Sprinkled silver nanocubes enhance light absorption

Just as salt sprinkled over a piece of meat enhances its flavor, tiny silver cubes sprinkled at random on a polymer-coated gold surface enhance the material’s ability to “perfectly” absorb light of a given wavelength.

A simple chemical synthesis method from Duke University uses a dusting of silver nanocubes to modify the absorptive properties of a metallic surface, yielding a simple and tunable way to create large-area “perfect” absorbers. When separated from the underlying metal by a very thin insulating layer, the cubes act as tiny antennas that cancel out the reflectance of the metal surface. The cost-effective absorbers show potential for applications ranging from energy-harvesting devices to sensors.

(a) Scanning electron microscopy images of silver nanocubes as fabricated, and (b) after deposition on the gold film with remarkably uniform spacing (c). Dark-field images of the nanocubes randomly adsorbed on a nanoscale polymer spacer on a gold film, showing the light scattered by the individual nanocubes.

Manufacturing ideal perfect absorbers of infrared or visible light using lithography is expensive and does not scale well for applications requiring large surface areas.

“Our new approach is more of a bottom-up process,” said Cristian Ciracì, research scientist at the university’s Pratt School of Engineering. “It may allow us to create devices – such as efficient solar panels – that cover much larger areas. In our experiments, we demonstrated an extraordinarily simple method to achieve this.”

The new material is composed of a thin layer of gold film coated with a nanothin layer of an insulator and dusted with millions of self-assembled silver nanocubes.

Developed at Duke University, metallic nanocubes sprinkled at random on a polymer-coated gold surface provide a simple way to create a material that “perfectly” absorbs light of a given wavelength.

“The nanocubes are literally scattered on the gold film, and we can control the properties of the material by varying the geometry of the construct,” Ciracì said. “The absorptivity of large surface areas can now be controlled using this method at scales out of reach of lithography.”

By combining different components of the metamaterial elements into a single composite, more complicated reflectance spectra could be engineered, achieving a “level of control needed in more exotic applications, such as dynamic inks,” Ciracì said.

The research, published in Nature (doi: 10.1038/nature11615), was conducted in the lab of senior researcher David R. Smith.