Reduction of Phonon Lifetimes and Thermal Conductivity of a Carbon Nanotube on Amorphous Silica

TL;DR

This study uses molecular dynamics simulations to show that supporting carbon nanotubes on amorphous silica significantly reduces phonon lifetimes and thermal conductivity, impacting their thermal management properties.

Contribution

It provides detailed phonon scattering rates and thermal conductance estimates for supported versus isolated CNTs, highlighting substrate effects on thermal properties.

Findings

Supported CNTs have shorter phonon lifetimes than isolated ones.

Thermal conductivity decreases by approximately 30% when CNTs are supported.

Thermal boundary conductance aligns with experimental data.

Abstract

We use molecular dynamics simulations to examine the phonon lifetimes in (10,10) carbon nano-tubes (CNTs), both when isolated and when supported on amorphous SiO2 substrates. We deter-mine the Umklapp, normal, boundary and CNT-substrate phonon scattering rates from the com-puted inverse lifetimes. Suspended CNTs have in-plane optical phonon lifetimes between 0.7-2 ps, consistent with recent experiments, but contact with the substrate leads to a lifetime reduction to the 0.6-1.3 ps range. The thermal conductivity of the supported CNT is also computed to be ~30 percent lower than that of the isolated CNT. The thermal boundary conductance estimated from the CNT-substrate phonon scattering rates is in good agreement with that computed from the Green-Kubo relation and with previous experimental results. The results highlight that solid substrates can strongly affect and could be even used to tune the thermal properties of CNTs.