SuperSuppression of Long Phonon MeanFreePaths in Nanoengineered Si due to Heat Current Anticorrelations
Abstract
The ability to minimize the thermal conductivity of dielectrics with minimal structural intervention that could affect electrical properties is an important capability for engineering thermoelectric efficiency in lowcost materials such as Si. We recently reported the discovery of special arrangements for nanoscale pores in Si that produce a particularly large reduction in thermal conductivity accompanied by strongly anticorrelated heat current fluctuations, a phenomenon that is missed by the diffuse adiabatic boundary conditions conventionally used in numerical Boltzmann transport models. This manuscript presents the results of molecular dynamics simulations and a Monte Carlo ray tracing model that teases apart this phenomenon to reveal that special pore layouts elastically backscatter longwavelength heatcarrying phonons. This means that heat carriage by a phonon before scattering is undone by the scattered phonon, resulting in an effective meanfreepath that is significantly shorter than the geometric lineofsight to the pores. This effect is particularly noticeable for the longwavelength, long meanfreepath phonons whose transport is impeded drastically more than is expected purely from the usual considerations of scattering defined by the distance between defects. This supersuppression of the meanfreepath below the characteristic length scale of the nanostructuring offers a route for minimizing thermal conductivity with minimal structural impact, while the stronger impact on long wavelengths offers possibilities for the design of bandpass phonon filtering. Moreover, the ray tracing model developed in this paper shows that different forms of correlated scattering imprint a unique signature in the heat current autocorrelation function that could be used as a diagnostic in other nanostructured systems.
 Publication:

arXiv eprints
 Pub Date:
 October 2021
 DOI:
 10.48550/arXiv.2110.11566
 arXiv:
 arXiv:2110.11566
 Bibcode:
 2021arXiv211011566A
 Keywords:

 Condensed Matter  Materials Science;
 Condensed Matter  Mesoscale and Nanoscale Physics