Anomalous thermal conductivity by surface phonon-polaritons of polar nano thin films due to their asymmetric surrounding media

The surface phonon-polaritons contribution to the thermal conductivity of a nano thin film of silicon dioxide is investigated based on the Maxwell equations and the Boltzmann transport equation. It is shown that: (1) a small difference between the permittivities of the substrate and superstrate of t...

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Bibliographic Details
Published in:Journal of applied physics 2013-02, Vol.113 (8)
Main Authors: Ordonez-Miranda, J., Tranchant, Laurent, Tokunaga, Takuro, Kim, Beomjoon, Palpant, Bruno, Chalopin, Yann, Antoni, Thomas, Volz, Sebastian
Format: Article
Language:English
Subjects:
Boltzmann transport equation
Condensed Matter
Heat transfer
Materials Science
Nanocomposites
Nanomaterials
Nanostructure
Phonons
Physics
Thermal conductivity
Thin films
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Summary:The surface phonon-polaritons contribution to the thermal conductivity of a nano thin film of silicon dioxide is investigated based on the Maxwell equations and the Boltzmann transport equation. It is shown that: (1) a small difference between the permittivities of the substrate and superstrate of the film can generate giant propagation lengths and therefore remarkably enhances its thermal conductivity with respect to values obtained for a freestanding one. (2) The propagation of surface phonon-polaritons is present in a broad band of frequencies and exhibits its largest propagation lengths at the frequency where the absorption of energy is minimal. (3) The increase of the thermal conductivity of the film as its thickness decreases is higher when it is deposited on potassium bromide instead of being suspended in air. The difference in the thermal conductivity for these two systems increases with increasing temperature and reducing the film thickness. A thermal conductivity as high as 2.5 W/m K is obtained for a 30 nm-thick thin film at room temperature, which is about 1.8 times larger than its bulk phonon value. The obtained results show that the propagation of surface phonon-polaritons has the potential not only to offset the reduction of the phonon thermal conductivity of a nano thin film, when its sizes are scaled down, but also to enhance it, by choosing properly the permittivity of its substrate.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4793498