Ballistic Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions

Abstract

In this article, the effect on the vibrational and thermal properties of gradually interconnected nanoinclusions embedded in an amorphous silicon matrix is studied using molecular dynamics simulations. The nanoinclusion arrangement ranges from an aligned sphere array to an interconnected mesh of nanowires. Wave-packet simulations scanning different polarizations and frequencies reveal that the interconnection of the nanoinclusions at constant volume fraction induces a strong increase of the mean free path of high frequency phonons, but does not affect the energy diffusivity. The mean free path and energy diffusivity are then used to estimate the thermal conductivity, showing an enhancement of the effective thermal conductivity due to the existence of crystalline structural interconnections. This enhancement is dominated by the ballistic transport of phonons. Equilibrium molecular dynamics simulations confirm the tendency, although less markedly. This leads to the observation that coherent energy propagation with a moderate increase of the thermal conductivity is possible. These findings could be useful for energy harvesting applications, thermal management or for mechanical information processing.

Atomistic evidence of hydrodynamic heat transfer in nanowires

“…The solid lines in figure 4, are obtained using this method, for the flux in the crystalline core. In the amorphous shell, the flux does not depend on the radius and is modeled by a Fourier law with κ = 1.5 W m −1 K −1 , which is consistent with the value reported for a-Si using the same inter-atomic potential [43].…”

“…This can help the representation of the flux and to get more physical insights of what is happening at the interfaces. They can, for example, inform on the shape and pathways taken by individual phonons in the nanostructures [43]. The method used here is very similar to the method used for asymmetric core-shell NWs [34].…”

“…The dynamical structure factor (DSF) is a spatial and temporal Fourier transform of the atomic displacements used to characterize the vibrational properties of a system. It is computed with the same method as in a previous publication [43]. First, the sample is heated to 300 K and equilibrated at this temperature for 50 ps using a Nosé-Hoover thermostat.…”

Buckling Hydrogenated Biphenylene Network with Tremendous Stretch Extent and Anomalous Thermal Transport Properties

“…To study the propagation of phonons inside the pristine material, we have employed the wave-packet (WP) propagation method within molecular dynamics (MD), in which mechanical excitation was imposed on the atoms of a small region and the propagation of the injected energy was monitored with time. This method has already been applied to study heat transport in a variety of systems, such as amorphous silicon-like materials, silicon nanocomposites, asymmetric two-phase silicon nanowires, core–shell silicon nanowires, and others. In this work, we aimed to study the propagation of phonons in HBPN from all three acoustic branches (LA, TA, and ZA), along both principal directions (armchair and zigzag), for three different strain states: unstrained, strained along zigzag (ε = 20%), and strained along armchair (ε = 25%).…”

Phonon Interference at the Atomic Scale

“…Here, two apertures are simulated and represented. Moreover the excitation is not continuous but a pulse as in a previous work [26] and the surperposition of multiple times steps is used to get the full pattern in figure 5. Comparing the two panels, it appears that using a-Si results in a broader ray at the exit of the aperture.…”