The growth of empty and filled graphitic nanostructures

Multiwalled carbon nanotubes can be thought of as very thin (diameter <50 run) carbon fibers with a very low defect density. This has led to many proposed applications, but there are many limitations in actually using carbon nanotubes. Nanotube production methods make other products such as polyhedral graphitic particles and graphitic sheets which need to be separated out. In addition, current production methods top out at ∼ 10 g/day of nanotubes, which is insufficient for real usage of nanotubes in many applications. Solving these problems requires further understanding of the growth mechanism of carbon nanotubes.; Initially, the arc discharge is studied to develop some trends that can be used to understand the carbon arc and nanotube growth. It is thought that nanotube growth may occur through a process similar to graphitization, where aromatic fragments assemble into nanotubes and nanoparticles. In this proposal, nanotubes are formed in the arc plasma instead of at the cathode surface.; Alternative methods to make muldwalled nanotubes are developed to help determine the conditions necessary to make nanotubes. Nanotubes can be made by heating amorphous carbons that are mixed with amorphous boron to 2200--2400°C. Boron is added to the fullerene soot to accelerate conversion of the amorphous carbon into graphitic structures. The yield of nanotubes is determined by the structure of the initial amorphous carbon as in graphitization. Nanotubes are also made by annealing anthracene (C14H10), a three ring polycyclic aromatic hydrocarbon (PAH), in the gas phase using a hot tungsten filament. Consequently, it is thought that only high temperatures and graphitic precursors are necessary for multiwalled nanotube growth.; New methods to make filled nanotubes and nanoparticles are also described. Nanotubes filled with pure copper and germanium are made by the arc evaporation of these elements with graphite in a hydrogen atmosphere. These nanotubes are found in the soot deposited on the chamber walls. Evaporating iron, nickel, and cobalt with graphite in hydrogen produces graphite encapsulated spherical nanoparticles instead of nanotubes. Similar experiments evaporating all of these elements in helium gives elemental nanoparticles dispersed in a amorphous carbon/fullerene matrix. The formation of PAH molecules in the hydrogen atmosphere is thought to be the parameter determining the formation of encapsulated nanowires and nanoparticles. Pyrene (C16H10), a four ring PAH molecule is then used as the sole carbon source to make graphite encapsulated nanowires and nanoparticles to show that PAH molecules can act as the carbon source for the graphitic coating.