A Monte-Carlo study of the phonon transport in nanowire-embedded composites

This work aims at investigating the thermal conductivities of nanowire-embedded composites in use of a Monte-Carlo simulator developed based on the assumptions of grey media, bulk phonon dispersion relations, and bulk intrinsic scattering rates. Those along and those perpendicular to the wire axis direction are both targeted. The simulation results show that when the interface surfaces are totally diffuse, the cross-wire thermal conductivities of either the silicon-wire-germanium-host or germanium-wire-silicon-host nanocomposites decrease with increasing wire volume fraction due to the increasing, dominant, interface scattering; when the interface surfaces are perfectly smooth, a competition exists between the decreasing intrinsic and increasing interface scatterings as the wire volume fraction increases and a minimum thermal conductivity associated with the silicon-wire-germanium-host composite is existent. When heat flows mainly along the wire axis direction in either the wire-host composites or the double-layered nanowires, the interface and boundary effects dominate the effective thermal conductivities of the two components, which together with the cross-sectional-area ratio determine the major heat pathway. A minimum effective thermal conductivity can thus also be observed when these two factors are well-matched in strength and when the effective thermal conductivity of the nanowires is larger than that of the host/shell component. (C) 2011 Elsevier Masson SAS. All rights reserved.