Engineering heat transport in nanoparticle-in-alloy composites: The role of Mie scattering

Abstract

Previous work toward engineering lower thermal conductivity of nanoparticle-in-alloy semiconductor composites have indicated that optimal nanoparticle sizes should lie between the Rayleigh and geometric phonon scattering regimes (i.e. the Mie regime); yet, phonon scattering models that are accurate in the Mie regime have never been employed to investigate the thermal transport. Here, we exploit exact solutions from continuum mechanics that separately treat longitudinal and transverse phonon scattering from nanoparticles across a wide spectrum of wavelengths, including the Rayleigh, Mie, and geometric scattering regimes. The solutions intrinsically account for material contrast effects from density and both normal and shear elastic constants. We find that consideration of Mie scattering effects drastically alters the material selection and particle sizing process for optimal nanocomposites. In particular, a previously unreported inter-relationship between density and elastic contrast is reported: in the Mie regime, a suppression of the scattering cross section is found in cases where the sound speeds of the matrix and nanoparticle are closely matched. This suppression can extend the transition wavelength to geometric scattering by more than an order-of-magnitude, with severe effects to thermal transport. We explore how these considerations change the optimal sizing of nanoparticles for metal/semiconductor composites, with specific application to the experimentally significant case of InGaAs composites.