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Plasmonics Simplify Printing and Imaging in Color and Infrared

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DURHAM, N.C., Dec. 15, 2016 — A new manufacturing technique promises to bring a simplified form of multispectral imaging into daily use. Using existing materials and production approaches that are scalable and inexpensive, Duke University researchers have found a way to print and image across a range of colors extending into the infrared.

Researchers tested a new technique for printing and imaging in both color and infrared with this image of a parrot. The inlay shows how a simple RGB color scheme was created by building rectangles of varying lengths for each of the colors, as well as individual nanocubes on top of a gold film that create the plasmonic element. Courtesy of Duke University.

Maiken Mikkelsen, the Nortel Networks assistant professor of Electrical and Computer Engineering and Physics at Duke University said it’s a challenge to create sensors that detect both the visible spectrum and the infrared.

"Traditionally you need different materials that absorb different wavelengths, and that gets very expensive," Mikkelsen said. "But with our technology, the detectors' responses are based on structural properties that we design rather than a material's natural properties. What's really exciting is that we can pair this with a photodetector scheme to combine imaging in both the visible spectrum and the infrared on a single chip."

The novel technology relies on plasmonics — the use of nanoscale physical phenomena to trap certain frequencies of light. With plasmonics, engineers create silver cubes just 100 nanometers wide and place them only a few nanometers above a thin gold foil. When incoming light hits a nanocube, it excites the silver's electrons and traps the light's energy — but only at a certain frequency.

The size of the silver nanocubes and their distance from the base layer of gold determines that frequency, while controlling the spacing between the nanoparticles allows tuning the strength of the absorption. By tailoring these spacings, researchers can make the system respond to any specific color they want, from visible to infrared.

A close-up of the colorful parrot picture printed on a thin gold wafer using the new nanocube-based technology. The colors appear off because of the underlying gold, as well as the difficulties that typical cameras have of imaging the new technology. Courtesy of Maiken Mikkelsen, Duke University.

Current imaging technology is bulky and expensive. That’s where the Duke University researchers and engineers come into play. They were tasked to create a device that was not only useful, but scalable and inexpensive.

Jon Stewart, researcher and graduate student, said, "We've come up with a fabrication scheme that is scalable, doesn't need a clean room and avoids using million-dollar machines, all while achieving higher frequency sensitivities. It has allowed us to do things in the field that haven't been done before."

To build a detector, Mikkelsen and Stewart used a process of light etching and adhesives to pattern the nanocubes into pixels containing different sizes of silver nanocubes. Each nanocube is sensitive to a specific wavelength of light. When incoming light strikes the array, each area responds differently depending on the wavelength of light it is sensitive to. By teasing out how each part of the array responds, a computer can reconstruct what color the original light was.

The technique can be used for printing as well.

"The exciting part is being able to print in both visible and infrared on the same substrate," said Mikkelsen. "You could imagine printing an image with a hidden portion in the infrared, or even covering an entire object to tailor its spectral response."

Instead of creating pixels with six sections tuned to respond to specific colors, they created pixels with three bars that reflect three colors: blue, green and red. By controlling the relative lengths of each bar, they can dictate what combination of colors the pixel reflects.

Plasmonics help make the end product scalable, more affordable and the color scheme will not fade over time. Researchers say images can be reproduced to create color schemes in the infrared.

The entire study appeared in the journal Advanced Materials (DOI: 10.1002/adma.201602971).
Dec 2016
The engraving of a surface by acid, acid fumes or a tool; a process extensively used in the manufacture of reticles.
camerasDuke UniversityResearch & TechnologyeducationimagingSensors & DetectorsMaiken MikkelsenJon StewartetchingTech Pulse

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