準直性奈米碳管合成之技術開發

Development of synthesizing well-aligned carbon nanotubes

蕭博元(Po-Yuan Hsiao)

指導教授 ： 楊啟榮

國立臺灣師範大學/科技學院/工業教育學系/碩士(2010年)

摘要

隨著奈米科技研究風潮的興起，許多材料於奈米尺度下的特殊物理與化學性質，逐漸被人所發現，而奈米碳管更是其中價值最高，潛力最大，並且最受矚目的先進材料。有鑒於奈米碳管優異的性質和未來的應用性，以及期望盡速實現其與微/奈米機電系統技術接軌之目標，故本研究選擇於半導體製程中，扮演重要角色之化學汽相沉積(chemical vapor deposition, CVD) 技術，進行奈米碳管之製備，以期有效促進奈米碳管與半導體製程相容性的發展，而化學汽相沉積法中，又以熱裂解法之系統較單純，且其製備出之碳管之結晶品質也較佳。因此，本研究主要以熱裂解化學汽相沉積(Thermal-CVD)技術為骨幹，實現製作準直性奈米碳管陣列結構之目的。
根據研究結果顯示，本研究所製備之奈米碳管為多壁形式，且竹節狀(bamboo-like)奈米碳管，以及其頂部具觸媒顆粒的現象，可判斷其成長機制為完全成長。拉曼頻譜分析其ID/IG值約為0.626，顯示此多壁奈米碳管之結構與結晶品質相當良好。
選擇鎳觸媒金屬，並施以適當裂解溫度與活化參數，再藉由輔助及碳源氣體比例間的控制，可獲得約20 cm2趨近完美之準直性奈米碳管陣列結構。當使用7.5 vol之氨/氬混合氣進行前處理，最後於1050 C以甲烷30 sccm及氬氣370 sccm等條件，進行10分鐘之成長後，能合成出垂直高度83.33 m，管徑為57 nm，且深寬比可逼近1500:1，並具可選區成長之奈米碳管準直性陣列結構，而以甲烷30 sccm、氨氣30 sccm及氬氣340 sccm等條件，所製備之奈米碳管則具最佳表面形貌。
另外，無論於活化或是成長階段加入氨氣，均有助奈米碳管成長之準直性，倘若活化與成長階段間為不連續關係，則將出現碳管密度及高度不足等現象。於成長階段通入適量氨氣，可有效提升奈米碳管之準直性，並抑制管徑的增加，若氨氣與碳源間之比例高於1.66，則氨氣對碳管之縱向蝕刻速率將大於橫向成長速率，導致粗且短的碳管生成，並產生奈米碳管陣列之垂直高度，由氣體入口端向出口端遞增之不均現象。若同時將不同材質之基板，同時置於爐管中進行成長，推測可能的原因為高溫下鎳金屬與基材形成不同形態或組成的化合物，導致觸媒金屬的活性因而改變，直接影響觸媒對碳源的吸收行為，遂發生具材質選擇性之成長現象。
奈米碳管成長之參數測試已告一段落，未來將進行準直性奈米碳管陣列結構之物理性質量測，例如導電性、氣體感測能力、熱傳導性、可濕性、場發射性能及抗反射頻譜等，藉而尋求更多元之應用層面，例如生物感測器、氣體感測器、燃料電池、散熱元件、太陽能電池抗反射層、場發射顯示器等元件之開發。

關鍵字

多壁奈米碳管 ； 熱裂解化學汽相沉積 ； 準直性陣列結構

並列摘要

With the raise of nanotechnology researching, many special physical and chemical properties were found gradually in nanoscale. Most of all, carbon nanotube (CNT) is the advanced material which has the highest value, greatest potential, and attract the most attention. Because of excellent properties and many applications for CNT, and it is expected to achieve for integrating with micro/nano-electro mechanical-system technology as soon as possible. As thus, this study will select chemical vapor deposition (CVD), which plays the important role in semi-conductor process technology. Above all, CNT which fabricated by thermal-CVD has better crystalline, and its system is more simple than others. So this study will use thermal-CVD to fabricate a well-aligned CNT array structure.
According to experimental results, the variety of CNTs which synthesized by this study are classified in multi-walled carbon nanotubes (MWCNTs). Fully growth mechanism could be proved due to the bamboo-like structure and catalysts at the top of CNTs. Follow the ID/IG from Raman spectrum analysis of 0.626, it indicates the MWCNTs with good structure and crystallization.
The well-aligned CNT which is fabricated by Ni catalyst, temperature, activation and growth parameter with a nearly perfect arrangement can be obtained in the sample of 20 cm2. When 7.5 NH3/Ar is used in pretreatment stage, then use CH4/Ar (30/370 sccm) to synthesize CNTs during 10 minutes at 1050 C, the growth height of CNT is about 83.33 m; its diameter is about 57 nm, such that the aspect ratio of the nanotube can reach about 1500:1, and it has the advantage of in situ synthesis. Otherwise, growth stage uses by CH4/NH3/Ar (30/30/340 sccm) will obtain the best profile for CNT.
NH3 which promotes well-alignment of CNTs remarkably has been confirmed by this study. Especially, pretreatment and growth stage must be successional, and a nearly perfect arrangement structure will be fabricated. Besides, CNTs growth with adding NH3 at growth stage, it could improve well-alignment and control increase of diameter for CNTs. However, once the ratio which NH3 versus CH4 (NH3/CH4) is higher than 1.66, the lengthways etching rate will be higher than transverse etching rate, the phenomenon of nonuniform and podgy CNTs will occur. If CNTs grown on different substates at the same process time, this situation might change activity of Ni catalyst cause by interact between Ni and substrate under high temperature, and the change of activity brought growth selectivity for CNTs.
In future, this study will keep measuring the physical properties which include conductivity, wettability, field emission properity and reflective spectrum et cetera for the CNTs array, and try to search more and more applications, for example: bio-sensors, gas sensors, fuel cells, cooling devices, anti-reflection layer of solar cell and field emission display et cetera.

並列關鍵字

Multi-walled carbon nanotube (MWCNT) ； thermal chemical vapor deposition (thermal CVD) ； well-aligned array structure

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