Functional Coatings

Context

The performance of certain optical devices strongly depends on their ability to avoid and/or eliminate stray light. Stray light reduction is an important issue, particularly for space-borne astronomical instruments, where it can notably affect both geometric and radiometric image quality. To prevent light originating from outside the desired field of view of the instrument, baffles are typically arranged around the optical axis. As an alternative, a number of companies have developed black coatings to cover all mechanical surfaces close to the optical beam.

Overview

The Luxembourg Institute of Science and Technology (LIST) has developed a new type of coatings made of a ceramic composite material .
Also referred to as an “advanced cermet”, this ceramic composite corresponds to a carbon-pigmented cermet. It comprises a ceramic matrix with embedded carbone-metal complex nanoparticles.

Benefits

The advanced cermet coating provides a number of benefits:

• good absorbancy
• can be tuned to meet the requirements of a superblack coating
• Lambertian reflection behavior can be achieved.
• suitable for heat radiation (emittance):
• compatible with different kinds of substrates including those produced by additive manufacturing.
• surface density (mass per unit area) compatible with most applications
• due to the chemical vapor deposition (CVD) fabrication process, outgassing is not a major issue, making it advantageous for space and high-vacuum applications
• can withstand intense radiation, such as direct sun illumination, without alteration
• the chemical inertness of the advanced cermet is an advantage (e.g. low sensitivity to atomic oxygen) for many applications

Potential Applications

Aside from optical instruments, this advanced cermet black coating can be used for:

• passive thermal management, requiring high emissivity
• solar energy harvesting, such as solar water heating, concentrated solar power generation, etc.
• infrared sensing, such as MEMS IR sensors
• thermal actuation, such as MEMS thermal actuators)