Energy transport at the nanoscale involving thermal phonons

Orateur : Benoit LATOUR (Centrale-SupElec, Paris)

Their spatial confinement in nanostructure materials implies the invalidation of the macroscopic laws of heat transfer. Therefore, new mechanisms arise and lead to novel thermal properties. This seminar will be devoted to the numerical study of phonon transport in nanomaterials, especially to the dissipation processes involving phonon/phonon, photon/electron and electron/phonon interactions. We will first discuss about the wave properties of thermal phonons due to nanostructuration of the materials. A theory has been developed to quantitatively assess the coherence of these carriers and Molecular Dynamics simulations have been performed to compute their coherence lengths. These tools allow to better understanding how the wave nature of phonons can impact the thermal properties of nano materials. Then, we will present a numerical method which couples both plasmonics (photon/electron interaction) and phonon transport in metallic materials. The objective is to quantify how the heat generated by the absorption of an electromagnetic energy impacts the surrounding medium. Finite-Difference Time-Domain simulations have been coupled to Molecular Dynamics simulations to provide a general tool to study the structure change caused by light absorption by metallic nanoparticles. In the last part of this seminar, we will try to modify the classical Molecular Dynamics simulations in order to include the Bose-Einstein quantum statistics. As Molecular Dynamics is a classical method based on Newton’s laws, one of its main limitations is to remain valid only at high temperature. A quantum thermal bath has been developed to try to impose the quantum distribution in these simulations to compute thermal properties of nanomaterials at low temperatures.

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