Thermal Conductivity of Suspended Graphene with Defects

TL;DR

This study explores how introducing defects affects the thermal conductivity of suspended graphene, revealing a decrease with defect density and a saturation at high defect levels, using experimental and simulation methods.

Contribution

It provides a detailed analysis of defect-induced thermal conductivity changes in graphene using combined experimental and theoretical approaches.

Findings

Thermal conductivity decreases with increasing defect density.

At high defect densities, conductivity saturates around 400 W/mK.

Defect density impacts phonon scattering significantly.

Abstract

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. Graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5-micrometer size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0x10^10 cm-2 to 1.8x10^11 cm-2 the thermal conductivity decreases from ~(1.8+/-0.2)x10^3 W/mK to ~(4.0+/-0.2)x10^2 W/mK near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation behavior at a relatively high value of ~400 W/mK. The thermal conductivity dependence on defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.