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Carbon Diffusion from Methane into Walls of Carbon Nanotube through Structurally and Compositionally Modified Iron Catalyst

Published online by Cambridge University Press:  27 May 2011

Michael J. Behr ,
K. Andre Mkhoyan  and
Eray S. Aydil
Michael J. Behr
Affiliation:
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA
K. Andre Mkhoyan*
Affiliation:
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA
Eray S. Aydil*
Affiliation:
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA
*
Corresponding author. E-mail: mkhoyan@umn.edu
Corresponding author. E-mail: aydil@umn.edu
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Abstract

To understand diffusion processes occurring inside Fe catalysts during multiwall carbon nanotube (MWCNT) growth, catalysts were studied using atomic-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Nanotube walls emanate from structurally modified and chemically complex catalysts that consist of cementite and a 5 nm amorphous FeOx cap separated by a 2–3 nm thick carbon-rich region that also contains Fe and O (a-C:FexOy). Nonuniform distribution of carbon atoms throughout the catalyst base reveals that carbon molecules from the gas phase decompose near the catalyst multisection junction, where the MWCNT walls terminate. Formation of the a-C:FexOy region provides the essential carbon source for MWCNT growth. Two different carbon diffusion mechanisms are responsible for the growth of the inner and outer walls of each MWCNT.

Keywords

carbon nanotubecatalystironcementitediffusionSTEMEELS
Type
Materials Applications
Information
Microscopy and Microanalysis , Volume 17 , Issue 4 , August 2011 , pp. 582 - 586
Copyright
Copyright © Microscopy Society of America 2011

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