Scientists see the light – and capture it

Photo: Thinkstock

Photo: Thinkstock

In summary: 
  • High levels of light absorption in ultra-thin materials have been possible only at cryogenic temperatures (-200C), making the technology inefficient.
  • Scientists at UTS have collaborated on a breakthrough that shows 99 per cent light absorption at room temperature, opening the door for innovation in solar energy and infra-red technology.

Researchers employing their own highly specific light show have pushed science a step closer to cheaper, more efficient innovations in solar energy, computing and infra-red technology.

The team has shown that materials as thin as a single micron – a human hair is at least 45 microns thick – can achieve 99 per cent light absorption. The key lies in etching the surface with grooves that cause the light to bounce and remain within the structure rather than pass straight through.

Associate Professor Christopher Poulton, from the UTS School of Mathematical and Physical Sciences, says the breakthrough is one that “others had not thought possible but our demonstration has proved the theory”.

Until now, high levels of light absorption in ultra-thin materials have been possible only at cryogenic temperatures (-200C), with the maximum level of light absorption at room temperature reaching just 7 per cent.

“The discovery opens the door to a range of applications, including imaging of objects on the nanoscale, to the creation of ultra-compact solar cells that can be integrated into computer chips to power the ‘internet of things’, says Associate Professor Poulton.

Used as infra-red detectors, these new nanostructures could also allow autonomous systems to “see” through fog and difficult weather conditions without bulky and expensive cooling apparatus, he says.

Associate Professor Poulton and UTS colleagues Dr Kokou Dossou and Emeritus Professor Lindsay Botten worked with collaborators to create a theoretical and numerical model that provided insight into the physical processes involved when light hits the ultra-thin material.

The resulting nanostructure design was then fabricated and measured by collaborators at the Australian National University (ANU).

Associate Professor Poulton says most theoretical and numerical tools ignore light absorption under the assumption it’s something you want to get rid of.

“But in this case we wanted as much light as possible to be captured by the material,” he says.

“The clever thing about this new model is not only that it is extremely efficient, but it also gives you a really good idea about what’s going on in the material.

“We were effectively able to look under the hood to see what was happening to the light when it hit the material, and try to coax the light to stay in the material for as long as possible. If you have the insight into the physical processes, you can then use that as a basis for a design.”

The technology offers affordable potential for nanophotonics laboratories such as the Microstructural Analysis Unit (MAU) at UTS, where light detection is an important part of research, but currently requires the use of very expensive equipment.

The UTS researchers worked in collaboration with the University of Sydney, the Australian National University (ANU) and the National Computational Infrastructure (NCI). The research was conducted with the Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS), with funding from the Australian Research Council.

Total absorption of visible light in ultrathin weakly-absorbing semiconductor gratings is published in the journal Optica.

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