LAUSR

This perspective describes the key physical concepts at play capturing transport regimes in gaps with sizes ranging from the micrometer down to the Angstrom. The roles of photons, phonons, and electrons are highlighted and illustrated across several examples from the literature. Particularly, two situations for which atomistic calculations provide insights into the microscopic mechanisms at play in thermal transport across nanoscale gaps will be expounded, namely, thermal transport across silica clusters and in 2D materials. While experimental investigations are highly challenging and a vast field of opportunities remain open in this matter, several related domains of applications, such as thermophotovoltaics, thermoionics, thermal management, imaging, and 2D materials, are involved.