Vaporized metals serve as inks

Scientists at the Center for Nanoscale Systems have found a way to coat objects with an extremely thin layer of semiconductor that shines in vivid colors from bright pink to deep blue. This coating could replace paint in certain circumstances since it does not add any significant amount of weight and does not alter the flexibility of the substrate.

Painting with electron beams and vaporized metals? What sounds like science fiction is actually real science coming out of Harvard’s Laboratory for Integrated Science and Engineering. Scientists at the Center for Nanoscale Systems have found a way to coat objects with an extremely thin layer of semiconductor that shines in vivid colors from bright pink to deep blue.

This coating could replace paint in certain circumstances since it does not add any significant amount of weight and does not alter the flexibility of the substrate. Because only tiny amounts of metal are used, the coating is most likely inexpensive if it is developed for large-scale applications.

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The technique is considered a real breakthrough. While the semiconductor is gray, the result is brightly colored because the technique exploits interference effects in the thin films, which is best-known from thin films of oil that shine in rainbow colors. Other than the oil film colors, however, the color of the coating can be controlled and remains stable.

The technique, developed by Ph.D. student Mikhail Kats and his adviser, physicist Federico Capasso, initially only worked with smooth surfaces like silicon and on rigid metal surfaces. With further development, however, the researchers say they have been able to apply the process to virtually any material, from fabrics to electronics.

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Kats tried the process on a piece of paper that he tore out of his notebook and it worked. The paper remained flexible. That finding, deceptively simple given the physics involved, now suggests that the ultrathin coatings could be applied to essentially any rough or flexible material, from wearable fabrics to stretchable electronics.

“This can be viewed as a way of coloring almost any object while using just a tiny amount of material,” Capasso says. The thin layers of vaporized metal are about 10 nanometers thick and are applied in layers. To demonstrate their technique, the scientists have used mostly germanium and gold but other metals are also viable.

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Adding an extra layer changes the color – the coating could go from indigo to crimson with just one extra layer of germanium. Because the metal coatings absorb a lot of light, reflecting only a narrow set of wavelengths, Capasso suggests that they could also be incorporated into optoelectronic devices like photodetectors and solar cells.