Molecular dynamics simulations of thermal conductivity and spectral phonon relaxation time in suspended and supported graphene

TL;DR

This study uses molecular dynamics simulations and spectral analysis to investigate how thermal conductivity in graphene varies with temperature and substrate support, revealing the dominant phonon modes involved.

Contribution

It provides new insights into the phonon mode contributions to thermal conductivity in suspended and supported graphene, especially highlighting the impact of substrates on phonon scattering.

Findings

ZA phonon contribution is 25-30% in suspended graphene at room temperature

Substrate reduces thermal conductivity by increasing phonon scattering

In supported graphene, in-plane phonons dominate thermal transport

Abstract

We perform molecular dynamics (MD) simulations with phonon spectral analysis aiming at understanding the two dimensional (2D) thermal transport in suspended and supported graphene. Within the framework of equilibrium MD simulations, we perform spectral energy density (SED) analysis to obtain the lifetime of individual phonon modes. The per-mode contribution to thermal conductivity is then calculated to obtain the lattice thermal conductivity in the temperature range 300-650 K. In contrast to prior studies, our results suggest that the contribution from out-of-plane acoustic (or ZA) branch to thermal conductivity is around 25-30% in suspended single-layer graphene (SLG) at room temperature. The thermal conductivity is found to reduce when SLG is put on amorphous SiO2 substrate. Such reduction is attributed to the strengthened scattering in all phonon modes in the presence of the substrate. Among them, ZA modes are mostly affected with their contribution to thermal conductivity reduced to around 15%. As a result, thermal transport is dominated by in-plane acoustic phonon modes in supported SLG.