高品質石墨烯成長及Cu2O在其轉印及光電化學上之應用

Growth of High Quality Graphene and the Role of Cu2O on its Transfer and Photoelectrochemical Application

吳承翰(Cheng-Han Wu)

指導教授 ： 陳俊維

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201700688

摘要

石墨烯是近年來最熱門的新穎材料，其是由碳原子之間以sp2鍵結而形成的六角形二維結構，因為石墨這樣特殊的結構使得其有著許多極優良的物理性質，這些特性使得科學家們相信能應用到現今的科技上，並且大大改善人類的生活品質。但是，透過機械剝離法所得到的石墨烯尺寸相當不固定，也無法用於大面積的製造，所以這在未來工業化將大大受到限制，因此，科學家們開始尋找不同的方法來製造出高品質且大面積的石墨烯，綜觀所有方法當中，就屬化學氣相沉積法最吸引人，透過過鍍金屬跟碳源還有氫氣的催化，在高溫下自行排列出石墨烯的六角二維結構，這樣方法下所得到的石墨烯不但品質好，又可以大量製造，所以近年來科學家們爭先恐後投入心力在這領域，希望能為未來石墨烯工業化鋪路。
既然石墨烯的製造如此重要，本論文在第四章就開始討論如何透過化學氣相沉積法成長出高品質的石墨烯，因為不同的參數或基板，會使長出來的品質大不相同，因此我們參考文獻後，評估用銅基板並且搭配甲烷當碳源來做我們石墨烯成長的材料，透過成長基板的前處理、溫度還有氫氣跟甲烷的比例的研究討論，我們試圖找到長出高品質石墨烯的條件與參數，來為我們實驗室後續的元件應用打下良好的基礎。
成長後的石墨烯會貼附在過鍍金屬上，必須經過「轉印」的步驟才能將石墨烯應用到我們所希望的基板上，因此，轉印方法的好壞也會大大影響未來元件應用時石墨烯的品質與效果，所以在本論文的第五章，我們透過Cu2O的引入，改善了靜電轉印法的效果，讓大面積的石墨烯能完整地轉印出來，我們發現銅箔需放置兩天進行氧化，其所產生的氧化亞銅才能完全幫助完整的石墨烯靜電轉印，也讓電阻值下降了五倍。我們也透過研究分析來解釋了這層氧化亞銅在靜電轉印法當中所扮演的角色，完美解釋了整個靜電轉印法的機制。
最後第六章，我們應用了前面第四章和第五章的技術與發現，將石墨烯/氧化亞銅/銅這樣的異質接面結構應用到能源元件上面來解決現今的能源危機。第五章所發現的氧化亞銅已被科學家認為是極優良的光觸媒材料，我們想再利用第四章成長石墨烯的方法，將其優越的電學性質跟氧化亞銅做結合，應用於光電化學水分解當中，進行產生氫氣的研究。首先使用自然氧化法，將石墨烯/銅箔放置在大氣當中一個月進行自然氧化，但是電流值不高且相當耗時，因此，設計了一個直接成長的方式來得到我們的光電化學水分解元件，透過這樣直接成長的方法，我們可以一步驟的得到石墨烯跟氧化亞銅，經過簡單的封裝就可以進行量測，在水分解的量測上不但成功產生較高的電流，也可以看到石墨烯在整個元件當中所扮演的角色，最後我們分析這樣方法所得到的能源元件的優缺點，以及討論未來可改進或發展的方向，期待未來能將在解決能源危機這議題上有所貢獻。

關鍵字

石墨烯 ； 化學氣相沈積 ； 銅 ； 氧化亞銅 ； 光電化學 ； 電化學

並列摘要

Graphene, a two-dimensional material formed of a honeycomb lattice structure of sp2 carbon atoms, has been attracting wide attention owing to its remarkable thermal, mechanical and electronic properties. Scientists believe that these attractive properties can be applied to nowadays technology and make human’s life better. However, the size of graphene produced by mechanical exfoliation is not stable and large-sized. It will definitely limit the development of graphene in industry. Therefore, Scientists start to find a new way that can produce graphene with the quality that can be industrialized. Among all the methods, chemical vapor deposition (CVD) is the best way. With the catalyst of transition metal and carbon source, graphene can be synthesized in perfect sp2 bonding and large-sized. That is why there are more and more scientists involved in this area and working on paving the way for graphene industrialization.
In the first section, we introduced the procedure for growing high quality graphene. Because of different parameters and conditions leading to different morphology of graphene, it is greatly important to study the effect of factor. Therefore, we discuss three factors that highly influence CVD graphene quality－ growing substrate, temperature and the ratio of H2/CH4. With the paper survey and our study, we successfully find out the parameters to grow high quality CVD graphene. These techniques give a good foundation for graphene-based device.
After growing graphene on transition metal, it is also important to transfer it. We consider how to transfer it without causing any damage during the process, which is always the key point to get better performance in our graphene-based device. Therefore, in the next section, we optimize the electrostatic force transfer method by introduce copper oxide. With this kind of semiconductor between graphene and copper foil, we can greatly improve the quality of transferred graphene to our target substrate. The resistance is getting lower while the uniformity becomes better. We not only optimize the transfer quality of graphene but also explain the role of Cu2O in electrostatic force transfer.
Finally, we combine the technique in chapter4 and chapter5 to make a graphene-based energy device. In literature review, we know that Cu2O has been widely applied in photoelectrochemical (PEC) cells because of its physical properties. However, the main problem is its stability in solution. It will self-reduce while PEC measurement. To overcome this issue, we combine the CVD growth of graphene by direct growth method. By this method, we can automatically get the graphene and Cu2O in the same time. After simple encapsulation, we can transfer solar energy and water into hydrogen energy. Most importantly, with the presence of graphene, the photocurrent density increase over 70% compared to the device without graphene.

並列關鍵字

Gaphene ； CVD ； Copper ； Copper oxide ； Photoelectrochemical Cell ； electrochemistry

參考文獻

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