전기 중합법을 이용한 전도성 고분자 나노와이어 합성 및 화학 센서 응용을 위한 연구

Abstract

Conducting polymers are the fascinating electrically conducting materials due to their good environmental stability and biocompatibility. Moreover, electrical conductivity of conducting polymers is easily tunable through controlling the concentration of doping elements, which allows them to be adopted to various applications, much attentions have focused on the role of the conducting polymer as an active layer in chemical and biosensors. One-dimensional(1-D) nanomaterials including nanowires and nanotubes have great potential to provide alternatives for bulk materials in chemical and biosensors due to its high surface to volume ratio which exhibits unique physical and chemical properties that offers the prospect of high sensitivity and rapid detection. However, it is difficult to obtain micro or nanoscale patterning of conducting polymers with the conventional photolithography technique, because the conducting polymers are organic materials which could be easily damaged by photoresist removing solvent. In this study, three experimental groups were conducted to electrochemically fabricate Ppy nanowires-based NH3 gas sensor. First, Ppy films were synthesized on the metal electrodes(Ni, Au) by the electropolymerization. The anodic potentials of the pyrrole monomer were measured by cyclic voltrmmetry and were set to a fixed value in the range 0.7 - 1 V vs Ag/AgCl electrode for a desired time. The effect of applied potentials and times on growth of Ppy film was observed by the potentiostatic electropolymerization. Second, the new electropolymerization mehod was investigated for synthesizing Ppy microwire, in which, pre-fabricated dumbbell-shaped Ni pattern electrode by the microfabrication was used as sacrificial seed layer, and Ppy was deposited on its electrodes by the electropolymerization. As result of removing Ni sacrificial layer by wet etching in 5% HNO3 solution, sole interconnect of Ppy microwire with a width of 3-5 μm and a electrical resistance of 843 kΩ could be obtained. Ppy microwire synthesized by the new method was applied to chemiresistive sensor, and gas sensing performance to NH3 gas was investigated with two-probe method. Although Ppy microwire-based NH3 sensor exhibits response to NH3 gas, the performance of NH3 sensing was too bad to detect low concentration of NH3 gas. Finally, in a similar way, Ppy nanowires were electrochemically synthesized using a new electropolymerization method which was that Ni nanowires fabricated by AAO template method was magnetically aligned on Au electrodes as a sacrificial seed layer to grow Ppy nanowires and then the Ni nanowires were selectively removed in acidic solution. The contact resistance(~35 Ω) between the Ppy nanowires and Au electrodes and the electrical resistivity(0.242 Ωcm) of Ppy was calculated with extrapolation of the serial resistance by varying the dimension of Ppy nanowires. The contact resistance between the Ppy nanowires and Au electrodes was found to be significantly low value, which is effectively improved the sensitivity of Ppy based gas sensor for the detection of a sub-ppm level concentration of NH3 gas.