A new coating exploits interference effects in thin films, creating a range of vivid colors.

The new technique coats a metallic object with an extremely thin layer of semiconductor, just a few nanometers thick. Although the semiconductor is a steely gray color, the object ends up shining in vibrant hues.

The ultrathin coatings could be applied to essentially any rough or flexible material, from wearable fabrics to stretchable electronics.

A machine called an electron-beam evaporator applies the gold and germanium coating. The paper sample is sealed inside the machine's chamber, and a pump sucks out the air until the pressure drops to a staggering 10-6 Torr (a billionth of an atmosphere). A stream of electrons strikes a piece of gold held in a carbon crucible, and the metal vaporizes, traveling upward through the vacuum until it hits the paper. Repeating the process, a second layer is added. A little more or a little less germanium makes the difference between indigo and crimson.

"This is a way of coloring something with a very thin layer of material, said Mikhail Kats, postdoctoral researcher at the Harvard School of Engineering and Applied Sciences, "so in principle, if it's a metal to begin with, you can just use 10 nanometers to color it, and if it's not, you can deposit a metal that's 30 nm thick and then another 10 nm. That's a lot thinner than a conventional paint coating that might be between a micron and 10 microns thick.”


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