Session: Panel-2 Textbooks and Pedagogy in Micro/Nanoscale Heat and Mass Transfer / 05-04 Micro/Nanoscale Thermal Radiation

Paper Number: 140768

140768 - Near-Field Radiative Heat Transfer Between a Sphere and a Flat Surface Up to High Temperatures and Down to the Sub-100 Nm Regime 

Abstract: 

When the distance between objects decreases below the characteristic wavelength of thermal radiation (few micrometres in the 300-1000 K range), the radiative heat exchanged between these objects is increased beyond the blackbody limit imposed by Planck’s law in far field. This increase of thermal radiation, which is due to the additional contribution of evanescent waves, can reach several orders of magnitude. This phenomenon can be of interest for thermal-energy harvesting. For instance, thermophotovoltaics (TPV) can take advantage of this enhancement of the radiative heat flux in order to increase the electrical output power density when the emitter is brought closer to the cell [1].

As radiative heat flux in near field depends dramatically on distance, it is imperative to control and determine it with accuracy. We report on recent efforts to improve the evaluation of distances in the sub-100 nm regime in our experiment. It involves a heated micrometric 40 µm-in-diameter sphere (graphite or SiO₂) glued on a Scanning Thermal Microscopy probe cantilever, which is moved using a piezoelectric actuator, towards a flat sample of interest. In our setup, temperatures of the emitter larger than 1000 °C can be achieved, while samples can be cooled down to nitrogen ones (77 K). Radiative heat transfer is monitored during the approach by means of resistive thermometry, which includes a preliminary fine calibration of the cantilever. We have previously shown that the temperature dependence of radiative heat transfer does not scale accordingly to the Stefan-Boltzmann law [2]. However, an issue was the difficulty in analyzing data below distances of 50 nm. In the present work, the emitter-sample distance is further evaluated by combined means of interferometry and optical deflection. Such a control allows us to determine the movements of the emitter at nanometric scale, its stability with respect to vertical oscillations and provides accurate results in the sub-100 nm distance regime. Clear snap-in jumps are observed between 10 and 30 nm before contact, as a result of attractions forces, and correlated to maximal thermal conductances achievable with this geometry in practice. Other regimes where either intermittent contact or limited jumps are observed are also highlighted. 
 

[1] Near-field thermophotovoltaic conversion with high electrical power density and efficiency above 14%, C. Lucchesi, D. Cakiroglu, J.-P. Perez, T. Taliercio, E. Tournié, P.-O. Chapuis, R. Vaillon, Nano Letters 21, 4524 (2021)
[2] Temperature dependence of near-field radiative heat transfer above room temperature, C. Lucchesi, R. Vaillon and P.-O. Chapuis, Materials Today Physics 21, 100562 (2021)

We acknowledge financial support by EU projects TPX-Power and OPTAGON, as well as French ANR projects STORE and CASTEX.

Presenting Author: P-Olivier Chapuis CNRS

Presenting Author Biography: P-Olivier Chapuis is a CNRS researcher at the Centre for Thermal Sciences of Lyon (CETHIL), where he leads the 'Nano and Microscale Heat Transfer' group. The Centre is located on the campus of INSA, the National Institute for Applied Sciences, in Lyon.

Authors:

Mathieu Thomas CNRS
P-Olivier Chapuis CNRS