利用簡單製程及低成本材料與創新技術相結合，以提升化學感測器的便利性及功能性，對研究學者而言，一直是個有趣且具實用的課題。本論文敘述應用於二氧化氮 (NO2) 氣體感測器的材料設計、製造和特性分析。氧化鋅 (ZnO) 是一種典型的 n 型半導體，被選作此化學電阻式氣體感測器的基礎材料。透過水熱法生長的氧化鋅奈米柱(nanorods, NRs) 直徑為 100 nm、長度為 2 μm。在濃度為 500 ppb NO2 的情況下，平均響應約為 370%。而在 350 °C 下退火的樣品，其響應為 28%。如此發現初成長的氧化鋅相較退火氧化鋅具有更高的靈敏度，其結果可歸因於存在更多充當氣體吸附位置的氧空缺。
近年來，使用 MoS2 奈米片作為氣體感測材料已被廣泛報導。在實驗上，我們開發了一種基於液相剝離法所製備的 MoS2 奈米片的 NO2 氣體感測器，在 100 °C 下對 5 ppm NO2 氣體的響應為 330%。其優異的性能是由於在室溫下所產生了硫空缺（未配位的 Mo 原子）所致。通過密度泛函理論(density functional theory, DFT)計算，MoS2-NO2 吸附錯合物的形成佔據主導地位，且NO2 氣體分子對硫空缺誘導的 MoS2 的獲得了更高的吸附能，硫空位 (VS) 會充當單電離受體能階（高於價帶 0.54 eV）。最終，可提出將VS視為具有（0 / 1）帶電狀態之單電子受體的p 型MoS2 奈米片溫度相關感測機制
當這種 ZnO 與通過不同技術製備的二維 (2D) MoS2 奈米結構結合並形成異質接面時，可以進一步提高感測性能。由於它們增大了 MoS2/ZnO 異質接面處的空乏區，而使材料的表面性質和電子性質發生了顯著地改變。MoS2 奈米片與初成長出的 ZnO 相結合的奈米複合物形成了用於室溫下的高性能NO2 化學電阻式氣體感測器。以表面分析技術，證實了 MoS2 奈米片在ZnO NRs上形成了均勻網絡狀的分佈，在紫外線激發下，奈米複合物感測器在 25 和 2500 ppb NO2 下分別表現出 91% 和 2310% 的顯著響應。吸附/脫附動力學乃是透過朗繆爾(Langmuir)吸附模型來詳細解釋。飽和響應、吸附以及脫附常數分別為 2744%、7.0 × 10–6 ppb–1 s–1 和 3.50 × 10–3 s–1。此感測器的出色性能可歸因於 MoS2 和 ZnO 的協同效應，其影響包括產生豐富的吸附位點以及快速的電荷載子遷移。此外，以方便且高效的低溫光沉積方法，可將MoS2 奈米顆粒修飾在 Cu2O/ZnO 異質接面陣列上。該方法利用了基底材料的還原半反應電位和導帶位置關係。首先選擇合適紫外光波長 (254 nm) 將Cu2O奈米簇以及MoS2 奈米顆粒依次沉積於水熱生長的 ZnO 奈米柱上。45 分鐘光沉積時間的 MoS2 對 500 ppb NO2 具有 890% 的最高響應，並展現了出色的氣體選擇性以及實現了 18.7 ppm–1 的高靈敏度。研究結果表明，一維ZnO奈米柱可以作為改善Cu2O和MoS2分散性的優良模板，此奈米複合材料中存在大量異質結、缺陷和空缺，它們會做為電荷分離和遷移有效的活性位點，讓感測器的性能有顯著提升。

There has been an increasing interest among researchers to improve the functionality and portability of chemical sensor devices, while utilizing simple and low-cost materials combined with innovative techniques. The research described in this thesis involves the design, fabrication, and characterization of hybrid gas sensors for the analyses of nitrogen dioxide (NO2) gas. Zinc oxide (ZnO), a typical n-type semiconductor has been chosen as the template for the chemoresistive gas sensing. ZnO NRs with a diameter of 100 nm and a length of 2 μm are grown by a hydrothermal method. The average response is around 370% for 500 ppb NO2. The sample is annealed at 350 oC and the response obtained is 28%. It is found that the pristine ZnO has higher sensitivity than the thermally annealed ZnO and the consequence can be attributed to the presence of more oxygen vacancies that act as adsorption sites.
The use of MoS2 nanosheets as a gas sensing material has been reported extensively in recent years. Experimentally, we developed a NO2 gas sensor based on liquid-exfoliated MoS2 nanosheets with the response of 330% at 100 °C for 5 ppm NO2 gas. The excellent performance is due to the creation of sulfur vacancies (undercoordinated Mo atoms) at room temperature. From density functional theory (DFT) calculations, a dominant MoS2−NO2 adsorption complex is formed and higher adsorption energy of the NO2 gas molecule on sulfur vacancy-induced MoS2 is obtained. The sulfur vacancies (VS) acts as the singly ionized acceptor level (0.54 eV above the valence band). Finally, a detailed temperature-dependent sensing mechanism for p-type MoS2 nanosheets has been proposed considering the VS as a single electron acceptor with the (0/−1) charged states.
The sensing performance can be further improved when this ZnO are combined with two-dimensional (2D) MoS2 nanostructures prepared by several techniques and form a hetero-junction. These modifications can substantially change the surface properties as well as electronic properties due to their enhancement of the depletion layer at the MoS2/ZnO hetero-interfaces. The MoS2 nanosheets are combined with as-grown ZnO forming a nanocomposite for a high-performance room temperature NO2 chemoresistive gas sensor. The uniform network-like distribution of MoS2 nanosheets on the nanorods is confirmed by various characterization techniques. Under UV-activation, the nanocomposite sensor exhibits remarkable responses of 91% and 2310% at 25 and 2500 ppb NO2, respectively. The adsorption/desorption kinetics has been studied in detail using the Langmuir adsorption model. The saturated response, the adsorption, and the desorption constant are determined to be 2744%, 7.0 × 10–6 ppb−1 s−1, and 3.50 × 10–3 s−1, respectively. The outstanding performance of the sensor can be attributed to the synergetic effects of MoS2 and ZnO including creation of abundant adsorption sites and fast charge carrier migration.
MoS2 nanoparticles have been successfully deposited on Cu2O/ZnO heterostructure arrays by a convenient and highly efficient in-situ low temperature photodeposition method. This method utilizes the reduction half-reaction potential and conduction band position of the base material. A suitable wavelength of 254 nm is chosen to photo-deposit Cu2O nanoclusters followed by MoS2 nanoparticles on hydrothermally grown ZnO nanorods. MoS2 photodeposited at 45 min has shown the highest response of 890% towards 500 ppb NO2 with an excellent selectivity. An excellent sensitivity of 18.7 ppm–1 has also been achieved for this sample. The results reveal that one-dimensional ZnO nanorods can serve as excellent templates for improving the dispersion of Cu2O and MoS2. The improved performance of the nanocomposite is attributed to the presence of numerous heterojunctions combined with the defects and vacancies which provided active sites for efficient charge separation and migration.

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