Thin film coatings can be applied to magnesium alloys for aerospace and optical applications. Sometimes you need complete black to see clearly. For astronomy and precision optics, black ink devices can improve images and increase performance by reducing stray light. For the most advanced telescopes and optical systems, every detail matters, so their manufacturers look for the blackest colors to cover them.

INSIDE Journal of Vacuum Science and Technology A Researchers from AIP Publishing, Shanghai University of Science and Technology and the Chinese Academy of Sciences have developed an ultra-black thin-film coating for magnesium alloys used in aerospace. Their coating absorbs 99.3% of light and is durable enough to survive harsh environments. For telescopes operating in vacuum or optical equipment in extreme conditions, existing coatings are often inadequate.

Improving black coatings

“Current black coatings, such as vertically aligned carbon nanotubes or black silicon, are limited by brittleness,” said author Yunzheng Cao. “Many other coating methods are also difficult to coat inside the tube or other complex structures. This is important for their applications in optical devices, as they often have significant curvature or complex shapes.”

To solve these problems, researchers turned to atomic layer deposition (ALD). With this vacuum-based fabrication technology, the target is placed in a vacuum chamber and repeatedly exposed to certain types of gases that adhere to the surface of the object in thin layers.

“A big advantage of the ALD method is its excellent gradual coating capability, which means we can achieve uniform film coating on very complex surfaces such as cylinders, columns and trenches,” Cao said.

The team used alternating layers of aluminum-doped titanium carbide (TiAlC) and silicon nitride (SiO2) to make the ultra-black coating. These two materials work together to prevent almost all of the light from reflecting off the coated surface.

“TiAlC served as an absorbing layer, and SiO2 was used to form an anti-reflective structure,” Cao said. “As a result, almost all of the incident light enters the multilayer film, providing efficient light absorption.”

Future Programs and Improvements

In tests, the team found an average absorbance of 99.3% across a wide range of light wavelengths, from 400 nanometers of violet light to 1,000 nanometers of near-infrared. Using a special barrier layer, they even coated magnesium alloys, which are frequently used in the aerospace industry but are prone to corrosion.

“What’s more, the film exhibits excellent stability under adverse conditions and is strong enough to withstand friction, heat, moisture and extreme temperature changes,” Cao said. said.

The authors hope that their coating will be used to improve the performance of space telescopes and optical equipment operating in the harshest conditions, and they are working to further improve its performance.

“Now that the film can absorb more than 99.3% of incoming visible light, we hope to further expand the light absorption range to include the ultraviolet and infrared regions,” Cao said.