Interfacial thermal transport spectroscopy: a review of theory and experiment.

Thermal transport across interfaces is a critical bottleneck in the thermal management of modern microelectronics, particularly as devices scale toward the nanoscale with increasingly high-power densities. While bulk material properties are well understood, the physics governing heat transfer at interfaces, defined by carrier transmission and scattering, remains a complex challenge. Here, we review methods and studies on interfacial thermal transport spectroscopy, bridging fundamental theory with the state-of-the-art modelling and experiments. We first examine the fundamentals of the phonon gas model and carrier coupling, followed by a detailed discussion of computational approaches ranging from atomistic Green's functions (AGF) and molecular dynamics (MD) simulations at the nanoscale to the Boltzmann transport equation (BTE) at the microscale. Then, we evaluate popular experimental techniques, such as frequency-domain thermoreflectance (FDTR), time-domain thermoreflectance (TDTR) and electron energy loss spectroscopy (EELS), emphasizing their role in resolving spectral phonon contributions. We further highlight emerging data-driven methods and machine learning approaches that accelerate physical understanding and materials discovery. Finally, we outline open challenges in characterizing spectral interfacial thermal transport within computational and experimental frameworks, as well as the persistent gaps between them. This review aims to provide a unified perspective on understanding and optimizing interfacial heat dissipation for next-generation electronic and energy devices.