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Traps Written for Light with Tiny Ink Droplets Developed

24 October 2017

A microscopic ‘pen’ that can write structures small enough to trap and harness light using a commercially available printing technique could be used for sensing biotechnology, lasers and studying the interaction between light and matter.

This printing based approach was developed by researchers at the University of Cambridge and the Hitachi Cambridge Laboratory. The method combines high-resolution inkjet printing with nanophotonics, the study of the harnessing of light on the scale of a billionth of a meter. This is the first time that this combination has been successfully demonstrated.

Light trapped by a tiny droplet on a photonic crystal surface. The droplet has been printed by a super high-resolution inkjet printer. (EurekaAlert)Light trapped by a tiny droplet on a photonic crystal surface. The droplet has been printed by a super high-resolution inkjet printer. (EurekaAlert)

Over the last ten years, inkjet printing has advanced to the point where it can be used to print very small devices using a range of printable materials, including living cells as the ‘ink’. This approach is simple and low-cost and is widely used in electronics and biotechnology.

"Most inkjet printers push the ink through the nozzle by heating or applying pressure, producing ink droplets about the size of the diameter of a human hair," said the paper's co-first author Dr. Vincenzo Pecunia, a former PhD student and postdoctoral researcher, and now visiting researcher, at the University's Cavendish Laboratory.

Pecunia’s research focuses on printable optoelectronic materials for a range of applications and his group obtained a printer based on electrohydrodynamic jets. This means a printer is capable of ultra-high resolution printing. This printer applies a voltage to the ink, instead of relying on the pressure of heat. The voltage provides enough force to push it through a much smaller nozzle, which produces ultra-small ink droplets that are ten to a hundred times smaller than those produced by conventional printers.

The researchers found that the new printer could print structures small enough to be used in nanophotonics, which is Dr. Frederic Brossard’s, from the Hitachi Cambridge Laboratory, area of research.

"Previous efforts to combine these two areas had bumped into the limitations of conventional inkjet printing technology, which cannot directly deposit anything small enough to be comparable to the wavelength of light," said Pecunia. "But through electrodynamic inkjet printing, we've been able to move beyond these limitations."

Researchers could deposit ultra-small ink droplets onto photonic crystals. The ink droplets are small enough that they can be ‘drawn’ on the crystals on demand as if from a fine pen and locally change the properties of the crystals so that light could be trapped. This technique enables the creation of many types of patterns onto the photonic crystals at a high speed over a large area. The patterns can be made of all kinds of printable materials and the method is scalable, low-cost and photonic crystal is reusable since the ink can just be washed away.

"This fabrication technique opens the door for diverse opportunities in fundamental and applied sciences," said Brossard. "A potential direction is the creation of a high density of highly sensitive sensors to detect minute amounts of biomolecules such as viruses or cancer cells. This could also be a very useful tool to study some fundamental phenomena requiring very strong interaction between light and matter in new materials and create lasers on demand. Finally, this technology could also enable the creation of highly compact optical circuits which would guide the light and which could be modified by inkjet printing using the photonic crystal template."

The research paper was published in the journal Advanced Materials.

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