Effect of ammonia in the synthesis of carbon nano-tube

• Main Authors: Szu-Hsien Lin, 林思賢
• Other Authors: Jyh-Ming Ting
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/99671987181267649102

碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 93 === 　NH3 as a reaction gas had been profoundly used in various kind of process to synthesize carbon nanotube including plasma enhanced chemical vapor deposition (PE-CVD), microwave plasma enhanced chemical vapor deposition (MPE-CVD) and thermal chemical vapor deposition (thermal CVD) et al. Generally, the major effect of ammonia is to enhance the alignment of carbon naotubes but the mechanism of how NH3 promote such an important characteristic of carbon nanotube is still uncertain. 　In this experiment, ammonia is used as heat treatment gas and is compared with hydrogen gas. Also, under the same total flow rate but different carbon source concentration, it’s introduced in reaction gas with different concentration to mix with carbon source, acetylene. Fe thin film which acts as catalyst will crack into nano-scale particles after the heat treatment because of internal and thermal strength. Then, through the chemical vapor deposition in horizontal tube furnace with mixing reaction gas at 1atmosphere, carbon nanotubes with good alignment were thus obtained. 　SEM & TEM were used to analyze the microstructure of carbon nanotube and Raman spectroscopy was also used to analyze the quality of carbon nanotube. By adopting Field emission measurement of our laboratory, the field emission properties and the cycle-times test results were also acquired. Beside, EELS information of CNTs was collected during TEM observation. 　Results show that carbon nanotubes growing with NH3 heat treatment has better alignment than those growing with H2 heat treatment and the quality of carbon nanotubes become worse when the NH3 concentration in mixing reaction gas getting higher. In the mean while, the field emission properties of carbon nanotubes don’t have close relation with the quality of CNTs obviously and it seems the field emission properties were more likely affected by the alignment of carbon nanotubes. With increasing concentration of ammonia, more and more bamboo-structure appears in carbon nanotubes. In EELS results, we observed the K edge signal of N which come from the interaction between electron beam and π* orbital of the pyridine-like orbital. The K edge signal of N show the existence of N atoms in CNT’s structure and we suspect this is the reason why the CNT’s loss it’s alignment when the concentration of NH3 exceed 50%. 　By the theoretical analysis of Thermal Dynamics calculated by some research groups and our experimental results, this experiment gives the basic explanation of how ammonia affects the growth behavior of carbon nanotubes with different properties.