Suppressed thermal transport in silicon nanoribbons by inhomogeneous strain

• Published in: Nature (London) Vol. 629; no. 8014; pp. 1021 - 1026
• Main Authors: Yang, Lin, Yue, Shengying, Tao, Yi, Qiao, Shuo, Li, Hang, Dai, Zhaohe, Song, Bai, Chen, Yunfei, Du, Jinlong, Li, Deyu, Gao, Peng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 30.05.2024; Nature Publishing Group
• Subjects: 142/126; 639/301/119/544; 639/925/357/1016; Coexistence; Electron energy; Electron energy loss spectroscopy; Electrons; Finite element analysis; First principles; Heat conductivity; Humanities and Social Sciences; Material properties; multidisciplinary; Nanoribbons; Phonons; Science; Science (multidisciplinary); Silicon; Spectroscopy; Spectrum analysis; Thermal conductivity; Vibrational spectra
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-024-07390-4

Nanoscale structures can produce extreme strain that enables unprecedented material properties, such as tailored electronic bandgap 1 – 5 , elevated superconducting temperature 6 , 7 and enhanced electrocatalytic activity 8 , 9 . While uniform strains are known to elicit limited effects on heat flow 10 – 15 , the impact of inhomogeneous strains has remained elusive owing to the coexistence of interfaces 16 – 20 and defects 21 – 23 . 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 10 , 12 , 14 , 15 . 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. We report on a method for inducing uncontaminated and precise inhomogeneous strain in nanoscale silicon ribbons and its use for determining physical effects in these strained materials, in particular, an increase in the range and control of thermal conductivity.