- 學位論文
高效率合成超長奈米碳管叢與扭轉機電性質探討
High efficiency synthesis of ultralong multi-walled carbon nanotubes forest and its electro-mechanical behavior under torsion
摘要
本論文主要在探討多壁奈米碳管叢合成過程中，可能影響成長效率之因素，之後利用新發展的合成方法作大長寬比之奈米碳管叢成長後，對其扭轉時的機械性質與機電反應作相關的研究與討論。本研究首先自行組裝可個別控制溫度之三段溫度式化學氣相沉積系統，以蒸鍍薄膜之方式備製合成奈米碳管叢時所需的催化劑，並固定三段溫度式化學氣相沉積系統之高溫爐內的溫度梯度，藉由控制催化劑膜厚、碳源氣體(C2H4)流率與合成時間，最終可獲得超長多壁奈米碳管叢。其結果顯示三段溫度式化學氣相沉積系統內的溫度變化，確實可維持催化劑之使用壽命並且增加成長效率。取得成長時變化參數之最佳化數值後，三段溫度式化學氣相沉積法可在60分鐘內成長高達4.27釐米之多壁奈米碳管叢，利用無因次參數「奈米碳管叢合成率」客觀地與其他文獻作比較後可發現，三段溫度式化學氣相沉積法之「奈米碳管叢合成率」為單段溫度式化學氣相沉積法的712倍，且碳源氣體之使用流率僅為單段溫度式化學氣相沉積法之4 %。 利用黃光微影製程在二氧化矽基材上定義成長奈米碳管之位置與形狀，配合三段溫度式化學氣相沉積系統，可成功合成大長寬比之奈米碳管叢，接著使用自行設計之扭轉量測機構，可對圓柱狀之奈米碳管叢施予扭矩，並同時可量測其機電反應與扭轉角度。施加扭矩後可在奈米碳管叢表面產生皺折，過程中奈米碳管叢整體的電阻值會隨剪應變增加而微幅上升，當扭轉角度超過80°後之電阻值則會快速地增加，經由實驗結果可推測奈米碳管叢可承受較大的剪應變量，且扭轉過程中，奈米碳管叢內部結構會歷經剪應變、微幅斷裂與大量的破壞。臨界彎曲扭轉角度總是在電阻改變量超過5 %之角度後才發生，因此可由電阻改變量來預測奈米碳管叢之挫曲時間、臨界挫曲扭矩與臨界挫曲角度。與單根奈米碳管作比較時，奈米碳管叢擁有相當低的臨界剪力強度，其值僅有數個MPa左右。
並列摘要
This dissertation reports on the effect factors during synthesis of multi-walled carbon nanotubes (MW-CNTs) forest. Utilizing this novel method to synthesize high aspect ratio carbon nanotubes forest, electro-mechanical behaviors when a torque is applied were reported and discussed. A self-assembled apparatus with three individually controlled heating zones constitute a three-zone temperature chemical vapor deposition (TZT-CVD) system. Catalyst film was deposited by electron beam evaporator and temperature difference was fixed in the TZT-CVD furnace. By controlling the catalyst film thickness, carbon source (ethylene) flow rate and synthesis time, ultralong MW-CNTs forest can be obtained. The results reveal that the effect of temperature difference in the TZT-CVD is to sustain the lifetime of the catalyst and hence increase the growth efficiency. By optimizing the growth variables, TZT-CVD produced MW-CNTs forest with a height up to 4.27 mm in 60 min. Compare with other references objectively, the CNT synthesis ratio, an ultimate figure of merit, is 712 times and the carbon source consumption is 4 % compared to that of single-zone temperature CVD. The position and shape was first defined by photolithography on silicon oxide substrate. High aspect ratio CNT turfs can be successfully obtained by a TZT-CVD. A special apparatus was designed to apply a torque to the cylindrical CNT turfs. The apparatus allows simultaneously measuring the electrical resistance and the corresponding torsional angle of the turf. Applied torque will lead to wrinkles on the exterior of CNT turfs. The electrical resistance will rise with the increasing shear strain and will rise suddenly at torsion angle of 80°. It indicates that the structure of CNT turf can sustain large shear strain and go through shear strain, slightly rupture and large break during the torsional process. The critical buckling angle always occurred after the angle at the resistance change rate is over 5 %. From the resistance change rate, the buckling time, critical buckling torque, and critical buckling angle can be forecast. Compared with individual carbon nanotube, the CNT turf possesses relatively low critical shear strength of several MPa only.
參考文獻
延伸閱讀
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