Heat current anticorrelation effects leading to thermal conductivity reduction in nanoporous Si

Abstract

Prevailing nanostructuring strategies focus on increasing phonon scattering and reducing the mean-free-path of phonons across the spectrum. In nanoporous Si materials, for example, boundary scattering reduces thermal conductivity drastically. In this work, we identify an unusual anticorrelated specular phonon scattering effect which can result in additional reductions in thermal conductivity of up to ~ 80% for specific nanoporous geometries. We further find evidence that this effect has its origin in heat trapping between large pores with narrow necks. As the heat becomes trapped between the pores, phonons undergo multiple specular reflections such that their contribution to the thermal conductivity is partly undone. We find this effect to be wave-vector dependent at low temperatures. We use large-scale molecular dynamics simulations, wave packet analysis, as well as an analytical model to illustrate the anticorrelation effect, evaluate its impact on thermal conductivity, and detail how it can be controlled to manipulate phonon transport in nanoporous materials.

arXiv comment24 pages, 5 figures

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Cited by in corpus (6)

• Interpretation of apparent thermal conductivity in finite systems from equilibrium molecular dynamics simulations
• 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
• Super-suppression of long wavelength phonons in constricted nanoporous geometries
• Reduced-Order Model to Predict Thermal Conductivity of Dimensionally-Confined Materials