利用液態臨場穿透式電子顯微鏡觀測氧化亞銅奈米粒子成長及溶解之研究

Observing Growth and Dissolution of Cuprous Oxide by In-Situ liquid cell TEM

林亞萱(Ya-Hsuan Lin)

指導教授 ： 吳文偉

國立交通大學/工學院/材料科學與工程系所/碩士(2018年)

摘要

近年來，金屬氧化物因其具有優越的物理性質、化學性質，所以被廣泛應用在半導體領域而受到許多學者關注。氧化鋅、四氧化三鐵、……等皆為金屬氧化物，在眾多金屬氧化物中，氧化亞銅(Cu2O, copper (I) oxide)被視為最具有商業潛力之材料，因其成本低、無毒、在低球上資源多，且常被應用在催化劑、感測器、太陽能電池及p型半導體上。然而，現今已有許多文獻研究氧化亞銅之合成方式，但關於其如何成長及如何溶解過程並沒有太多研究。所以，在本研究中，我們藉由電子束刺激水溶液合成氧化亞銅，以取代傳統利用還原劑合成氧化亞銅之方式，使得合成過程更簡易，並針對氧化亞銅的成核成長及溶解機制作進一步探討及分析，使此研究有助於日後更易達成合成形貌上的控制並廣泛應用。
在觀測過程中，電子束之加熱效應為合成反應的驅動力，使銅離子被還原為氧化亞銅，而氧化亞銅成核主要以LaMer model來解釋，一開始單體濃度提升，達一定濃度後開始大量成核，粒子大小差異較明顯，而後單體附著到核上，濃度開始下降進入成長階段，粒徑大小較均一。成長部分則以Lifshitz-Slyozov-Wagner (LSW)理論來解釋，粒子成長速率約為1062.9 nm2/s，成長速率隨時間下降，因為溶液供應充分，故為反應控制。至於溶解將分為兩部分，一部分為在液態環境下的溶解，另一部分為氧化亞銅奈米粒在真空環境下的溶解。在液態環境下，電子束劑量較低時，較容易發生氧化反應，使奈米氧化亞銅以9873.1 nm2/s溶解；而在真空環境下氧化亞銅奈米立方體因為電子輻射損害，導致奈米粒會溶解，並裸露出，如棋盤狀，最終漸漸溶解。
另外，因電子束會使水輻射分解出活性自由基與其他副產物，而氫氣自由基彼此鍵結會產生氫氣分子，達過飽和後，會以氣泡的形式析出並影響觀測的品質。雖然液態臨場觀測顯微鏡會有觀測時間上的限制，但我們仍成功觀測到氧化亞銅奈米粒之各種不同反應過程，並有系統地針對氧化亞銅奈米粒之成長、溶解之過程及機制加以分析，並提供了解實驗與理論機制直接關聯的證據，使氧化還原反應過程更加明朗化，並對日後形貌上的控制有所幫助。

關鍵字

液態臨場穿透式電子顯微鏡 ； 氧化亞銅奈米粒子

並列摘要

Metal oxides have attracted great attention due to the widely applications, which are commonly used in semiconductor industry due to their excellent physical and chemical properties. Among various metal oxides, cuprous (Cu2O, copper (I) oxide) is regarded as one of the most promising materials. It is cheap, earth-abundant, and nontoxic; therefore, it can be applied in catalysis, sensor, solar cell and p-type semiconductor. However, the redox reaction of cuprous is still uncertain, which strongly influent its size, morphology, and nanostructure.
In this work, we find a new approach to synthesize Cu2O by electron beam without using reducing agent. The growth and dissolution of cuprous were observed via in situ liquid cell transmission electron microscopy (LCTEM). The study of cuprous nanoparticles evolution, such as kinetics analysis, nucleation, growth, dissolution, and redox reaction in liquid phase can be achieved. In the cuprous growth, the accumulation of copper ions resulted in a rapidly growth of cuprous nanostructures. The results indicated that the electron beam reduced the precursor which led the copper ions transfer into copper (I) oxide in the speed of 1062.9 nm2/s. Whereas in the cuprous dissolution, the cubic shape dissolved in the speed of 9873.1 nm2/s, and finally fully disappeared. The dissolution is resulted from the higher dose of electron beam exposure, the radiation-damage-caused vacancies accumulated and formed porous checkerboard-like nanostructure.
The growth/dissolution of cuprous were systemically analyzed through the viewpoint of kinetics and dynamics. The direct observation of the dynamic process sheds light on the preparation of metal oxide by redox reaction method and extends the study of reaction kinetics.

並列關鍵字

LCTEM ； cuprous oxide

參考文獻

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