Coherent and incoherent phonon transport in a graphene and nitrogenated holey graphene superlattice

The transition between coherent and incoherent phonon transport in a graphene (GRA) and nitrogenated holey graphene (C₂N) superlattice is investigated by non-equilibrium molecular dynamics (NEMD) simulation. We find that the thermal conductivity of the GRA-C₂N superlattice is much lower than those of graphene and C₂N, and exhibits a positive correlation with the system length. Owing to three mechanisms, i.e., phonon wave interference, phonon confinement and phonon interface scattering, the calculated thermal conductivity shows a decreasing trend at small period length scales and gradually increases at large period length scales. The coherence length of the superlattice at 300 K is 4.43 nm, which is independent of the total length. In addition, the effects of temperature and uniaxial tensile strain on phonon transport are investigated. At 100 K, the coherent phonons play a more dominating role in the superlattice and the responding coherence length is enlarged to 7.38 nm. On the other hand, tensile strain can effectively reduce the thermal conductivity, which results from the phonon softening.