本論文分為二部分，第一部分探討不同成長濃度的氧化鋅奈米柱及不同數量的二氧化鈦複合氧化鋅奈米柱之氫氣感測器，並進行物性及電性之分析；第二部分探討在基底加入由化學氣相沉積法製造的石墨稀，接著成長氧化鋅奈米柱及不同數量的二氧化鈦複合氧化鋅奈米柱之氫氣感測器，並進行物性及電性之分析。
研究發現，氧化鋅奈米柱在成長濃度為45 mM時，擁有最大的氧缺陷比值，其在500ppm的氫氣流量下，靈敏度為26.3%；接著再在水熱法成長氧化鋅奈米柱的時候，添加不同數量之二氧化鈦粉末，造成響應值提升，其原因有二個，第一個原因是二氧化鈦附著在氧化鋅奈米柱的表面，整體的比表面積提升，導致更多的氧氣吸附；第二個原因是氧化鋅與二氧化鈦兩種材料接觸時，因為功函數的不同，導致二氧化鈦的電子會從導帶轉移到氧化鋅的導帶直到費米能階達導同個水平，在氧化鋅和二氧化鈦接面形成空乏層，使電阻增加，當在氫氣的環境下，自由電子濃度注入，空乏層寬度降低，使電阻下降，導致氫氣響應值的提升。二氧化鈦複合氧化鋅奈米柱在500ppm的氫氣流量下之靈敏度提升為54.9%。
為了使費米能階平衡，氧化鋅和石墨烯的交界處會有些微能帶彎曲現象，使空乏區形成，但其較二氧化鈦與氧化鋅接面的空乏區小，且因氧化鋅之功函數比石墨烯大，當在氫氣的環境中，自由電子可以輕易的從氧化鋅的導帶傳到石墨稀的導帶，使空乏層寬度降低，電阻下降，氧化鋅奈米柱複合石墨烯在500ppm的氫氣流量下之靈敏度提升為53.6%。
最後綜合二氧化鈦與石墨烯之優點與氧化鋅奈米柱結合，以更提升氫氣感測響應值，二氧化鈦-氧化鋅複合石墨烯奈米結構在500ppm的氫氣流量下之靈敏度提升為75.6%。

Hydrogen (H2) is known as clean energy source for future generation requirements. However, it is dangerous when leak about 4 vol % in the atmosphere, therefore it is essential to sense with suitable sensors. At present, there are many types of the commercially available H2 sensors with semiconductors so on. In this context, ZnO materials have gained significant attention in hydrogen gas sensing applications due to their excellent properties. However, the stability, poor response time and inferior recovery at room temperature limit their use in high-performance real-time gas sensors. Herein, we report highly enhanced H2-gas-sensing performance of a TiO2-doped ZnO hybrid composites on graphene substrate.
First section of this study focus on the fabrication of hybrid gas sensors using TiO2-doped ZnO nanorods (TiO2-ZNR). In the second section, we develop novel nanostructure using TiO2-ZNR composites on graphene substrates and studied their structural and gas sensing properties. The systematic investigations were revealed that adding different amount of TiO2 in the hydrothermal process of ZNRs, strongly influence the gas sensing performance. The TiO2-ZNR based gas sensor shows superb enhancement in hydrogen sensitivity of 54.9 % comparing to ZNR gas sensor (26.3%). It is believed that the TiO2 nanoparticles onto ZNR induces more active sites for the adsorption of O2. Moreover, the electrons transfer from conduction band of TiO2 to that of ZnO, leading to higher conductance of TiO2-ZNR nanocomposites than that of the pure ZNR.
Finally, TiO2-doped ZNR hybrid composites on graphene exhibits an ultrahigh sensor response even at small detection level. This TiO2-doped ZNR/Graphene hybrid sensors exhibits the superior sensitivity of 75.6%, which is overwhelmingly better than ZNRs (26.3%), TiO2-ZNR (54.9 %) and ZNRs/graphene (53.6 %). The enhancement is due to the efficient O2 defects in the TiO2-doped ZNR/graphene hybrid, also, the chemisorbed O2 ions in the surface react with H2, leading to desorption of H2O, and release a huge number of electrons to the conduction band. Thus, the accumulation layer is formed and the depletion region is decreased and enhanced the sensitivity. The outstanding features such as selectivity, stability and repeatability of TiO2-doped ZNR/Graphene, makes them as a promising candidate for high performance gas sensors.

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