Two orders of magnitude reduction in silicon membrane thermal conductivity by resonance hybridizations

TL;DR

This study demonstrates that attaching nanoscale pillars to silicon membranes causes phonon resonance hybridizations, significantly reducing thermal conductivity by up to two orders of magnitude at room temperature.

Contribution

It introduces a novel approach of using nanoscale pillars to induce phonon resonance hybridizations, drastically lowering silicon membrane thermal conductivity.

Findings

Two orders of magnitude reduction in thermal conductivity.

Resonance hybridizations cause group velocity reductions.

Effect tunable across silicon's phonon spectrum.

Abstract

The thermal conductivity of a freestanding single-crystal silicon membrane may be reduced significantly by attaching nanoscale pillars on one or both surfaces. Atomic resonances of the nanopillars locally and intrinsically couple with the base membrane phonon modes causing these modes to hybridize and flatten at each coupling location in the phonon band structure. The ensuing group velocity reductions, which in principle may be tuned to take place across silicon's full spectrum, lead to a lowering of the in-plane thermal conductivity in the base membrane. Using equilibrium molecular dynamics simulations, we report a staggering two orders of magnitude reduction in the thermal conductivity at room temperature by this mechanism.