Phonon thermal transport outside of local equilibrium in nanowires via molecular dynamics

TL;DR

This study investigates phonon-mediated thermal transport in nanowires, revealing size-dependent effects and non-equilibrium phenomena influenced by vibrational frequency mismatches at interfaces, supported by molecular dynamics simulations and a simplified 1D model.

Contribution

It introduces a model explaining non-equilibrium thermal transport in nanowires with frequency-dependent effects, validated by molecular dynamics simulations.

Findings

Thermal conductivity increases as contact vibrational frequency decreases.

Interfacial resistivity depends on nanowire size and vibrational mismatch.

Non-equilibrium phonon distributions occur in nanowires with low-frequency contacts.

Abstract

We study thermal transport through Pt nanowires that bridge planar contacts as a function of wire length and vibrational frequency of the contacts. When phonons in the contacts have lower average frequencies than those in the wires thermal transport occurs under conditions away from local equilibrium with low-frequency phonons experiencing a higher thermal gradient than high-frequency ones. This results in a size-dependent increase in the effective thermal conductivity of the wire with decreasing vibrational frequencies of the contacts. The interfacial resistivity when heat flows from the wire to the contact is also size-dependent and has the same physical origin in the lack of full equilibration in short nanowires. We develop a model based on a 1D atomic chain that captures the salient physics of the MD results.