Ultralow Thermal Conductivity of Single‐Crystalline Porous Silicon Nanowires

• Published in: Advanced functional materials 2017-10, Vol.27 (40), p.n/a
• Main Authors: Zhao, Yunshan, Yang, Lina, Kong, Lingyu, Nai, Mui Hoon, Liu, Dan, Wu, Jing, Liu, Yi, Chiam, Sing Yang, Chim, Wai Kin, Lim, Chwee Teck, Li, Baowen, Thong, John T. L., Hippalgaonkar, Kedar
• Format: Article
• Language: English
• Subjects: Amorphous silicon; Crystal structure; Electron beams; electron‐beam technique; Group velocity; Heat transfer; Materials science; Modulus of elasticity; Molecular dynamics; Nanoelectromechanical systems; Nanomaterials; Nanowires; Porosity; Porous materials; Porous silicon; porous silicon nanowires; Reduction; Silicon; Single crystals; Thermal conductivity; Transport; Young's modulus
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201702824

Porous materials provide a large surface‐to‐volume ratio, thereby providing a knob to alter fundamental properties in unprecedented ways. In thermal transport, porous nanomaterials can reduce thermal conductivity by not only enhancing phonon scattering from the boundaries of the pores and therefore decreasing the phonon mean free path, but also by reducing the phonon group velocity. Herein, a structure–property relationship is established by measuring the porosity and thermal conductivity of individual electrolessly etched single‐crystalline silicon nanowires using a novel electron‐beam heating technique. Such porous silicon nanowires exhibit extremely low diffusive thermal conductivity (as low as 0.33 W m−1 K−1 at 300 K for 43% porosity), even lower than that of amorphous silicon. The origin of such ultralow thermal conductivity is understood as a reduction in the phonon group velocity, experimentally verified by measuring the Young's modulus, as well as the smallest structural size ever reported in crystalline silicon (