Specular Reflection Leads to Maximum Reduction in Thermal Phonon Conductivity

A material thermal conductivity is not a fixed physical property but it can be controlled by modifying the transport properties of thermal phonons. In recent years, a large number of experiments have been reported where phonon mean free paths in nanostructures are reduced by orders of magnitude. In contrast to established work that use the diffuse surface scattering of phonons as the physical mechanism to reduce the thermal conductivities, in this talk we show that the largest reduction of thin film heat conduction is achieved via specular surface scattering. Our results create new opportunities for heat conduction manipulation since smooth surfaces – in contrast to rough surfaces – can be more effective on suppressing thin film phonon heat conduction.