Chirality control of single -walled carbon nanotubes on surfaces and optimization of their growth in vertically -aligned arrays
Pheasant, Sean T.
Hauge, Robert H.
Doctor of Philosophy
In order to use single walled carbon nanotubes (SWNTs) for electronic, mechanical, and medical applications, there must be control over the types and orientation of the SWNTs that are produced, and they also need to be produced in large quantities. Results from research focusing on these issues are described in this thesis. The first part talks about growing SWNTs with chirality control on a surface. The second part discusses how to optimize the growth of vertically-aligned nanotube arrays (SWNT carpets) with oxidants, carbon feedstock, temperature and pressure. The focus of the chirality-control research was to prove that an existing nanotube could be grown longer on a surface. The thought is that the initial SWNT seed will act as a template, and determine the chirality of the elongated SWNT. It was found that it is possible to re-grow SWNTs on silicon and highly oriented pyrolytic graphite, but that it is rare and can be very slow. A CVD apparatus was built to optimize the growth of vertical arrays of SWNTs. It reduced the background level of oxidants so that exact amounts of oxidants could be injected into to the growth gas flow to see how they affected growth. A hot filament was also used during the nucleation stage to dissociate molecular hydrogen for the rapid reduction of the iron oxide catalyst particles to iron. It was found that using carbon dioxide or water in conjunction with the hot filament catalyst activation increased the growth rate. Using a small amount of oxygen hindered growth, or prevented it completely. It was also found that while atomic hydrogen allowed better growth in many scenarios, too much could deter growth. The results of the carpet growth also gave some insight as to the mechanism by which carbon is incorporated into a SWNT from molecules in the gas phase.
Inorganic chemistry; Pure sciences; Chirality control; Single-walled carbon nanotubes; Vertical arrays