Strain effect analysis on phonon thermal conductivity of two-dimensional nanocomposites

Abstract

In this paper, we present a model that combines lattice dynamics and the phonon Boltzmann transport equation (BTE) to analyze strain effect on the cross-plane phonon thermal conductivity of silicon wire-germanium host nanocomposites. For a given strain condition, mechanical strain is translated to crystal lattice deformation by using the Cauchy–Born rule. Strain-dependent phonon thermal properties of Si and Ge obtained from lattice dynamics with Tersoff empirical interatomic potential are then incorporated into the BTE, in which ballistic transport within one material and diffuse scattering between Si–Ge interface are employed. The strain-dependent BTE is solved numerically on an unstructured triangular mesh by using a finite volume method. Nanocomposites with different Si nanowire cross sections are also investigated. The results show that the phonon thermal conductivity of the nanocomposites can be significantly decreased (or increased) by a tensile (or compressive) strain. With the same length change, hydrostatic strain produces a larger variation in phonon thermal conductivity than uniaxial strain. In addition, it is shown that with the same atomic percentage, the cross-sectional shape makes little difference to the thermal conductivity except at very small characteristic lengths of the Si nanowire.