近日，北京大学的高鹏&杜进隆及其研究团队取得一项新进展。经过不懈努力，他们揭示非均匀应变抑制硅纳米带中的热输运。相关研究成果已于2024年5月15日在国际权威学术期刊《自然》上发表。

据悉，纳米级结构可以产生极端应变，从而实现前所未有的材料特性，例如定制电子带隙，提高超导温度和增强电催化活性。尽管已知均匀应变对热流的影响较为有限，但鉴于界面与缺陷的共存状态，非均匀应变的影响仍然显得复杂且难以预测。

该研究团队通过在定制的微器件上弯曲单个硅纳米带来引入非均匀应变，并测量其对热输运的影响，同时以亚纳米分辨率表征应变相关的振动谱，从而填补了这一研究空白。这项研究结果表明，每纳米0.112%的应变梯度可以导致热导率急剧下降34±5%，与均匀应变下测量的几乎恒定值形成鲜明对比。研究人员进一步利用电子能量损失谱绘制了局部晶格振动谱，结果显示声子沿应变梯度的峰值位移高达数百万电子伏特。

第一性原理计算进一步证明，这种独特的声子谱展宽效应显著增强了声子散射，从而极大地阻碍了热输运。 这项研究不仅揭示了非均匀应变下晶格动力学的一个关键方面，这在均匀应变下是不存在的，还打破了传统的理解框架。

附：英文原文

Title: Suppressed thermal transport in silicon nanoribbons by inhomogeneous strain

Author: Yang, Lin, Yue, Shengying, Tao, Yi, Qiao, Shuo, Li, Hang, Dai, Zhaohe, Song, Bai, Chen, Yunfei, Du, Jinlong, Li, Deyu, Gao, Peng

Issue&Volume: 2024-05-15

Abstract: Nanoscale structures can produce extreme strain that enables unprecedented material properties, such as tailored electronic bandgap, elevated superconducting temperature and enhanced electrocatalytic activity. While uniform strains are known to elicit limited effects on heat flow, the impact of inhomogeneous strains has remained elusive owing to the coexistence of interfaces and defects. Here we address this gap by introducing inhomogeneous strain through bending individual silicon nanoribbons on a custom-fabricated microdevice and measuring its effect on thermal transport while characterizing the strain-dependent vibrational spectra with sub-nanometre resolution. Our results show that a strain gradient of 0.112% per nanometre could lead to a drastic thermal conductivity reduction of 34±5%, in clear contrast to the nearly constant values measured under uniform strains. We further map the local lattice vibrational spectra using electron energy-loss spectroscopy, which reveals phonon peak shifts of several millielectron-volts along the strain gradient. This unique phonon spectra broadening effect intensifies phonon scattering and substantially impedes thermal transport, as evidenced by first-principles calculations. Our work uncovers a crucial piece of the long-standing puzzle of lattice dynamics under inhomogeneous strain, which is absent under uniform strain and eludes conventional understanding.

DOI: 10.1038/s41586-024-07390-4

Source: https://www.nature.com/articles/s41586-024-07390-4