Tuning the Anisotropic Thermal Transport in {110}-Silicon Membranes with Surface Resonances

Understanding the thermal transport in nanostructures has important applications in fields such as thermoelectric energy conversion, novel computing and heat dissipation. Using non-homogeneous equilibrium molecular dynamic simulations, we studied the thermal transport in pristine and resonant Si membranes bounded with {110} facets. The break of symmetry by surfaces led to the anisotropic thermal transport with the thermal conductivity along the [110]-direction to be 1.78 times larger than that along the [100]-direction in the pristine structure. In the pristine membranes, the mean free path of phonons along both the [100]- and [110]-directions could reach up to ∼100 µm. Such modes with ultra-long MFP could be effectively hindered by surface resonant pillars. As a result, the thermal conductivity was significantly reduced in resonant structures, with 87.0% and 80.8% reductions along the [110]- and [100]-directions, respectively. The thermal transport anisotropy was also reduced, with the ratio κ110/κ100 decreasing to 1.23. For both the pristine and resonant membranes, the thermal transport was mainly conducted by the in-plane modes. The current work could provide further insights in understanding the thermal transport in thin membranes and resonant structures.

Shockwave Response of Polymer and Polymer Nanocomposites

We present non-equilibrium molecular dynamic simulations of the shock compression of polyurethane and its graphene-based nanocomposite systems. Using the projectile/wall approach, planar shock waves with piston velocity range from 0.1 to 2.5 km/s is applied for both systems. In this study, direct molecular-level simulations of shock-wave generation and propagation are utilized in order to construct the appropriate shock-Hugoniot relations. Through this study, we determined that inclusion of graphene into the polyurethane system has a significant effect on the shock propagation behavior when incorporated in the polymer matrix

Influence of Core-Shell Architecture Parameters on Thermal Conductivity of Si-Ge Nanowires

ABSTRACTIn this work, we investigate the influence of the core-shell architecture on nanowire (1D) thermal conductivity targeting to evaluate its validity as a strategy to achieve a better thermoelectric performance. To obtain the thermal conductivity values, equilibrium molecular dynamic simulations is applied to Si and Ge systems that are chosen to form core-shell nanostructures. To explore the parameter space, we have calculated thermal conductivity values of the Si-core/Ge-shell and Ge-core/Si-shell nanowires at different temperatures for different cross-sectional sizes and different core contents. Our results indicate that (1) increasing the cross-sectional area of pristine Si and pristine Ge nanowire increases the thermal conductivity (2) increasing the Ge core size in the Si-core/Ge-shell structure results in a decrease in the thermal conductivity values at 300 K (3) thermal conductivity of the Si-core/Ge-shell nanowires demonstrates a minima at specific core size (4) no significant variation in the thermal conductivity observed in nanowires for temperature values larger than 300 K (5) the predicted thermal conductivity around 10 W m−1K−1 for the Si and Ge core-shell architecture is still high to get desired ZT values for thermoelectric applications. On the other hand, significant decrease in thermal conductivity with respect to bulk thermal conductivity of materials and pristine nanowires proves that employing core–shell architectures for other possible thermoelectric material candidates would serve valuable opportunities to achieve a better thermoelectric performance.