The 'super black' coating increases the sensitivity of optical devices

In 2011, NASA announced a study of a super-black super-black coating to increase sensitivity for optical sensors and devices used in space.

However, at that time the coating could only be made on flat surfaces. This limit has now been overcome by optical engineer John Hagopian and his team from NASA's Goddard space aviation center. By a technique called Atom layer deposition , they were able to create a layer of heterogeneous carbon nanotubes on many different shaped surfaces. Thereby, the team believes that the technique will expand the technological potential when carbon nanotubes can be "grown" on three-dimensional optical components.

Before talking about ALD technology, we need to understand what is super-black material (super-black )? On the scientific side, the name super-black is reserved for materials that are nearly non-reflective. Hagopian and his team sought to refine so that the material absorbs an average of more than 99% of infrared, visible light, ultraviolet light and far infrared light when illuminated. To do this, they use carbon nanotubes. They are planted like a forest on the surface of materials used on spacecraft. The micro gap between nanotubes will catch light, while carbon will absorb photons. Thereby, no light is reflected from the material as its super black name. Ultra-black materials contain a coating made up of multi-walled carbon nanotubes, 10,000 times thinner than a human hair.

Regarding the Atomic Layer Deposition (ALD) technique, engineers deposited a basic layer of iron oxide catalyst, acting as a substrate to grow nanotubes in a reaction chamber. Conventional ALD reactions use 2 chemicals and each chemical will in turn react to the surface in a certain time. Inside the reaction chamber, many of the following gases will be pumped in to deposit a thin sheet of atomic film on a three-dimensional part. The researchers then put it in a furnace, heating it up to about 750 degrees Celsius and simultaneously heating it into carbon-containing gas.

The team combined ALD technology with the process of growing nanotubes to create a heterogeneous catalyst. Hagopian explains that conventional techniques can only "create a surface coating similar to the way you use a paint bottle to spray at a fixed angle". Such techniques could make the catalyst surface used to grow nanotubes become rough when applied to three-dimensional parts. Meanwhile, ALD technology allows controlling the thinness and composition of atomic film.

Vivek Dwivedi - co-author of the study collaborated with the University of Maryland at College Park to improve ALD reaction technology to optimize space applications. Hagopian, meanwhile, relied on the services of Melbourne's nano-fabrication center (MCN) and through the Science Exchange online trading portal where scientific and laboratory service providers can collaborate to determine the reach Look at ALD technology.

Lachlan Hyde is working with 1 of 2 ALD systems at MCN

The team at MCN led by Lachlan Hyde - an expert in the field of atomic layer deposition proposed a precise chemical formula for the aforementioned thin film of catalytic films. The formula includes the necessary gases with appropriate temperature and pressure inside the reactor.

Hyde and his colleagues succeeded in depositing the catalytic film on various parts of NASA's optical device, typically a very sophisticated disk component (occulting disk) that was used in a very sophisticated way. Telescope to observe planets far away from other stars. They hope to be able to apply Hyde's technique to many parts with Dwivedi's customized reaction technology.

In addition, Hagopian's team has also successfully planted carbon nanotubes on three-dimensional specimens and they are seeking to bring super-black properties to other optical technologies.