ICT2014 Abstracts

Accurate modeling of non-equilibrium heat transport in nanostructures demands an appropriate description of phonon dispersion relation and proper treatment of anharmonic effects such as thermal expansion, interaction of lattice waves, effect of strain on spring stiffness, and phonon-phonon interactions. In this work, we develop and employ a coupled molecular mechanics-Monte Carlo (MM-MC) platform to solve the phonon Boltzmann Transport Equation (BTE) to predict the thermal conductivity in nanostructures having specified geometry. The use of the quasi-anharmonic MM approach (as implemented in the open source NEMO 3-D software toolkit) not only allows one to capture the true atomicity of the underlying lattice but also enables the simulation of realistically sized structures containing millions of atoms. As compared to the approach using an empirically fitted phonon dispersion relation, here, we report a 17% increase in the thermal conductivity for a silicon nanowire due to the incorporation of atomistic corrections in the LA branch alone. The atomistically determined thermal conductivity as calculated from the MM-MC framework is then used in the modular design of a silicon nanowire based thermoelectric cooler unit. It is demonstrated that the use of empirically fitted phonon bandstructure parameters in the calculation of thermal conductivity overestimates the temperature difference between the hot and the cold sides and the overall cooling efficiency of the system. A comparison with the DFT based first principles calculation of phonon dispersions and the thermal conductivity in the ballistic regime in reduced dimensionality structures will be the subject of a future work and presented at the conference.

^*Supported by National Science Foundation Grant No. CCF-1218839