A Never Before Seen Optical Trick Creates Ultra-Secure Cash

Imagine a bill covered with microscopic holes that make it glow slightly in the light. It's tech borrowed from a butterfly, and it may soon be foiling counterfeiters around the world.

If all goes as planned, the world's supply of cash will soon be secured with a nano-scale optical defense that is as secure as it is visually impressive. Using arrays of holes no bigger than a virus, scientists at Toronto-based Nanotech Security have created an atoms-thick display that can be read by humans or machines and that shines with the brightness of a typical LED despite using nothing but reflected light.The technology was inspired by the Blue Morpho butterfly, whose brilliant blue coloration comes not from pigment but the way that tiny holes in its scales reflect light. But the tech, called Nano-Optic Technology for Enhanced Security (NOtES), is different from the Morpho butterfly's wings, and pretty much all other bio-inspired reflective optical technologies, in that it is both extraordinarily thin and functions even in dim light.NOtES exploits an obscure area of physics to accomplish its bright and sharp display, known as plasmonics. Light waves interact with the array of nano-scale holes on a NOtES display--which are typically 100-200 nanometers in diameter--in a way that creates what are called "surface plasmons." In the words of the company, this means light "[collects] on the films surface and creates higher than expected optical outputs by creating an electromagnetic field, called surface plasmonic resonance."[twistage d64c98a213330]

The inventors of the NOtES technology, Clint Landrock and Bozena Kaminska at Simon Fraser University, stumbled into the potential security applications of plasmonics while trying to find a way to increase the efficiency of solar cells."We came across idea of using something called plasmonics, where you have geometries smaller than wavelength of light that can resonate the light," says Landrock, who is now at Nanotech Security.And security, surprisingly, is one of the major applications of these light-amplifying tiny holes. Compared with things like holograms, NOtES has a number of advantages. For one, the technology consists of nothing more than an array of tiny holes, which means it can literally be stamped into anything--even currency.Using a physical stamp, Nanotech Security can imprint its minuscule holes into bills even after they've been printed, instantly transforming the area of the bill that's been stamped into something that resembles a tiny LED. It's just like the old-school printing process that yields embossed invitations and business cards, except that instead of pressing "save the date" into cardstock, a nickel stamp covered with nano-scale bumps presses corresponding holes into a material.The results aren't just visually crisp, they're also good for keeping things top secret. That's because the NOtES process yields a surface that reflects light from ultraviolet all the way into the far infrared, or wavelengths outside what we can see, but which can easily be read by machines. This opens up the potential for NOtES to be used to create watermarks on bills that counterfeiters can't even see.It also means that NOtES could be used to encode data at densities in excess of what can be achieved even on a Blu-ray disc. Landrock estimates that he could use the process to encode information up to "gigabytes per centimeter."Of course, it's not easy to rewrite arrays of thousands of nanoscopic holes, so replacing physical storage media isn't high on the list of priorities for Nanotech Security. The difficulty of reproducing or altering these holes is, though, precisely what makes the technology such a potentially unconquerable anti-counterfeiting measure.Currently, creating a NOtES display begins in a class-1 cleanroom, the same kind inhabited by technicians in shiny bunny suits rolling out high-performance microchips. In this cleanroom, a master stamp is created in quartz. Nanotech Security is cagey about the exact process, but early prototypes were created by using an electron microscope and an ion beam to literally burn off material, atoms at a time. Once this quartz master, called a shim, has been created, nickel copies of it can be made by growing the metal directly on top of the original shim.This technology could even be used to imprint something resembling tiny holograms directly onto pills, allowing a kind of anti-counterfeiting measure to be attached to individual pharmaceuticals. The process shouldn't require FDA approval because it's literally just tiny indentations on the surface of each pill.There have been many other technologies that ape the properties of butterfly wings--everything from Qaulcomm's Mirasol e-reader display technology to better LEDs--but all of them rely on many layers of different materials to control how light is reflected back to the user. Secure Nanotechnology's NOtES technology is the only one that works on ultra-thin substrates, as little as 100 nanometers thick, and doesn't require an elaborate manufacturing process to lay down multiple substrates. Thanks to the Blue Morpho butterfly, the degree to which nature continues to embarrass our engineers with its profligate creativity is the inspiration at the root of this new technology.

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