Future Chips Constellation

Team Creates World’s First
Ideal Anti-Reflection Coating

A team of Rensselaer researchers has created the world’s first material that reflects virtually no light. The research could open the door to much brighter LEDs, more efficient solar cells, and a new class of “smart” light sources that adjust to specific environments, among many other potential applications.

Most surfaces reflect some light — from a puddle of water all the way to a mirror. The new material has almost the same refractive index as air, making it an ideal building block for anti-reflection coatings. It sets a world record by decreasing the reflectivity compared to conventional anti-reflection coatings by an order of magnitude.

A fundamental property called the refractive index governs the amount of light a material reflects, as well as other optical properties such as diffraction, refraction, and the speed of light inside the material. “The refractive index is the most fundamental quantity in optics and photonics,” says E. Fred Schubert, the Wellfleet Senior Constellation Professor of the Future Chips Constellation at Rensselaer and senior author of the paper.

Schubert and his team have created a material with a refractive index of 1.05, which is extremely close to the refractive index of air and the lowest ever reported.

Using a technique called oblique angle deposition, the researchers deposited silica nanorods at an angle of precisely 45 degrees on top of a thin film of aluminum nitride, which is a semiconducting material used in advanced light-emitting diodes (LEDs).

The new optical coating could find use in just about any application where light travels into or out of a material, and the development could also advance fundamental science.

A material that reflects no light is known as an ideal “black body.” No such material has been available to scientists, until now. Researchers could use an ideal black body to shed light on quantum mechanics, the much-touted theory from physics that explains the inherent “weirdness” of the atomic realm.

Several other Rensselaer researchers also were involved with the project: Professors Shawn-Yu Lin and Jong Kyu Kim; and graduate students J.-Q. Xi, Martin F. Schubert, and Minfeng Chen.