Microscale radiative heat transfer

Microscopic electromagnetic near field has a great potential for direct applications and is applied in integrated optics, lithography, thermo-photovoltaics and NSOM microscopy. With development of techniques of analysis and manipulation of microscopic objects, such as the AFM, STM and optical tweezers, to give some examples of today’s micro-electromechanical systems, the knowledge of various interactions between objects at microscopic distances becomes important.
Thermally excited electromagnetic near-field is responsible for interactions between electrically neutral small objects or between small and macroscopic objects, resulting in adhesion, viscous drag and enhanced radiative heat transfer.

T. Kralik, V. Musilova, P. Hanzelka, M. Zobac, V. Musilova, T.Fort, and M. Horak, Strong Near-Field Enhancement of Radiative Heat Transfer between Metallic Surfaces,  Phys. Rev. Lett. 109 (2012)  224302

T. Kralik, P. Hanzelka, M. Zobac,  M. Horak, A. Srnka,  Radiative heat transfer at low temperatures over microscopic distances in vacuum, 
IIR Int. Conf. Cryogenics 2012, September 11-14, 2012, Dresden

T. Kralik, P. Hanzelka, V. Musilova, A. Srnka, M. Zobac, Cryogenic apparatus for study of near-field heat transfer,  
Review of Scientific Instruments, 82 (2011) 055106;  

Principle of measurement - Apparatus scheme

Apparatus scheme

Measured mutual emissivity of  tungsten samples
in dependence on the vacuum gap between planeparallel samples for various temperatures of the "hot"sample. Cold sample was kept at 5 K.

Heat transfer over the gap is compared with the black-body radiation. The mutual emissivity of the hot sample at temperature TR and the cold sample at TA  is evaluated as a ratio between the measured heat power QR and the radiative heat which would be transferred between the samples with fully absorbing (black) surfaces:
mutual emissivity
where "sigma" is Stefan-Boltzmann constant and A is the sample area.

At distances 10 - 100 micrometres the emissivity increases due to the near-field effect and below 10 micrometres it can exceed the black-body value (100%).


Apparatus without vacuum jacket
Open guard and measurement chambers


Planeparallelism equalizer


Thermal stress relieving mount

Sample mount