Creating nanoscale rainbows

King’s College London scientists have discovered how to separate colours – “creating rainbows” using nanoscale structures on a metal surface. The findings may have applications in improved solar cells, television screens and photodetectors. Researchers from the Biophysics and Nanotechnology Group at KCL were able to trap light of different colours at different positions, using specially designed nanostructures. If the geometry of the nanostructure was optimised, a trapped rainbow could be created on a gold film with a dimension about 100 times smaller than the width of a human hair.

The research was led by Professor Anatoly Zayats, who said: “Nanostructures of various kinds are being considered for solar cell applications to boost light absorption efficiency. Our results mean that we do not need to keep solar cells illuminated at a fixed angle without compromising the efficiency of light coupling in a wide range of wavelengths. When used in reverse for screens and displays, this will lead to wider viewing angles for all possible colours.”

The researchers were able to control where the rainbow colours would be in the nanostructures. Unlike natural rainbows where red always appears on the outer side and blue on the inner side, by controlling the nanostructure’s parameters, the scientists could separate colours on different sides of the nanostructures.

Dr Jean-Sebastien Bouillard who co-authored the paper said: “The effects demonstrated here will be important to provide ‘colour’ sensitivity in infrared imaging systems for security and product control. It will also enable the construction of microscale spectrometers for sensing applications.”

The research is published in Nature’s Scientific Reports.