| With the growing interest in nanoscale devices and structures, there is an increasing need to understand thermal transport mechanisms on submicron lengthscales, which often cannot be explained by traditional macroscale thermal models. This is particularly the case for heat transport across interfaces in the increasingly complex structures of integrated circuits, superlattices, and nanocomposites. A heat flux across interfaces leads to a temperature drop across the interface, due to a thermal boundary resistance (TBR). TBR has only recently been addressed for room temperature applications such as thermoelectrics, thin-film high temperature superconductors, vertical cavity surface emitting lasers, and optical data storage media. More applications are sure to follow. Unfortunately, our current understanding of room temperature TBR is not adequate for proper thermal design of interface dense devices. Most TBR theoretical work has been an extension of the mismatch theories and has been limited to phonon elastic scattering processes for perfect interfaces. Other transport mechanisms have been considered such as electron-phonon (e-p) scattering and inelastic phonon scattering. There has been very little effort to systematically measure room temperature TBR and verify the proposed models.; This work discusses the current understanding of interface thermal transport theories for high temperature interfaces and describes the transient thermoreflectance technique, a technique used to directly measure interface thermal conductance. A series of measurements on a range of interfaces to investigate differing phonon spectra impact on interface thermal transport is presented. The measurements are the first made on several interface types at room temperature. Because of the difficulty of systematically controlling the interfaces between real materials, a molecular-dynamics simulation (MDS) approach is also developed to gain a better understanding of the key factors for interface thermal resistance. The MDS approach allows the analysis of controlled and well-defined interfaces. MDS enables the ability to alter material properties and atomic-level structure of the interface. This work presents the most comprehensive study of thermal interface transport by MDS to date, including the impact of interface disorder, strain, and electron-phonon coupling. The MDS results are compared to the diffuse mismatch theory. Inelastic and electron scattering appear to be critical mechanisms for interface thermal transport. These mechanisms have not received much attention in the development of interface transport theory, which has primarily been dominated by acoustic mismatch concepts. |
