Growth and Characterization of Multi-walled Carbon Nanotubes by Using CH4-CO2 Gas Mixture

• Main Authors: Mi Chen, 陳 密
• Other Authors: Chia-Fu Chen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/249gpm

博士 === 國立交通大學 === 材料科學與工程系 === 91 === Since carbon nanotubes (CNTs ) were discovered, relevant research fever and developments of commercial applications such as hydrogen storage, atomic force microscope probe, microelectronic transistor, electrical field emitter of flat panel display and scanning tunneling microscope tip have been stimulated tremendously. High-quality and well-aligned carbon nanotubes are essential to the potential applications in the field of microelectronic industries. Microwave plasma chemical vapor deposition (MPCVD) has been regarded as the potential method because of high quality and well-aligned carbon nanotubes can grow at low temperature In the thesis, carbon nanotubes were grown vertically and aligned on Fe catalytic nanoparticles deposited on a Si substrate at low temperature by using CH4 and CO2 gas mixtures. This is apparently different from the conventional reaction in gas mixtures of hydrogen and methane, hydrogen and acetylene, and hydrogen and benzene, etc. In microwave plasma deposition of CNTs, many reactions are involved in plasma and on substrate surface. A dynamic form of optical emission spectroscopy was used to detect the species in the plasma. These data show the dominant species in gas phase reaction. The composition of plasma significantly affects the reaction mechanism of carbon nanotubes growth. It is concluded that in the CH4-CO2 gas system can increase the amount of C2. In the C2-rich plasma the higher excited C2 emission intensity is beneficial to graphite deposition, and enhance carbon nanotubes synthesis on catalyst-deposited surface quality. Then a CNTs growth model in catalysts and gas environment of CH4-CO2 gas mixture was investigated Various catalyst, Fe, Ti, and Fe/Ti, were used to synthesize CNTs by CH4-CO2 gas sources. Significant difference of morphology in the carbon deposition was observed among Fe, Ti and Fe/Ti catalyst. By proper adjusting growth parameters a high yield of vertically aligned CNTs can be found in Fe-deposited substrate, but Ti is not suitable as a catalyst in CNTs production. The effects of H2 plasma pretreatment on the CNTs growth were investigated in the view point of CNTs morphology when Fe was used as the catalyst. After the H2 pretreatment, the diameter of CNTs increased significantly as the H2 plasma pretreated time increased because of the catalyst particle sintering to enlarge the catalyst particles. However, the diameter of CNTs was governed by the catalyst particle size. The CNTs diameter distributed in the range about 10~20 nm when Fe-deposited substrate was not pretreated. But the diameter of CNTs changed from 30nm to 300 nm when Fe-deposited substrate was pretreated from 1 min to 15 min. CNTs with various diameter by using MPCVD of CH4-CO2 gas mixture have good field emission properties Vertically aligned CNTs with multi-walled structures were successfully grown at low temperatures below 350oC by MPCVD using a CH4-CO2 gas mixture. The low temperature would be beneficial for reducing the diameter of CNTs but it will also decrease the growth rate on the substrate. Thus the CNTs grown at low temperature by the MPCVD using CH4-CO2 gas mixture have good field emission properties.