Universal features of phonon transport in nanowires with correlated surface roughness

The ultralow thermal conductivity, κ, 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 et al., Nano Lett. 12, 2475 (2012)]. Universal features of thermal transport are revealed by presenting κ as a function of the normalized geometric mean free path λ¯ (0<λ¯<1); the diffusive (Casimir) limit corresponds to λ¯=1/2. κ vs λ¯ is exponential at low-to-moderate roughness (high λ¯), where internal scattering randomly interrupts phonon bouncing across the SiNW, and linear at high roughness (low λ¯), where multiple scattering events at the same surface results in ultralow, amorphous-limit thermal conductivity.