Theoretical investigation of phonon thermal transport in carbon nanostructures

Abstract

Phonon thermal transport in two-dimensional material, especially graphene monolayer, has been a subject of intensive studies both theoretically and experimentally. In this dissertation, first, the evolution of defects on graphene by using molecular dynamics simulation using reactive force field and the effect of healing the defects on thermal conductivity are investigated. It is found that defective graphene is healed through the process which the Pt atoms directly fill the single or double vacancies and took C adatom defects away from the surface with the help of O2 molecules and that only the latter one contributes to enhancement of thermal conductivity from defective graphene. Secondly, massive molecular dynamics simulations were carried out to examine thermal transport in GNRs at room temperature (RT) and demonstrate that non-diffusive behaviors including Poiseuille-like local thermal conductivity and second sound are obtained, indicating quasiballistic thermal transport. For narrow GNRs, Poiseuille-like thermal conductivity profile develops across the nanoribbon width, and wider GNRs exhibit mixed nature of phonon transport in that diffusive transport is dominant in the middle region whereas non-uniform behavior is observed near the lateral GNR boundaries. In addition, transient heating simulations reveal that the driftless second sound can propagate through GNRs regardless of the GNR width. By decomposing the atomic motion into the out-of-plane and in-plane modes, it is further shown that the observed quasiballistic thermal transport are primarily contributed by the out-of-plane motion of C atoms in GNRs.