The Alignment And Field Emission Properties Of Carbon Nanotubes

Since the discovery of carbon nanotubes (CNTs) in 1991, the investigation on carbon nanotubes has become a hot topic in the world. However, the limitation of large-scale production and the alignment of carbon nanotubes have restrained the development of the research on their application. The field emission characteristic is the most important application among the excellent properties. The factor of electric field enhancement is the important parameter that influencees emission characteristics of carbon nanotubes arrays. The mechanism of the electric field enhancement being influenced by the nanotuble size and the density of nanotube arrays is studied. So the study of the mechanism of the electric field enhancement is important to enhance the emission characteristics.The well aligned single-walled carbon nanotubes (SWNTs) with low impurity is grown by using chemical-vapor-deposition method. The single-walled carbon nanotubes and multi-walled carbon nanotubes aligned along the axes in the deposited rod-like substance on cathode by using anode arc method. The impurities such as amorphous carbon soot, metallic nanoparticles and carbolic metal particles which can be eliminated easily by using oxidation with concentrated nitric acid and oil of vitriol. Owe to the magnetic pinching effect of arc current, the carbon nanotubes arrange in parallel lines along the arc current direction.The mechanism of the realignment of purified carbon nanotubes in the shear flow, electric field and strong magnetic field are studied using different theoretical models. The SWNTs/E-51 composite with good alignment, uniformity and dispersion of SWNTs were fabricated by in situ polymerization and using repeated mechanical stretching method. The SEM micrograph, the TEM micrograph and the Polarized Raman spectra demonstrated that SWNTs were aligned in the stretching direction and well dispersed in the matrix. The composite presented distinct anisotropic electrical and mechanical properties. The SWNTs/E-51 composite presented higher electrical conductivity and the mechanical properties along the stretching direction than vertical to it. This experimental result is consistent with our theory analysis.The tip electric field and the field enhancement factor of the hexagonal carbon nanotube array were calculated using a simple model of carbon nanotube arrays. The influences to the enhancement factor such as the nanotube's size, the shape and the density of the array were studied. The results indicate that the field enhancement factor increases with the increasing aspect ratio of the carbon nanotubes. For carbon nanotubes array with definite aspect ratio, there are optimum densities correspond with best field enhancement factor. The field enhancement factor of the hexagonal carbon nanotubes array was higher than the square carbon nanotubes array in the same density. The distribution curves of the electric potential upside the hexagonal carbon nanotubes array were calculated.