U-M Nanoparticle Research Boosts LED, Invisibility Technology

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Researchers at the University of Michigan have developed a new technique that peppers metallic nanoparticles into semi-conductors and can improve the quality of LED lighting by 50 percent and could pave the way for invisibility cloaking devices. The technique is the first to inexpensively grow metal nanoparticles both on and below the surface of semi-conductors and could allow manufacturers cut further costs in the future.

The metal nanoparticles can increase the efficiency of LEDs in several ways, including acting as tiny antennas that alter and redirect the electricity running through the semi-conductor, turning more of it into light. They can also reflect light out of the device, preventing it from being trapped inside and wasted.

“This is a seamless addition to the manufacturing process, and that’s what makes it so exciting,” says Rachel Goldman, U-M professor of materials science and engineering, and physics. “The ability to make 3-D structures with these nanoparticles throughout is going to open a lot of possibilities.”

While the idea of adding nanoparticles to increase LED capabilities is not new, Goldman’s team discovered a similar way that integrates easily with the molecular beam epitaxy process used to make semiconductors. Molecular beam epitaxy sprays multiple layers of metallic elements onto a wafer. This creates exactly the right conductive properties for a given purpose.

“If you carefully tailor the size and spacing of nanoparticles and how deeply they’re embedded, you can find a sweet spot that enhances light emissions,” adds Myungkoo Kang, a former graduate student in Goldman’s lab and first author on the study. “This process gives us a much simpler and less expensive way to do that.”

Because the technique allows precise control over the nanoparticle distribution, the researchers say it may one day be useful for cloaks that render objects partially invisible by inducing a phenomenon known as “reverse refraction.” The process uses bent light waves backwards in a way that doesn’t occur naturally, potentially driving them away from the human eye. Researchers believe that carefully sizing and spacing an array of nanoparticles may allow them to induce and control reverse refraction in specific wavelengths of light.

“For invisibility cloaking, we need to both transmit and manipulate light in very precise ways, and that’s very difficult today,” says Goldman. “We believe that this process could give us the level of control we need to make it work.”

The research was supported by the National Science Foundation through the Materials Research Science and Engineering Center at U-M.

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