Thermal-conductivity measurement by time-domain thermoreflectance

The flow of heat in materials is generally perceived to be a slow process and, therefore, pump-probe techniques originally developed for ultrafast time-resolved optical spectroscopy are not an obvious source of technologies for advances in thermal-property measurements. Nevertheless, over the past 18 years, the work of approximately 30 dedicated students and postdoctoral researchers at the University of Illinois at Urbana-Champaign has developed time-domain thermoreflectance (TDTR) into a nearly universal, high-throughput tool for measuring the thermal conductivity of materials and the thermal conductance of materials interfaces. This article illustrates the utility of TDTR and surveys current topics in the science of heat conduction in materials with recent examples drawn from high-thermal-conductivity crystals of cubic boron phosphide and boron arsenide, structure-property relationships for thermal conductivity of amorphous polymers, and thermal conductivity switching in liquid-crystal networks.