THESIS
2020
Abstract
Miniaturization of the electronic devices and the pursuit of high-efficiency thermoelectric
materials have pushed the research of thermal transport down to meso/nanoscale. At mesoscales,
wave-like behavior could play an important role in phonon transport.
The wave effect in the nanostructures has been predicted with simulations and confirmed
by experimental measurements. To verify the existence of the wave-like phonon transport, it is
important to have an in-depth understanding of the pure particle-like phonon transport. The
computation cost for the mesoscale problem is formidable even with the solution of the phonon
Boltzmann transport equation. To speed up the calculation while maintaining the accuracy, a
phonon Monte Carlo based on MFP-cumulative bulk thermal conductivity is...[
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Miniaturization of the electronic devices and the pursuit of high-efficiency thermoelectric
materials have pushed the research of thermal transport down to meso/nanoscale. At mesoscales,
wave-like behavior could play an important role in phonon transport.
The wave effect in the nanostructures has been predicted with simulations and confirmed
by experimental measurements. To verify the existence of the wave-like phonon transport, it is
important to have an in-depth understanding of the pure particle-like phonon transport. The
computation cost for the mesoscale problem is formidable even with the solution of the phonon
Boltzmann transport equation. To speed up the calculation while maintaining the accuracy, a
phonon Monte Carlo based on MFP-cumulative bulk thermal conductivity is developed.
Benefiting from the linearized and steady-state formulation, it is efficient and directly
parallelizable. Since the input is obtainable from experiments or first principle calculations, the
accuracy is guaranteed. Validated with the experimental results of the nanomeshes, the proposed
method has the potential to predict the effective thermal conductivities of very complex
nanostructures.
To address the wave interference in the superlattices, an Interfering Monte Carlo is
proposed. Integrating a hybrid interface model, we applied the IMC to a realistic Si/Ge
superlattices to explain the unexpected phenomena with aperiodic superlattices, and the
computational results faithfully reproduce what molecular dynamics predicts. Through a series
of the comparison of the computational results, it is confirmed that wave effect could be less
important for the Si/Ge SLs under study.
Combining the Green-Kubo formula and the elastic wave calculation through finite difference time domain (FDTD) method to predict the pure wave-like phonon transport
behavior seem to be promising. For the future study, this method is extended to 3D cases for a
better understanding of the pure wave-like phonon transport in nanostructures and may serve
as a benchmark to compare with the real experiments.
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