藉由化學摻雜提升石墨烯做為TOC的電性

石墨烯為二維導體薄膜，近來被認為是很有淺力的材料。石墨烯有著很高的穿透度與很高的導電度，是非常適合當作TOC(Transparent optical conductor穿透光學導體)1的材料。TOC被應用於手機面板，太陽能電池…等，最常被提及的是ITO(Indum tin oxide)，也具有低電阻高穿透的特性，但是石墨烯有更低的片電阻，堅固和可撓曲的特性，我們想用石墨烯代替ITO成為新世代的TOC材料。為了達到此目標，石墨烯的導電性需要更進一步的提升，有兩種方式能夠實行，分別是提升載子濃度(Carrier Concentration)和提升電子遷移率(Electron Mobility)，已知提升電子遷移率需要精良的儀器，在製程上也需要更高的成本，相對上提升載子濃度更為簡單方便，通過化學參雜的方式可以大量提升載子濃度，這樣的方式也在文獻上被廣泛的使用。我們提供了三種不同的參雜方式，分別是金離子3，紫外光4與高溫去除壓克力5，找到一種順序可以得到最高的FOM(Figure of merit)2。FOM指的是在一系統中，定義不同參數對系統的影響度，在此系統中，兩種參數為穿透度和片電阻，高穿透與低片電阻皆會提升此數值。實驗上我們利用高溫爐製成單層的石墨烯，在高溫通入甲烷解離出碳原子之後沉澱上銅箔上，製成高品質的單層石墨烯。石墨烯的參雜被廣泛的應用在許多文獻上，但是導電度有一定的極限，而穿透度卻一直沒有很高。為了最大化參雜濃度，我們微調摻雜物的濃度同時降低雜質，保持石墨烯原有的高穿透度，並降低片電阻，找到最高的FOM。降低參雜金離子的濃度，調整CVD的溫度與改變紫外光的曝光時間，找到三種參雜方式的最高FOM。我們利用多步驟的參雜，找到一個最佳的順序去做參雜，可以使片電阻降低90%，並且保持93%的穿透度。參雜石墨烯可以提升石墨烯的電性，但是在石墨烯的缺陷邊界上並不能做參雜，我們利用蝕刻銅箔的檢測方式去量測缺陷的多寡。化學蝕刻被廣泛應用在量測化學反應速率。實驗上利用硫酸鈉蝕刻石墨烯/銅箔樣品，由於石墨烯能保護銅箔免於蝕刻，石墨烯的完整度將決定反應速率。此結論提升了我們對參雜的了解，提升了將近一倍的導電度相對於文獻，我們的發現打開了石墨烯作為TOC的一個新的領域。

關鍵字

透明穿透導體；石墨烯

並列摘要

Graphene is a two dimension conductive film, its property has a lot of potential that is confirm by literature. Graphene has very high transmittance, due to its unique structure, and its electrical conductive is very well too. So graphene is very well suited as a transparent optical conductor (TOC)1 . There’s a lot of other TOC material that is found, like Indum tin oxide (ITO), which has very high transmittance and low resistance, but graphene is much stronger, flexible and other unique property that has a lot of potential. To compete with TOC material, graphene’s performance in electrical conductor has to be improved. There’s two ways to increase graphene’s conductance, increase the carrier mobility or increase the number of carriers. Increase the mobility of graphene is very difficult, high sensitive instrument is needed, and the fabricate cost will be very high. So instead, we increase the carrier concentration in most feasible and efficiency way. Chemical doping is widely used in doping graphene, charge transfer between graphene and doping provide more carrier to the device. Our impressive result show the potential to replace ITO, with higher trancemittance and conductivity. Figure of merit (FOM) 2is widely use to define the influence with more than two parameter’s in one system . Here we use for transmittance and conductivity, higher transmittance and lower sheet resistance will increase the FOM. For experiment, we fabricate single layer graphene by chemical vapor deposition (CVD), deposit the methane on copper foil substrate. This way provide high quality, single layer graphene in center meter scale. Doping experiment has been done with many papers, but the conductivity is limited and the transmittance is usually not very well. To maximizing the doping density , we tuning the concentration of the dopant to a limited density and reduce the impurity at the same time .We accomplish this set of doping consequences and find the conductivity of graphene film increase by 300% . We doped graphene film with many different way that has been published in many literature , such like gold particle3 , UV ozone4 and CVD remove PMMA5 . We tuning with every doping parameter like concentration, time, pressure to find the best performance with each doping method and then we doping step by step with many different consequence, our goal is to reach the highest FOM, which means the highest ratio with transmittance and conductivity. Doping increase the electrical performance of doping, graphene provide carbon bounds for more carrier concentration while doping, but this will not happened on graphene defect, such like graphene grain boundary. Chemical corrosion is widely use to figure the reaction rate. The Na2SO4 solution will etch copper foil and graphene will protect the copper, we can figure out how much the defect on the sample by this method. The result improve our understanding of doping process, increase the conductivity by almost on order that compete to literature. Our finding open the field of graphene TOC and future applications.

並列關鍵字

Graphene ； TOC

參考文獻

1 Alam, M. J. & Cameron, D. C. Optical and electrical properties of transparent conductive ITO thin films deposited by sol–gel process. Thin Solid Films 377–378, 455-459, doi:http://dx.doi.org/10.1016/S0040-6090(00)01369-9 (2000).

2 Sevinçli, H. & Cuniberti, G. Enhanced thermoelectric figure of merit in edge-disordered zigzag graphene nanoribbons. Physical Review B 81, 113401 (2010).

3 Shi, Y. et al. Work Function Engineering of Graphene Electrode via Chemical Doping. ACS Nano 4, 2689-2694, doi:10.1021/nn1005478 (2010).

4 Huh, S. et al. UV/Ozone-Oxidized Large-Scale Graphene Platform with Large Chemical Enhancement in Surface-Enhanced Raman Scattering. ACS Nano 5, 9799-9806, doi:10.1021/nn204156n (2011).

5 Pirkle, A. et al. The effect of chemical residues on the physical and electrical properties of chemical vapor deposited graphene transferred to SiO2. Applied Physics Letters 99, -, doi:doi:http://dx.doi.org/10.1063/1.3643444 (2011).

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藉由化學摻雜提升石墨烯做為TOC的電性

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