- 學位論文
水光電解過程之奈米超音波影像
In Situ Nanoultrasonic Imaging of Anodic Oxidation during Photoelectrochemical Water Splitting
摘要
自然界中有許多有趣且重要的現象發生於固體與液體介面，像是電極在水溶液介面發生的化學反應。電解水是產生氫能源的方法之一，也被視為解決能源危機的方法，其能量轉換的化學反應即是發生在固液介面。包含水光電解，發生在固液介面的能量傳遞反應中常面臨穩定度及轉換效率的問題，因此須藉由微觀技術來觀測固體在溶液中的表面結構變化。目前能觀測固液介面化學反應結構變化的技術各有優缺點，穿透式電子顯微鏡 (Transmission electron microscopy, TEM) 、掃描式電子顯微鏡 (Scanning electron microscopy, SEM) 及X射線光電子能譜儀 (X-ray photoelectron spectroscopy, XPS) 皆需要在真空環境下操作，而原子力顯微鏡 (Atomic force microscopy, AFM) 及掃描穿隧式顯微鏡 (Scanning tunneling microscope, STM) 能觀測表面形貌但無法提供次表面及元素分析的訊息。 聲納技術具有非破壞性檢測性質，且不需在真空的環境操作，在大氣環境下即能進行固液體介面量測，與超快雷射結合，可產生具有兆赫頻段的奈米超音波達到原子級的影像解析度。本文主要研究奈米超音波應用於觀測固液介面化學反應的表現。利用n型氮化鎵電極表面水光電解法中的變化當作奈米超音波應用於觀測固液介面的量測模型，本文發現奈米超音波可原位 (in situ) 觀測電極與水介面的氧化過程，且奈米超音波影像提供了隨反應時間下，電極的侵蝕厚度及氧化層的成長厚度。文中並討論奈米超音波及現有技術 (TEM, SEM, XPS, AFM 及STM) 應用在觀測固液介面的影像空間解析度及影像速度之比較。在比較中發現，奈米超音波的優點為可提供一個在大氣環境下觀測固液介面的結構變化，並具有原子等級解析度的影像技術。
並列摘要
Phenomenon at solid/liquid interface is interesting and plays a key role in many natural processes. Examples include chemical reactions at electrode surfaces in electrolyte. Photoelectrochemical (PEC) water splitting, one of the methods for hydrogen generation, takes the advantage of using solar energy to split water is regarded as a solution to the energy issue. Including PEC, the chemical reaction of energy transfer happening at solid/liquid interface faces the problem of stability and efficiency. To study and monitor the stability and efficiency problems of an electrode, a technique with capability to in situ image the structure of an electrode at solid/liquid interface is needed. Among all current techniques capable to in situ monitor the structure change of a chemical reaction at solid/liquid interface, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) all require a vacuum environment for operation. Atomic force microscopy (AFM) and scanning tunneling microscope (STM) lack the sub-surface and element analysis information. Taking the development of ultrashort optical pulses, applying sonar technique to thin films and nanostructure has now become possible. Nanoultrasonics with THz coherent acoustic phonons has the capability to image the sub-surface nanostrucutres without the need of vacuum environment. In this thesis, the capability of nanoultrsonics to in situ monitor a chemical reaction at solid/liquid interface is investigated. The surface of n-GaN used as photoelectrode in PEC water splitting is taken as an imaged model for nanoultrasonics technique. In this thesis, we in situ monitor a growth of oxide film process at n-GaN/water interface in PEC water splitting for hydrogen generation. The in situ real time ultrasound image can show the thickness of etched n-GaN cap layer and the thickness of growth Ga2O3 thin film with atomic resolution. The performances of spatial resolution and imaging rate of the nanoultrasonics and current techniques (TEM, SEM, XPS, AFM and STM) with capability monitoring the structure change of a chemical reaction at solid/liquid interface are discussed. The nanoultrasonics gives a way to image a dynamic change of structure at solid/liquid interface with atomic spatial resolution under atmospheric conditions.
參考文獻
延伸閱讀
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