Phonon Transmission Calculation in Nano-Phononic Crystals

Nano-phononic crystals and diameter-modulated nanowires have attracted significant attention due to their low thermal conductivities and their potential application as thermoelectric materials. Tuning the geometry of these nanostructures to change the scattering mechanics and thus engineering a lower thermal conductivity has been proven in recent publications. However, the modal phonon transmission coefficients across these geometrically irregular nanostructures and the effect of nanostructure geometry on thermal transport has not been fully understood. In this work, a harmonic lattice dynamics and scattering boundary method based atomistic modeling tool was created to calculate phonon spectra and modal phonon transmission coefficients in nano-phononic structures and diameter-modulated nanowires. Three key geometrical parameters including the size ratio of irregularity, the length of periodicity, and the number of irregularity have been studied in this work. The phonon transmission results in the three studies gave direction on how to achieve lower thermal conductivity in these nanostructures.