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Issue 23, 2018
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Impact of thermally dead volume on phonon conduction along silicon nanoladders

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Abstract

Thermal conduction in complex periodic nanostructures remains a key area of open questions and research, and a particularly provocative and challenging detail is the impact of nanoscale material volumes that do not lie along the optimal line of sight for conduction. Here, we experimentally study thermal transport in silicon nanoladders, which feature two orthogonal heat conduction paths: unobstructed line-of-sight channels in the axial direction and interconnecting bridges between them. The nanoladders feature an array of rectangular holes in a 10 μm long straight beam with a 970 nm wide and 75 nm thick cross-section. We vary the pitch of these holes from 200 nm to 1100 nm to modulate the contribution of bridges to the net transport of heat in the axial direction. The effective thermal conductivity, corresponding to reduced heat flux, decreases from ∼45 W m−1 K−1 to ∼31 W m−1 K−1 with decreasing pitch. By solving the Boltzmann transport equation using phonon mean free paths taken from ab initio calculations, we model thermal transport in the nanoladders, and experimental results show excellent agreement with the predictions to within ∼11%. A combination of experiments and calculations shows that with decreasing pitch, thermal transport in nanoladders approaches the counterpart in a straight beam equivalent to the line-of-sight channels, indicating that the bridges constitute a thermally dead volume. This study suggests that ballistic effects are dictated by the line-of-sight channels, providing key insights into thermal conduction in nanostructured metamaterials.

Graphical abstract: Impact of thermally dead volume on phonon conduction along silicon nanoladders

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Publication details

The article was received on 02 Mar 2018, accepted on 29 May 2018 and first published on 30 May 2018


Article type: Paper
DOI: 10.1039/C8NR01788C
Citation: Nanoscale, 2018,10, 11117-11122
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    Impact of thermally dead volume on phonon conduction along silicon nanoladders

    W. Park, J. Sohn, G. Romano, T. Kodama, A. Sood, J. S. Katz, B. S. Y. Kim, H. So, E. C. Ahn, M. Asheghi, A. M. Kolpak and K. E. Goodson, Nanoscale, 2018, 10, 11117
    DOI: 10.1039/C8NR01788C

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