声子金属晶格中的弹道限制实现最小热导率
Achieving Minimal Heat Conductivity by Ballistic Confinement in Phononic Metalattices
摘要：
控制半导体的热导率在优化热电和声子器件的性能方面具有实际意义。在半导体中插入纳米尺寸的夹杂物是实现这种控制的有效手段;已经提出，使用这种方法可以将硅的热导率降低到1 W/m/K，并且对于夹杂物的某些最佳尺寸，热导率将达到最小值。然而，这一设计规则的实际验证是有限的。在这项工作中，我们解决这个问题，通过研究硅金属晶格的热性能，包括一个周期性分布的球形夹杂物的半径从7到30 nm，嵌入到硅。实验测量证实，硅金属晶格的热导率对于二氧化硅夹杂物低至1 W/m/K，并且对于具有空孔的硅金属晶格，该值可以进一步降低至0.16 W/m/K。弹道声子输运的一个详细的模型表明，这种热导率接近于通过调整周期性不均匀性的半径和间距所能达到的最低值。这项研究是阐明硅和其他半导体纳米级弹道热传输的标度定律的重要一步。
英文摘要：
Controlling the thermal conductivity of semiconductors is of practical interest in optimizing the performance of thermoelectric and phononic devices. The insertion of inclusions of nanometer size in a semiconductor is an effective means of achieving such control; it has been proposed that the thermal conductivity of silicon could be reduced to 1 W/m/K using this approach and that a minimum in the heat conductivity would be reached for some optimal size of the inclusions. Yet the practical verification of this design rule has been limited. In this work, we address this question by studying the thermal properties of silicon metalattices that consist of a periodic distribution of spherical inclusions with radii from 7 to 30 nm, embedded into silicon. Experimental measurements confirm that the thermal conductivity of silicon metalattices is as low as 1 W/m/K for silica inclusions, and that this value can be further reduced to 0.16 W/m/K for silicon metalattices with empty pores. A detailed model of ballistic phonon transport suggests that this thermal conductivity is close to the lowest achievable by tuning the radius and spacing of the periodic inhomogeneities. This study is a significant step in elucidating the scaling laws that dictate ballistic heat transport at the nanoscale in silicon and other semiconductors.
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