Synthesis And Characterization Of Carbon Nanotubes And Aligned ZnO Nanorod Arrays

Recently, synthesis and characterization of one-dimensional (1D) nanostructures have become the focus of intensive research in crystal growth. In this thesis, two kinds of 1D nano-materials , i.e. carbon nanotubes (CNTs) and ZnO nanorods, have been synthesized. Many potential applications have been proposed for CNTs , including field emission displays, modified electrodes, nanometer-sized semiconductor devices, probes, high-strength composites, energy storage and energy conversion devices and catalysts support, based on their good thermal conductivity similar to diamond, the special mechanical property, the high aspect ratio and hollow structure with nano-scale of carbon nanotubes. Zinc oxide (ZnO) is a novel II -VI compound semiconductor with a wide direct bandgap (3.37ev), a high excitation binding energy (60mev) and a hexagonal wurtzite structure. ZnO is a unique material that exhibits optoelectronic, piezoelectronic, ferroelectric and ferromagnetic multiple properties, and many new potential applications have been proposed for its 1D nanostructures, including laser, field emission of electron, wave-guide of photons, non-linear optics and optoelectronic devices. However, the mass production of high quality CNTs, doping and synthesis of ZnO 1D nanostructures in large scale are the preconditions of their applications.In the thesis, the morphologies, structures, physical properties, preparation methods and growth mechanism of CNTs and ZnO nanorods were briefly reviewed. The syntheses of CNTs by CVD method using nanocrystalline CaCO₃ as catalyst support were discussed in details, especially the effects of experimental parameters on the CNTs syntheses. Moreover, well-aligned ZnO nanorod arrays were fabricated by chemical solution deposition on Si substrate (ZnO/Si substrate) which was spin coated with ZnO sol as nucleation seeds, and the growth mechanism of the ZnO nanorod arrays was discussed in details. ZnO nanorod arrays and ZnO:AI nanoplate arrays were respectively prepared on ZnO/Si and ZnO/Al substrates by a low temperature hydrothermal method. The possibility of using this hydrothermal method to synthesize Zn_1-xCo(Ni)_xO diluted magnetic semiconductor was also discussed.In order to easily remove catalyst impurities, nanocrystalline CaCO₃ was used as catalyst support. Some important parameters were investigated in the thesis, such as composition and content of metallic catalyst, reaction temperature and time, et al. The purification of the rawproduct could be achieved in one step, possessing little structural destructivity. The yield of CNT was greatly affected by the stability of the catalyst and its support at reaction temperature. Though a higher temperature usually results in a larger extent of disassociation of hydrocarbon gas and a better activation of catalytic metal, the disintegration of calcium carbonate was also strongly correlated to the elevated temperature. The distribution and agglomeration of the catalytic nanoparticles tightly depended on the condition of catalyst support. The rapid decomposition of the catalyst would decrease the CNT yield. So a moderate temperature is necessary for a high CNT yield.Mono-dispersed and well-aligned ZnO nanorod arrays were fabricated by chemical solution deposition on Si substrate (ZnO/Si substrate) which was spin coated with ZnO sol as nucleation seeds. This facile technique greatly facilitates the approach to scale-up fabrication of aligned ZnO nanorods with relative low-cost at a remarkably low temperature. The growth mechanism of ZnO nanorod is anisotropic growth, kinetically controlled by low super-saturation. In the reaction system, heterogeneous nucleation occurs firstly on nano-ZnO film of the substrate, and the growth process of ZnO nanorods is actually continuing the growth of grain of nano-ZnO film. The nano-ZnO film of substrate has critical influence on the morphology of ZnO nanorod arrays. The uniformity of morphology, distribution of diameters and orientation of ZnO nanorods are controllable by adjusting the process of nano-ZnO film substrates.Highly aligned ZnO nanorod arrays with a narrow diameter distribution of the ZnO nanorods were fabricated on ZnO/Si substrate by a low temperature hydrothermal method. The average diameter of the ZnO nanorods increases with the higher concentration of the aqueous. The process to prepare ZnO/Si substrates also has strong influence on the orientation and distribution of the diameter distribution of the ZnO nanorod arrays. In the same reaction aqueous, ZnO:Al nanoplate arrays have been synthesized on the ZnO/Al substrates. The ZnO:Al nanoplates are single-crystalline with wurtzite structure, and the normal direction of the nanoplate is [001]. Al ions doping is considered as an important role in the growth of the ZnO: Al nanoplates, which was also proved in another reaction system. Using this hydrothermal method, the Co and Ni elements could not be doped into the ZnO nanorods by only elevate the synthesis temperature.