CUED Publications database

The phase of iron catalyst nanoparticles during carbon nanotube growth

Wirth, CT and Bayer, BC and Gamalski, AD and Esconjauregui, S and Weatherup, RS and Ducati, C and Baehtz, C and Robertson, J and Hofmann, S (2012) The phase of iron catalyst nanoparticles during carbon nanotube growth. Chemistry of Materials, 24. pp. 4633-4640. ISSN 0897-4756

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Abstract

We study the Fe-catalyzed chemical vapor deposition of carbon nanotubes by complementary in situ grazing-incidence X-ray diffraction, in situ X-ray reflectivity, and environmental transmission electron microscopy. We find that typical oxide supported Fe catalyst films form widely varying mixtures of bcc and fcc phased Fe nanoparticles upon reduction, which we ascribe to variations in minor commonly present carbon contamination levels. Depending on the as-formed phase composition, different growth modes occur upon hydrocarbon exposure: For γ-rich Fe nanoparticle distributions, metallic Fe is the active catalyst phase, implying that carbide formation is not a prerequisite for nanotube growth. For α-rich catalyst mixtures, Fe3C formation more readily occurs and constitutes part of the nanotube growth process. We propose that this behavior can be rationalized in terms of kinetically accessible pathways, which we discuss in the context of the bulk iron-carbon phase diagram with the inclusion of phase equilibrium lines for metastable Fe3C. Our results indicate that kinetic effects dominate the complex catalyst phase evolution during realistic CNT growth recipes. © 2012 American Chemical Society.

Item Type: Article
Uncontrolled Keywords: carbide carbon nanotube catalyst CVD ETEM Fe XRD
Subjects: UNSPECIFIED
Divisions: Div B > Solid State Electronics and Nanoscale Science
Depositing User: Cron Job
Date Deposited: 07 Mar 2014 11:20
Last Modified: 08 Dec 2014 02:13
DOI: 10.1021/cm301402g