Ostwald Ripening-Induced Termination of Carbon Nanotube Growth

One of the most challenging problems in carbon nanotube synthesis today is understanding the termination of growth. Many mechanisms have been proposed for the termination of carpet growth. In particular, the impact of growth environment and catalyst/support interaction are known to be critical to growth, but have not been investigated explicitly in the context of Ostwald ripening. Here, we explore the role Ostwald ripening plays in inducing the termination of carpet SWNT growth by studying the ripening rate of the catalyst as a function of the annealing ambient and the catalyst support interaction. Coarsening rates of iron catalysts on alumina supports deposited by three different methods are investigated: atomic layer deposition, magnetron sputtering and e-beam evaporation. The Ostwald ripening rates of each alumina/Fe combination also is studied as a function of thermal treatment in H2, atomic H, H2 and H2O, and inert ambients.