Tunable Materials Clear the Way for Advanced Optics

Estimated reading time: 3 minutes

Now you see it, now you don’t. In books and movies, wizards use magic spells to make the visible see-through.

In reality, materials with properties called phase transitions can pull off a similar trick, changing from clear to cloudy depending on the temperature or application of an electric field.

A multi-institutional team of researchers has developed a way to precisely engineer the temperatures at which vanadium dioxide — a material used in high-tech applications ranging from homes to satellites — will undergo phase transition. Their work, published today in the journal Nano Letters, could lead to new types of tunable materials for optics, camouflage and thermal regulation.

“Essentially, any optical component would be better if it were tunable,” says Mikhail Kats, senior author of the study and a University of Wisconsin–Madison professor of electrical and computer engineering.

Rather than relying on mechanical components to focus a camera lens or telescope eyepiece, a tunable material could change its innate optical properties on demand.

Scientists have known for more than 50 years that substances like vanadium dioxide can transition between opaque and transparent. However, these materials typically switch under only one particular set of conditions, limiting their applicability.

“In most phase-transition materials, the change occurs at conditions that are far from room temperature, and thus are difficult to incorporate into useful devices,” says Kats.

The researchers not only changed vanadium dioxide’s intrinsic shift point from 155 degrees Fahrenheit to below 70 degrees, they successfully tuned the transition for that material across a variety of specific temperatures — ranging from typical indoor comfort to medium-rare hamburger.

“This finding is going to open up new frontiers in photonic devices,” says collaborator Shriram Ramanathan, a professor of materials engineering at Purdue University.

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