivity by more than 2 orders of magnitude is observed in the case of the sample irradiated with the fluence 1 x 10¹⁶ cm^-2, and this effect is much smaller than that induced by the heavier projectile bombardment with the same fluence.