奈米介孔材料之合成、結構及其氣體感測性質

Abstract

近年來，隨著工業的進展及環保意識的重視，各種廢氣量日益增加，對於有毒氣體如CO, CO2, SO2, NO2等外在環境的控制亦趨重要。它們對人體有害，同時也對環境造成嚴重的傷害。因此，偵測汙染源並提出預警變的更顯重要。為了改善傳統氣體感測器之昂貴、笨重與偵測耗時等缺點，近年來已有許多研發專注於新型氣體感測器之上。 本研究利用模版複印法製備三種新型態的奈米孔洞氣體感測器。在多孔的二氧化矽模板上分別製備p型半導體的多孔碳及多孔氧化鈷感測材料 ; 另外，利用多孔碳為模板製備n型半導體的多孔氧化鋅感測材料。初製備的此三種奈米孔洞材料均具有均勻尺寸與多孔性，利用X光繞射(XRD)光譜對不同的樣品做相鑑定；利用掃描式(SEM)及穿透式電子顯微鏡 (TEM)量測材料的結晶結構和顯微結構；利用氮氣吸脫附分析儀(BET)分析材料的表面積及孔洞的尺寸。並研究奈米孔洞材料的結構、表面形態對於ㄧ氧化碳感測特性的影響。由實驗結果得之，此三種孔洞感測材料在相當低濃度(10-100 ppm)的ㄧ氧化碳環境下均具有良好的感應能力，其中具有單晶結構的多孔氧化鋅感測材料具有51.7%的敏感度，並提出此新穎氣體感測器之可能的感測機制。 另外，為了減少能量的消耗，本研究也結合微機電技術設計並製作新型微型薄膜氣體感測器。感測器以矽為基材，並包括了加熱器、絕緣層、電極、感測層等結構，而感測材料則是在室溫下利用電泳方式排列沉積。在電泳過程中感測材料因為受到電場極化作用下聚集並沿著電場方向排列，最後成功的吸附在電極上。由實驗結果得之，多孔材料的規則排列的結構提供更多的活性反應面積使得多孔氧化鋅感測材料在70 ppm CO下有60.0%的敏感度且反應時間約為90秒。此種新穎的氣體感測器具有高靈敏度、快速的反應時間及良好的可逆性等特性，為一新穎且簡易之氣體感測器。

Recently, environmental protection has gained attention as a result of industrial development and an increase in the emission of various kinds of exhaust gases. Noxious gases such as CO, CO2, SO2, and NO2 are presented in the atmosphere. They are highly toxic for the human body and also cause indirect harm to the environment. Traditional gas sensors that have been used thus far are expensive, heavy, and prone to delay; in order to overcome these problems, many studies have focused on developing gas sensors. In this study, three novel nanoporous gas sensors were synthesized by using the template replication method. P-type semiconducting sensors for example mesostructured carbon and mesostructured cobalt oxide were synthesized using a porous SiO2 template. Further, an n-type semiconducting porous ZnO sensor was synthesized using porous carbon as a template. The prepared mesostructured materials were highly ordered porous atructure with uniform particle sizes. Powder x-ray diffraction (XRD) spectra of the different mesostructured materials confirm the phase of these materials. The crystal structure and microstructure of the mesostructured materials were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface areas and pore-size distributions of the mesostructured materials were analyzed by N2 adsorption-desorption isotherms. Structural and morphological studies were carried out in order to investigate the influence of these materials on the sensing properties of sensors synthesized using mesostructured materials. All of the sensing materials have good sensitivity for low CO concentrations (10–100 ppm). Among the porous sensing materials, porous ZnO had a sensitivity of 51.7%. The sensing-mechanism of these novel gas sensors was reviewed. In order to reduce the power consumption in sensors, in this study, we have designed and developed a system for measuring energy consumption on the microscopic scale. Sensors were fabricated on silicon substrates using micro electromechanical systems (MEMS) technologies and compatible with integrated circuit (IC) process. The layers in the device include a micro-heater, an isolator, electrodes, and a sensing film. The sensing materials were aligned and immobilized between electrodes by using the dielectrophoresis process, which is known to be a convenient method for the manipulation of dielectric substances in a liquid. Experimental results showed that the regular aligned structure of these mesostructured materials provide number of active areas on the sensor; porous ZnO had a sensitivity of 60.0% and had a fast response time of 90 s. These mesostructured gas sensors have been developed in this study with high sensitivity, good response properties and good repeatability. Moreover, the preparation process of the mesostructured sensor was a simple method.