Abstract
Carbon nanotubes have shown their abilities in a wide range of electronic applications due to their unique electronic properties. In order to match the different needs of applications, the issue of selectively growing specific types of single-walled carbon nanotubes has received considerable attention. In this study, a parametric study is implemented to solve this issue. Firstly, the growth windows for selectively synthesising high quality single-walled carbon nanotubes via photo-thermal chemical vapour deposition (PTCVD) are determined. The growth process of the PTCVD is free of oxygen-containing precursors and corrosive catalysts, and is fully compatible with the integrated circuit process. Only acetylene and hydrogen are used and the catalyst is a layer of sputtered iron. The multi-variables, which include the process temperature, reactant gas ratio and total flow rate, are studied in terms of their influence on the growth rate, the quality and the preferential growth of carbon nanotubes. The highest growth rate obtained in this study is 442 nm/s, which is the highest growth rate reported so far, without using water and/or a corrosive catalyst to assist the growth. By studying the growth rate, we find that it can be correlated to the bulk iron and carbon phase diagram. Generally, above the eutectoid temperature of a and g iron, the growth rate decreases with increasing temperature and inversely, the growth rate is enhanced with increasing temperature below the eutectoid temperature of the a iron and carbide. Moreover, a novel growth model is also proposed to interpret the high growth rate. Owing to the topdown heating of the PTCVD, three factors are concluded to enhance the growth rate that are the gradients of the temperature and the carbon concentration and the chemical potential along the axis of the catalyst. The selective growth of high-quality single-walled carbon nanotubes is achieved by optimising the reactant gas ratio and the process temperature, and is confirmed by the radial breathing modes in Raman spectroscopy. The growth window for semiconducting single walled carbon nanotubes is relatively larger than that for growing metallic single-walled carbon nanotubes. The semiconducting single-walled-carbon nanotubes prefer to grow above 800°C with the acetylene ratio being below 10%. The metallic single-walled carbon nanotubes tend to grow between 750 and 800°C,which correspond 420 and 450°C at the substrate temperature and the acetylene ratio of 16-18% are suggested. The preferential growth of the semiconducting and metallic single-walled carbon nanotubes are confirmed again by analysising the Breit-Wigner-Fano lineshape of the G^(-)-band and the 2D-band. The results are highly consistent with those deduced from analysing the radial breathing modes Finally, the field emission properties of different types of carbon nanotubes are investigated. We find that multi-walled carbon nanotubes have the better performance compared to semiconducting and metallic single-walled carbon nanotubes. Moreover, different morphologies of the carbon nanotubes and different substrates are also studied with respect to the field emission properties. Consequently, honeycomb-patterned multi-walled carbon nanotubes are grown on the a layer of indium tin oxide on a glass slide that can be used for the flat panel display and lightings.