Near-field radiation in nanoscale gaps

Abstract

The theoretical calculations for near-field radiation heat transfer based on a local dielectric constant approach indicate that the heat transfer will go to infinity as the gap becomes very small. To correct this anomaly, it has been proposed that the heat transfer through very small gaps will saturate due to the influence of nonlocal effects on the dielectric constant. Previous experiments using an AFM bi-layer cantilever reported near-field radiation heat transfer between a silica sphere and a flat plate down to a 30 nm gap. The objective of this thesis is to experimentally study thermal radiative transfer at very small separation distances. Experimental results on near-field radiation heat transfer between a silica sphere and a flat glass substrate are presented for sphere-plate separation down to a few nanometers. The experimental results deviate substantially from the theoretical predictions for separation distance of 100 nm and start to saturate at a separation distance of 30 nm. In addition to the effect of the spatial dispersion of the dielectric constant, this saturation may be influenced by the surface roughness of the microsphere and/or repulsive electrostatic forces. Surface roughness is included in the analytical analysis of the radiative heat transfer through an approximate model based on the Proximity Force Approximation.