現在由於大家對空氣品質與工業環境的環保意識逐漸抬頭，如何製作出一個優良的氣體感測器受到許多學者與廠商們所廣泛研究，而隨著奈米顆粒金屬氧化物氣體感測器的問世，其氣體響應度能隨著奈米粒徑減少而有大幅的的提升。對於傳統薄膜型氣體感測器而言，奈米微粒等級材料由於粒徑小、可與偵測氣體接觸的表面積大，大大提升了感測器的靈敏度，具有相當高的應用價值，而氧化鐵正好符合了奈米顆粒結構，作為量測薄膜能有著很好的氣體偵測性質。
在本實驗中我們選擇共沉降法去合成兩種不同型態的氧化鐵奈米顆粒，藉由適當改變製程參數就能配出氧化鐵的磁鐵礦(Fe3O4)與赤鐵礦(α-Fe2O3)型態，以進行後續氣體量測與材料研究，而共沉降法在製程上有著便宜、安全且大量生產的優點。
結果顯示利用金屬中心爐管退火的磁鐵礦(Fe3O4)氣體感測器在對於二氧化氮的偵測上有很高的響應，而一樣是利用金屬中心爐管退火的赤鐵礦(α-Fe2O3 )氣體感測器則是對酒精有很高的選擇比，皆比利用台灣半導體研究中心的快速熱退火機台有更好的量測結果，因此對於金屬氧化物半導體材料來說，適當的選擇退火方式將能把氣體感測器的響應最佳化，而選擇正確的材料將能對特定的氣體去進行最有效的偵測。

The increasing awareness of the environmental pollutions and industrial onsite safety demands have prompted the development of sensors in full thrust. The gas sensing properties of metal-oxide material are closely related to their composition, crystalline size, and surface morphology. Due to its small particle size and large surface area, the iron oxide nanoparticles greatly enhance the sensitivity of the sensor and has a high application value.
In this experiment, the co-precipitation is utilized to synthesize two different types of iron oxide nanoparticles, namely, both magnetite (Fe3O4) and hematite (α-Fe2O3) are formulated for subsequent gas measurements and fundamental material characteristics evaluations by appropriately changing the relevant process parameters. The co-precipitation method is regarded as an economic way to synthesize iron oxide with the advantages of a low-cost, handling safety, and production in great quantity.
The results show that the magnetite (Fe3O4) gas sensor annealed by muffle furnace has a high response to the detection of nitrogen dioxide, while the hematite (α-Fe2O3) gas sensor annealed by the same muffle furnace, on the other hand, has a high detecting selectivity towards ethanol. Consequently, comparatively better gas measurement results are obtained compared with those found using the rapid thermal annealing (RTA) furnace.
For metal oxide semiconductor materials, the appropriate annealing method must be adopted to optimize the response of the gas sensor and also to choose the right material to perform the most effective detection of a particular gas.

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