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Technical Briefs

Postgrowth Microwave Treatment to Align Carbon Nanotubes

[+] Author and Article Information
A. Sharma

George W. Woodruff
School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

B. A. Cola

e-mail: cola@gatech.edu
George W. Woodruff
School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332;
School of Materials Science and Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF Micro AND Nano-Manufacturing. Manuscript received September 3, 2012; final manuscript received November 26, 2012; published online March 22, 2013. Assoc. Editor: Ashutosh Sharma.

J. Micro Nano-Manuf 1(1), 014501 (Mar 22, 2013) (6 pages) Paper No: JMNM-12-1052; doi: 10.1115/1.4023162 History: Received September 03, 2012; Revised November 26, 2012

We show that a commercial microwave oven can be used after growth to increase alignment of carbon nanotubes (CNTs) and reduce their resistance as thermal and electrical interface materials. Forests of multiwall CNTs were grown directly on both sides of aluminum foils by thermal chemical vapor deposition (CVD) and subsequently exposed to a microwave treatment in air. Scanning electron micrographs revealed enhanced vertical alignment of CNTs after postgrowth microwave treatment. The microwave treatment creates an electric field near the CNT growth substrate that aligns the CNTs orthogonally to the growth substrate. Microwaved CNT forests produced increased mechanical stiffness by approximately 58%, and reduced thermal and electrical contact resistances by 44% and 41%, respectively, compared to as-grown forests. These performance changes are attributed to an increase in the real contact area established at the CNT distal ends because of the enhanced forest alignment. This conclusion is consistent with several prior observations in the literature. This work demonstrates a facile method to enhance the alignment of CNTs grown by thermal CVD without the use of in situ plasma or electric field application.

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Figures

Grahic Jump Location
Fig. 1

(a) Scanning electron micrograph of CNT arrays grown on both sides of aluminum foil before microwave treatment. (b) Illustration of CNT alignment on one side of the aluminum foil substrates as a result of the electric field applied to the sample during microwave treatment. Electric field forces perpendicular to the substrate pull individual CNTs into alignment.

Grahic Jump Location
Fig. 2

Morphological characterization of double-sided, CNT-coated foil structures. (a) Scanning electron micrograph of CNTs on aluminum foil substrate before microwave treatment. (b) Scanning electron micrograph of the CNT sample in frame (a) after microwave treatment. (c) Raman spectra of CNTs before and after microwave treatment. (d) Transmission electron micrographs of a representative CNT before and after microwave treatment.

Grahic Jump Location
Fig. 3

Mechanical, thermal, and electrical testing of double-sided, CNT-coated foil structures. (a) Load–displacement curve for CNT samples before and after microwave treatment. (b) Measured phase shift in PA measurement of CNT samples before and after microwave treatment. (c) Current–voltage characteristics of CNT samples before and after microwave treatment.

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