Beyond diffusive scattering: Phonon coupling to reduce thermal conductivity

Diffusive scattering has remained the only mechanism to reduce thermal conduction at the nanoscale. In this talk, we show that phonon coupling in layered nanomaterials (bi-layers and tri-layers) can be engineered to reduce the thermal conductivity of a silicon thin-film below its free-standing value. We present a methodology to quantitatively evaluate the impact of phonon coupling on each layer in layered nanostructures. We evaluate the dependence of resultant thermal conductivity modulations on structural parameters and find that they are critically dependent on layer spacings and interface properties. The results of this work open new avenues within the rational thermal design by elucidating a new method that can be used to reduce thermal conductivities beyond the traditional diffusive scattering based approaches. The prospects of being able to modulate the thermal conductivity can radically change how we control heat flow in electronic, optoelectronic, and thermoelectric materials.