Ph.D. Thesis Defense: Matthew Panzer

Stanford University Ph.D. Thesis Defense
Thermal Characterization and Modeling of Nanostructured Materials
Matthew Panzer
Advisor: Prof. Ken Goodson
Department of Mechanical Engineering
 
November 2, 2009, 2-3 PM
Paul G. Allen CISX-101 Auditorium
(Refreshments served at 1:45 PM)
 
Thermal conduction resistances are becoming increasingly complicated as advanced materials, photonics, and electronic devices incorporate more nanostructured features (e.g. carbon nanotubes (CNTs), ultra-thin films, nanoparticles, etc.). The reduced dimensions and large interface densities of nanostructured materials modify the energy transport physics, requiring the development of new thermal models and thermal metrology techniques with deep sub-micron spatial resolution. This work develops and applies ultra-fast (nanosecond thermoreflectance (TR) and picosecond time-domain thermoreflectance (TDTR)) to characterize thermal resistances in carbon nanotube arrays and thin-film materials. In conjunction, this work develops novel models of thermal transport within the nanostructured material and interfaces. 
 
Owing to their high intrinsic thermal conductivities (~3000 W/m/K), aligned arrays of CNTs are promising for use in advanced thermal interface materials. Nanosecond TR data for metal-coated aligned nanotube films show that the thermal resistance of the films is dominated by interfaces due to incomplete CNT-metal contact, and that the thermal resistance of these films can be significantly reduced by varying the metallic composition at the interface. This work presents data for the growth-interface thermal resistance of multiwalled carbon nanotubes measured directly using TDTR with a variable modulation frequency technique. 
 
The thermal properties of hafnium oxide and silicon-rich nitride thin films, which are becoming increasingly incorporated in device and energy conversion materials, can significantly influence local phonon temperatures. TDTR data for these films show that the nanoscale features and microstructure reduce the thermal conductivity compared to bulk.
 
The abrupt changes in geometry at nanostructured interfaces induce phonon confinement, which creates additional contributions to the interface resistance. This work investigates model problems of thermal transport through abrupt junctions between a one-dimensional lattice in contact with a two- and three-dimensional lattice using a Green�s function approach. The model indicates that the thermal resistances due to dimensional mismatch are comparable to those due to material property mismatch effects. The results suggest that engineering an intentional impedance mismatch at a nanostructured interface may enhance the transmission of energy.