Lattice Thermal Boundary Resistance

Control and modelling of thermal transport at the nanoscale has emerged either as a key issue in modern nanoscience or as a compelling demand for the ever- increasing miniaturization process in information technologies: here the thermal budget of nanodevices is basically ruled over by heat exchanges across interfaces, and the relevant physics is cast in terms of a thermal boundary resistance. In this chapter, we present a unified discussion about the fundamental knowledge developed in this framework. Starting from the most general thermodynamical description of an interface, where the driving force for heat transport is identified together with the actual location and thickness of the interface itself, we define what the thermal boundary resistance is in fact. We then delve into the most successful modelling approaches, based either on the phonon picture or on the atomistic picture. Adopting different assumptions and employing different implementation strategies, they offer a complementary description of the physi- cal mechanisms underlying thermal boundary resistance, and they provide useful computational protocols to predict its value in realistic systems

Giant heat transfer in the crossover regime between conduction and radiation

Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum. At large distances the heat transfer can be described by black body radiation, at shorter distances evanescent modes start to contribute, and at separations comparable to inter-atomic spacing the transition to heat conduction should take place. We report on quantitative measurements of the near-field mediated heat flux between a gold coated near-field scanning thermal microscope tip and a planar gold sample at nanometre distances of 0.2–7 nm. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black body radiation and four orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics. Different theories of phonon tunnelling are not able to describe the observations in a satisfactory way. The findings demand modified or even new models of heat transfer across vacuum gaps at nanometre distances