By Josh Perry, Editor
[email protected]

Researchers from several academic institutions are using the facilities at the Lawrence Berkeley National Laboratory (Berkeley, Calif.) to study thermal radiation at the micro- and nanoscale to see if there is a better way of controlling it.

Researchers are looking for ways to deviate from Planck’s Law at the nanoscale.
(Advanced Thermal Solutions, Inc.)

According to a report from the Berkeley Lab Energy Technologies Area, researchers are trying to find a deviation to Planck’s Law, which states that electromagnetic radiation from heat bodies is distributed over a wide range of wavelengths and wide range of angles.

The law forms the basis of quantum theory leaves room for doubt at the nanoscale, with the note that energy distribution would deviate from the law when the emitting object was smaller than the thermal wavelength (around 10 micrometers).

“The researchers set out to determine the deviation from Planck’s Law in order to understand this impact on technologies based on nano- and micro-structured geometries,” the article explained. “Imagine a thermal storage material that converts electricity to heat and then radiates it to a photovoltaic cell to get the electricity back when desired. The radiative emitter from the thermal storage could be made from nanostructures to maximize the performance.”

Researchers modeled thermal radiation from nanoribbons of silica glass using supercomputers from the National Energy Research Scientific Computing Center (NERSC).

The research was recently published in Nature Communications. The abstract read:

“Coherent thermal emission deviates from the Planckian blackbody emission with a narrow spectrum and strong directionality. While far-field thermal emission from polaritonic resonance has shown the deviation through modelling and optical characterizations, an approach to achieve and directly measure dominant coherent thermal emission has not materialised.

“By exploiting the large disparity in the skin depth and wavelength of surface phonon polaritons, we design anisotropic SiO₂ nanoribbons to enable independent control of the incoherent and coherent behaviours, which exhibit over 8.5-fold enhancement in the emissivity compared with the thin-film limit. Importantly, this enhancement is attributed to the coherent polaritonic resonant effect, hence, was found to be stronger at lower temperature.

“A thermometry platform is devised to extract, for the first time, the thermal emissivity from such dielectric nanoemitters with nanowatt-level emitting power. The result provides new insight into the realisation of spatial and spectral distribution control for far-field thermal emission.”