High tEmperature therMal Emissivity of Refractory mEtamaterials – HEMERE

Thermal emission is one of the main mechanisms of heat transfer, which will allow a hot object to cool down. The radiation emitted has a spectrum described by Planck's law, and is mainly in the infrared. This radiation can be detected as soon as it occurs in the transparency bands of the atmosphere (3-5 µm and 8-12 µm), which is one of the original motivations for the development of infrared detection in a defence framework. Furthermore, Stefan-Boltzmann's law stipulates that the evolution of exitance is at the fourth power of temperature. In a defence context, this means that hot objects (reactors, missiles) will have a very high emission that will make them detectable by optronic systems at a long distance.
For civilian applications involving light emission, such as thermophotovoltaics, it is essential to work at high temperatures to obtain reasonable yields.
The field of optical metamaterials has grown considerably over the last fifteen years and it has been demonstrated that it is possible to use them to modify the emissivity of a surface at will. However, materials classically used in nanophotonics have melting points that are generally in the range [1000-1500 K] and the maximum temperature is strongly limited by interdiffusions between materials.
In this context, still in search of high-performance solutions, the Héméré project proposes to develop metamaterials based on ultra-refractory ceramic materials operating at high temperature, to control the infrared signature of hot objects. The project will combine the skills and knowledge of nanophotonics and refractory ceramic materials. Nanophotonics can modify the emissivity of a surface using optical nano-antennas, but has been demonstrated at low temperatures, and the materials used have melting points generally below 1000 K. Ultra-refractory ceramics have higher melting temperatures, but there are several technical issues to overcome in order to combine these two scientific disciplines. Firstly, there is a need to increase the knowledge of the electromagnetic behaviour of ultra refractory ceramic materials as a function of temperature. Secondly, the electromagnetic design of metamaterials must be rethought by integrating these new materials. Finally, the ability to structure ceramics to make optically resonant nanostructures is a final challenge.
In this project, we are aiming for two categories of objectives around two families of materials (ZrC and Y2O3-stabilised ZrO2).

A - Knowledge of ceramic materials
These objectives are methodological and are intended to develop:
i) Refractory targets and substrates with controlled properties
ii) Thin layers of ceramic materials
iii) Nanostructuring techniques for these materials
iv) Thermo-optical models

B - High temperature ceramic metamaterials

We aim to develop 3 families of transmitters based on optical resonances:
i) Lambda/4 optical cavity
ii) Nano Fabry-Pérot coupled
iii) Multi-MIM metamaterial

The criteria for the success of the HEMERE project are:
1. Thin film deposition processes
2. Temperature-dependent infrared optical models of ceramic materials
3. Processes for nano-structuring of ceramic materials.
4. Design of conventional nano antennae integrating ceramic materials.
5. Experimental demonstration at high temperature of a fine spectral IR emitting device (T > 1000 K).
6. Experimental demonstration at high temperature of a wide spectral emitting device (T > 1000 K).

The development of these metamaterials opens up important perspectives towards applications ranging from stealth, to the development of infrared sources or thermophotovoltaics.