Investigation On Thermal Transport Properties In Carbon-based Superlattices Structures

The superlattice structure is a new type of man-made structure that can change the energy band structure and other physical properties of materials.Its regulation of the heat transport properties of materials has attracted the interest of many researchers.Current research on the observation of phonon coherence effects in superlattices is still a huge challenge.Carbon nanotubes and diamonds are two kinds of carbon-based materials with high thermal conductivity,and they have a long phonon mean free path at room temperature.These features make it an ideal material for studying the coherent effects of phonons.Therefore,the thermal transport properties of carbon nanotube superlattices and diamond superlattice nanowires have been investigated using classical molecular dynamics simulation methods.The results of the study show that the heat current autocorrelation function calculation results show that there is obvious phonon coherence resonance effect in the carbon nanotube superlattice.The analysis of the phonon vibration mode participation rate found that the phonon vibration mode participation rate of the CNT superlattice has a higher with the same concentration of S W defects.This is due to the phonon coherent resonance effect caused by SW defects in the periodic distribution of carbon nanotube superlattices,allowing some phonons to tunneling through the SW defect.In order to study the effect of superlattice structure interface on the phonon coherence effect,we compared and calculated the thermal conductivities of diamond superlattice nanowire and silicon germanium superlattice nanowire.The calculation results show that the thermal conductivities of diamond superlattice nanowires and SiGe superlattice nanowires have the same increasing trend with the number of period,when the period length is 25A.The phonon localization effect was not observed at the interface between the two superlattices.This indicating that the interface effect did not destroys the coherent phonon transport mechanism.When the period length is 103 A,the thermal conductivity of diamond superlattice nanowires increases continuously with the number of period.No obvious phonon localization effect was observed at the interface.Coherent transport mechanism still dominates in diamond superlattice nanowires.However,the thermal conductivity of SiGe superlattice nanowires converges to a constant,and obvious phonon localization effects are observed at the interface.This indicates that the interface scattering destroys the phonon coherent transport mechanism in SiGe superlattice nanowires,and the incoherent transport mechanism dominates.Our research helps people to better understand the phonon coherence effect in the superlattice and better use the superlattice to regulate the thermal conductivity of the material.