With a STM based near field scanning thermal microscope (NSThM)  we investigate the heat transfer at ultimate short distance 0.2 nm - 7 nm. At these separations the observed heat transfer is five orders of magnitudes larger than than black body radiation and three orders of magnitudes larger than predictions by conventional theory of fluctuational electrodynamics [2 - 9]. After an accurate calibration procedure we are able to measure the local heat transfer in a quantitative way. We have investigated the influence of thin films of metals and dielectric material on the near-field mediated heat transfer at the fundamental limit of single monolayer islands on a metallic substrate. Spatially resolved measurements by NSThM are presented which are showing a distinct enhancement in heat transfer above NaCl islands compared to the bare Au(111) film . Experiments at this sub-nanometer scale call for a microscopic theory beyond the macroscopic fluctuational electrodynamics used to describe near-field heat transfer today. The method facilitates the possibility to develop designs of nanostructured surfaces with respect to specific requirements in heat transfer down to a single atomic layer. These findings open up the possibility for a local surface modification by means of local heating, e.g. chemical modification and heat assisted magnetic recording, on a scale of a few nanometers.
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