Low-cost method creates any colour filter

Northwestern University researchers have created a new technique that can transform silver into any colour on the visible spectrum. 

Their method is claimed to be a fast, low-cost alternative to colour filters currently used in electronic displays and monitors.

‘Our technique doesn’t require expensive nanofabrication techniques or a lot of materials,’ said Koray Aydin, assistant professor of electrical engineering and computer science at Northwestern’s McCormick School of Engineering. ‘And it can be completed in a half hour or so.’

Aydin and his team created a three-layer design, where glass is wedged two thin layers of silver film. The silver layers are thin enough to allow optical light to pass through, which then transmits a certain colour through the glass and reflects the rest of the visible spectrum. By changing the thickness of the glass, Aydin was able to filter and produce different colours.

‘Controlling the thickness of the glass controls the colour,’ Aydin said in a statement. ‘This way, we can create any colour desired.’

Supported by the US Air Force Office of Scientific Research, the research was published online in ACS Photonics on January 28, 2015. PhD student Zhongyang Li and postdoctoral researcher Serkan Butun, who are both in Aydin’s lab, were co-authors of the paper.

By making the bottom silver layer even thicker, Aydin found that the structure also acts as a colour absorber because it traps light between the two metal layers.

The team demonstrated a narrow bandwidth super absorber with 97 per cent maximum absorption, which could have potential applications for optoelectric devices with controlled bandwidth, such as narrow-band photodetectors and light-emitting devices.

The performance of Aydin’s structure is said to be comparable to that of nanostructure-based devices but bypasses the complications of nanotechnology.

‘People in the nanophotonics community are dealing with nanostructures, making nanoparticles, and using lithography or chemistry techniques,’ he said. ‘That can be really challenging. We’re combatting that difficulty with a simple design.’

Aydin is also developing a similar structure out of aluminium and glass to filter or absorb ultraviolet spectrum. By controlling the thickness of the materials, he plans to design devices for other wavelengths of light.