"Sprinkled Nanocubes hold light tight", Nature News

NATURE News recently released the article "Sprinkled nanocubes hold light tight" by Katharine Sanderson discusiing how scattering silver nanocubes over a mettalic film may help harvest the sun's rays. Read the full article below;

05 December 2012




Trapped in a gap



Smith and his team took a different approach. They mounted a thin piece of gold on a piece of glass, and dipped it into two organic chemicals to build a uniform polymer layer just a few nanometres thick on top of the gold. They then made silver cubes about 74 nanometres wide, and scattered them on top of the polymer.



Different wavelengths



'It’s time consuming to make a very large structure' using lithography, agrees Min Qiu, who works on similar systems at the Royal Institute of Technology in Kista, Sweden. A square of etched light absorber 100 micrometres across takes up to an hour to prepare, he says, and a patch 1 millimetre across would take up to 100 times longer.



The method could help to make metamaterials much more practical, says Junpeng Guo, who works on nanophotonics at the University of Alabama in Huntsville. 'This brings the technology to ordinary people’s lives,' he says. For example, the nanocube absorber could be used to make solar-powered rooftop water heaters more efficient."

Nature doi:10.1038/nature.2012.11965


Moreau, A. et al. Nature 492, 86–89 (2012).

Efficient and tunable absorption is essential for a variety of applications, such as designing controlled-emissivity surfaces for thermophotovoltaic devices1, tailoring an infrared spectrum for controlled thermal dissipation2 and producing detector elements for imaging3. Metamaterials based on metallic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design4. So far, metamaterial absorbers in the infrared or visible range have been fabricated using lithographically patterned metallic structures2, 5, 6, 7, 8, 9, making them inherently difficult to produce over large areas and hence reducing their applicability. Here we demonstrate a simple method to create a metamaterial absorber by randomly adsorbing chemically synthesized silver nanocubes onto a nanoscale-thick polymer spacer layer on a gold film, making no effort to control the spatial arrangement of the cubes on the film. We show that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer). Each nanocube is the optical analogue of a grounded patch antenna, with a nearly identical local field structure that is modified by the plasmonic response of the metal’s dielectric function, and with an anomalously large absorption efficiency that can be partly attributed to an interferometric effect10. The absorptivity of large surface areas can be controlled using this method, at scales out of reach of lithographic approaches (such as electron-beam lithography) that are otherwise required to manipulate matter on the nanoscale.