Interfacial coupling effects on the thermal conductivity of few-layer graphene

Abstract

Abstract The thermal conductivities of both suspended and supported few-layer graphene (FLG) were investigated via molecular dynamics simulations. The results indicate that the thermal conductivity of a suspended FLG sample decreases by 3.9% from 511.2 W m−1 K−1 upon an increase in the number of layers from 1 to 20 layers, whereas it increases by 5.5% to 486.8 W m−1 K−1 in the case of supported FLG specimens on a smooth crystalline silicon surface. Both trends converge when the number of layers is higher than five. The effects of the substrate roughness on the supported FLG samples were also investigated. The results show that their thermal conductivity on a rough silicon surface is lower than that on a smooth silicon surface. In order to demonstrate the importance of interfacial coupling on the phonon transport properties, the coupling strength parameter was enhanced by a factor of 3 or 10 to see the influence on the thermal conductivity. The simulations show that the thermal conductivity decreases with an increasing coupling strength. Lastly, the phonon dispersion of a two-layer graphene specimen was calculated by varying the interlayer coupling strength. The calculations show that the coupling strength is mainly influenced by the out-of-plane phonon dispersion relation. The frequency of flexural acoustic (ZA’) phonons around the center of the first Brillouin zone increases significantly from 2.14 to 6.78 THz when the interlayer coupling strength is enhanced by a factor of 10. This may decrease the phonon group velocity and provide more scattering channels, and thus reduce the thermal conductivity.