Ab-initio Heat Transfer: Predicting thermal transport in nanostructures and materials from the atoms up – Derek Stewart

Date: Mon. April 4th, 2011, 12:30 pm-1:30 pm
Location: Rockefeller 221

While electronic transport has been the focus of intensive research for nearly a century, thermal transport has proven difficult to quantify and model. However, a predictive model for thermal conductivity can improve our understanding of thermoelectric materials, thermal resistance barriers, nanoscale heat transport, and even geologic heat transfer. In this talk, I will discuss the development of a new first principles framework to model thermal transport in materials and nanostructures. Using density functional perturbation theory, we are able to calculate both harmonic and anharmonic interatomic force constants. Coupling these terms with a Boltzmann transport approach, we are able to demonstrate excellent agreement between the calculated and measured lattice thermal conductivities of technologically relevant semiconductors (silicon, germanium, and diamond) without the use of any adjustable parameters[1,2]. Nanoscale systems present unique opportunities for potential heat mitigation and thermoelectric applications. However, due to the atomic scale of these structures, their thermal transport properties can be significantly affected by impurities, defects, and even isotopic composition[3]. In order to accurately model heat conduction in nanoscale systems, it is important to describe these systems using an approach that can model both interatomic interactions as well as structural relaxations due to defects. I will discuss a non-equilibrium Green’s function thermal transport approach that builds on interatomic force constants calculated from density functional theory. With this approach, we can reproduce the experimentally observed thermal enhancement in isotopically pure boron nitride nanotubes[4], examine potential nanoscale phonon localization effects[5], and study the impact of Stone-Wales defects and symmetry breaking on thermal transport in carbon nanotubes[6]. Finally, I will discuss the exciting frontier of engineering phonons in nanostructures[7] to develop new devices with specific thermal and electronic properties.
[1] D. A. Broido, M. Malorny, G. Birner, N. Mingo, and D. A. Stewart, Applied Physics Letters, 91, 231922 (2007).
[2] A. Ward, D. A. Broido, D. A. Stewart, and G. Deinzer, Physical Review B, 80 125203 (2009).
[3] C. W. Chang et al., Physical Review Letters, 97, 085901 (2006).
[4] D. A. Stewart, I. Savic, and N. Mingo, Nano Letters, 9, 81 (2009).
[5] I. Savic, D. A. Stewart, and N. Mingo, Physical Review Letters, 101, 165502 (2008).
[6] N. Mingo, D. A. Stewart, D. A. Broido, and D. Srivastava, Physical Review B, 77, 033418 (2008).
[7] N. Mingo, K. Esfarjani, D. A. Broido, and D. A. Stewart, Physical Review B, 81, 045408 (2010).