Thermal conductivity of graphene with defects induced by electron beam irradiation

Abstract

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, N_D, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ∼7.5 μm 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 2.0 × 10¹⁰ cm⁻² to 1.8 × 10¹¹ cm⁻² the thermal conductivity decreases from ∼(1.8 ± 0.2) × 10³ W mK⁻¹ to ∼(4.0 ± 0.2) × 10² W mK⁻¹ near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ∼400 W mK⁻¹. The thermal conductivity dependence on the 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.