- 學位論文
從優直徑單壁奈米碳管成長之研究
Study of Preferred Diameter Single-Walled Carbon Nanotube Growth
摘要
單壁奈米碳管是由僅一層石墨層捲曲成中空圓柱狀，兩端分別由似C60的半球結構組合而成的一維結構材料(1-Dimension Material)。單壁奈米碳管會隨著石墨層捲曲的方向(稱為螺旋性)變化而改變其結構與直徑，此改變將影響其能帶結構使之呈現金屬性或半導體性的電氣特性。為了與奈米碳管電性有關之各種元件(至少包含電子、光電及生醫元件)的應用，單壁奈米碳管的臨場成長與直徑控制儼然已成為目前研究團隊爭相研究的目標。在以元件應用及臨場成長的考量之下，我們選擇利用催化裂解化學氣相沈積法搭配金屬多層催化劑系統，生長高品質的單壁奈米碳管。經由對單壁奈米碳管生長機制與催化劑系統中各元素功能的瞭解，我們發現不同主催化劑(Fe、Co、Ni)的材料特性差異，對單壁奈米碳管生長具有關鍵性的影響。以金屬多層催化劑系統而言，利用我們最佳化的催化系統參數Mo(0.2 nm)/Fe(1 nm)/Al(15 nm)/SiO2(100 nm)搭配甲烷碳源氣體，可以合成幾乎無雜質、結晶性佳(拉曼光譜G/D比超過55)的單壁奈米碳管。利用上述研究結果，我們進一步以藍寶石基板代替矽基板，利用基板效應(Substrate Effect)直接控制催化劑顆粒，並間接控制單壁奈米碳管的生長條件。最後，我們提出機制解釋並歸納說明從優直徑單壁奈米碳管的生長機制及其限制。並期望在本實驗室的研究努力下，將利用催化裂解化學氣相沈積法所生長的從優直徑單壁奈米碳管應用在相關元件上。
關鍵字
奈米碳管並列摘要
A single-walled carbon nanotube (SWCNT) is a one-dimension material composed of graphene layer rolled up into a cylinder, with its end cap structure similar to the half of C60. SWCNT structure can be presented by their (m, n) indices, which determine SWCNT diameter and chirality. According tight-binding method calculation, SWCNT can be metallic, semiconducting or small-gap semiconducting, depending on their structure and diameters. For these SWCNT physical characteristics, the control of the diameter of SWCNT becomes the challenge of developing SWCNT-based nanoelectronic devices. In this thesis, a reliable method using chemical vapor deposition (CVD) method of growing high-purity SWCNTs was demonstrated. A high quality, almost bundle-free, SWCNTs with G/D area ratio of 55 was obtained by optimizing the catalytic system with SiO2(100 nm)/Al(15 nm)/Fe(1 nm)/Mo(0.2nm) multi-layer catalyst and the CVD growth process parameters. In addition, the sapphire wafer was utilized to be the substrate for SWCNT growth. Based on substrate effect to catalytic system, the growth of preferred diameter SWCNTs was demonstrated. Finally, we summarized these results by proposing a SWCNT growth mechanism with a growth model based on the lattice matching interaction (i.e. substrate effect to catalyst nanoparticles), the surface tension theory and the difference between surface and bulk diffusivities.