Effects of metal silicide inclusion interface and shape on thermal transport in silicon nanocomposites

Abstract

While various silicon nanocomposites with their low thermal conductivity have received much attention for thermoelectric applications, the effects of inclusion interface and shape on thermal transport remain unclear. Here, we investigate thermal transport properties of silicon nanocomposites, in which metal silicide inclusions are periodically arranged within silicon. Using the known phonon dispersion relations and the diffuse mismatch model, we explore the effects of different silicide-silicon interfaces, and using Monte Carlo ray tracing simulations, we explore the effects of silicide inclusion shapes. Our investigations show that the thermal conductivity of silicon nanocomposites can be reduced to the range of nanoporous silicon of the same geometry, depending on the interface density, crystal orientation, and acoustic mismatch. For instance, CoSi2 inclusions of [111] orientation can reduce the nanocomposite thermal conductivity more effectively than inclusion materials with lower intrinsic thermal conductivity, such as NiSi2, when the inclusion density is up to 12.5% with an interface density of 7.5 μm−1. Among the silicide inclusion materials investigated in this work, Mn4Si7 leads to the lowest nanocomposite thermal conductivity due to a combination of low intrinsic thermal conductivity and high acoustic mismatch. Compared to widely spaced and symmetric inclusions such as a circular shape, narrowly spaced and asymmetric inclusions such as a triangular shape are more effective in limiting the phonon mean free path and reducing the nanocomposite thermal conductivity. These findings regarding thermal transport in silicon nanocomposites with respect to inclusion interface and shape will guide optimal material designs for thermoelectric cooling and power generation.