本研究透過摻雜鋁元素來提升氧化鋅奈米柱壓電式奈米發電機的效能，並探討其在濕度感測上的應用可能性。我們採用低成本且安全性高的水熱法合成不同鋁摻雜濃度的ZnO奈米柱，分別為摻雜0.15 mM、0.30 mM和0.45 mM的鋁，加上做為對照組的純氧化鋅奈米柱，一共有四個氧化鋅奈米柱壓電式奈米發電機元件 (AZO-000, AZO-015, AZO-030 和 AZO-045)。
在物性分析結果中，以掃描電子顯微鏡（SEM）觀察到氧化鋅奈米柱沿著垂直基板方向生長，並有六方纖鋅礦結構的六邊形特徵。X射線繞射（XRD）可以證明因為摻雜鋁進入氧化鋅結構中而縮小原子間間距。光致發光光譜（PL）結果可以觀察到在摻雜鋁之後，氧化鋅奈米柱結構中的氧空缺量減少，因為鋁摻雜進入氧化鋅結構中取代鋅的位置，並提供更多的自由載子填補氧空缺。透射電子顯微鏡（TEM）結果可以發現氧化鋅奈米柱結構為單晶排列。X射線光電子能譜（XPS）及感應耦合電漿質譜（ICP-MS）可分析出氧化鋅奈米柱中的鋅、氧、鋁元素。
在電性分析結果中，摻雜鋁的氧化鋅奈米柱具有良好的晶體結構和優異的壓電性能，且隨著鋁摻雜濃度的增加，奈米發電機的輸出功率有顯著提升，摻雜0.45 mM鋁的氧化鋅奈米柱奈米發電機 (AZO-045) 的平均輸出功率達到2600 nW，是未摻雜鋁的氧化鋅奈米柱奈米發電機 (AZO-000) 的173.3倍。此外，將摻雜0.45 mM鋁的氧化鋅奈米柱奈米發電機 (AZO-045) 應用於濕度感測器中，性能會比未摻雜鋁的氧化鋅奈米柱奈米發電機 (AZO-000) 弱，因為其氧空缺受鋁摻雜而減少，氧空缺減少會損失與水分子反應的機會，因此若想要將氧化鋅奈米柱奈米發電機應用於濕度感測元件上，在透過摻雜鋁提升奈米發電機性能的同時需要考量氧空缺的數量。

This study enhances the performance of zinc oxide (ZnO) nanorod (NR) piezoelectric nanogenerator (NG) by doping them with aluminum and investigates their potential applications in humidity sensing. We employed a low-cost and highly safe hydrothermal method to synthesize ZnO NRs with varying aluminum doping concentrations, specifically 0.15 mM, 0.30 mM, and 0.45 mM, along with undoped ZnO NRs as a control group. Four types of ZnO NR piezoelectric NGs were created (AZO-000, AZO-015, AZO-030, and AZO-045).
In the physical property analysis, scanning electron microscopy (SEM) revealed that the ZnO NRs grew perpendicular to the substrate and exhibited the hexagonal characteristics of the wurtzite structure. X-ray diffraction (XRD) confirmed the narrowing of the inter-atomic spacing due to the incorporation of aluminum into the ZnO lattice. Photoluminescence spectroscopy (PL) showed that aluminum doping reduced the number of oxygen vacancies in the ZnO NR structure, as aluminum atoms replace zinc atoms and provide additional free carriers that fill these vacancies. Transmission electron microscopy (TEM) indicated that the ZnO NRs had a single-crystal structure. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS) were used to analyze the presence of zinc, oxygen, and aluminum elements in the ZnO NRs.
In the electrical analysis, the aluminum-doped ZnO NRs demonstrated good crystallinity and excellent piezoelectric properties. As the aluminum doping concentration increased, the output power of the NGs rose significantly. The average output power of the ZnO NR NG (AZO-045) doped with 0.45 mM aluminum reached 2600 nW, which is 173.3 times higher than that of the undoped ZnO NR NG (AZO-000). Furthermore, when the ZnO NR NG (AZO-045) doped with 0.45 mM aluminum was used in a humidity sensor, its performance was inferior to that of the undoped ZnO NR NG (AZO-000) due to the reduction in oxygen vacancies caused by aluminum doping. The decrease in oxygen vacancies reduces the ZnO NRs’ ability to interact with water molecules. Therefore, when aiming to use ZnO NR NGs in humidity sensing applications, it's important to consider the balance between enhancing NG performance through aluminum doping and maintaining an adequate number of oxygen vacancies.

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