Electrically conducting thin films obtained by ion implantation in pyrolyzed polyacrylonitrile

Abstract 

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.