- 學位論文
光學以及電化學對於一氧化碳及二氧化碳感測器的研究
Study of CO/CO2 sensing with optical/electrochemical detection method
摘要
根據資料指出，室內二氧化碳濃度在700ppm時，會使人感到空氣汙濁；而當二氧化碳濃度在1000ppm以上時，會影響人類呼吸器官而造成氣喘、頭暈等症狀；當二氧化碳濃度在5000ppm以上時，會嚴重危害生命安全。 對於一氧化碳而言，其為無色無味的氣體，但吸入對人體的危害非常大。當待在一氧化碳濃度為100ppm的室內一段時間時，就會產生噁心、頭痛等症狀；而在一氧化碳濃度為1600ppm的環境兩小時，就會死亡。 本研究是利用光學感測的方法，來進行二氧化碳濃度的感測，並且使用模擬軟體加以改良以及微縮，探討其結構及光源的強度對二氧化碳濃度的靈敏度的影響。針對各種氣體皆會有對光源的吸收頻譜，我們利用了二氧化碳對紅外光的吸收頻譜，再經由感測器讀出來的讀值，來反推此時二氧化碳的濃度。當二氧化碳濃度較濃時，其吸收的光源較多，而導致感測器的讀值與沒有二氧化碳濃度時的讀值的變化量較大，隨著濃度愈來愈小，感測器的讀值與沒有二氧化碳濃度時的讀值的差距也會愈來愈小。此時，要如何讓光源能有效的被吸收，也是一個需要深入探討的方向。 接下來是探討石墨烯改質前後對二氧化碳濃度以及一氧化碳濃度的反應。由於石墨烯電阻率低、電子移動速度快、且為一種二維材料，因此被認為是新一代的電子材料。然而，功能化的石墨烯相比於原始的石墨烯，不僅能夠改善其物理特性，也可提高石墨烯元件的性能。因此，此研究也針對了石墨烯的製備及其改質前後的量測作為探討。 在製備石墨烯的過程中，我們使用的是化學氣相沉積法(CVD)，而所使用的氣體分別為氮氣、氬氣、氫氣、甲烷，並且在拋光後的銅箔上生長。我們在製備的過程中，分別探討了每種氣體對石墨烯成長的影響，進而調整其參數，使得我們做出來的石墨烯為單層，且2D/G的比值要大，缺陷要小。 之後，再將製備好的石墨烯利用低損傷電漿系統(LD-plasma)對其進行改質，並且探討其改質後電性與物理特性的變化、以及對氣體感測的應用。此改質是利用氮電漿改質單層石墨烯，並且對改質時間做不同的調整，再經由拉曼光譜量測結果得知，可以藉由增加改質的時間，穩定地調控石墨烯改質的程度，而低損傷電漿系統中的互補式遮版架設，阻擋了大部分的離子轟擊與紫外光輻射，因此大大降低對石墨烯的改質傷害；然而，若改質時間過長，則依然會對石墨烯造成傷害。而氮氣本身活性小，較難在石墨烯表面進行鍵結，由於低損傷電漿系統的架設，會使得氮原子僅藉由擴散機制，對石墨烯進行改質，這降低氮改質石墨烯的成效，但我們在氮改質製程中發現，在石墨烯的基板上加熱，利用溫度的效應，可以促使氮改質石墨烯的形成，並且藉由加熱溫度的調整，可以穩定控制氮改質石墨烯的程度。最後我們再相較先前文獻中，傳統電漿氮改質石墨烯的成果，其結果顯示我們氮改質的製程，是非常良好的，對於氮改質石墨烯的製程上，是相當大的研究突破。 最後再將改質前後的石墨烯進行了二氧化碳及一氧化碳的量測，針對5000~500ppm濃度的二氧化碳以及1000~100ppm濃度的一氧化碳做了電性的量測，並將其結果與光學感測的方法做比較。
並列摘要
According to the report, when the indoor carbon dioxide concentration becomes 700ppm, people will feel air pollution; while the carbon dioxide concentration becomes 1000ppm, it will affect people’s respiratory organs and cause symptoms such as asthma and dizziness. When the carbon dioxide concentration becomes 5000ppm and above, it will endanger people’s life safety. For carbon monoxide, it is colorless and odorless, but it is harmful to the human body. When staying in a space with a carbon monoxide concentration of 400 ppm for a while, people will feel nauseous and headache; while staying in a space with a carbon monoxide concentration of 1600 ppm for two hours, will cause death. In this work, we used the optical sensing method to measure the carbon dioxide concentration, and used simulation software, COMSOL Multiphysics, to improve and scale the chamber. Also, we discussed the influence of its structure and the intensity of the light source on the sensitivity of carbon dioxide concentration. Regarding the absorption spectrum of the light source for various gases, we used the absorption spectrum of infrared light by carbon dioxide and reversed it from the readings of the sensor. When the concentration of carbon dioxide was higher, it absorbed more light sources, which resulted in a larger change between the readings of the sensor when there was carbon dioxide concentration and the readings of the sensor when there was no carbon dioxide concentration. As the concentration became smaller and smaller, the difference between the sensor reading with carbon dioxide concentration and the reading without carbon dioxide concentration would also become smaller. At the same time, how to make the light source be effectively absorbed was also a direction that needed to be discussed. The next step was to discuss the reaction of the carbon dioxide concentration and carbon monoxide concentration before and after the graphene modification. Since graphene had the characteristics of low resistivity and high electron mobility. Also, it was a two-dimensional material, and it was considered a new generation of electronic materials. However, compared with the original graphene, functionalized graphene can improve its physical properties and improve the performance of graphene components. Therefore, this work also focused on the preparation of graphene and the measurement before and after graphene modification. In the process of growing graphene, we used the method of chemical vapor deposition, and the gases we used were nitrogen, argon, hydrogen, and methane, then they were grown on a polished copper foil. After the Raman analysis, we discussed the influence of each gas on the growth of graphene respectively and then adjusted their parameters so that the graphene we made would be single-layer graphene with a large 2D to G ratio and small D to G ratio. After that, the prepared graphene was modified with a low-damage plasma system, and the changes in electrical and physical properties after modification and the application of gas sensing were discussed. We used nitrogen plasma to modify the single-layer graphene, and the time of the modification was adjusted differently for one to seven minutes, then, the Raman spectroscopy measurement results showed that the modification degree of the graphene could be stably controlled by increasing the modification time. The complementary mask setup in the low-damage plasma system blocked most of the ion bombardment and ultraviolet radiation, thus greatly reducing the damage to the modification of the graphene. However, if the modification time was too long, it would still cause damage to the graphene. Nitrogen was less active and was difficult to bond on the surface of graphene, thus, due to the low-damage plasma system, nitrogen atoms would only use diffusion mechanisms to modify graphene, which reduced the efficiency of the nitrogen-modified graphene. However, in the nitrogen modification process, we found that using the effect of temperature to heat on the graphene substrate can promote the formation of nitrogen-modified graphene, and by adjusting the heating temperature, the nitrogen-modified graphene could be stably controlled. Finally, we compared the results of traditional plasma nitrogen-modified graphene in the previous literature, and the results showed that our nitrogen-modified process was well-performed. Finally, carbon dioxide and carbon monoxide were measured for the graphene before and after the modification. The electrical measurements were made for carbon dioxide with a concentration of 5000~500ppm and carbon monoxide with a concentration of 1000 to 100ppm, and the results were compared with optical sensing methods.