Ballistic phonon lensing by the non-planar interfaces of embedded nanoparticles

Abstract

In this work, we investigate the scattering behavior of a ballistic phonon wave incident on a dopant spherical nanoparticle embedded within a pure crystal through molecular dynamics simulations. Unique to this work, we also conduct conjugate simulations of ballistic phonon scattering on a dopant thin slab to compare and contrast scattering by non-planar heterogeneous interfaces (nanoparticle) and planar heterogeneous interfaces (thin slab). Analysis of the wave dynamics in real and reciprocal spaces reveal phonon mode-conversion in the nanoparticle scattering system is due to an unreported ‘phonon lensing’ effect where the phonon wave propagation is altered by refraction and reflection through the non-planar interfaces of the nanoparticle. The specific states of mode-conversion is shown to change with the character of the lensing that varies with nanoparticle size. Most significantly, the lensing phenomenon is absent in the phonon scattering by the thin slab and consequentially, results in differences in the scattering behaviors between the planar and non-planar interfaces.