N+ion–target interactions in PPO polymer: A structural characterization

Abstract

N+ ion beam induced effects on the spin coated amorphous poly(2,6-dimethyl phenylene oxide) (PPO) films in terms of chemical structure and electronic and vibrational properties were investigated using Fourier Transform Infrared spectroscopy (FTIR) and Ultraviolet–Visible (UV–VIS) spectroscopy. Both techniques revealed that the stability of PPO was very weak towards 100 keV N+ ions revealing the threshold fluence to be 1014 ions/cm2 for fragmentation of the polymer. FTIR analysis showed disappearance of all characteristic IR bands at a total fluence of 1014 ions/cm2 except for the band CC at 1608 cm−1 which was found to shift to a lower wave number along with an enhancement in the full width half maximum (FWHM) value with increasing fluence. A new bond appeared due to oxidation as a shoulder at 1680 cm−1 in FTIR spectra indicating the presence of CO type bond as a result of N+ implantation on PPO films. The optical band gap (Eg) deduced from absorption spectra, was observed to decrease from 4.4 to 0.5 eV with fluence. The implantation induced carbonaceous clusters, determined using Robertson’s formula for the optical band gap, were found to consist of ∼160 fused hexagonal aromatic rings at the maximum energy fluence. An enhanced absorption coefficient as a function of fluence indicated incorporation of either much larger concentration of charge carriers or their mobility than that of the pristine sample. Calculated band tail width from Urbach band tail region for the implanted samples pointed the band edge sharpness to be strongly dependent on fluence indicating an increased disorder with increasing fluence.