Spherical and Cylindrical Pores with Amorphous Shells, Impact on the Thermal Transport
Résumé
With the rapid development of materials’ elaboration techniques, one can produce easily and controllably low dimensional nanostructures and nanostructured materials. Several emerging fields are based on this capacity and today the question is how to manipulate with precision the energy carrier transport in them. Thermal management at the nanoscale, efficient thermoelectric devices, information and communication technologies, and several other applications are seeking insights of the transport of phonons and electrons.
During the last two decades nanoporous materials have undergone important development. The synthesis methods are quite advanced today to produce uniform diameters and shapes with controllable pore size distribution as well as spatial dispersion of pores. The majority of the nanoporous materials contain amorphous phase and interfaces between the amorphous and the crystalline phases. Both affect the transport of phonons, thus the thermal conductivity in such nanostructured materials. The impact of the amorphous shells around the pores started recently to interest the scientific community.
In this theoretical work, we report results obtained with Molecular Dynamics Simulations on the impact of the amorphous shells around spherical and cylindrical pores. Two amorphous shells are modeled: a-Si and a-SiO2. The impact of amorphous silica is much more pronounced compared to amorphous silicon. A small fraction of amorphous shells can reduce the thermal conductivity to values inferior to the bulk amorphous silicon or silica. Physical insights will be presented with the use of the phonon density of states. Combined results show that there are two key parameters which control the thermal transport in nanoporous materials: the non-crystalline fraction and the total surface of interfaces between crystalline and amorphous phase to volume ratio.