Universal behavior of highly-confined heat flow in semiconductor nanosystems: from nanomeshes to metalattices

TL;DR

This paper investigates how nanoscale confinement affects heat flow in silicon nanostructures, revealing a universal behavior that can be modeled by separating geometric and viscous contributions, applicable across various nanosystems.

Contribution

The authors develop a universal theory for phonon transport in highly-confined silicon nanosystems, combining experimental and simulation data to explain reduced thermal conductivity.

Findings

Thermal conductivity is significantly reduced in nanoscale silicon structures.

A new universal model separates geometric permeability and viscous effects.

The theory applies broadly to different silicon nanostructures.

Abstract

Nanostructuring on length scales corresponding to phonon mean free paths provides control over heat flow in semiconductors and makes it possible to engineer their thermal properties. However, the influence of boundaries limits the validity of bulk models, while first principles calculations are too computationally expensive to model real devices. Here we use extreme ultraviolet beams to study phonon transport dynamics in a 3D nanostructured silicon metalattice with deep nanoscale feature size, and observe dramatically reduced thermal conductivity relative to bulk. To explain this behavior, we develop a predictive theory wherein thermal conduction separates into a geometric permeability component and an intrinsic viscous contribution, arising from a new and universal effect of nanoscale confinement on phonon flow. Using experiments and atomistic simulations, we show that our theory applies to a general set of highly-confined silicon nanosystems, from metalattices, nanomeshes, porous nanowires to nanowire networks, of great interest for next-generation energy-efficient devices.