Phonon scattering and thermal conductivity of pillared graphene structures with carbon nanotube-graphene intramolecular junctions

摘要

We present results of a reverse non-equilibrium molecular dynamics study of thermal transport in single-walled carbon nanotube (SWCNT)-graphene junctions comprised of carbon-carbon (C-C) bonds with either sp~2 or mixed sp~2/sp~3 hybridization. In both cases, a finite interfacial thermal resistance is observed at the SWCNT-graphene junctions for thermal transport in the out-of-plane direction. The interfacial thermal resistance at the junctions is attributed to the combined effects of scattering of the phonons at the SWCNT-graphene junctions due to the presence of distorted sp~2 bonds in the junction region and the change in dimensionality of the medium along the phonon transport path as the phonons propagate from SWCNT pillars (quasi-ID) to graphene sheet (2D) and then again to SWCNTs. Moreover, the thermal resistance is found to depend on the C-C bond hybridization at the intramolecular junctions with mixed sp~2/sp~3 hybridization showing a higher interfacial resistance when compared to pure sp~2 bonding. Thermal conductivity of typical SWCNT-graphene unit cells was observed to increase nearly linearly with an increase in cell dimensions, and then reaches a plateau as the pillar height and the inter-pillar distance approach the critical length for ballistic thermal transport in SWCNT and single layer graphene. These results indicate that the thermal transport characteristics of the three-dimensional SWCNT-graphene (hybrid) structures can be tuned by controlling the unit cell size.