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Block-copolymer assisted synthesis of arrays of metal nanoparticles and their catalytic activities for the growth of SWNTs

Sreekar Bhaviripudi1, Alfonso Reina1, Jifa Qi1, Jing Kong2 and Angela M Belcher1,3

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Block copolymer micellar templates were used for the controlled synthesis of large arrays of mono-metallic (Fe, Co, Ni, Mo) and bi-metallic (Fe–Mo) nanoparticles with average diameters ranging from 1 to 4 nm and the distance between the nanoparticles ranging from 40 to 45 nm. XPS data reveal the presence of mono-metallic nanoparticles in their oxidized states. These uniform arrays of nanoparticles serve as an excellent tool to investigate the catalytic effect of different metal/metal oxide nanoparticles for the growth of carbon nanotubes, and in this work, they were used to investigate the growth of single-walled carbon nanotubes with the chemical vapour deposition (CVD) process, using both ethanol and hydrocarbon (methane + ethylene) gases as carbon sources. The periodicity and the arrangement of nanoparticles were unaffected even at high growth temperatures, indicating that nanoparticle agglomeration on the Si substrate does not take place during growth. AFM and SEM results reveal uniform growth of nanotubes with diameters smaller than the initial size of the catalyst nanoparticles. The Fe, Co and Ni nanoparticles all serve as effective catalysts for nanotube growth with both types of carbon feed stock, and Co and Ni give rise to a relatively higher yield than Fe. The catalytic activity of Fe and bi-metallic Fe–Mo nanoparticles of similar size and identical densities using ethanol CVD are also compared.


PACS

81.07.De Nanotubes

81.16.Hc Catalytic methods

81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, etc.)

82.70.Dd Colloids

Subjects

Soft matter, liquids and polymers

Surfaces, interfaces and thin films

Nanoscale science and low-D systems

Chemical physics and physical chemistry

Dates

Issue 20 (28 October 2006)

Received 6 July 2006, in final form 17 August 2006

Published 22 September 2006



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