Research Papers

Chemical Vapor Deposition Growth, Optical, and Thermal Characterization of Vertically Aligned Single-Walled Carbon Nanotubes

[+] Author and Article Information
Shigeo Maruyama

 Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japanmaruyama@photon.t.u-tokyo.ac.jp

Rong Xiang

 State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275, Chinaxiangr2@mail.sysu.edu.cn

J. Heat Transfer 134(5), 051024 (May 01, 2012) (6 pages) doi:10.1115/1.4005713 History: Received August 16, 2010; Revised November 23, 2010; Published April 13, 2012; Online May 01, 2012

Vertically aligned single-walled carbon nanotubes (VA-SWNTs) is expected to be an extra-ordinal material for various optical, electrical, energy, and thermal devices. The recent progress in growth control and characterization techniques will be discussed. The chemical vapor deposition (CVD) growth mechanism of VA-SWNTs is studied based on the in situ growth monitoring by laser absorption during CVD. The growth curves are characterized by an exponential decay of the growth rate from the initial rate determined by ethanol pressure. The initial growth rate and decay of it are discussed with carbon over-coat on metal catalysts and gas phase thermal decomposition of precursor ethanol. For the precisely patterned growth of SWNTs, we recently propose a surface-energy-difference driven selective deposition of catalyst for localized growth of SWNTs. For a self-assembled monolayer (SAM) patterned Si surface, catalyst particles deposit and SWNTs grow only on the hydrophilic regions. The proposed all-liquid-based approach possesses significant advantages in scalability and resolution over state-of-the-art techniques, which we believe can greatly advance the fabrication of nanodevices using high-quality as-grown SWNTs. The optical characterization of the VA-SWNT film using polarized absorption, polarized Raman, and photoluminescence spectroscopy will be discussed. Laser-excitation of a vertically aligned film from top means that each nanotube is excited perpendicular to its axis. Because of this predominant perpendicular excitation, interesting cross-polarized absorption and confusing and practically important Raman features are observed. The extremely high and peculiar thermal conductivity of single-walled carbon nanotubes has been explored by nonequilibrium molecular dynamics simulation approaches. The thermal properties of the vertically aligned film and composite materials are studied by several experimental techniques and Monte Carlo simulations based on molecular dynamics inputs of thermal conductivity and thermal boundary resistance. Current understanding of thermal properties of the film is discussed.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

In situ measurement of film thickness of vertically aligned SWNTs by laser absorption during CVD. Reproduced from Einarsson (2008) [17].

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Figure 2

Anomalous radial breathing mode of Raman scatterings excited from the top of a VA-SWNT film. Raman spectra taken from the top of a VA-SWNT array. Inset shows the RBM region with high-resolution (topmost) and with normal resolution before (middle) and after (lower) dispersion in D2 O. Excitation laser wavelength is 488 nm. Reproduced from Zhang (2010) [25].

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Figure 3

(a) Temperature distribution inside the quartz tube during CVD. (b) Growth curves at 800 °C for different ethanol flow rates show a change for slow flow rates. (c) Ethanol decomposition curves calculated by chemkin and experimentally measured ethanol concentrations (circles) by FT-IR spectroscopy. Reproduced from Xiang (2010) [18].

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Figure 4

(a) Schematic showing the substrate fabrication and selective growth; (b) top and (c) side view SEM images of an electrode-shaped pattern, where SWNTs only grew in the SiO2 regions; (d) top and (e) side view images of hexagon-shaped patterns. The growth behavior of SWNTs at the edges is slightly different from that in the center of a vertically aligned forest. Reproduced from Xiang (2010) [11].

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Figure 5

(a) Various contact angles of water droplets on hydrophilic surface terminated by OH after standard cleaning 1 (SC1) and hydrophobic surface functionalized by OTS monolayer with different SAM converge; (b) SEM images of SWNTs grown on substrate shown in (a) after catalyst dip-coating. Reproduced from Xiang (2009) [12].

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Figure 6

(a) Schematics describing the fabrication procedure of hydrophilic/hydrophobic patterns using a selective removal of OTS SAM by UV exposure; (b) SEM images of random and vertically aligned SWNT line-shape patterns. Reproduced from Xiang (2009) [12].

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Figure 7

Length dependences of SWNT thermal conductivity for two different diameters. λp and λNH denote the values obtained by using phantom and Nose–Hoover thermostats, respectively. The error bars are based on the fitting residuals in the thermal conductivity calculations. The residuals were largest in the case of (3, 3) SWNTs. The thermal conductivity profiles of (3, 3) and (5, 5) SWNTs for L  > 100 nm were fitted to power laws. The dashed line shows λ∝L with an arbitrary slope. Reproduced from Shiomi & Maruyama (2008) [33].




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