Phonon Heat Conduction in Corrugated Silicon Nanowires Below the Casimir Limit

TL;DR

This study measures thermal conductance in silicon nanowires and reveals that corrugation significantly reduces phonon mean free path, surpassing the Casimir limit, indicating a transition towards phonon glass behavior.

Contribution

It demonstrates that surface corrugation in silicon nanowires can reduce phonon transport below the Casimir limit, a novel approach to phonon scattering control.

Findings

Corrugated nanowires show reduced thermal conductance compared to straight ones.

Phonon mean free path is smaller than nanowire diameter, below the Casimir limit.

Multiple scattering on corrugated surfaces causes this reduction.

Abstract

The thermal conductance of straight and corrugated monocrystalline silicon nanowires has been measured between 0.3 K and 5 K. The difference in the thermal transport between corrugated nanowires and straight ones demonstrates a strong reduction in the mean free path of the phonons. This averaged mean free path is remarkably smaller than the smaller diameter of the nanowire, evidencing a phonon thermal transport reduced below the Casimir limit. Monte Carlo simulations highlight that this effect can be attributed to significant multiple scattering of ballistic phonons occuring on the corrugated surfaces. This result suggests an original approach to transforming a monocrystalline material into a phonon glass.