Investigation of Optimal Parameters for Oxide-Assisted Growth of Vertically Aligned Single-Walled Carbon Nanotubes

An investigation into the optimal growth of single-walled carbon nanotubes (SWNTs) in vertical arrays, or carpets, is presented utilizing atomic hydrogen catalyst activation with hot filament chemical vapor deposition. Using acetylene decomposition over Fe catalyst, we study the effect of oxidant-assisted growth using O2, CO2, and H2O. Whereas trace amounts of O2 result in the lack of any catalytic activity, CO2 and H2O are found to dramatically enhance the catalyst lifetime. On the basis of the saturation effect of oxidant concentration for both CO2 and H2O, we present this as being due to catalyst stabilization from surface hydroxyl groups, with H2O having the most dominant effect upon carpet growth. Utilizing water-assisted growth, this process is further optimized to yield high-quality single-walled carbon nanotubes. High temperature growth (∼775 °C) yields the highest-quality SWNTs, whereas controllable growth of doubleand few-walled nanotubes can also be achieved at lower temperatures (550-600 °C). Finally, ultralong carpets are demonstrated by utilizing the optimal SWNT growth conditions under an enhanced carbon flux environment.