Preparation And Characterization With Thermal, Electric And Optical Properties Of Carbon Nanotubes

The primary focus of this research work has been made to prepare, purify and decentralize novel carbon nanotubes. Prepared carbon nanotubes were characterized with their thermal, electric and optical properties.In order to prepare highly oriented and multi-walled carbon nanotubes, we treated with diluted acid to remove the metal catalyst particles and cut into pieces by Ultrasonic oscillation, which was subjected to filter by filter paper with different pore sizes for several times. Subsequently, the purified carbon nanotubes with similar diameter and length were characterized by Raman, terahertz and atomic force microscopy.In this thesis, more aligned carbon nanotubes were prepared by chemical vapor deposition (CVD). However, only a small amount of aligned carbon nanotubes were obtained by the traditional CVD. As a result, efforts have been given to optimize the conditions of preparation by redesign the structure of CVD furnace.We have discussed the methods for purification and dispersion treatment of carbon nanotubes. Usually, carbon nanotubes were purified by using dilute acid to remove catalyst particles, acid oxidation amorphous carbon or centrifugation, and dispersed by mechanical stirring, ultrasonic dispersion or dispersion reagent. But these methods often accompanied with defective carbon nanotubes. In order to circumvent the problems, we have developed an efficient method for purification and dispersion treatment of carbon nanotubes.A series of different diameters and lengths of multi-walled carbon nanotubes (MWCNTs) were characterized by Raman spectroscopy and THz. It was showed that the G peak and D peak of MWCNTs are all red shift as compared to that of polycrystalline graphite. At the same conditions, the peak intensity (G peak and D peak) is direct proportion to the diameter of the MWCNTs, and inversely proportional to the length of the MWCNTs. G peak frequency shift is closely related to the MWCNTs diameter and length, which inversely proportional to the diameter (with identical results of the single-walled carbon nanotube radial breathing modes) and direct proportional to the length. Influences of the diameter and length on D peak frequency shift are weak in the frequency range extending from 0.2 to 2.0 THz. The results suggested that the characteristic absorption of MWCNTs was not observed, and absorption value of the sample increase with increasing frequency. Additionally, the curve of terahertz absorption could be fitted by a straight line with a kind of slope. Therefore, we learned that the terahertz absorption is direct proportion to the diameter and length of the MWCNTs. In another hand, the refractive indexes of the sample decrease with increasing frequency and could not be fitted by a straight line. It has also been achieved that diameter is an important factor affecting its refractive index, while the length has little influence.High thermal conductivity of carbon nanotubes is an important aspect of its excellent properties. In this thesis, we summarized the various test methods of micro and nano materials. The scanning thermal microscopy was tested the thermal property of carbon nanotubes and the corresponding topography and heat map were also obtained. Moreover, the thermal conductivity of in some areas was calculated as well.Finally, the topography of carbon nanotubes was obtained by AFM in semi-contact mode. According to the comparative analysis of AFM and SEM topography, advantages and disadvantages for each other were easily found. The diffusion resistor was measured by AFM in contact mode in order to calculate the resistance.