DISSERTATION DEFENSE
Zhiliang Pan, Mechanical Engineering
*under the direction of Deyu Li
“Thermal Transport in Low Dimensional Polar Nanostructures“
03.16.23 | 9:00am | 135 Olin Hall
Thermal conductivity of nanostructures and materials are of fundamental importance as well as application values for its potential in a broad variety of technologies. While the past two decades have witnessed remarkable progress in understanding thermal transport in nanostructures, questions related to phonon particle interactions as well as low dimensional effects remain to be answered. Limited efforts on these topics have demonstrated previously unrecognized exotic features. Besides, transport phenomenon associated with extreme geometry, complex structure, and potential energy particle contributing to thermal transport requires more experimental efforts.
Utilizing a well-established microthermal bridge method, systematic thermal conductivity measurements have been done on low dimensional nanowires, i.e. NbSe3 and Ta2Se3 nanowires. The combination of weak intra-chain van der Waals bonding and strong along-chain covalent bonding gives exotic thermal transport features such as the charge density wave (CDW), tunable electron phonon interaction, and one-dimensional phonon transport. On another note, to better understand the contact thermal resistance in polymer composites, we studied thermal transport at contacts between individual boron nitride nanotubes (BNNTs) with and without a thin interlayer. Different interlayer materials have been explored, among which using PVP as interlayer material gives an interesting bidirectional modulation of the contact thermal resistance by eliminating phonon reflection at tube contact. More interestingly, in an attempt to further reduce the contact thermal resistance, PVP was replaced by Au, which demonstrates to an unexpected negative contact thermal resistance facilitated by promoting new energy transport channel from surface phonon polaritons (SPhPs). Systematic study of SPhP mediated heat conduction has been performed, revealing the SPhP launching mechanism, non-equilibrium thermal transport, and configurable thermal conductivity in 3C-SiC nanowires. The above reported findings shine lights on the new understandings in thermal transport as well as novel approaches for engineering thermal conductivity in various polar nanostructures.