A room temperature surface acoustic wave CO sensor based on Au-coated ZnO nanorods

近年來，隨著生活水準的提昇,環境空氣品質在工業以及住家環境中，對於人體健康的影響日益重要。一氧化碳是碳氫化合物燃燒不完全所產生的一種無色，無味以及無刺激性的有毒氣體，因為其不易察覺的特性使得因一氧化碳危害人體生命安全的事件層出不窮，此外，一氧化碳也會對燃料電池中作為電極的貴重金屬如白金造成毒化的現象。有鑑於此，對於一氧化碳氣體有高靈敏度，快速反應以及高穩定度的監測系統為現今一氧化碳感測科技發展的方向。去對於一氧化碳感測器的研究主要是利用半導體金屬氧化物來當作感測材料，並結合奈米結構的優點來進行量測。實驗的結果顯示這些感測器操作的溫度絕多數在80°C以上，需要加熱器，有著較大的能量消耗等缺點。由於表面聲波式之感測器對於表面的物理量變動相當靈敏，因此非常適合用來作為一氧化碳室溫下的感測平台。本論文中‭，首先製作一組中心頻率為145 MHz以128°YX-LiNbO3 當作基底的表面聲波振盪器‭，使用氧化鋅奈米柱與奈米金粒子之結合來作為一氧化碳感測的材料並以週期性之結構塗佈於表面聲波共振器表面‭。此外，使用雙振盪器之量測架構來降低環境擾動所造成的影響。由於氧化鋅奈米柱具有較大的表面積對體積比，較快的電子擴散速率以及奈米金粒子在室溫下對一氧化碳的觸媒特性，實驗結果顯示表面聲波式之一氧化碳感測器在室溫下有良好靈敏度，穩定度以及快速反應之感測性質，實為未來攜帶型一氧化碳監測系統一個很好的選擇。There is a growing demand for developing a sensing system to measure carbon monoxide (CO) not only for industry applications but also for human health in the recent years. CO is generated from the combustion of the organic matter with insufficient oxygen supply, which is colorless, odorless and tasteless. Moreover, CO is able to poison the noble metals making poor performance on the catalyst like Pt used in fuel cells. Due to the fatal danger and poisoning effect, the demand for CO detection at room temperature with high sensitivity, stability, selectivity and short response time is urgently required.he previous research of the CO sensor employed the variety of sensing material as the metal oxide semiconductor with various nanostructure, and most of them showed the operating temperature higher than 80?C causing large power consumption and problems of size reduction of the heater circuit. Since the surface acoustic wave (SAW) sensor device having high sensitivity to the surface perturbation, a CO SAW sensor based on Au-coated ZnO nanorods is realized to pursue the goals of CO detection at the room temperature. In the thesis, a SAW resonator is fabricated on 128?YX-LiNbO3 with the central frequency of 145 MHz. The ZnO nanorods and the adsorption of gold nanoparticles are adopted as the sensing material with periodic pattern structure coated on the delay line of the surface. A dual delay line configuration was also applied to eliminate the environmental fluctuations. Due to the ZnO nanorods posing high surface-to-volume ratio, fast charge diffusion rate and the room temperature catalyzing properties of the gold nanoparticles, we have successfully demonstrated the CO SAW sensor having fast response, high sensitivity, and short-term repeatability at room temperature, which is a good candidate for the portable CO monitoring application.Acknowledgements Ihinese Abstract IIbstract IIIists of Notations IVable of Contents VIIist of Figures IXist of Tables XIhapter 1 Introduction 11-1 Motivation 11-2 Category of Carbon Monoxide Sensors 21-3 Literature Review 41-4 Contents of the Chapters 5hapter 2 Theories of SAW Sensor 72-1 Coupling-of- Modes Model 72-1.1 [P] Matrix 72-1.2 Simulation of Two-Port SAW Filter 92-2 Sensing Mechanism of SAW sensor 122-2.1 Mass Loading Effect 122-2.2 Acoustoelectric Effect 142-2.3 Chemical Reaction 16hapter 3 Fabrication of SAW Sensor System 213-1 Configuration of SAW-based Oscillators 213-1.1 Fabrication of the SAW Resonator 21 3-1.2 Amplifier Design 23-2 Dual Channel Configuration 24-3 Fabrication of Sensing Material 253-3.1 Growth of ZnO nanorods 25-3.2 Adsorption of Au nanoparticles 26-4 Sensing Film with Periodic Pattern Structure 26hapter 4 Measurements of Au-caoted ZnO nanorods SAW CO Sensor 414-1 Experimental Configuration 414-1.1 Data Acquisition System 414-1.2 Gas Flow System 414-2 Thermal Effect 424-3 Measurement Results of SAW CO Sensors 434-3.1 Repeatability 434-3.2 Sensitivity 444-3.3 Limit of Detection 45hapter 5 Conclusion and Future Work 555-1 Conclusion 555-2 Future Work 56ppendix A 57ppendix B 60ppendix C 62eferences 6