Controlled synthesis of single-walled carbon nanotubes
McJilton, Laura Anne
Doctor of Philosophy
The chemistry and applications of carbon nanotubes are critically dependent on nanotube chirality. To date, no one has demonstrated chirality-selective synthesis of single-walled carbon nanotubes from pre-synthesized catalyst nanoparticles. A proposed chemical approach to the mass production of chirality-selective SWNTs is their "cloning" by chemical cutting, decoration with catalyst nanoparticles, and continued growth. The progress of this process will be reviewed. Purified HiPco nanotubes were sidewall functionalized to allow suspension in water and organic solvents. Methods were developed to end-functionalize suspended nanotubes with linkers used to attach preformed catalyst particles. SWNT-catalyst complexes (SWNTcats) were deposited on a surface and exposed to hydrogen to show the feasibility of controlled etching of a single nanotube resulting in removal of the functional linker. To orient the nanotubes for growth, SWNTcats were assembled into open structures on a carbon fiber grid. Vertically oriented carbon nanotube carpets grown by catalytic CVD have received enormous attention because of their suitability in a growing number of important technological applications. An area of concern is the sudden termination of growth that occurs after micron heights are attained. A previously unexplored factor in this termination is the coarsening of the catalyst particles used for growth by Ostwald ripening. The coarsening behavior of Fe catalyst films supported on alumina deposited by atomic layer deposition as a function of thermal annealing in H2 and H2/H2O is demonstrated. The results reveal that the addition of water in water assisted growth of single-walled carbon nanotube carpets may be a means of inhibiting Ostwald ripening through the ability of oxygen and hydroxyl species to reduce diffusion rates of catalyst atoms and thus delay the termination of growth.
Chemistry; Physical chemistry