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Research Papers

Structure Controlled Synthesis of Vertically Aligned Carbon Nanotubes Using Thermal Chemical Vapor Deposition Process

[+] Author and Article Information
Myung Gwan Hahm

Department of Mechanical and Industrial Engineering, NSF Nanoscale Science and Engineering Center for High-Rate Nanomanufacturing, Northeastern University, Boston, MA 02115mghahm@coe.neu.edu

Young-Kyun Kwon

Department of Physics and Research Institute for Basic Sciences, Kyung Hee University, Seoul 130-701, Koreaykkwon@khu.ac.kr

Ahmed Busnaina

Department of Mechanical and Industrial Engineering, NSF Nanoscale Science and Engineering Center for High-Rate Nanomanufacturing, Northeastern University, Boston, MA 02115

Yung Joon Jung1

Department of Mechanical and Industrial Engineering, NSF Nanoscale Science and Engineering Center for High-Rate Nanomanufacturing, Northeastern University, Boston, MA 02115jungy@coe.neu.edu

1

Corresponding author.

J. Heat Transfer 133(3), 031001 (Nov 15, 2010) (4 pages) doi:10.1115/1.4002443 History: Received June 15, 2009; Revised January 13, 2010; Published November 15, 2010; Online November 15, 2010

Due to their unique one-dimensional nanostructure along with excellent mechanical, electrical, and optical properties, carbon nanotubes (CNTs) become a promising material for diverse nanotechnology applications. However, large-scale and structure controlled synthesis of CNTs still have many difficulties due to the lack of understanding of the fundamental growth mechanism of CNTs, as well as the difficulty of controlling atomic-scale physical and chemical reactions during the nanotube growth process. Especially, controlling the number of graphene wall, diameter, and chirality of CNTs are the most important issues that need to be solved to harness the full potential of CNTs. Here we report the large-scale selective synthesis of vertically aligned single walled carbon nanotubes (SWNTs) and double walled carbon nanotubes (DWNTs) by controlling the size of catalyst nanoparticles in the highly effective oxygen assisted thermal chemical vapor deposition (CVD) process. We also demonstrate a simple but powerful strategy for synthesizing ultrahigh density and diameter selected vertically aligned SWNTs through the precise control of carbon flow during a thermal CVD process.

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Figures

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Figure 1

Schematics of ethanol CVD systems and experimental procedures for the growth of vertically aligned SWNT

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Figure 2

(a) A cross-sectional optical image of highly dense and vertically aligned SWNTs grown with ethanol vapor as a carbon source, (b) low magnification SEM image of vertically aligned SWNTs, (c) low magnification SEM image of vertically aligned SWNT microblocks, (d) high magnification SEM image showing aligned nature of SWNTs grown in a thermal ethanol CVD process, high-resolution TEM images showing selectively synthesized (e) SWNTs and(f) DWNTs

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Figure 3

(a) D, G band spectra of vertically aligned SWNTs grown with 50 SCCM (red) and 200 SCCM (blue) flow rates of ethanol; (b) representative RBM spectra of vertically aligned SWNTs synthesized with 50 SCCM and 200 SCCM ethanol flow rates extracted from RBM mapping process, Raman RBM hyperspectral images from SWNTs grown with (c) 50 SCCM and (d) 200 SCCM; (c) the spatial diameter distribution of VA-SWNTs grown with 50 SCCM flow rate of ethanol is very uniform (blue color occupied 93% of the entire SWNT film); (d) the RBM image showing wide diameter distribution of vertically aligned SWNTs grown with 200 SCCM

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Figure 4

The charts of the major diameter distribution of VA-SWNTs grown with two different flow rates of ethanol (50 SCCM and 200 SCCM). The major SWNTs diameters grown with 50 SCCM ethanol flow rate are 0.79 nm (93%) and 1.06 nm (5%). In the case of 200 SCCM flow rate of ethanol, the four major SWNTs diameters (1.10 nm, 1.17 nm, 1.30 nm, and 1.42 nm) are distributed in similar ratio on the surface.

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Figure 5

Schematics of our simple model for SWNT growth with different flow rates: (a) and (b) shows different flow rates of carbon sources at the Co nanoparticle perimeters, which will make nucleation of carbon nanotubes with different sizes; (a) corresponds to the flow rate of 50 SCCM, which makes smaller diameter nanotubes, while (b) corresponds to 200 SCCM making larger diameter nanotubes. (c) If the flow rate is too low, then collected carbon source at the perimeter of the Co particle is not enough to form a nucleation, so no carbon nanotube would grow. (d) In the case of overflow rate, the collected carbon source at the perimeter of the Co nanoparticles covers the surface of Co nanoparticles and the catalyst nanoparticles are deactivated for the growth of SWNTs (13).

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