Experimental constraint on extreme near-field heat transfer

At extreme sub-10 nm gaps, heat transfer becomes highly complex, involving electrons, phonons, and photons. While near-field radiative heat transfer has been well established, several studies have reported puzzling phonon-mediated signals that conventional theories cannot explain. Two leading theories are force-mode phonon transfer and unknown organic contamination. To gain insight into this debate, we performed heat-flux experiments using a scanning thermal microscope capable of sub-nanometer control and pico-watt sensitivity, mapping the complete transition from photonic near-field to true contact across metallic, dielectric, and cross-material interfaces.

Understanding thermal interactions in these extreme gaps not only sheds light on an unresolved fundamental problem but also points toward new routes for non-contact heat management at the nanoscale. Such mechanisms could enable applications in ultrafast thermal switching, nanoscale thermionic and thermophotovoltaic devices, and heat-assisted data storage.