摘要

本研究以感應耦合電漿化學氣相沉積法(ICP-CVD)結合矽基氧化鋁奈米模板成長順向奈米碳管陣列。利用製程參數的控制，提高奈米碳管的成長速率、結晶性、密度，並探討碳管結構、形態、密度對場發射性質的影響。

結果顯示，於ICP-CVD系統中，感應射頻功率和外加直流偏壓分別控制碳氫氣體的解離和離子至基板的通量，感應射頻功率增加，碳氫自由基和離子的濃度隨之提高；外加直流偏壓增加，則吸引更多離子至基板進行碳管的成長。成長其速率隨射頻功率、外加直流偏壓的增加而提升，在本研究條件下碳管最快成長速率為44.6 nm/min。

利用ICP-CVD結合矽基氧化鋁模板成長奈米碳管，藉由改變氧化鋁奈米模板的孔洞深度、孔徑、外加直流偏壓及觸媒前處理，可有效控制碳管的成長密度。成長密度和進入模板中之碳氫自由基及離子的通量及觸媒表面活性有關。此外，於場發射測試中發現碳管之成長密度在5×108 CNTs/cm2時具有最低之起始電場1.5 V/m，但成長密度在大於5×108 CNTs/cm2之後，場發射屏蔽效應隨之增加。

使用氧化鋁模板結合電鍍而成長(420  20 nm)的鐵、鈷及鎳奈米線做為觸媒，奈米碳管可完整包覆金屬奈米線。此外，奈米碳管的結構隨奈米線觸媒之不同而異。當中使用鐵、鎳奈米線為觸媒者，所成長之奈米碳管的順向性和石墨層之結晶性均優於使用鈷金屬線者。

由奈米碳管之電漿改質得知，利用氬氣電漿可有效降低碳管之成長密度(6×108 CNTs/cm2)，並使蝕刻碳管之頂端變成針狀；然而以氮氣電漿後處理者，由於氮原子會摻雜進入石墨層中，改變碳管表面的鍵結，其於150 W之氮氣電漿改質處理30分鐘後的起始電場由1.5 V/m降至0.7 V/m。

Abstract

Carbon nanotubes (CNTs) arrays were synthesized by inductively coupled plasma chemical vapor deposition (ICP-CVD) combined with anodic alumina oxide (AAO) on Si as nanotemplate. The parameters determining the growth characteristics of CNTs, such as growth temperature, inductive RF power, DC bias, gas ratio, AAO length and pore diameter were investigated. Besides, the factors affecting the field emission properties such as crystallinity of graphite layer and packing density of CNTs were also investigated.

The results show that both plasma intensity and ion flux to the substrate, as controlled by the inductive RF power and DC bias voltage, respectively, can greatly affect the growth of CNTs. The relative importance of the generation of ions and the subsequent transport of ions to the substrate as serial process steps are considered as the two underlying factors in determining the growth characteristics of CNTs. The highest growth rate of CNTs in this study is about 44.6 nm/min, for the growth conditions of inductive RF power -400 V and DC bias 250 W.

CNTs with different packing density were synthesized by ICP-CVD using AAO/Si as a nanotemplate and pre-electroplated Ni nanowires and CH4 were used as catalyst and reaction gas, respectively. The parameters determining the growth density of CNTs arrays, such as AAO pore length, pore diameter, growth time, DC bias, and pretreatment conditions were investigated. It is found that the transport of ion species flux in the AAO channel and the catalytic activity of Ni nanowires determine the growth behavior of CNTs. The field emission measurement shows that CNTs arrays with a medium density of 5×108 CNTs/cm2 grown on the AAO/Si substrate have the lowest turn-on field of 1.5 V/m. Either a decrease or an increase of the CNTs density results in inferior emission properties.

Aligned CNTs fully filled with Fe, Co, and Ni were synthesized by ICP-CVD using nanowires as catalysts. The nanowires were prepared by electroplating using AAO as template. By properly selecting the length of nanowires (420  20 nm), CNTs fully filled with metal catalyst can be directly obtained. The effect of nanowires (Fe, Co, Ni) on the growth of aligned CNTs is also systematically studied. It is found that the catalyst has a strong effect on the nanotube alignment and crystallinity. The CNTs catalyzed by Ni and Fe have a better alignment and a higher degree of graphitization, however, those from Co show a little curled character in the tips and somewhat tangle between CNTs.

The density, morphology and structure of CNTs were modified using plasma treatment. Using Ar plasma for treatment results in the highest etching efficiency comparing to that using the N2 or the H2 plasma. The density is decreased and the tip of CNTs is etched into a needle shape as treated with 150 W Ar plasma for 30min.The incorporation of nitrogen into graphite-like structures would introduce pentagon defects in the hexagon network for CNTs treated by N2 plasma. The turn-on field of CNTs is reduced from 1.5 to 0.7 V/m as treated with 150 W N2 plasma for 30 min. The field emission property is improved after N2 plasma treatment due to the doping of N atom into the carbon network.

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