Graphene ‘smart surfaces’ now tunable for visible spectrum – iiTECHNOLOGY

Researchers at the National Graphene Institute of the University of Manchester have created optical devices with uniqueness, covering the entire electromagnetic spectrum, including visible light.

A paper published in Nature Photonics outlines the next generation of display devices for this ‘smart surface’ technology, from the dynamic thermal blanket of satellites and multi-spectral adaptive camouflages.

The tunability of the devices is achieved by a process called electro-intercalation, in which case lithium ions are added between sheets of multilayer graphene (MLG), offering control over electrical, thermal and magnetic properties.

The MLG device is laminated and vacuum-sealed in a low-density polyethylene pouch with more than 90% optical transparency from visible light to microwave radiation.

Charge turns gray to gold

The electrical and optical properties of MLG change dramatically during charge (intercalation) or discharge (de-intercalation). The discharged devices appear dark brown due to the high absorptivity (> 80%) of the top graphene layer in the visual regime.

When the device is fully charged (at ~ 3.8V), the graphene layer appears in gold color. The achievable color space can be enriched to include the range from red to blue using optical effects such as thin-film film.

The study’s lead author, Professor Coskun Kokabas, said: “We have merged Graphene and battery technology to create a new class of multispectral optical devices with previously unacceptable color-changing capabilities.

“The successful demonstration of graphene-based smart optical surfaces enables potential advances in many scientific and engineering fields.”

For example, a dynamic thermal blanket can selectively reflect visible or infrared light and allow a satellite to reflect radiation facing toward the sun, while emitting radiation from its shaded face. Similarly, when in the shadow of the Earth, it can see the blanket satellite cooling the deep space [figure below]. These actions control the internal temperature more effectively than static thermal coating.

Previous studies have investigated devices at specific wavelength ranges of microwaves, terahertz, infrared and visible, using single and multilayer graphene. But overcoming established difficulties in the integration of optical devices with electrical cells requires innovation in the device’s structure, which was a challenge to extend coverage to visible light while maintaining optical activity at longer wavelengths.

“Here we used a Graphene-based lithium-ion battery as an optical device,” he said. “By controlling the electron density of graphene, we are now able to control light from the microwave wavelength seen on a single device.”

Nobel Prize winner Professor Sir Kostya Novoselov was a co-author on the paper and said: “Some of the layers provide unprecedented control over their optical properties through graphene charging. Such devices can find their applications in many areas: adaptive From Physics to Thermal Management. ”

The device is sealed in a low density polyethylene pouch and vacuumed, with 90% optical transparency ranging from visible light to microwave radiation.

The electrical and optical properties of MLG change dramatically between charge, or intercalation, and discharge, or de-intercalation. The discharge device appears dark brown due to more than 80% high absorption of the top graphene layer in the visible regime. When the device is fully charged at around 3.8 V, the graphene layer appears gold.

The achievable color space can be enriched to include the range from red to blue using optical effects such as thin-film film.

“We designed a new class of multispectral optical devices with color-changing capability prior to the merger of graphene and battery technology,” said Coskun Kokabas, the study’s lead author and a professor at the University of Manchester. “The successful demonstration of graphene-based smart optical surfaces enables potential advances in many scientific and engineering fields.”

For example, in the case of thermal blankets, the device can be tuned by reflecting the satellite’s temperature selectively by visible or infrared light, or by insulating the satellite with deep-space cooling.

Previous studies on single and multilayer graphene have focused on specific wavelength ranges of microwaves, terahertz, infrared, and visual spectra. Overcoming the difficulties in the integration of optical devices with electrochemical cells, extending the coverage to visible light while maintaining optical activity at longer wavelengths in the device structure.

“Here we used a Graphene-based lithium-ion battery as an optical device,” Kokbas said. “By controlling the electron density of graphene, we are now able to control the light reflected at the same device with microwave wavelengths.”

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