利用化學氣相沉積法對有結構缺陷的石墨烯進行修補和還原以及其結構變化的觀測

石墨烯(graphene)是由碳原子所組成，僅有單原子厚度的材料。石墨烯具有獨特的物理性質，比如高速的電子遷移率，良好的機械強度，高度的化學穩定性。有鑒於常見的力學剝落法(mechanical exfoliation)無法得到可以進行工業以及工程應用的大面積石墨烯，近年來已發展出利用化學液相剝落法，將石墨分離成近似單原子厚度的氧化石墨烯(graphene oxide)。氧化石墨烯具有諸多優點，例如面積比傳統力學剝落法廣大，可達到毫米等級的面積;生產過程簡單，利用修飾過的Hummers method，可以大量地被製備。然而，化學方法製備得到的氧化石墨烯之物理性質，以及電性上的表現卻無法和石墨烯的電性比擬。由於製備過程是在酸性溶液中進行，所以不可避免的氧化石墨烯附著了大量的酸根。因此，如何對氧化石墨烯進行有效率的還原，使其物理性質與化學結構可達到石墨烯的水準，成了一個有趣的研究方向。本論文的第一部分，著重於如何將電化學方式製備的石墨烯(electrochemically exfoliated graphene)晶格上，於製備過程中所帶來的缺陷，比如銜接了功能基(functional group)後轉變成了不完整晶格結構，利用高溫爐以及氫氣，氬氣，甲烷，在攝氏1000度到1500度之間對電化學方式製備的石墨烯進行退火還原以其結構上的修復以及還原。為了釐清還原機制，以及樣本的物理以及化學性質，利用拉曼散射光譜儀(Raman spectroscopy)，X射線光電子能譜(XPS)量測分析，原子力顯微鏡，對樣本進行最直接的量測與分析以對石墨烯的結構之還原機制作驗證。本論文的第二部分將討論將氧化石墨烯(graphene oxide)在金屬元素，銅，作為催化劑下，進行高溫退火以及化學氣相沉積法，移除鍵結於氧化石墨烯之晶格上的功能基，並且在銅的催化之下，幫助氧化石墨烯之晶格上的碳原子重新排列形成六角苯環。初步的研究成果觀測到，氧化石墨烯顏色變深，代表其已經被強力還原;還原的樣本之拉曼光譜數據則顯示出，氧化石墨烯原本的非定相結構(amorphous structure)，在銅的催化下，轉變為 sp2鍵結結構。銅在化學氣相沉積法方式製備石墨烯中扮演了石墨烯結晶的平台，但是能否扮演有效修補氧化石墨烯結構的角色仍然未知，此為本論文第二部分待為討論的方向。

關鍵字

石墨烯；氧化石墨烯；拉曼光譜儀；拉曼譜線；石墨烯還原

並列摘要

Graphene, a single layer of carbon atoms in a honeycomb network lattice, has attracted many interests due to its unique physical properties and high optical transparency. In order to achieve large scale production, the electrochemical exfoliation of graphene was demonstrated. However, the honeycomb lattice of as-exfoliated graphene was damaged due to the slight oxidation in the synthesis process. The main goal of this thesis focuses on the recovery efficiency of the sp2 domain in the graphene-like composites by different heat treatments, utilizing a combination of argon (Ar) and hydrogen (H2) at a temperature between 1000oC and 1500oC and methane (CH4) alone at around 900oC, respectively. In the first part of this thesis, the chemical vapor deposition process, flowing an Ar-H2 mixture at a temperature above 1000oC, utilized to recover the broken honeycomb structure in the defective graphene will be demonstrated. The evolution of the crystallite-domain size in the defective graphene has been monitored and studied by the Raman spectra and the X-ray photoelectron spectroscopy (XPS).The recovery of the sp2 structure in the honeycomb network was revealed from the Raman spectroscopy by the decreasing ratio of D band to G band integrated intensity and the increase of the 2D-to-G integrated intensity ratio. The Tuinstra-Koenig (TK) relation is also used for the characterization of the crystallite-domain size in the annealed samples. XPS measurement was also conducted to characterize the different binding energies of oxygen-containing functional groups in the annealed samples to discover the changes, which may be referred to the loss of oxygen atoms occupying the sp3 carbon sites during the heat treatment, of the atomic structures. The second part of this thesis investigated the efficiency of recovering the sp2 domain in the carbon honeycomb structure by annealing the graphene oxide (GO) in a chemical vapor deposition (CVD) process using methane (CH4), in which the carbon atom can repair the interrupted sp2 network, as a precursor at a lower processing temperature. Prior to the CVD process, a thin film of copper was deposited onto the GO film by thermal sputtering because copper has been known as an effective catalyst to assist the carbon adatoms to access the broken carbon bonds for the recovery of the graphene structure. The Raman spectra of the reduced graphene oxide (rGO) processed by this method demonstrate a narrowing of G band and an increasing intensity ratio of 2D to G band reaching a value of 0.76, which is a significant improvement compare with a value of ~0 from an amorphous GO.

並列關鍵字

Graphene ； Graphene oxide ； Raman spectroscopy ； Raman spectra ； Reduced graphene

參考文獻

References for chapter 1

[1] Jorio A. et al, Raman spectroscopy in graphene related system,

Wiley (2011).

[2] Geim A. K. and Novoselov K., Nat. Mater., 6: 183 (2007).

[3] Allen, M. J. et al., Chem. Revs., 110: 132 (2010).

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利用化學氣相沉積法對有結構缺陷的石墨烯進行修補和還原以及其結構變化的觀測

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