Nanowalls for Smartphones

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The researchers produced these tiny metal walls using a printing process known as Nanodrip, which Poulikakos and his colleagues developed three years ago. Its basic principle is a process called electrohydrodynamic ink-jet printing. In this process scientists use inks made from metal nanoparticles in a solvent; an electrical field draws ultra-small droplets of the metallic ink out of a glass capillary. The solvent evaporates quickly, allowing a three-dimensional structure to be built up drop by drop.

What is special about the Nanodrip process is that the droplets that come out of the glass capillary are about ten times smaller than the aperture itself. This allows for much smaller structures to be printed. “Imagine a water drop hanging from a tap that is turned off. And now imagine that another tiny droplet is hanging from this drop – we are only printing the tiny droplet,” Poulikakos explains. The researchers managed to create this special form of droplet by perfectly balancing the composition of metallic ink and the electromagnetic field used.

Cost-efficient production

The next big challenge will now be to upscale the method and develop the print process further so that it can be implemented on an industrial scale. To achieve this, the scientists are working with colleagues from ETH spin-off company Scrona.

They have no doubt that once it is upscaled, the technology will bring a host of advantages compared with existing methods. In particular, it will likely be more cost-efficient, as Nanodrip printing, unlike the production of indium tin oxide electrodes, does not require a cleanroom environment. The new electrodes should also be more suitable for large touchscreens due to their higher conductivity. And finally the process is also the first to allow you to vary the height of the nanowalls directly while printing, says ETH PhD student Rohner.

Another possible future application could be in solar cells, where transparent electrodes are also required. The more transparent and conductive they are, the more electricity that can be harnessed. And lastly, the electrodes could also play a role in the further development of curved display using OLED technology.

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