Universal features of phonon transport in nanowires with correlated surface roughness

TL;DR

This study demonstrates that phonon transport in nanowires with correlated surface roughness exhibits universal behavior, with thermal conductivity depending on a normalized mean free path, revealing exponential and linear regimes linked to surface scattering.

Contribution

It introduces a universal framework for understanding phonon transport in rough nanowires using normalized mean free path and correlates surface roughness with thermal conductivity regimes.

Findings

Thermal conductivity shows exponential dependence at moderate roughness.

At high roughness, conductivity reaches an amorphous limit.

Universal behavior is characterized by the normalized mean free path.

Abstract

The ultralow thermal conductivity $\kappa$ observed experimentally in intentionally roughened silicon nanowires (SiNWs) is reproduced in phonon Monte Carlo simulations with exponentially correlated real-space rough surfaces similar to measurement [J. Lim, K. Hippalgaonkar, S. C. Andrews, A. Majumdar, and P. Yang, Nano Lett. 12, 2475 (2012)]. Universal features of thermal transport are revealed by presenting $\kappa$ as a function of the normalized geometric mean free path $\bar\lambda$ ($0<\bar\lambda<1$); the diffusive (Casimir) limit corresponds to $\bar\lambda=1/2$. $\kappa$ vs $\bar\lambda$ is exponential at low-to-moderate roughness (high $\bar\lambda$), where internal scattering randomly interrupts phonon bouncing across the SiNW, and linear at high roughness (low $\bar\lambda$), where multiple scattering events at the same surface results in ultralow, amorphous-limit thermal conductivity.