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Creating a super thin light absorber

If you look at the sun through a sheet of paper, you can see the light shining through. Now imagine you take that sheet of paper and shave it into 720 separate layers, each 90 nanometres thick. Holding one of those up to the sun will do so little to block the light you may as well not be holding anything at all.

Yet a 90-nanometre thick material that blocks 80% of incoming light from all angles and all wavelengths is exactly what Dr Bjorn Sturmberg and colleagues from The Australian National University, Swinburne University and the University of Sydney have produced. The remarkable thinness of this material hides the complexity going on inside it. Zoom in and you’ll see dozens of layers of graphene oxide – single-atom thick sheets of carbon and oxygen – separated by layers of an electrical insulator known as a dielectric.

Carved into the graphene-dielectric layers are deep grooves that capture and channel incoming light further into the material. The particular, laser-carved arrangement of the layers and grooves is what makes the material such a good absorber of incoming light. Figuring out the ideal spacing, width, depth and shape for the grooves is a job for a supercomputer.

Schematic of the material showing rows of alternating layers of graphene oxide and dielectric absorbing incoming light.

Unpolarised light hits the material from a wide range of angles. The material couples the light sideways into waveguide modes that propagate along the surface, leading to large absorption in the metamaterial. The image inset shows the structure of the metamaterial.

Other materials exist that absorb very specific wavelengths of light to a high degree, but nothing this thin that absorbs this much solar light from infrared to ultraviolet. Finding the best arrangement of grooves and layers required Dr Sturmberg to simulate incoming light coming in from 25 different angles and at dozens of different wavelengths.

He says, “There’s no way for us to do these kinds of calculations without a supercomputer. The grooves and the layers really do need to be arranged properly if the material is going to absorb the way it should.

“Ultra-thin materials like this open up new possibilities for creating light sensitive devices and technologies. The combination of theoretical and experimental expertise, and the computing infrastructure that plays a key role, are all required for making advances like this.”

New materials open up plentiful possibilities in all aspects of future technologies, manufacturing, industry and society. Materials like this ultra-thin sheet of light-absorbing layers might one day appear in our everyday objects and tools. Designing molecular structures at the atomic level lets us customise exactly the behaviour we need, and computational simulations let us push forward the boundaries of what is possible.

You can read the full research paper in the journal Nature Photonics.

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