Temperature- and magnetic field-dependent electrical transport studies of poly(-3,4 ethylenedioxythiophene) nanoparticles

Poly(3,4-ethylenedioxythiophene) nanoparticles with average diameter of 13 nm have been synthesized by oxidative polymerization method using dodecylbenzene sulfonic acid (DBSA) as surfactant. Thermogravimetric analysis shows the improvement of thermal stability with increasing surfactant concentration. The red shifting of the 1,381 cm−1 band with increasing DBSA concentration indicates the transition from benzenoid to quinoid structure. The temperature dependence of resistivity reveals that the charge transport takes place through variable range hopping (VRH) mechanism. The slopes of reduced activation versus temperature plot confirm that the charge transport takes place through 3D VRH mechanism. The negative slope of the reduced activation energy versus temperature plot indicates that our samples fall in the insulating regime. Magnetoresistance study shows a transition from positive to negative with increasing temperature. The negative value of magnetoresistance at higher temperature is due to the quantum interference effect where the charge carrier hopping distance in comparable to the localization length and the positive magnetoresistance at low temperature results due to the shrinkage of impurity orbitals under magnetic field. The higher value of positive magnetoresistance than that of the negative magnetoresistance indicates that wave function shrinkage effect is stronger compared to quantum interference effect.