RELATION BETWEEN OPTICAL AND ELECTRICAL-PROPERTIES OF ION-IMPLANTED PPV

Poly(p-phenylene vinylene) has been synthesized using the sulphonium p recursor route. Heat treatments have led to the formation of free-stan ding PPV films, which have been implanted at increasing ion fluences i n the energy range 50-150 keV. Optical absorption and specular reflect ance have been studied in the wavelength domain 200-3000 nm. The progr essive shift of the absorption edge from the UV towards the visible ha s been attributed to the narrowing of the band gap, whereas the signif icant increase of the reflectance in the near infrared has been interp reted by the development of aromatic domains. A permanent increase by more than 13 orders of magnitude of the conductivity has been obtained in correlation with the progressive narrowing of the band gap. The co mparison between implantations performed with doping ions and rare gas es, producing comparable damage, shows significant differences at ener gies lower than 80 keV for heavy ions (iodine and xenon) and lower tha n 150 keV for light ions (sodium and neon), providing evidence for a d oping effect, which is screened by the radiation damage at high implan tation energies. The magnitude of this effect is, however, limited (on e order of magnitude) in comparison to the conductivity enhancement (1 3 orders of magnitude) resulting from the radiation damage. The irreve rsible structural changes induced in ion implanted PPV films lead to t he conclusion that the electronic doping occurs in a new material, whi ch may be compared to (DLC) diamondlike films involving a significant sp2 component.