本論文以銅氧化物與銀修飾的氧化鋅奈米線做成的氣體感測器，偵測氮氧化物氣體吸附前後的電阻變化，探討其氣體感測的效果與機制。首先在以黃光微影製程製作鈦金屬電極圖案的矽基板上，利用簡單又低成本的水熱法合成氧化鋅奈米線，並再對氧化鋅奈米線以光還原法分別進行銅氧化物與銀的修飾，進而製作成氣體感測元件。本實驗使用310 nm的紫外光激活模式，在大氣環境下對不同製程參數製作而成的氣體感測元件，進行低濃度一氧化氮與二氧化氮的氣體感測。
由掃描式電子顯微鏡、穿透式電子顯微鏡與能量色散X射線光譜，分析材料的表面形貌、材料結構與元素組成，確認了氧化鋅奈米線的良好結晶性，以及分布於其上的氧化銅、氧化亞銅和銀。未經修飾的氧化鋅奈米線，對1 ppm的一氧化氮氣體響應度為46%；而在氧化鋅奈米線加上銅氧化物或銀的修飾後，皆可增加其對一氧化氮氣體的響應度。其中在氧化鋅奈米線上分別加上以10-4 M之硫酸銅水溶液光還原50分鐘的銅氧化物，以及以0.05 M之硝酸銀水溶液光還原1.5分鐘的銀，於 1 ppm的一氧化氮氣體感測，分別得到401%與168%的響應值。若在氧化鋅奈米線上共修飾最佳參數的銅氧化物與銀，對1 ppm一氧化氮氣體響應度則可以達628%，對0.03 ppm的一氧化氮也可以達到43%的響應。而以銅氧化物與銀的最佳參數共修飾的元件，對1 ppm的二氧化氮氣體感測響應度可達到4305%，對0.03 ppm二氧化氮的響應度也高達600%。
加銅氧化物與銀修飾的氧化鋅奈米線，使氣體感測響應度提升的原因，除了表面空乏區增加，使感測前後的電阻率變化更為敏銳外；從照光前後的電阻率變化，推測修飾後的氧化鋅奈米線在異質接面產生能帶變化，促使照光後產生的電子電洞對的再結合率降低，增加氣體吸附的可能；另外銅氧化物和銀對於氮氧化物的活性也是增強氣體感測響應度的原因之一。
本實驗以簡單與便宜的製程製作出對氮氧化物氣體響應良好的材料，在未來開發商業化的低濃度氮氧化物氣體感測器有很大的潛力。

In this work, the gas sensors based on CuxO and Ag modified ZnO nanowires (NWs) for NOx gas are reported. Detecting the changes in resistances due to the adsorption of NOx, the property and mechanism of the NOx gas sensors is discussed. The ZnO NWs were first grown by simple and low-cost hydrothermal growth method on Si substrate with patterned Ti electrodes realized by photolithography. Then the ZnO NWs were modified by adding CuxO and Ag respectively by photoreduction processes. In this experiment, the gas sensors fabricated with different photoreduction parameters were used to sense NO and NO2 gas under ambient environment by using 310 nm UV light activation mode.
The results of scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy show the morphology, structure and elemental composition of the materials. Besides, they confirm the good crystallinity of the ZnO NWs and the decoration of CuO, Cu2O and Ag. The response of ZnO NWs for 1 ppm NO gas is 46%, and the ZnO NWs modified with CuxO or Ag show better response for NO gas. The responses of CuxO/ZnO sensor under the condition of 50 minutes photoreduction with 10-4 M copper sulfate aqueous solution and Ag/ZnO sensor under the condition of 1.5 minutes photoreduction with 0.05 M silver nitrate aqueous solution are 401% and 168% respectively. The response of Ag/CuxO/ZnO sensor with the best photoreduction parameters for NO gas sensing is 628% at 1 ppm, and 43% at 0.03 ppm. Moreover, the response of the Ag/CuxO/ZnO sensor for NO2 gas sensing achieved 4305% at 1 ppm, and 600% at 0.03 ppm.
The reasons for the enhancement of gas sensing with the modification of ZnO NWs by CuxO and Ag attribute to the more sensitive resistance changes caused by the increase in surface electron-depletion layer. In addition, from the change of resistivity before and after UV light illumination, it can be inferred that the modified ZnO NWs produce energy band changes at the heterojunction, which decreases the recombination probability of electron hole pairs produced after illumination and increase the possibility of gas adsorption. Furthermore, the activities caused by CuxO and Ag also enhance the gas sensing responsivity for NOx gas.
In this work, the NOx gas sensor with excellent sensing capability and low fabrication cost is demonstrated. It shows a great potential on the development of a commercial low-concentration NOx gas sensor in the future.

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