Reduction dynamics of locally oxidized graphene

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题名:	Reduction dynamics of locally oxidized graphene
作者:	蔡宏傑;Tsai, Hung-Chieh
贡献者:	物理學系
关键词:	石墨烯;缺陷;還原動態;掃描式探針顯影術;拉曼光譜;光電子能譜;graphene;defect;reduction dynamics;scanning probe lithography;Raman spectroscopy;photoelectron spectroscopy
日期:	2017-01-19
上传时间:	2017-05-05 17:19:09 (UTC+8)
出版者:	國立中央大學
摘要:	作為第一個被成功製備出的二維材料，石墨烯的各項優異性質，從極高的表面積比到電子遷移率，吸引了廣大領域研究者們的目光。然而，缺乏能隙使得石墨烯的應用受限。近年，有許多研究致力於調控石墨烯的能隙。其中，還原的氧化石墨烯是最常見的方法之一。此方式藉由調控石墨烯的氧化與還原程度，進而調控電性。但是，常見以熱處理還原法，並無法完全移除石墨膝上的氧化官能基，使得電性難以回到原先的良好電子遷移率。這突顯了了解氧化石墨烯的還原機制之重要性。若能直接觀測到還原過程，將不只對石墨烯的應用有所幫助，也能了解在二維材料上官能基的交互作用。在本研究中，我們展示了微米級局部氧化石墨烯的還原動態學。首先藉由以掃描探針顯影術為基底的局部陽極氧化術，在以化學氣相成積法成長出的石墨烯上，製造出微米級的局部氧化圖樣。接著以軟X光聚焦在這些氧化圖樣上，由X光所激發出的光電子提供能量，還原氧化過的石墨烯。再還原的過程中，各化學鍵的濃度由X光光電子能譜監控，藉以直接監測局部氧化石墨烯的還原動態。再還原前後，我們藉由微拉曼光譜，觀測這些局部石墨烯缺陷的結構；化學組成則以掃描式光電子顯影術與X光光電子能譜測得。最後，經由我們所觀測到，各鍵結的還原動態，我們提出一組相互耦合之微分方程作為還原機制的模型。藉由此模型，我們取得每種鍵結的組成與分解的特徵時間，與作為限制反應的階段。這些發現給了我們較為細節的還原過程之圖像。 ;With all range of striking properties from high surface-to-volume ratio to extremely high electron mobility, graphene, the truly two-dimensional (2D) material, has gathered attention of researchers in various fields. However, the lack of band gap limits applicability in graphene device. Reduction form of graphene oxide (GO) is one the most popular method to engineer band gap through introduction of sp3 bonding. The electric properties can be tuned by controlling the degree of oxidation. Nevertheless, reduction of GO done by thermal process cannot recover the excellent electronic properties of graphene due to residue of oxygen-related functional groups. Hence, understanding the mechanism of reduction of graphene oxide is necessary for both the application of graphene and interaction of functional groups on a 2D material. In this study, we show the reduction dynamics of micron-scaled defective graphene oxide patterns done on CVD-grown graphene by scanning probe lithography (SPL), which provides localized functionalization of graphene. These patterns were subsequently reduced by the irradiation of photoelectrons induced by a focused beam of soft x-ray. By in-situ monitoring the chemical configuration of the irradiated defects during the reduction process, the evolution of each oxygen functional group is resolved by scanning photoelectron microscopy (SPEM) and x-ray photoelectron spectra (XPS). Micro-Raman spectroscopy acquired before and after the reduction process revealed the structural evolution. Moreover, the characteristic time for each functional group dissociation/ formation process involved during reduction have been identified by the proposed reaction model using a set of coupled differential equations. These finding gives the details physic picture of the reduction dynamics.
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