Anomalous thermal conductivity by surface phonon-polaritons of polar nano thin films due to their asymmetric surrounding media
Anomalous thermal conductivity by surface phonon-polaritons of polar nano thin films due to their asymmetric surrounding media
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DOI：
10.1063/1.4793498
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发表时间：
2013-02-28
影响因子：
3.2
通讯作者：
Volz, Sebastian
中科院分区：
文献类型：
--
作者：
Ordonez-Miranda, J.;Tranchant, Laurent;Volz, Sebastian
基于麦克斯韦方程和玻尔兹曼输运方程，研究了表面声子-极化激元对纳米二氧化硅薄膜热导率的贡献。结果表明：（1）薄膜的衬底和覆盖层的导热率之间的小差异可以产生巨大的传播长度，因此相对于独立式薄膜获得的值，显著地提高了其导热率。(2)表面声子-极化激元的传播存在于宽频带中，并且在能量吸收最小的频率处表现出其最大的传播长度。(3)当薄膜沉积在溴化钾上而不是悬浮在空气中时，薄膜的热导率随着其厚度的减小而增加。这两个系统的热导率的差异随着温度的升高和膜厚度的减小而增大。在室温下，30 nm厚的薄膜的热导率高达2.5 W/m K，这是约1.8倍大于其体声子值。结果表明，当纳米薄膜的尺寸减小时，表面声子极化激元的传播不仅可以抵消纳米薄膜声子热导率的降低，而且可以通过适当选择衬底的介电常数来增强纳米薄膜的声子热导率。(C)2013年美国物理学会。[http：//dx.doi.org/10.1063/1.4793498]
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. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793498]