Temperature Dependence of AC Electrical Conduction in Plasma Polymerized Pyrrole-N,N,3,5 Tetramethylaniline Bilayer Composite Thin Films

Abstract

The temperature dependence of alternating current (ac) electrical conduction in Plasma Polymerized Pyrrole-N,N,3,5 tetramethylaniline (PPPy-PPTMA) bilayer composite thin films have been discussed in this article. The thin films were deposited by using a parallel plate capacitively coupled glow discharge reactor. To study the temperature dependence of ac electrical conduction the variation of dielectric constant (<i>ε</i>′), the dielectric loss factor (<i>ε</i>"), and the ac conductivity (<i>σ_ac</i>) of the thin films were investigated in the frequency range 100 Hz to 10 MHz and in the temperature range 298K to 398K. The decrease of dielectric constant <i>ε</i>′ with increasing frequency was observed and was attributed to the dielectric relaxation process. The dielectric constant, however, is observed to be increased with temperature in all frequency regions which is due to greater freedom of movement of dipole molecular chain in polymer films at high temperature. The variation of dielectric loss factor <i>ε</i>" with frequency showed a loss minimum then rises to a sharp peak which was also attributed to the relaxation phenomena of polymer. It is, however, observed that the loss peaks have shifted towards the higher frequency side with the increase of temperature which is usually attributed to dipolar orientation. The dielectric loss factor is also observed to be increased with temperature in all frequency regions. At lower frequencies the increase of loss factor with temperature was attributed to the effective chain motion of polymer and at high frequencies this increase might indicate the orientational polarization due to chain motion in bilayer film. The linear behavior of the ac conductivity <i>σ_ac</i> with the frequency and the observed weak temperature dependence of <i>σ_ac</i> led to interpret the ac conduction mechanism as the hopping between localized states at the Fermi level.