Division of Chemistry and Chemical Engineering, MC 127-72 1200 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
Nat Nanotechnol. 2010 Oct;5(10):718-21. doi: 10.1038/nnano.2010.149. Epub 2010 Jul 25.
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 and in the cooling of integrated circuits. In principle, the thermal conductivity κ and the electrical conductivity σ 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 κ generally decreases as the surface-to-volume ratio increases. In contrast, σ 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. Here, we demonstrate an approach to independently controlling κ 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.
控制材料的热导率而不影响其电导率，这一直是研究用于能源应用和集成电路冷却的热电材料的研究人员的目标。原则上，在半导体纳米结构中，热导率 κ 和电导率 σ 可以独立优化，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。声子在表面和界面处散射，因此 κ 通常随着表面积与体积比的增加而降低。相比之下，尽管在足够小的尺寸下，由于电荷载流子在界面处的散射，σ 将降低，但它对纳米结构尺寸减小的敏感性较小。在这里，我们通过在半导体薄膜中形成声子纳米网薄膜来展示一种基于改变声子能带结构来独立控制 κ 的方法。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进行图案化。纳米网结构表现出比同等制备的硅纳米线阵列低得多的热导率，尽管该阵列具有更高的表面积与体积比。保留了类似块状的电导率。我们认为这一发展是朝着降低热导率的相干机制迈出的一步。
