Modification of PET Foil by 150 keV Li+ Ion Implantation.

Very thin (3 μm in thickness) polyethylene terephthalate polymer foils were implanted with 150 keV Li+ with fluences in the range from 1×1014 cm^-2 up to 2×10¹⁶ 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 × 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 × 1016 cm^-2, and this effect is much smaller than that induced by the heavier projectile bombardment with the same fluence. [ABSTRACT FROM AUTHOR]