Frequency-Dependent Monte Carlo Simulations of Phonon Transport in Nanostructures

Journal of Applied Physics

Zhao

2016

Self Cite

In the past two decades, phonon transport within nanoporous thin films has attracted enormous attention for their potential applications in thermoelectrics and thermal insulation. Various computational studies have been carried out to explain the thermal conductivity reduction within these thin films. Considering classical phonon size effects, the lattice thermal conductivity can be predicted assuming diffusive pore-edge scattering of phonons and bulk phonon mean free paths. Following this, detailed phonon transport can be simulated for a given porous structure to find the lattice thermal conductivity [Hao et al., J. Appl. Phys. 106, 114321 (2009)]. However, such simulations are intrinsically complicated and cannot be used for the data analysis of general samples. In this work, the characteristic length K Pore of periodic nanoporous thin films is extracted by comparing the predictions of phonon Monte Carlo simulations and the kinetic relationship using bulk phonon mean free paths modified by K Pore . Under strong ballistic phonon transport, K Pore is also extracted by the Monte Carlo ray-tracing method for graphene with periodic nanopores. The presented model can be widely used to analyze the measured thermal conductivities of such nanoporous structures. Published by AIP Publishing. [http://dx

Section: Introductionmentioning

confidence: 93%

Section: Characteristic Length and Its Validationmentioning

confidence: 99%

See 1 more Smart Citation

Characteristic length of phonon transport within periodic nanoporous thin films and two-dimensional materials

Journal of Applied Physics

Zhao

2016

Self Cite

“…1, phonons incident on pore edges will be randomized for their traveling directions after diffusive poreedge scattering, with all other parameters unchanged [3,50]. This random resetting of phonon traveling directions has been discussed for cubic pores [3,50]. For spherical pores, the detail of the direction resetting is given in the Appendix.…”

Section: Extracting From Mcrtmentioning

confidence: 99%

Analytical model for phonon transport analysis of periodic bulk nanoporous structures

Applied Thermal Engineering

Zhao

2017

Self Cite

Phonon transport analysis in nano-and micro-porous materials is critical to their energy-related applications. Assuming diffusive phonon scattering by pore edges, the lattice thermal conductivity can be predicted by modifying the bulk phonon mean free paths with the characteristic length of the nanoporous structure, i.e., the phonon mean free path ( ) for the pore-edge scattering of phonons. In previous studies (Jean et al., 2014), aMonte Carlo (MC) technique have been employed to extract geometry-determined for nanoporous bulk materials with selected periods and porosities. In other studies (Minnich and Chen, 2007;Machrafi and Lebon, 2015), simple expressions have been proposed to compute . However, some divergence can often be found between lattice thermal conductivities predicted by phonon MC simulations and by analytical models using . In this work, the effective values are extracted by matching the frequency-dependent phonon MC simulations with the analytical model for nanoporous

“…Figure2compares our new measurements and previous measurements (symbols) with kL predicted by two-dimensional phonon Monte Carlo simulations that assume bulklike phonon transport and diffusive phonon scattering by pore edges. Only the porosity Φ=20% is computed as the line in Fig.2[6,7,29], whereas previous measurements cover Φ of 7-64%. In general, the simulations agree well with the new measurement,…”

mentioning

confidence: 99%

(Invited) Nanostructures for Reduced Lattice Thermal Conductivity — Case Studies for Nanopores and Grain Boundaries

et al. 2017

ECS Trans.

Solid-state thermoelectric devices have the ability to directly convert heat into electricity for power generation. A good TE material should possess a high electrical conductivity, a high Seebeck coefficient, and a low thermal conductivity. This requirement is hard to be satisfied within the same material. To address this issue, the nanostructuring approach has been widely used to reduce the lattice part of the thermal conductivity (kL) but still maintain the bulk electrical properties. High TE performance has thus been achieved in various nanostructured materials, such as nanoporous thin films and different nanostructured bulk materials. To better understand the observed kL reduction by nanostructures, two major types of nanostructured materials are studies here, including nanoporous thin films and nanograined bulk materials. In the latter case, a super-flexible thin film was hot pressed onto a wafer to represent a grain boundary.