臺灣博碩士論文加值系統

本研究以天然石墨粉為原料，以改良式哈莫法(Modified Hummer method)製備氧化石墨烯(graphene oxide, GrO)，以拉曼光譜分析其碳原子結構組成；以電子顯微鏡觀察其表面形貌。所得GrO粉體以純水混合適量酒精為溶劑，配製石墨烯懸浮液，以電泳沉積法(Electrophoretic Deposition, EPD)於導電玻璃(Indium Tin Oxide, ITO)基板上沉積石墨烯薄膜。為探討電場模式對EPD薄膜的影響，分別使用正弦波、三角波、方波等不同波型之非對稱式交流電源(Asymmetric AC Electric Field)。先導研究找出適當的電泳電壓與操作頻率，再固定電壓與頻率，比較各種不同電場模式隨沉積時間增加(5秒、10秒、20秒、30秒)，對於薄膜厚度、形貌與光電特性之影響，並與傳統的直流電泳沉積(DC-EPD)結果比較。
上述各種樣品的鍍膜厚度分析結果顯示：與DC-EPD相比，交流電場的電泳沉積速率明顯減慢；不同波型的AAC-EPD沉積速率彼此間沒有顯著的差異。石墨烯薄膜厚度與沉積時間作圖指出：方形波與正弦波的AAC-EPD樣品厚度，符合Hamaker公式，其餘三角波型AAC-EPD所得者則偏離此線性關係。由於交流電場的Stotz-Wien效應，作用於石墨烯片的電場力隨電壓變化而非線性改變，導致不同波型的鍍膜結構。值得注意的是：由於正弦波、三角波的AAC-EPD是由原對稱波型施以一定電壓偏移(offset)，其淨作用可能類似直流或是脈衝直流電泳(pulse DC-EPD)。反之，方波電源為典型的非平衡式交流電源(unbalanced AC electric fields)，單位週期之淨電流為零。再足夠高的頻率下，電流幾乎完全流入電及附近的電雙層中，因此不會造成氫氣的析出等現象，導致薄膜堆疊較為平整。
綜合各項特性分析結果指出：以非對稱的方波AAC-EPD系統具有最佳的可見光穿透度與最低的片電阻。在下列操作參數下：工作電壓40V，頻率50Hz，25%負載循環(duty cycle)，沉積時間30秒之的石墨烯薄膜成品具有平整的表面形貌(RMS roughness = 4.40 nm)、最低的片電阻(25.93  0.85/)與穿透度(84.59%)。隨著沉積的時間增加，石墨烯薄膜表面越不均勻，並且電阻值上升，穿透度下降。

In the present study, graphene oxides (GrO) were synthesized by the Modified Hummer method with natural graphite powder as the raw material. The chemical structures and the surface morphology of the as-synthesized GrO were characterized by Raman and FE-SEM, respectively where aqueous GrO dispersions were prepared by adding aliquots of alcohol as solvent. The GrO thin films were prepared by electrophoretic deposition (EPD) over Indium Tin Oxide (ITO) glass substrates in asymmetric alternating current (AAC) and direct current (DC) electric fields, respectively. A preliminary study was conduct to find the appropriate EPD operation window after which the as-deposited GrO films by different deposition duration (5, 10, 20, 30 s), at identical operation voltage and frequency were compared comprehensively to investigate the effects of various modes of electric fields on the properties of the deposited GrO films. For AAC-EPD mode, all the three common waveforms has been choose, including square wave, square wave and sine wave, respectively. The former (square wave) could be named as the unbalanced electric field whose waveform was asymmetric in which the positive and negative area of the same size. In contrast, the remaining two waveforms could not meet the requirement of unbalanced electric field, i.e., a net DC current flows toward a given electrode leading to a DC and/or pulse-DC mode-like electric field.
It shows that, compared to those deposited by DC-EPD, the deposition rate for those deposited by AAC modes were apparently much slower whereas different kind of waveform has made little difference in the rate of GrO film deposition. For those deposited by AAC-EPD with waveform of both square and sine wave, the behaver of rate increment about deposition time did follow the relationship of Hamker equation whereas the triangular wave did not show similar linear relationship. The complexity of the deposition behavior under the AAC electric fields could be attributed to the Stotz-Wien effect where the variation of electric filed strength with applied voltage were nonlinear, leading to different films structure and properties. It is noteworthy that for AAC-EPD films with square waveform, there is no hydrogen evolving on the cathode surface owing that all charges were flowed within the double layers in the vicinity of electrodes.
In summary, the best result was obtained by AAC-EPD with square waveform at 40V, 50Hz, 25% duty cycle with deposition duration of 30s under which the as-deposited GrO films has compact surface morphology with RMS surface roughness of 4.40 nm, lowest sheet resistance of 25.93  0.85(/), and optical transmittance of 84.591%. By applying AAC-EPD with waveform of sine and triangular wave, the wrinkle on film surface becomes prominent, whereas both the optical transparency and electric conductivity for the as-deposited GrO films were deteriorated accordingly which might be ascribed to the hydrogen evolution at cathode surface during the prolonging deposition process.

封面內頁
簽名頁
中文摘要 ...iii
ABSTRACT...v
誌謝...vii
目錄...viii
圖目錄...xi
表目錄...xiv
第一章 緒論...1
1.1 前言...1
1.2 研究動機...1
第二章 文獻回顧與原理...3
2.1 石墨...3
2.1.1 石墨烯...4
2.2 石墨烯備製...6
2.2.1 氧化石墨及氧化石墨烯...8
2.3 膠體懸浮液...10
2.3.1 膠體表面電荷來源...11
2.4 電沉積的機制...14
2.4.1 電泳沉積法...15
2.4.2交流/直流電泳沉積...17
第三章 實驗方法與步驟...19
3.1 使用藥品...19
3.2 實驗儀器...20
3.3 量測儀器...22
3.3.1冷場發射型掃描式電子顯微鏡...22
3.3.2三維顯微拉曼/光致發光光譜影像系統...23
3.3.3四點探針...24
3.3.4原子力顯微鏡...25
3.3.5 紫外線/可見光分光光譜儀...26
3.3.6 化學分析電子能譜儀...27
3.4 實驗方法...28
3.4.1 ITO透明導電玻璃之清洗...28
3.5 氧化石墨烯薄膜製備...30
3.5.1 氧化石墨烯合成...30
3.5.2 氧化石墨烯電泳液調配...33
3.5.3 以交流電泳(AC-EPD)製備氧化石墨烯薄膜 ...34
3.5.4 直流電泳(DC-EPD)製備氧化石墨烯薄膜...37
第四章 結果與討論...39
4.1 石墨稀成品的分析鑑定...40
4.2 FE-SEM及AFM表面結構...43
4.2.1 FE-SEM表面觀察...43
4.2.2 FE-SEM剖面膜厚...48
4.3 片電阻(SHEET RESISTANCE)...56
4.4 穿透度...59
4.5 化學分析電子能譜分析(ECSA)...64
第五章 結論...67
參考文獻..69

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