| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 104 === Recently, metal-oxide semiconductor-based gas sensors have gotten a great attention due to their special advantages, such as low cost, high performance and easily fabricated. ZnO has been extensively studied, because it can be applied to sense various gases. One-dimensional ZnO nanostructures can enhance the sensing performance. The vertical nanowire array is a common structure for ZnO nanowire-based gas sensor. However, the seed layer under the nanowire array reduces the sensing capability. Therefore, in this study, the gas sensing devices were fabricated by the arrangement of nanowires between the electrodes.
ZnO nanowires were synthesized on the ZnO seed layer by hydrothermal method. The alternating current electrical field was used to align ZnO nanowires of different lengths between the electrodes. For gas sensing application, two types of the nanowire structured devices were used to detect CO.
The results show that a flat surface and small grain of seed layer was received by annealing at 300℃, and it can be used to fabricate ZnO nanowires with small fluctuation in length and width by hydrothermal method. ZnO nanowires had the highest aspect ratio when the concentration of precursors was 0.04M. The length of nanowires increased by adding an appropriate concentration of Polyetherimide (PEI). In the process of ZnO nanowires aligment by dielectrophoresis method, the parallel and crossed ZnO nanowire-based devices were achieved by adjusting the frequency and the peak-to-peak voltage of alternating current electrical field. For the CO sensing , the sensing sensitivity and stability of the crossed structure nanowires-based devices were enhanced after annealing. The sensing sensitivity and limit-of-detection of the crossed nanowire-based devices were better than the parallel nanowire-based ones due to the potential barrier modulation at the nanojunctions between two nanowires.
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