Investigating carbon nanotube growth with the transmission electron microscope
Abstract
Vertically aligned single walled carbon nanotube carpets or arrays are of great technological importance, with various potential applications inspired by their unique properties. Nonetheless, these structures are still not widely utilized, largely because of a lack of understanding of the termination mechanism whereby carpet growth suddenly stops after growing to a certain height. In order to solve this perplexing problem, we systematically perform a series of experiments, including controlled thermal annealing, carpet growth, and in-situ monitoring of carpet growth. These experiments are closely correlated with both ex-situ plan-view and cross section imaging in the transmission electron microscope (TEM), and real time observation of individual carbon nanotube growth and termination in-situ to the TEM. With these various approaches, we show that catalyst particles that have existing nanotubes can undergo dynamic evolution in size and that carbon nanotube growth can cease due to complete loss of the catalyst particle. Also, we develop a solid correlation between termination of carpet growth and the dynamic evolution of catalyst particles during thermal annealing or growth processes. The dynamic evolution of catalyst particles is governed by Ostwald ripening and sub-surface diffusion. Based on this correlation, we can explain four growth termination related phenomena: (i) how can a small amount of H2O dramatically enhance the lifetime of catalyst? (ii) how can only 30 seconds of a rapid reduction process using atomic hydrogen significantly enhance the lifetime of catalyst? (iii) why is the growth temperature is so sensitive to the carpet growth termination? (iv) why is the support material so important in carpet growth? In addition, based on the understanding of the termination mechanism obtained through this work, we demonstrate one possible way to improve the carpet growth.
Degree
Ph.D.
Advisors
Stach, Purdue University.
Subject Area
Materials science
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