Near-Field Heat Transfer
Near-Field Heat Transfer
At the surface of each body with nonzero temperature there exists an evanescent electromagnetic field, caused by thermal fluctuations of charge carriers. When two bodies with different temperatures are brought close to each other, such that their respective evanescent fields overlap, one encounters a heat transfer which can be orders of magnitude higher than that which is mediated by the familiar Planckian far-field radiation.
This tantalizing effect, which had been discussed theoretically already in 1971 by Polder and van Hove, also allows one to design a near-field scanning thermal micoscope which is based on evanescent photons tunneling between a tip and a sample, in analogy to a standard scanning tunneling microscope which relies on a current of tunneling electrons.
In an experiment-theory collaboration we have given a detailed discussion of such a set-up in Phys. Rev. Lett. 95, 224301 (2005), obtaining quantitative agreement between theory and experiment, thereby demonstating the feasibility and practical advantages offered by this novel instrument.
The above figure refers to the near-field heat transfer between a spheriodal nanoparticle and a nonplanar surface, as published in J. Appl. Phys. 108, 014312 (2010), illustrating the potential usage of such nanoparticles as thermal near-field sensors.
This line of research has been continued, and extended way beyond our initial efforts, by Svend-Age Biehs (website for own research group still under construction).