Near-Field Radiative Heat Transfer Between Spherical Surfaces

Nearfield radiative transfer is known to be significantly different from that of far-field radiative transfer based on Plancks theory of blackbody radiation. Theoretical predictions point to a significant enhancement of radiative transfer between closely spaced objects due to the tunneling of surface phonon polaritons. Despite extensive theoretical predictions of enhancement between parallel surfaces, experimental evidence of near-field radiative transfer in excess of Plancks limit has been elusive due to experimental difficulties. In this talk, we will present results of our theoretical and experimental investigations into near-field radiative transfer between spherical surfaces. We have developed a sensitive technique of measuring nearfield radiative transfer between a microsphere and a substrate using a bimaterial atomic force microscope (AFM) cantilever, resulting in heat transfer-distance curves. Measurements of radiative transfer between a sphere and a flat substrate show the presence of strong nearfield effects resulting in enhancement of heat transfer over the predictions of the Planck blackbody radiation theory.