The Conducting Polymer Nanostructures: Fabrication Methods And Their Application In Nanosensor Areas

Conducting polymers are particularly appealing materials that could be used at all levels of microelectronics as alternatives for metal and semiconductors. Their ease of processing, flexibility, light weight, together with their chemically tunable properties make them especially useful in low-end microelectronics where expensive silicon technology is not necessary. Conducting polymers are also good sensing materials. The sensing mechanism involves doping/dedoping of the polymer chain in the case of PH sensors, or the charge transfer between polar molecules and polypyrrole in the case of Volatile Organic Compounds (VOC) sensors. By scaling down the conducting polymer films into nanometer wires, the nanosensor showed higher sensitivity, faster response and lower power consumption. However, due to the lack of nanofabrication methods, it is rather difficult to obtain conducting polymer structures with the dimensions equal to or less than 100 nm, especially on insulating surfaces. Therefore, we demonstrate that by in-situ synthesis of strongly adherent polypyrrole, sub-micron wires and sensor devices with feature size as small as 200 nm in width can be successfully fabricated through a lift-off process. Since this method offers the opportunity to grow polypyrrole wires in-situ at a desired position, sub-micron wires can thus be introduced between two microelectrodes. Thus, we successful developed a novel fabrication method for constructing conducting polymer nanosensors. We further evaluated the sensing performance of the as-fabricated conducting polymer nanosensor. However, due to the lack of control over the film thickness during deposition, the above method is not suitable for high resolution (< 100 nm) fabrication. In the following study, we use copolymer strategy to control the thickness, adhesive and electrical properties of conducting polymer by incorporating a surface active monomer into their main chains, thus make it suitable for the fabrication of devices exclusively based on conducting polymers with a sub 100 nm resolution through a lift off process. Due to the generality of the copolymerization process, this method is applicable to a wide range of conducting polymer species. Two different types of nanostructures consisting exclusively of polypyrrole or polyaniline are fabricated and their use as nanosensors is demonstrated. The prepared nanosensors exhibit sensing performance superior to the micrometer scale sensors fabricated with the same method. The above developed methods can already be used to fabricate conducting polymer nanodevice-that is, conducting polymer nanosensors. However, these methods are not expected to be useful in obtaining the real product due to their cost. To go toward the realization of real nanosensor procucts, low cost fabrication methods are required. Therefore, in the following work, we report the fabrication of a high density conducting polymer nanostructures, which is achieved by nanoimprint lithography through a lift off process. The constructed conducting polymer nanowires, through further electrical connection, could be easily functioned as nanowire nanosensors. Giving the nanoimprint lithography's merits, particularly low cost, this work provides a low cost fabrication method to obtainnanosensors. In addition, the generality feature of this method makes it suitable to be used as a way to construct conducting polymer nanostructure that may find applications in many other areas.