- 學位論文
在矽基板上以熱裂解法成長奈米碳管的研究
Studies of CNTs grown on Si substrate by thermal CVD
摘要
中文摘要 本論文主要探討以熱裂解法熱解甲烷在摻有催化劑的基板上成長奈米碳管。我們使用兩種不同的系統成長奈米碳管，第一種是在無氨氣氛下來進行，第二種是在氨氣氛下進行，兩種系統都是使用高溫爐加熱熱裂解甲烷進行化學氣相沉積。 在第一部分，我們利用SEM探討表面形貌的觀察，溫度、甲烷與氬氣氣體流量比、催化劑厚度等參數，對長成奈米碳管特性（管徑、成長率及結構等）的影響。 在第二部分，不管是矽基板或氮化矽基板在氨氣氛下都可形成的竹節奈米碳管（bamboo-like CNTs），主要研究氨氣對於碳管成長的三階段（前處理、碳管成核與碳管成長）的影響，我們先探討氨氣在前處理階段對催化金屬顆粒成核的影響，利用AFM 及SEM 觀察催化金屬顆粒的大小及表面形貌；其次，探討氨氣在碳管成長過程的影響，利用SEM及TEM觀察碳管的表面形貌及管璧結構；最後，我們探討奈米碳管的成長機制及造成方向性的成因。 我們的研究結果發現有使用氨氣時，催化金屬薄膜在成核時較易形成均勻性的金屬顆粒。奈米碳管的管徑與催化金屬薄膜所形成的顆粒大小成正比，而且發現並不是每一個催化劑金屬顆粒都能形成碳管，催化劑在成核後會有一個臨界厚度，大於臨界厚度容易形成碳顆粒；小於臨界厚度比較容易長成碳管，隨著催化金屬薄膜越厚所長成的奈米碳管就越粗，成長速率也越慢（1μm/min），催化金屬越薄所長成的奈米碳管越細，成長速率越快（2.4μm/min）。利用TEM所觀察的碳管為bamboo 結構，使用氮化矽基板長出的碳管較為矮胖，而使用矽基板長出的碳管的較細長。
並列摘要
Abstract Growth and characteristics of carbon nanotubes (CNTs) on Ni-sputtered substrates Via the pyrolysis of methane by thermal CVD are studied in this thesis. The growth of CNTs was conducted with and without the introduction of NH3. Pure silicon and 200nm-Si3N4-coated silicon were used as our substrates. In all cases CH4 was used as carbon source. In the first part, the growth of CNTs without the use of NH3, by the observations of SEM, we studied the effect of temperature, CH4/Ar flow-rate ratio, and the thickness of the catalyst on the characteristics of the grown CNTs. In the second part, the growth of CNTs with the use of NH3 on the three growing stages of CNTs. We first studied the effect of the pretreatment of NH3 on the nucleation of the catalyst, by the use of AFM and SEM to observe the surface morphology and particle size of the catalyst. We then studied the effect of NH3 on the growth of CNTs, by the use of SEM and TEM to observe the surface morphology and structure of the grown CNTs. Finally we studied the growth mechanism and the vertical alignment of the grown CNTs. Ours results show that, under the pretreatment of NH3, the nucleation of the catalyst is more uniform in particle size, and the diameter of the CNTs is proportional to the particle size of the catalyst. We found that there is a critical thickness after the nucleation of the catalyst. Beyond the critical thickness of the catalyst, carbon nanoparticles are apt to be formed; under the critical thickness of the catalyst, CNTs are apt to be grown and, the thicker the catalyst, the bigger the tubes, the slower the growth rate. The growth rate of our CNTs ranges from 1μm/min for the bigger ones to 2.4μm/min for the smaller ones. The TEM observations of our bamboo-like CNTs show that, the CNTs growth on the Si3N4 substrate are shorter and thicker than those.