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Research Papers: Micro/Nanoscale Heat Transfer

Heat Dissipation Mechanism at Carbon Nanotube Junctions on Silicon Oxide Substrate

[+] Author and Article Information
Liang Chen

G.W. Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: lchen64@gatech.edu

Satish Kumar

G.W. Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: satish.kumar@me.gatech.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received November 30, 2012; final manuscript received September 2, 2013; published online March 6, 2014. Assoc. Editor: Patrick E. Phelan.

J. Heat Transfer 136(5), 052401 (Mar 06, 2014) (7 pages) Paper No: HT-12-1637; doi: 10.1115/1.4025436 History: Received November 30, 2012; Revised September 02, 2013

This study investigates heat dissipation at carbon nanotube (CNT) junctions supported on silicon dioxide substrate using molecular dynamics simulations. The temperature rise in a CNT (∼top CNT) not making direct contact with the oxide substrate but only supported by other CNTs (∼bottom CNT) is observed to be hundreds of degree higher compared with the CNTs well-contacted with the substrate at similar power densities. The analysis of spectral temperature decay of CNT-oxide system shows very fast intratube energy transfer in a CNT from high-frequency band to intermediate-frequency bands. The low frequency phonon band (0–5 THz) of top CNT shows two-stage energy relaxation which results from the efficient coupling of low frequency phonons in the CNT-oxide system and the blocking of direct transport of high- and intermediate-frequency phonons of top CNT to the oxide substrate by bottom CNT.

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Figures

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Fig. 5

(a) Equivalent thermal resistor circuit of systems I, II, and III. (b) Rate of heat transfer via CNT-SiO2 direct contact and CNT-CNT junction in system II. L and LB are the lengths of top and bottom CNTs, respectively. Lcontact is the length of top CNT directly contacted with SiO2 in system II.

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Fig. 4

Temperature variations of top CNT in the three systems shown in Fig. 1 as a function of heating power

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Fig. 3

Temperature distribution along the top CNT in system III at heating power of 26.5 nW

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Fig. 2

Minimum distance between top CNT and SiO2 substrate in system II (see Fig. 1(b)). Here, x = 0 corresponds to the midpoint of the bottom CNT.

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Fig. 6

(a) Phonon dispersion relations of top CNT in system III at T = 375 K. k* is wave vector normalized with respect to 2π/az. (b) Normalized phonon spectral energy of system III at different frequencies at T = 375 K. The spectral energy of C (in top and bottom CNTs), Si, and O is normalized to the maximum value of spectral energy of C atoms in top CNT. The frequency ranges of four phonon bands (1–4) are shown.

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Fig. 1

Configurations of (a) system I, (b) system II, and (c) system III. These systems are equilibrated at 375 K.

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Fig. 7

Top CNT total temperature, substrate temperature, and spectral temperature (Tsp) of four frequency bands (see Fig. 6(b)) of top CNT in (a) system I and (c) system III. The transient decay of difference between top CNT total temperature (or spectral temperature of phonon bands) and substrate temperature (ΔT) for (b) system I and (d) system III. The unit of time constant is picosecond.

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