Clean Technology 2009

The birth, growth and death of a carbon nanotube: using in-situ transmission electron microscopy to observe CNT growth processes

E.A. Stach, S. Min Kim, D.N. Zakharov, C.L. Pint, R. Hauge, B. Maruyama
Purdue University, US

Keywords: Carbon nanotube growth, carbon nanotube growth termination, nanostructure growth


Vertically aligned single-walled carbon nanotube (SWNT) carpets have received enormous attention, as they have a large number of potential applications. However, a lack of understanding of the mechanisms of growth termination remains a limiting factor in optimizing these structures for widespread usage. In order to better understand the growth termination phenomena, we have investigated the evolution of catalyst morphology using both standard and in-situ transmission electron microscopy techniques. A series of tightly controlled annealing and growth studies were performed in a dedicated chemical vapor deposition system using three different gas ambients (hydrogen only, hydrogen and water and atomic hydrogen and water). Quantitative characterization of the catalyst sizes as a function of either annealing or growth time leads to an explanation for growth termination implicating both the processes of Ostwald ripening and iron diffusion into the substrate. These results are corroborated by real time observations of nanotubes growth and termination in a dedicated environmental cell transmission electron microscope, where both ripening and substrate diffusion are directly observed. We will also demonstrate how the experiments can be used to understand nucleation, growth and etchback processes during growth, with a focus on the ‘unit processes’ involved. These studies provide crucial insight into nanotube growth.
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