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Technical Brief

Mechanical Behavior of Carbon Nanotube Forests Grown With Plasma Enhanced Chemical Vapor Deposition: Pristine and Conformally Coated

[+] Author and Article Information
Parisa Pour Shahid Saeed Abadi

Department of Medicine,
Brigham and Women's Hospital,
Harvard Medical School,
65 Landsdowne Street,
Cambridge, MA 02139
e-mails: ppourshahidsaeedabadi@bwh.harvard.edu; pourshahid@gmail.com

Matthew R. Maschmann

Air Force Research Laboratory,
Materials and Manufacturing Directorate,
Composites Branch,
Wright-Patterson Air Force Base, OH 45433;
Universal Technology Corporation,
Beavercreek, OH 45432;
Department of Mechanical and Aerospace Engineering,
University of Missouri,
Columbia, MO 65211

Stephen L. Hodson, Timothy S. Fisher

School of Mechanical Engineering;Birck Nanotechnology Center,
Purdue University,
West Lafayette, IN 47907

Jeffery W. Baur

Air Force Research Laboratory,
Materials and Manufacturing Directorate,
Composites Branch,
Wright-Patterson Air Force Base, OH 45433

Samuel Graham, Baratunde A. Cola

George W. Woodruff School of Mechanical Engineering;School of Materials Science and Engineering,
Georgia Institute of Technology,
771 Ferst Drive,
Atlanta, GA 30332

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received June 28, 2015; final manuscript received November 24, 2016; published online March 23, 2017. Assoc. Editor: Ashraf Bastawros.This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government's contributions.

J. Eng. Mater. Technol 139(3), 034502 (Mar 23, 2017) (5 pages) Paper No: MATS-15-1149; doi: 10.1115/1.4035622 History: Received June 28, 2015; Revised November 24, 2016

Plasma-enhanced chemical vapor deposition (PECVD) is a well-known method for the synthesis of carbon nanotube (CNT) forests with the electric field in the plasma sheath being responsible for the vertical orientation of CNTs. Here, we investigate the deformation mechanism and mechanical properties of pristine and conformally coated PECVD CNT forests under compressive loading. Our in situ indentation experiments reveal that local buckles form along the height of pristine CNTs progressing downward from the starting point at the tips. For CNT forests coated from their roots to top with alumina using atomic layer deposition (ALD), the deformation mechanism depends strongly on the coating thickness. The buckling behavior does not change significantly when the coating is 5-nm thick. However, with a 10-nm-thick coating, the nanotubes fracture—that is, at both the CNT core and alumina coating. Ex situ indentation experiments with a flat punch reveal 8- and 22-fold increase in stiffness with the 5- and 10-nm coating, respectively. Comparing the behavior of the PECVD forests with CNTs grown with thermal chemical vapor deposition (CVD) shows that the mechanical behavior of PECVD CNTs depends on their characteristic morphology caused by the growth parameters including plasma. Our findings could serve as guidelines for tailoring the properties of CNT structures for various applications in which CNT compliance or deformation plays a critical role.

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Figures

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Fig. 1

Micro‐ and nano‐structure of PECVD CNTs: (a) an SEM micrograph illustrating the entire height of the forest, the growth substrate, and the free CNT tips, (b) a magnified SEM micrograph showing more clearly the individual CNTs and the degree of alignment and entanglement, and (c) a TEM micrograph illustrating the nanostructure of the individual CNTs and an inset showing schematically the bamboo structure

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Fig. 2

Indentation of the MPCVD forest: (a) indenter touching the surface, (b) the CNT tips are bent/buckled, (c) and (d) a second buckle is formed under the first one, (e) maximum deformation of CNTs, and (f) recovered CNT forest after unloading. The schematics on the right side of the images show the side view of the buckles.

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Fig. 3

Structure of PECVD CNTs coated with ALD alumina in SEM micrographs: (a) low magnification micrograph illustrating the entire height of a forest coated by 100 cycles, (b) and (c) high magnification micrograph of a CNT forest coated by 50 and 100 ALD cycles, respectively

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Fig. 4

Comparison of deformations in indentation of uncoated and coated MPCVD CNT forests: (a)–(c) uncoated, (d)–(f) coated with 5 nm of ALD alumina, and (g)–(i) coated with 10 nm of ALD alumina. Left column: middle of loading, middle column: end of loading, and right column: end of unloading.

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Fig. 5

Comparison of typical indentation load-depth curves for MPCVD CNT forests in the uncoated condition and coated with 5 and 10 nm of ALD alumina

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