Heat treatment of polyacrylonitrile (PAN) leads to products with semiconductor-to-metal range of conductivities. The electrical properties of these materials are further modified by ion implantation. The conductivity, 1×10–7 (Ω cm)–1, of heat treated PAN at 435°C (PAN435) increases upon ion implantation with As+, Kr+, Cl+ or F+, reaching the maximum value of 8.9×10–1 (Ω cm)–1 at a dose of 5×1016 ion/cm2 and an energy of 200 KeV for the case of F+ implantation. On the other hand, ion implantation in the more conducting heat-treated PAN at 750 °C (PAN750) leads to a decrease in the electrical conductivity. It is shown that the conductivity modifications are primarily due to structural rearrangements induced by the energetic ions. Specific chemical doping contribution to conductivity is noted for halogen implantation in PAN435. The temperature dependence of conductivity of PAN heat treated at 750°C suggests a two path conduction, namely a three dimensional variable range hopping conduction and a metallic conduction. After ion implantation, the conductivity-temperature dependence is interpreted in terms of a variable range hopping conduction mechanism.
Infrared (IR), Auger electron spectroscopy (AES) and X-ray photoelectron spectra (XPS) of pristine, pyrolyzed, and ion-implanted poly(acrylonitrite) (PAN) samples were obtained in order to correlate the structural changes accompanying pyrolysis and implantation with the electrical properties of the respective PAN products. The results show that PAN is first converted to a polyconjugated heterocyclic ladder structure at a temperature of 435 °C and then to a graphite-like structure at temperature above 750 °C. Pyrolysis studies took place in a temperature range of 350–750 °C. IR studies showed that upon heat treatment at 435 °C, major structural changes occur as indicated by the complete disappearance of the nitrile and methylene absorption bands and the formation of new bands. The degree of conjugation in pyrolyzed PAN can be selectively controlled by the proper choice of the heat treatment temperature. From the studies, ion implantation causes extensive nitrogen depletion and the nitrogen chemical state in the implanted sample is different from that found in the pyrolyzed materials. Upon ion implantation, the component assigned to the nitrogen in a sigma bonding state (401.27 eV) increased in intensity (46%) relative to the intensity (27%) of the component for which nitrogen is in a hetroaromatic structure. Both AES and XPS analysis showed the variation of C:N ratio as a function of heat treatment.