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EXPLORING THERMAL TRANSPORT ACROSS THE INTERFACES AND IN COMPLEX STRUCTURES

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Abstract

Heat dissipation is a critical issue that limits the performance, reliability and lifetime of microelectronics. Massive thermal resistance at interfaces often presents the major bottleneck for heat removal. People have explored various types of metal/dielectric and dielectric/dielectric interfaces, in which the phonon interfacial thermal transport plays an important role. The atomistic Green’s function (AGF), a technique developed in fully quantum regime, can investigate the phonon transport across all types of interface, and it only requires the first-principles force constants as input. However, traditional AGF is limited to harmonic interfaces, and it cannot include the inelastic phonon scatterings at the interface, which is crucial for phonon interfacial thermal transport in the practical temperature regime. The first two chapters of this dissertation discuss interfacial thermal transport. In the first chapter, I developed a rigorous formalism of anharmonic AGF to treat the inelastic phonon scattering processes at 3D interfaces. Without any fitting parameters, I incorporated both harmonic and anharmonic first-principles force constants into the AGF. In the second chapter, I employed such 3D anharmonic AGF to discover an intrinsic and universal phenomenon: nanoscale thermal interface rectification in quantum regime. I found that the anharmonic phonon scatterings across the interface act on the temperature-dependent phonon populations on both sides of the interface, generating the necessary nonlinearity to achieve this nanoscale thermal interface rectification. The new technique I developed and the new findings I obtained will guide the future design of solid-solid interfaces for desired interfacial thermal conductance. Along with understanding interfacial thermal transport, I also focused on seeking materials with high thermal conductivity. In the third chapter, I studied the thermal transport properties of both alpha- and beta-Boron suboxides (B6O) using first-principles calculations. Despite their complex unit cells, they exhibit higher thermal conductivity than many simple structures, such as silicon with only two atoms in the primitive cell. I demonstrated the importance of bond strength in determining thermal conductivity. Even if a material has complex structures like B6O, it is still possible to give high thermal conductivity if it is superhard. Such new findings show that alpha- and beta-B6O are promising materials for lightweight, multifunctional thermal management applications.

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57 pages

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2023-08

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Tian, Zhiting

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Jena, Debdeep
Kim, Eunah

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Mechanical Engineering

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Ph. D., Mechanical Engineering

Degree Level

Doctor of Philosophy

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Government Document

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dissertation or thesis

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