Interview: Cavendish Laboratory, University of Cambridge

• Features

• 07/12/2020

Nanotechnology could change the way we see displays, with gold-infused pixels a million times smaller than smartphone pixels potentially being used to create displays large enough to cover entire buildings. Reece Webb reports.

Everyone’s looking for a new way to break the mould and in the AV world, integrators are no exception. We are constantly looking for new ways to wow on unusual, large scale surfaces and for the large part, this need has been met by projection mapping techniques. But what about displays that could cover an entire building? It’s hard to visualise, however a team of researchers, led by Jeremy J Baumberg, Professor of Nanoscience, have claimed to have cracked it and developed the technology to create large scale, flexible displays that could transform how we bring moving graphics to building façades. The team say they are harnessing microscopic pixels and using a method that is considered unorthodox in the world of nanoscience.

Large scale displays on buildings are nothing new but are often severely limited in application by the unique geography of some structures, limiting the shape and size of displays that can be produced with current technology. Large area flexible displays can be prohibitively expensive due to the construction of these screens from multiple acutely precise layers that push cost through the roof.

Jailong Peng, a research student at the University of Cambridge’s Cavendish Laboratory, has played a leading role in the development of the pixels which could revolutionise the way we use and see displays. He explained: “The whole project idea came from Professor Baumberg, who always had the dream of making ‘colourchanging wallpaper’ on building scale, which is not easy with current technologies because of the expense and the complicated fabrication technologies involved. Before this, scientists in our group have managed to make bulk structural colour materials using nano-assembly on a large scale but they require a huge amount of energy to be electrically-switchable.”

Bringing Dr Hyeon-Ho Jeong into the team, they found a way to turn to surface effects. Peng explained: “By putting tiny electrically responsive polymer-coated metal nanoparticles on top of reflective surfaces, light can be trapped into the gaps in between. The scattering colour of this nanopixel can be changed electrically in a controllable way. “It’s really hard to make extremely small pixels to get higher resolution with current technology. But such ‘plasmonic’ structure offers resolutions that beat the fundamental diffraction limit for the wavelength of light. Another fascinating thing is that the whole process is solutionbased. We can simply coat these nanopixels onto metal films to generate distinct vivid colours under ambient light, or even print them onto flexible substrates to make patterns.”

The pixels are believed to be the smallest ever developed, designed to be a million times smaller than current smartphone pixels in addition to being created without high-cost nanolithographic fabrication techniques.

Baumberg noted: “That’s what we always try and do in my NanoPhotonics research, as it makes the results much more likely to be useful to society as well as give us a fundamental challenge.

“Since all the processes are solution-based, it’s quite straightforward to combine with industrial-scale tools like roll-to-roll processing, significantly reducing the production cost and showcasing an exciting example to bring nano-devices into everyday life.”

The research, funded as part of UK Engineering and Physical Sciences Research Council, European Research Council and China Scholarship Council investments in the university’s NanoPhotonics centre, led to the pixels which were created by coating vats of golden grains with an active polymer, polyaniline.

The polymer is then sprayed onto a flexible mirror-coated plastic, allowing a display made of these pixels to conform to unusual surfaces that conventional screens would be unable to cover seamlessly.

These gold-infused pixels are made to be compatible with roll-to-roll fabrication on plastic films, featuring a microscopic particle of gold, reportedly a “few billionths of a metre across” at the centre of the pixel, sitting on top of a reflective surface to trap light in the gap in between.

This development is significant not just in what it achieved in terms of its potential applications but also in the way it was achieved, using unconventional techniques to develop the nano-scale pixels. Research leader Professor Baumberg commented: “These are not the normal tools of nanotechnology, but this sort of radical approach is needed to make sustainable technologies feasible.

“The strange physics of light on the nanoscale allows it to be switched, even if less than a tenth of the film is coated with our active pixels. That’s because the apparent size of each pixel for light is many times larger than their physical area when using these resonant gold architectures.”

The team originally sprayed over aluminised food packets before switching to a more efficient thin, sticky coating that is applied via an aerosol, changing chemically when electrically switched which allows the pixel to change colour across the colour spectrum. The pixels are also able to be seen in bright sunlight conditions, without a need for constant power to keep the pixels’ set colours. This allows potential large scale displays to have an effective energy performance that is both sustainable and cost-effective.

The research team is exploring a variety of applications, with building-sized display screens being the technology’s primary application. Future possibilities include architecture which switches off solar heat loads in addition to chameleon-like active camouflage clothing to render military personnel almost invisible, whether stationary or on the move.

Peng said: “Currently we are targeting several future directions. We’re trying to use cheaper metals like silver and aluminium to further reduce the production costs. At the moment, it can generate red, yellow and green hues, but we’re trying to do material engineering with chemists to push the colour ranges to get good blue colours. In addition, we’re also attempting to make large-area demo flexible multipixel devices with our roll-to-roll processing tool.”

The research team also aims to find partners to develop the technology further in addition to fine-tuning the technology with further developments. Apart from this, endeavours are being made to understand the intriguing fundamental science questions about how fast the polymer can switch. Peng closes: “We can really make something that offers new applications that could be ground-breaking, that really excites us."