Thermal transport in nanocrystalline graphene investigated by approach-to-equilibrium molecular dynamics simulations

TL;DR

This study uses approach-to-equilibrium molecular dynamics to analyze how nanocrystalline graphene's thermal conductivity decreases with smaller grain sizes, revealing phonon scattering effects at grain boundaries.

Contribution

It introduces a detailed simulation approach to quantify thermal transport in nanocrystalline graphene with varying grain sizes and boundary effects.

Findings

Thermal conductivity drops to 3% of single crystal value with 1 nm grains.

Thermal conductivity follows an inverse rational function with grain size.

Vibrational density of states shows broadening and intensity reduction due to nanograins.

Abstract

Approach-to-equilibrium molecular dynamics simulations have been used to study thermal transport in nanocrystalline graphene sheets. Nanostructured graphene has been created using an iterative process for grain growth from initial seeds with random crystallographic orientations. The resulting cells have been characterized by the grain size distribution based on the radius of gyration, by the number of atoms in each grain and by the number of atoms in the grain boundary. Introduction of nanograins with a radius of gyration of 1 nm has led to a significant reduction in the thermal conductivity to 3% of the value in single crystalline graphene. Analysis of the vibrational density of states has revealed a general reduction of the vibrational intensities and broadening of the peaks when nanograins are introduced which can be attributed to phonon scattering in the boundary layer. The thermal conductivity has been evaluated as a function of the grain size with increasing size up to 14 nm and it has been shown to follow an inverse rational function. The grain size dependent thermal conductivity could be approximated well by a function where transport is described by a connection in series of conducting elements and resistances (at boundaries).