Researchers at NASA’s Jet Propulsion Laboratory have developed a robust alternative to the blackbody targets typically used to calibrate optical/thermal imaging systems. Typically, blackbody targets are formed via additive processes (e.g., high-emissivity paint, carbon nano tubes). JPL’s innovation utilizes highly doped black silicon formed via inductively coupled plasma (ICP) etching at cryogenic temperatures (i.e., a subtractive process), providing an ultrahigh-emissivity surface.
This rapid and cost-effective technique yields a uniform etched surface with extremely low reflectivity of visible and infrared (IR) radiation and near-zero transmission, resulting in a high-emissivity surface. Specifically, total emissivity is greater than 99.5 percent for wavelengths between 400 nm and 2,500 nm. This high level of light absorption is possible thanks to needle-like nanotips etched into a highly absorbing doped silicon substrate. This dense “forest” is completely inorganic. Furthermore, because it is formed by a subtractive process, it does not flake off.
Blackbodies produced with this technique are more robust than those produced with deposition techniques, which are prone to adhesion failure and are unable to be cleaned when contaminated. Because this method forms the needles directly from the base rather than coating or mechanically attaching them, the textured surface withstands vibration and thermal cycling without flaking. It even remains stable in liquid environments, enabling it to withstand liquid processing as well as to be cleaned with various solvents to remove contaminants without damage to the needles. Organic contaminants can also be removed using an oxygen plasma, which is not possible with organic paints or carbon nanotubes.