Phonon Transport Across Interfaces and Within Nanostructures
John C. Duda
Department of Mechanical and Aerospace Engineering, University of Virginia,
Charlottesville, VA 22904
Abstract
Thermal management has assumed a critical role in electronic devices, power generation, and waste energy
harvesting, where performance depends vitally on the effective thermal conductivity of the component materials.
The effects of insufficient thermal management in these systems and applications are clear: current microprocessor
clock speeds are up to 300% slower than those projected a decade ago, waste heat constitutes a 10 TW global source
of untapped energy, and commercial thermoelectric devices achieve only 15% of the Carnot limit. This seminar will
focus on novel ways in which one can both predict and tune thermal transport properties in nanomaterial systems.
The Role of Chemical Ordering on Phononic Thermal Conductivity of Binary Alloys: Non-equilibrium molecular
dynamics simulations are employed to study the thermal conductivity of binary Lennard-Jones alloys. It is shown
that through exploitation of chemical ordering processes, where atoms preferentially arrange themselves into
organized sublattices, can serve as a way to tune the thermal conductivity of binary alloys. Additionally, it is found
that the thermal conductivity of an ordered alloy is less than that of a random alloy at high temperatures due to
differences in the dominant phonon scattering mechanisms.
Predicting Thermal Interface Conductance in Novel Material Systems: In systems where the average distance
between material interfaces is smaller than the energy carrier mean-free-path, the effective thermal conductivities of
such systems are dictated by interface conductance. Consequently, it is important that device engineers have
accurate and easy-to-implement models for predicting thermal interface conductance. Here, two extensions of the
widely implemented diffuse mismatch model are presented for novel interfaces, namely, those between solids and
graphitic materials or self assembled monolayers.
Controlling Thermal Interface Conductance Through Quantum Dot Roughening: Thermal interface conductance
between a thin Al film and Si substrate is studied via the time-domain thermoreflectance technique. The RMS
roughness of the interface is varied through the inclusion of Ge quantum dots, grown on the Si substrate via
molecular beam epitaxy. It is shown that a clear relationship between interface roughness and interface conductance
exists. A predictive model is formulated to account for the roughness of the interface and is shown to agree with the
experimental data.