The Direct Growth of Carbon Nanotubes and Its Substrate Dependence

The unique combination of light weight, small dimensions, structural diversity, excellent mechanical strength and remarkable electronic properties make carbon nanotubes an attractive field of discovery for a wide range of applications, from reinforcing materials to molecular sensing. The immediate problem is in reliably and reproducibly fabricating carbon nanotubes and nanotube arrays with a certain exclusive structure. The reason for this is the large number of parameters integral to nanotube growth. This thesis describes the effect of several synthesis parameters - including temperature, catalyst, and water addition - on the growth of carbon nanotubes by a thermal chemical vapour deposition method. In all instances, multi-walled nanotubes were the only carbon nanotube products observed. The chemical vapour deposition method employed here involves hexane as a volatile carbon precursor and ferrocene as a floating catalyst. The hexane is introduced into the system by passing a stream of nitrogen carrier gas through a bubbler containing the carbon precursor, while the ferrocene catalyst is positioned inside the working tube where it can evaporate gradually. The products of this method are large, vertically aligned arrays of clean multi-walled nanotubes. The second part of this thesis describes the role of the supporting layer in affecting the growth of these extended nanotube arrays. A number of substrates have been examined - both conducting and non-conducting - and the products from these were analysed. It was found that all non-conductive, metal oxide substrates used - these included quartz, alumina, glazed porcelain, Pythagoras, and also fluorite - produced extended fields of carbon nanotubes. Conversely, many conductive substrates - including nickel, molybdenum, glassy carbon, highly ordered pyrolitic graphite and nickel-iron-silicon metal alloys - produce only small amounts of carbon nanotubes. This difference is likely caused by the deactivation of the iron catalyst at high temperature due to diffusion into the substrate surface.