Near Field Radiative Heat Transfer About Nanoparticles And Semi-Infinite Media

Questions about radiative heat transfer at micro- and nanoscale have been raised by recent developments of nanotechnology. Design of micro- and nanostrucutres requires a thorough understanding of physical phenomena involved in radiative energy exchange, when their sizes become comparable to the thermal mean free path or the thermal radiation wavelength. However, there is a lack of understanding of the physical mechanisms involved. For example, modeling RHT between two semi-infinite bodies, or between a tip and a substrate is a challenging problem for all near-field microscopes(scanning tunneling microscope, atomic force microscope) or for scanning thermal microscopes. So understanding and predicting the heat transfer between two bodies separated by a nanometric distance is a key issue both from the theoretical and applied points of view.We explore the radiative heat transfer between: (a) two spherical nanoparticles, (b) a semi-infinite media and a spherical nanoparticle separated by a distance on the order of a few nanometers. We considered the nanoparticle as a point-like dipole which could be a single molecule, a dust particle, or a model for the tip of a microscope probe. Using an electromagnetic approach, in the dipolar approximation, we have derived the expression of the radiative heat power exchanged between them. We use Green functions to relate the current and electric dipole moment in the material to the field above the interface, then we can use the fluctuation–dissipation theorem to calculate the required quantities. We derive both the spectral radiative heat flux and the total power (integrated over the frequencies) exchanged between them.For two nanoparticles, we first calculate the power dissipated in each of them, then get the power exchanged between the two nanoparticles. Note the spatial dependence of this transfer, going as 1 /d~6, typical of the induced dipole-induced dipole interaction. In addition to this, the results show that the transfer depends on the imaginary part of the polarization of each nanoparticle. We can also find that power is only exchanged at certain wavelengths corresponding to resonances of the material.For a nanoparticle and a semi-infinite media, we first calculate the power radiated by the bulk at a given frequency and absorbed by the particle, then calculate the power radiated by the particle locally dissipated by per unit volume of the media. The figure of the spectral power dissipated inside the particle displays remarkable peaks which are related to the evanescent waves. And the near field transfer is enhanced by several orders of magnitude than the far field one. The integrated power absorbed by the media decrease very fast (as 1 /d~6) with the distance d between the particle and the point in the media.