Nanoscale thermal radiation between two gold surfaces

In this letter, we measured the nanoscale thermal radiation between a microsphere and a substrate which were both coated with thick goldfilms. Although gold is highly reflective for thermal radiation, the radiative heat transfer between two goldsurfaces was demonstrated to be significantly enhanced at nanoscale gaps beyond the blackbody radiation limit due to the tunneling of non-resonant evanescent waves. The measured heat transfer coefficient between two goldsurfaces agreed well with theoretical prediction. At a gap d = 30 nm ± 5 nm, the heat transfer coefficient between two goldsurfaces was observed to be as large as ∼400 W/m²·K, much greater than the blackbody radiation limit (∼5 W/m²·K).