| 摘要: | 石墨烯(Graphene)為一種新穎的二維材料，相較於其他材料，具有良好的機械性質、導電性、光學特性等，像是其機械強度為1100 GPa、熱傳導為5300 Wm-1k-1、光穿透率大於97 %以及載子傳輸速率為200,000 cm2V-1s-1等。目前製備高品質石墨烯的主流方法為使用化學氣相沉積法 (Chemical Vapor Deposition, CVD)於銅基板成長，再進一步將石墨烯從銅基板轉印至目標基板，如何有效率地轉印成長後的石墨烯至目標基板是重要課題之。目前轉印主要面臨的難題為如何大面積轉印，以及高分子或金屬離子殘留的問題。
本研究探討石墨烯之大面積轉印，以及能達到高潔淨且高完整性的石墨烯於目標基板上。首先，討論捲對捲乾式轉印(Roll-to-roll dry transfer)分別搭配直接剝離及加熱剝離兩種不同方式，利用加熱剝離方式可轉印大面積石墨烯，並且同時具備高達92 %的表面完整性；另一方面，探討使用松香(Rosin)取代主流的PMMA，將rosin當作轉印緩衝層，於搭配捲對捲乾式轉印，可使石墨烯表面潔淨度高達97 %。
本研究更進一步透過電化學輔助剝離(Electrochemical delamination)結合捲對捲乾式轉印，藉由減少銅基板蝕刻步驟，達到提高轉印後的石墨烯潔淨度，並且，剝離下的銅箔能重複成長，重新利用銅箔成長石墨烯可大幅減少其成本。
電化學輔助剝離中，使用PMMA當作轉印緩衝層的效果優於使用rosin，可獲得表面潔淨性高達99 %的石墨烯。我們進一步探討其高潔淨的原因。得到鈉離子藉由插層的方式進入PMMA及石墨烯層之間，間接弱化了PMMA與石墨烯間的附著力，在洗淨步驟更能從石墨烯上洗掉PMMA，達到高潔淨的結果。;Graphene is a novel two-dimensional material, which has excellent properties in mechanical, optical fields, including high mechanical strength (~1100 GPa), thermal conductivity (5300 Wm-1k-1), transparency (>97%) and charge carrier mobility (200,000 cm2V-1s-1). One of the current methods for preparing graphene is that growing graphene on a copper foil by using chemical vapor deposition (CVD) and transferring graphene from the copper to a target substrate. Therefore, how to efficiently transfer graphene to the target substrate is one of the important issues. At present, transferring high-quality graphene with large area as well as without polymer or metal ion residues is the main problems to solve.
In this study, in order to achieve a large area of high-quality graphene transferring, as well as high cleanliness and integrity of graphene to the substrate, several methods were studied to optimize the transfer process of graphene. First, we discussed the roll-to-roll dry transfer through different release methods: (1) direct exfoliation (2) heated exfoliation. As much as 92 % of surface integrity can be obtained by the method of heat exfoliation in transfer graphene. Then, we discussed using rosin to replace PMMA as a buffer layer in roll-to-roll dry transfer, and the high surface cleanliness of 97% with the large-area graphene could be obtained.
In addition, electrochemical delamination combined with the roll-to-roll dry transfer was further carried out for reducing the etching steps of the copper substrate to improve the cleanliness of transferred graphene. Moreover, after tearing the copper foil with the top of graphene, the copper foil could be used repeatedly to grow graphene, and the cost of using copper foil to grow graphene could be greatly reduced. This method of graphene transferring will greatly reduce the cost of copper foil.
In electrochemical assisted delamination, using PMMA could obtain graphene with a surface cleanliness of up to 99%. We studied the mechanism of this transferring process with the high cleanliness. The intercalation of Na ions could weaken the adhesion between graphene and PMMA layer by electrochemical assisted delamination, as the result, PMMA on top of graphene could be easily washed away, which results in the high cleanliness of transferred graphene. |
