Optical and dielectric properties of fluorinated ethylene propylene and tetrafluoroethylene–perfluoro(alkoxy vinyl ether) copolymer films modified by low energy N and C ion beams

Fluorinated ethylene propylene (FEP) and tetrafluoroethylene–perfluoro(alkoxy vinyl ether) (PFA) copolymer films were irradiated in vacuum with 60 keV C⁴⁺ and N⁴⁺ ions to fluences ranging from 1.0×10¹² to 5.0×10¹⁵ cm⁻². Changes in optical and dielectric properties were analyzed by spectroscopic ellipsometry and ultraviolet–visible (UV–vis), Raman and dielectric relaxation spectroscopies. Direct and indirect energy band gap values were determined from the absorption edge in the 200–800 nm region using Tauc's relation. The values of the direct energy gap have been found to be greater than the corresponding values of the indirect energy gap. Significant changes in the index of refraction, and β and γ dielectric relaxations were observed in the case of N⁴⁺ irradiated FEP and PFA samples.