A Study On The Selective Growth And Growth Mechanism Of Carbon Nanotubes With Specific Structure

Due to their unique structure and outstanding physical and chemical properties,single-walled carbon nanotubes （SWNTs） have been considered as one of the most importantbuilding blocks for fabricating nanodevices. But the metal residual from catalyst andcoexistence of semiconducting and metallic SWNTs in as-grown carbon nanotubes bychemical vapor deposition （CVD） greatly limit their applications in this field. In order toenhance the performance of nanotube-based devices, the growth of carbon nanotubes withspecific structure, including metal-free, pure semiconducting or metallic or even specificchirality, should be given to priority. This dissertation focuses on selective growth ofmetal-free carbon nanotubes using oxide catalysts, including SiO₂and TiO₂, and highpercentage of semiconducting ones using metal catalysts including Pd and Pt. The mainresearch and findings are listed as follow:（1） It has been demonstrated that SiO₂nanoparticles （NPs） can be generated by simplyscratching the quartz or silicon wafer with SiO₂layer and confirmed to be active for thegrowth of SWNTs for the first time. Furthermore, the SWNTs from SiO₂have much narrowsize distribution and about90%of them are semiconducting ones. This may open a way tocontrol the diameter and structure of the SWNTs. More importantly, it has been found that aseries oxides including Al2O3, TiO₂and rare earth oxides to be active for SWNTs growth aswell. These findings provide not only alternative new type of catalysts for the growth ofSWNTs, but give more insight into the role of the catalysts and deep understand of thegrowth mechanism of SWNTs as well. The effective catalysts and catalytic activity forSWNTs growth seem to be more size-dependent than what the catalysts are. Theidentification of the structures of the long oriented SWNTs generated from these catalystsenable us to rule out the relationship between the catalysts and the structures of the SWNTs.Thus controlled growth of SWNTs including the diameter and chirality is expected to beeventually realized.（2） It has been demonstrated that titanium dioxide （TiO₂） nanoparticle （NPs） is anefficient catalyst for the growth of carbon nanotubes （CNTs）. TiO₂NPs can be generatedeither by sol-gel method or by sputtering metal titanium on silicon wafer followed by thermaloxidation in air. Highly dense single-walled carbon nanotubes （SWNTs） and/or multi-walledCNTs can be produced by ethanol-chemical vapor deposition （EtOH-CVD） method usingthose TiO₂NPs as catalyst by controlling the sputtering time. XPS measurements further prove that the TiO₂NPs are responsible for the SWNTs growth. SWNTs from TiO₂NPs bysputtering approach provide a facile way for patterning SWNTs for various applications. Thecatalytic behavior of TiO₂for CNTs growth was discussed as well.（3） High density SWNTs can be synthesized by CVD method using ethanol as carbonsource and Pd and Pt NPs as catalyst. The high quality SWNTs are characterized by SEM,AFM and Raman spectroscopy. Raman spectra with three different laser excitationwavelengths （488,514.5and632.8nm） show that more than90%of SWNTs from Pd NPsare semiconducting and85%from Pt NPs, which are higher than the theoretical value of66.7%. The mechanism of the semiconducting-SWNT selective growth is discussed. Also, itwas found that similar diameter distribution of SWNTs can be observed although Pd and PtNPs are different in mean size.