ION-IMPLANTATION IN CONJUGATED POLYMERS - MECHANISMS FOR GENERATION OF CHARGE-CARRIERS

Ion implantation in conjugated polymers can produce both doping (with suitable choice of ions) and damage in the form of broken covalent bon ds. We consider the electronic and transport properties as assessed fr om measurements on poly(paraphenylene) of d.c. conductivity, thermopow er and a.c. conductivity studied against temperature for various impla ntation parameters. Damage is produced at high implantation energies a nd high doses, and we find that transport phenomena occur mainly in de generate states near the Fermi energy, exhibiting a p-type thermopower . We propose a model in which the sp2 sigma-dangling-bond states forme d as a result of bond scission are filled from the pi valence band. Th is partial emptying of the valence band is consistent with the transpo rt properties. Lower implantation doses at lower energies induce dopin g in polaronic bands, with both p-type and n-type thermopower, dependi ng on the ion implanted, although the effects of the defects present c an appear, especially at low temperatures.