Study The Electrical Properties Of Conducting Polymer Nanostructures

Micro/nanostructures of conducting polymers with many novel and interesting properties are one of the most important fields in material science because they have potential application in nano-electronics. Usually, the conducting polymer micro/nanostructures can be synthesized by template synthesis, template-free method, electrospinning, et al. The research of this dissertation was focused on electrical transport properties of quasi-one dimensional conducting polymers nanofibers and the rectifying effect of fabricated schottky diodes and individual freestanding film made of conducting polymer nanostructures. The main results are summarized as follows:Schottky junctions between low work function metals (e.g. Al and In) and doped semiconducting polymer pellets (e.g. polyaniline (PANI) microsphere pellet and polypyrrole (PPy) nanotube pellet) have been prepared and studied. The Al/PANI/Ag heterojunction shows an obvious rectifying effect as shown in I-V characteristic curves (rectifying ratioγ= 5 at±6 V bias at room temperature). As compared to the Al/PANI/Ag, the heterojunction between In and PANI (In/PANI/Ag) exhibits a lower rectifying ratioγ= 1.6 at±2 V bias at room temperature. In addition, rectifying effect was also observed in the heterojunctions Al/PPy/Ag (γ=3.2 at±1.6 V bias) and In/PPy/Ag (γ= 1.2 at±3.0 V bias). The results were discussed in terms of thermoionic emission theory.The heterojunction has been fabricated between two sides of one single freestanding thin film of HCl-doped polyaniline (PANI) derivative containing azobenzene side-chain, which was synthesized through an N-alkyl-substituted reaction. One side of the film that was irradiated by UV light during preparation is represented as "A side"; the other side without irradiation is represented as "N side". We measured the electrical properties of the heterojunction and observed rectifying effect which is shown in the current-voltage characteristic curves with rectifying rationγ= 20 at±0.06 V at T= 77 K andγ= 4 at±0.02 V at T=300 K.The current-voltage (I-V) characteristics of a series of individual conducting polymer nanofibers were measured and investigated from 300 to 2 K. Considering the complex structures of such quasi-one-dimensional systems with an array of ordered conductive regions separated by disordered barriers, the extended fluctuation-induced tunneling (FIT) and thermal excitation model (Kaiser expression) was used to fit the temperature and electric-field dependent I-V curves. It is found that the I-V data measured at higher temperatures or higher voltages can be well fitted by the Kaiser expression. However, the low-temperature data around the zero bias clearly deviate from this model. The deviation (or zero-bias conductance suppression) could be possibly ascribed to the emerged Coulomb-gap in density of states near Femi level and/or enhanced electron-electron interaction resulting from nanosize effects, which have been revealed in previous studies on low-temperature electronic transport in conducting polymer films, pellets and nanostructures.