本研究利用STM探針局部放大電場的特性，我們系統性研究圍繞在針尖周圍的各類新奇AC電荷動力流動現象：交流電熱(ACET)噴流/漩渦流動、交流電滲式(Ohmic ACEO)衝擊流以及電化學交流電滲式(ACFS)噴流，本論文可分成兩個部分。首先，我透過實驗觀察在不同導電度的溶液中，這些不同的流態是如何隨施加的交流電壓和頻率而變化。在第二部分中，我重點介紹了ACET流動，並從實驗和理論上檢驗了ACET的流動特徵。
我的電極是由尖銳的鎢錐形針和鎢絲以正交方式排列所組成，並使用導電度為1.05μS/cm的去離子水，以及導電度為去離子水100倍、1000倍、5000倍的食鹽水溶液來進行實驗，使用螢光粒子做為追蹤劑來追蹤流態，發現ACET流動在去離子水和導電度為水100倍的溶液(稱為低導電度溶液)中與在導電度為水1000倍和5000倍的溶液(稱為高導電度溶液)中非常不同。前者是在尖端周圍以局部ACET噴流的形式，而後者則在針周圍呈現出較大的ACET旋渦。我測量了這兩種ACET流動類型的速度，發現它們對施加的AC電壓的依賴性不同，這表示控制這兩種ACET流動的機制也不相同。
在低導電度溶液中，尖端周圍的局部ACET噴流發生在頻率100k - 10M Hz，測得的流速U與尖端的距離r呈現1/r的速度變化，顯示出類似點力的流動特徵，且U隨電壓V的變化為U∝V²，這不同於經典理論中ACET流速表徵U∝V⁴。將施加的交流頻率降低到1k - 3M Hz，我發現ACET會逆轉為ACEO撞擊流。當我們將頻率進一步降低到100 - 10k Hz時，這種撞擊流會再次反轉，變成比ACET流速快很多的大範圍ACFS。當頻率選擇在這些不同流態的邊界處時，流動模式會變為混合類型，例如ACET噴流會受到ACEO衝擊流的干擾形成不規則的流態；ACEO撞擊流可以與ACFS共存，表現出雙漩渦對。
在高導電度溶液中，針周圍的ACET漩渦流動發生在頻率10k - 10M Hz，測得的流速U表現為U∝V⁴。與低導電度溶液相比，由於高導電度溶液的RC頻率較高，
因此ACEO會較少發生。在低頻1k - 10kHz，流動模式保持不變但速度會變得更快，是由於從ACET漩渦流動轉變為ACFS。
我將提出理論來解釋低導電度溶液與高導電度溶液ACET流動的差異。在低導電度溶液中，尖端周圍的電極加熱會比流體加熱更為重要，使尖端變成局部熱點，從而在流體中生成集中的電力，產生具有點力1/r流動特徵的ACET噴流，我提出了電雙層內結合切向傳導的加熱電阻電容模型，該模型能夠解釋實驗中觀察到的特殊尺度U∝V²。在高導電度溶液中，該模型還可以解釋所觀察到的ACET漩渦流動U∝V⁴，從誘導空間電荷的觀點來看，經典ACET理論也可獲得相同的結果。
這些流動現象和機制表示錐形電極的幾何形狀可能會從根本上改變交流電動流的特徵。在電化學或微流體應用中，這些流動具有促進分子感測或樣品運輸的潛力。

In this paper, we experimentally report that the AC charge-driven flow phenomenon around the STM probe has the potential to promote sample mixing or capture. Using of a sharp scanning tunneling microscope (STM) tip capable of amplifying local electric fields, we systematically investigate various flow phenomena around the tip under alternating current (AC) electric fields: AC electrothermal (ACET) jet/swirling flow, AC electro-osmotic (ACEO) impinging flow, and AC Faradaic streaming (ACFS). Among them, the ACET flow state changes due to the change of the conductivity of the solution. In low conductivity solutions, an ACET jet can emit from the tip that becomes a local hotspot undergoing heated capacitive charging. The resulting electric force thus becomes point-like but varies as V² instead of V⁴ commonly reported by literature, where V is the driving voltage. In high conductivity solutions, an ACET swirling flow which is heated by the fluid can flow forward along the shape of the needle and form a large vortex. The resulting electric force which varies as V⁴ is the same as the literature.

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