A new regime of nanoscale thermal transport: collective diffusion counteracts dissipation inefficiency

摘要

Understanding thermal transport from nanoscale heat sources is important fora fundamental description of energy flow in materials, as well as for manytechnological applications including thermal management in nanoelectronics,thermoelectric devices, nano-enhanced photovoltaics and nanoparticle-mediatedthermal therapies. Thermal transport at the nanoscale is fundamentallydifferent from that at the macroscale and is determined by the distribution ofcarrier mean free paths in a material, the length scales of the heat sources,and the distance over which heat is transported. Past work has shown thatFourier's law for heat conduction dramatically over-predicts the rate of heatdissipation from heat sources with dimensions smaller than the mean free pathof the dominant heat-carrying phonons. In this work, we uncover a new regime ofnanoscale thermal transport that dominates when the separation betweennanoscale heat sources is small compared with the dominant phonon mean freepaths. Surprisingly, the interplay between neighboring heat sources canfacilitate efficient, diffusive-like heat dissipation, even from the smallestnanoscale heat sources. This finding suggests that thermal management innanoscale systems including integrated circuits might not be as challenging asprojected. Finally, we demonstrate a unique and new capability to extract meanfree path distributions of phonons in materials, allowing the firstexperimental validation of differential conductivity predictions fromfirst-principles calculations.