A Study On The Growth And Growth Mechanism Of Single-walled Carbon Nanotubes

Growth of single-walled carbon nanotubes (SWNTs) on substrate surface by chemical vapor deposition (CVD) is the base of the fabrication and applications of the SWNTs-based devices. SWNTs can be electrical conductor or semiconductor and have potential applications in nanoelectronics such as field effect transistor etc.. The electrical properties of SWNTs depend on not only their helicity but also diameter. To control the diameter and helicity is still the big challenge for this research field.In this thesis, high quality SWNTs were synthesized by CVD method using Fe/Mo,Ag,SiO2 etc. as catalysts and methane or ethanol as carbon sources. The morphology, composition, structures of the catalysts and the as-grown CNTs were characterized by SEM, AFM, TEM, Raman, XPS, electrochemistry and so on. The relationship between the yields, qualities and structures of the SWNTs and structures of the catalysts, synthesizing conditions were discussed; The results from this study will be helpful for the realization controllable fabrication of SWNTs, the exploitation of novel catalysts and understanding the catalytic function and the growth mechanism of the SWNT.(1) We have demonstrated that ionic compounds are new kind of effective catalyst for the synthesis of SWNTs. The results show that the SWNTs from ionic catalysts have better conductivity and better structural uniformity with less defects than that from Fe/Mo catalyst. More importantly, it is found that 73% of the horizontal SWNT arrays from LiCl are are metallic. The generation of such high percentage of metallic-SWCNT array will represent a big step forward controlled growth of m- SWCNTs for electronics applications.(2) We utilize selective electrochemical deposition (SED) to evaluate the quality of the SWNTs on the substrate. The method is based on the SED of Ni metal nanoparticles on the defect sites of SWNTs which can be readily observed by SEM. Therefore we can observe the defect densities, location and distribution along the SWNTs efficiently and rapidly. It has been found that the quality of the SWNTs from methane is much better than that from ethanol, which is believed to be due to the etching effects of OH radicals on the SWNTs during nanotube growth process.(3) We investigate the ratio between the diameter of the catalyst particles of Fe/Mo, Ag, SiO₂ and the diameter of the SWNTs grown under the same CVD conditions. The results reveal that the ratio range from 1.4,1.7 and 2.0 for those three different catalysts, respectively. This results can be explained by the surface tension of the curved grapheme sheet and the adhesive between the catalyst and the sheet. This observation will help to understand the growth mechanism of the nanotubes and to control the nanotube diameters by selecting a appropriate catalyst for various applications.