Studies On Carbon Nanotubes

Abstract

The unique electronic, mechanical and physical properties led Carbon nanotubes (CNTs) to be potential candidate for field emitter, hydrogen storage, sensors, nano electronic devices, nano electromechanical systems, polymer composites. In order to make them in the industrial scale we need large quantity production of CNTs with low cost. The present thesis work deals with the preparation of CNTs by pyrolysis method from xylene and further studies on the grown CNTs. Magnetic characterization of CNTs has been done using SQUID. The interaction of CNTs with the microwave irradiation is studied and it was found for the first time that there is light emission from the CNTs apart from direct electric field. In this process we also observed that the static charge develops on the CNTs. A composite of CNTs/DNA has been prepared with varying CNT content and the electrical conductivity measurements have been done. The first chapter of the thesis provides an introduction to carbon family. Carbon nanotubes, which are potential candidates from carbon family, is a growing field for research in science and technology. A glimpse of various methods of preparation of CNTs like arc-discharge, laser ablation, chemical vapour deposition (CVD), hot-filament CVD, plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance (ECR PECVD), high-pressure catalytic decomposition of carbon monoxide (HiPCO), pyrolysis are discussed. Some applications of CNTs are also included in this chapter. The second chapter deals with the experimental techniques employed for the preparation of CNTs and their characteristics studied by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Raman Spectroscopy (RS). The preparation of CNTs from xylene as carbon source and ferrocene as catalyst in pyrolysis method is described in detail. Well aligned CNTs with a length of several tens of micrometers and diameter of 40 to 80 nanometers were obtained as confirmed by SEM. TEM and XRD confirms the graphitic crystal structure of the CNTs. RS also confirms the information about the crystal structure. The third chapter discusses the magnetic studies on CNTs using Superconducting Quantum Interference Device (SQUID) as a function of magnetic field and temperature. In the random mixture of parallel, perpendicular and oblique nanotubes, the applied field produces diamagnetic behavior, although the sample possess different kinds of tubes with various chirality and radii. Paramagnetic deviation was observed on the diamagnetic susceptibility at weak fields and low temperature, confirming qualitatively with the Aharonov-Bhom effect on the energy gap for the magnetic field parallel to the tube axis Chapter four presents the light emission from the CNTs. It describes the light emission from different processes reported in the literature. Here we have observed a new process to generate light from CNTs through microwave irradiation. Along with the light emission some of the tubes get charged and some tubes are physically broken. We provide a simple approach as to why the tubes break and the nature of the breakage is also discussed. The fifth chapter discusses the preparation of CNTs/DNA composites. The conductivity increases with increasing carbon nanotube weight percentage. The increase in conductivity as a function of the CNTs weight percent is attributed to the introduction of conducting CNTs path in the DNA matrix. A summary of the results obtained and the scope for future work are included in the chapter six of the thesis.