Reduction of thermal conductivity in phononic nanomesh structures
Reduction of thermal conductivity in phononic nanomesh structures
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DOI：
10.1038/nnano.2010.149
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发表时间：
2010-10-01
影响因子：
38.3
通讯作者：
Heath, James R.
中科院分区：
文献类型：
--
作者：
Yu, Jen-Kan;Mitrovic, Slobodan;Heath, James R.
控制一种材料的导热性，而不依赖于它的导电性，一直是研究热电材料在能源应用（1,2）和集成电路冷却(3)中的目标。原则上，导热系数kappa和电导率sigma可以在半导体纳米结构中独立优化，因为不同的长度尺度与声子（携带热量）和电荷（携带电流）有关。声子在表面和界面上散射，因此kappa通常随着表面体积比的增加而减小。相比之下，sigma对纳米结构尺寸的减小不太敏感，尽管在足够小的尺寸下，它会通过界面上载流子的散射而降解(4)。在这里，我们展示了一种独立控制kappa的方法，该方法是通过形成声子纳米膜来改变半导体薄膜的声子带结构。这些薄膜具有与声子平均自由程相当或更短的周期性间隔。纳米网结构表现出比同等制备的硅纳米线阵列低得多的导热性，尽管这种阵列具有明显更高的表面体积比。块状电导率被保留了下来。我们认为这一发展是朝着降低导热性的连贯机制迈出的一步。
Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications(1,2) and in the cooling of integrated circuits(3). In principle, the thermal conductivity kappa and the electrical conductivity sigma may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so kappa generally decreases as the surface-to-volume ratio increases. In contrast, sigma is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces(4). Here, we demonstrate an approach to independently controlling kappa based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity.