Two-Dimensional Phonon Polariton Heat Transport
Two-Dimensional Phonon Polariton Heat Transport
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DOI：
10.1021/acs.nanolett.9b02214
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发表时间：
2019-10-01
期刊：
影响因子：
10.8
通讯作者：
Miyazaki, Koji
中科院分区：
文献类型：
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作者：
Tranchant, Laurent;Harnamura, Satoki;Miyazaki, Koji
众所周知，由于尺寸效应，薄膜的声子和电子热导率通常随着其厚度缩小到纳米级而降低，这具有显著的工程效应，例如过热、低可靠性以及处理器和其他电子部件的寿命缩短。然而，考虑到较薄的薄膜具有较高的表面积与体积比，这些纳米材料中的主要表面效应不仅能够在其体积内而且还能够沿着其界面传输热能。在极性纳米膜中，这种界面传输是由表面声子极化激元驱动的，表面声子极化激元是主要通过沿其表面沿着的声子-光子耦合在中红外频率下产生的电磁波。理论预测，这些极化激元可以提高悬浮二氧化硅膜的面内热导率的值高于相应的散装的，因为它们的厚度通过小于200 nm的值减小。在这项工作中，我们通过实验证明了这种热导率的增强。结果表明，在室温下，20 nm厚的二氧化硅薄膜的面内热导率几乎是晶格振动对应物的两倍。另外的热扩散率测量揭示，二氧化硅膜的扩散率也随着其厚度的减小而增加，使得热导率/热扩散率（体积热容）的比率保持几乎与膜厚度无关。这里获得的实验结果将使人们能够建立在最近有趣的理论预测，突出了纳米尺度下新的热通道的存在，并提供了一个新的途径来设计导热纳米材料进行有效的热管理。
As is well-known, the phonon and electron thermal conductivity of a thin film generally decreases as its thickness scales down to nanoscales due to size effects, which have dramatic engineering effects, such as overheating, low reliability, and reduced lifetime of processors and other electronic components. However, given that thinner films have higher surface-to-volume ratios, the predominant surface effects in these nanomaterials enable the transport of thermal energy not only inside their volumes but also along their interfaces. In polar nanofilms, this interfacial transport is driven by surface phonon polaritons, which are electromagnetic waves generated at mid-infrared frequencies mainly by the phonon-photon coupling along their surfaces. Theory predicts that these polaritons can enhance the in-plane thermal conductivity of suspended silica films to values higher than the corresponding bulk one, as their thicknesses decrease through values smaller than 200 nm. In this work, we experimentally demonstrate this thermal conductivity enhancement. The results show that the in-plane thermal conductivity of a 20 nm thick silica film at room temperature is nearly twice its lattice vibration counterpart. Additional thermal diffusivity measurements reveal that the diffusivity of a silica film also increases as its thickness decreases, such that the ratio of thermal conductivity/thermal diffusivity (volumetric heat capacity) remains nearly independent of the film thickness. The experimental results obtained here will enable one to build on recent interesting theoretical predictions, highlight the existence of a new heat channel at the nanoscale, and provide a new avenue to engineer thermally conductive nanomaterials for efficient thermal management.