Study On Single Polymer Nanofiber Sensors

The nano-fabrication technology and micro electronics and mechanism system offer the promise of improved sensors with small size, low-power consumption, high sensitivity, fast response time and reliable repeatability. There are increasing demands for nano/micro sensors in physical, chemical and bio-sensing areas. Nano/micro fiber sensor, as part of nano/micro sensors, draws wide attention due to its adaptability to micro electronic system. This dissertation presents the synthetic procedure, piezoelectric sensing and gas sensing characteristics.Based on current electrospinning methods, near field electrospinning is used to synthesize controllable single polymer fiber and aligned fiber array. This synthetic procedure has unique properties over its bulk counterparts, which provides the possibility to analysis piezoelectrical and gas sensing mechanism deeply. Different materials, fabrication parameters and environment conditions are compared to optimize the fiber characteristics.poly(vinylidene fluoride) fiber is synthesized by near field electrospinning. Compared with conventional electrospinning, near field electrospinning provides higher electrical field which brings better fiber polling effect. PVDF fiber showed higher piezoelectricity efficiency than conventional PVDF film. These fibers will be attractive for many applications, including pressure sensor, tactile sensor and energy harvester.Singl e polyaniline nanof iber was investigated to understand electrical performance and sensing mechanisms. The fibers showed Schottky contact and ohmic contact based on different electrode materials. We studied the morphology, field effect characteristics and gas sensitivity of conductive nanofibers. Conductive nanofiber could be promising for flexible circuits and organic semiconductor applications. Applied higher gate voltage will contribute to the increase in gas sensitivity. The FET characteristics of sensor exposed to different gas concentrations indicate that adsorption of NH3 molecules reduce the carrier mobility in polyaniline nanofiber.The need for selective gas sensors with high sensitivity, and fast response is increasing for various applications. Metals and metal salts exhibit selective changes in the working function on exposure to specific gases. In this dissertation, polyaniline nanofibers doped with palladium nanoparticles have been deposited in control led 2-D patterns across two gold electrodes by near field electrospinning without the conventional lithography process. We successfully fabricated single polyaniline hybrid nanofiber with ultra low power consumption. Test results indicated the nanofiber gas sensors have the advantages of selectivity, sensitivity and reversibility. Polymer and palladium hybrid could form a flexible structure to minimize the effect of lattice expanding for stable sensing structure in hydrogen sensing.The diameter of fiber can be controlled by many factors, including bias voltage, needle-to-electrode distance, as well as the solution concentrations. Fibers with different diameters are tested to verify the response time. Metal-polymer hybrid equivalent model and gas diffusion mechanism are developed in the dissertation. This theory will contributes to future improvements of gas sensors.