Reduction-oxidation dynamics of oxidized graphene: Functional group composition dependent path to reduction

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/77113

Title:	Reduction-oxidation dynamics of oxidized graphene: Functional group composition dependent path to reduction
Authors:	洪翊哲;Hong, Yi-Zhe
Contributors:	物理學系
Keywords:	石墨烯;掃描探針微影;graphene;scanning probe lithography;oxidation and reduction;redox
Date:	2018-08-06
Issue Date:	2018-08-31 13:57:34 (UTC+8)
Publisher:	國立中央大學
Abstract:	近年，石墨烯因其超高的電子遷移率與超薄的完美二維六角晶格結構成為了熱門的研究議題，然而缺乏能隙使其無法良好地應用於電子產品上。而能隙可藉由製造缺陷於石墨烯晶格中產生，比如透過離子摻雜或氧電漿轟擊。其中，濕氧化處理的還原氧化石墨烯不僅克服了天然石墨烯無能隙的障礙外，還能有效地以低成本大量製造，因此有望實現於生活應用中。然而濕氧化處理過程會使石墨烯鍵結上大量且複雜的氧化官能基，導致後續的紫外光或熱還原無法完整地除去其氧化官能基，進階地影響其電子與光學性質，因此如何精確地控制石墨烯的氧化與還原程度成為了一大挑戰。在此研究中，我們使用了掃描探針微影術來精準地控制石墨烯的氧化程度，此項技術是於原子力顯微鏡探針上施加一偏壓，使空氣中的水分子被電解成氫氧根離子並鍵結於石墨烯上。此後再使用Ｘ光光電子能譜同時辨識氧化程度與進行氧化石墨烯的還原，還原的動態可藉由數據分析來觀察其氧化官能基的轉換。此外，我們發現在氧化石墨烯的還原過程中可能會發生再次氧化的現象，經過Ｘ光光電子能譜的數據分析指出再次氧化的現象需要被還原前的氧化石墨烯的氧化程度達到兩種門檻，包含其總氧化濃度需達到百分之七十外，同時還要符合環氧官能基濃度達分之二十二。 ;In recent years, graphene becomes a hot research issue rapidly because of its ultrahigh electron mobility and ultrathin two-dimension structure. Unfortunately, a lack of band gap causes its developed limitation on electronic application. While the band gap can be produced through defects creating in graphene lattices such as ion doping or oxygen plasma bombardment. Among them, reduced graphene oxide (rGO) manufactured by Hummers’ method not only overcomes the barrier of band gap-free in pristine graphene, but also can be manufactured effectively with low cost. Thus, these advantages make rGO may be applied in real life. However, there are lots of complex oxygen functional groups bond with graphene during the Hummers’ method. These complex oxygen functional groups will cause that GO can’t reduce back to rGO completely even through the UV light or thermal reduction. In addition, the electronic and optical properties of graphene will also be influenced by the residual oxygen functional groups. Therefore, how to control the oxidation and reduction of graphene precisely becomes a difficult challenge. In this research, we used the scanning probe lithography (SPL) to tune the extent of graphene oxidation precisely. During the SPL process, a bias was exerted between the tip and graphene to create hydroxide ions bonding with graphene by electrolysis the water in air. Then, the graphene oxidation was identified and reduced at the same time through measurement of x-ray photoelectron spectroscopy (XPS). The graphene reduction dynamics was observed through analyzing the transformation of functional groups. Furthermore, we found that graphene oxidation could be oxidized again during the reduction process. Through XPS spectrum analysis, the phenomenon was found only occurred when the original graphene oxidation conformed two thresholds simultaneously. The thresholds included that total oxygen concentration needed to exceed 70%, and the total concentration of ether and epoxy also need to exceed 22%.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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