Calculating Interfacial Thermal Transport Using Atomistic Simulation Methods

Abstract

At the nanoscale, many materials have properties different than they do in the bulk. Nanomaterials can exhibit interesting and useful optical, electronic, and physical properties. However, the very features that give these materials their novel applications also impact their thermal transport properties. Poor transport can negatively impact device function by limiting the ability to deliver thermal energy where it is wanted and remove waste heat from where it is not. A fundamental understanding of the mechanics of thermal transport at the nanoscale is required to successfully mitigate these transport issues without altering the nanomaterial in a way that destroys its unique properties. In this work, we use atomistic modeling methods to examine the fundamental mechanisms of thermal transport at the nanoscale. The work uses two modeling methods to examine two unique nanoscale transport problems. The first method is density functional theory, which was applied to thermal transport in an AlN/GaN superlattice structure. We solved the Boltzmann transport equation using properties from density functional theory to show that the primary driver of the low thermal conductivity in the AlN/GaN superlattice was an increase in scattering rather than a reduction in phonon group velocity due to zone folding. The second method is molecular dynamics, which focused on methods to include the thermal transport contributions of electrons in metallic systems. Molecular dynamics simulations are classical, and do not natively support electronic effects. This shortcoming has hindered the use of molecular dynamics simulations to model thermal transport in materials with delocalized electrons. We present a two-temperature model to include the effects of electronic thermal transport and demonstrate its use on Nickel. We also apply it to a graphite-coated Nickel catalyst system to model thermal transport in the catalyst under inductive heating. Next steps for further development of the two-temperature model are also discussed.