Large-scale molecular dynamics investigation of geometrical features in nanoporous Si

Abstract

Nanoporous materials are of broad interest for various applications, in particular advanced thermoelectric materials. The introduction of nanoscale porosity, even at modest levels, has been known to drastically reduce a materials thermal conductivity, in some cases even below its amorphous limit, thereby significantly increasing its thermoelectric figure of merit, ZT. The details of the important attributes that drive these large reductions, however, are not yet clear. In this work, we employ large-scale equilibrium molecular dynamics to perform an exhaustive atomistic-scale investigation of the effect of porosity on thermal transport in nanoporous bulk silicon. Thermal transport is computed for over 50 different geometries, spanning a large number of geometrical degrees of freedom, such as cylindrical pores and voids, different porosities, diameters, neck sizes, pore/void numbers, and surface-to-volume ratios, placed in ordered fashion, or fully disordered. We thus quantify and compare the most important parameters that determine the thermal conductivity reductions in nanoporous materials. Ultimately, we find that, even at the nanoscale, the effect of merely reducing the line-of-sight of phonons, i.e. the clear pathways that phonons can utilize during transport, plays the most crucial role in reducing the thermal conductivity in nanoporous materials, beyond other metrics such as porosity and surface/boundary scattering.

33 pages, 9 figures

References in corpus (4)

• Thermal conductivity of silicon nanomeshes: Effects of porosity and roughness
• Hierarchical nanostructuring approaches for thermoelectric materials with high power factors
• Monte Carlo phonon transport simulations in hierarchically disordered silicon nanostructures
• Low-dimensional phonon transport effects in ultra-narrow, disordered graphene nanoribbons

Cited by in corpus (8)

• Hierarchically nanostructured thermoelectric materials: Challenges and opportunities for improved power factors
• Thermal rectification optimization in nanoporous Si using Monte Carlo simulations
• Heat current anticorrelation effects leading to thermal conductivity reduction in nanoporous Si
• Mitigating the Effect of Nanoscale Porosity on Thermoelectric Power Factor of Si
• Universal Effective Medium Theory to Predict the Thermal Conductivity in Nanostructured Materials
• Enhanced Thermoelectric Performance of Polycrystalline Si0.8Ge0.2 Alloys through the Addition of Nanoscale Porosity
• Understanding Phonon Transport Properties Using Classical Molecular Dynamics Simulations
• Super-suppression of long wavelength phonons in constricted nanoporous geometries