Nanowalls to make touchscreens more efficient

Geneva: Scientists have developed new 3D printed transparent electrodes, comprising of a grid of gold or silver 'nanowalls' on a glass surface, which could help make more efficient and precise touchscreens for smartphones. It is the first time that scientists have created nanowalls like these using 3D printing.

Every touchscreen we use requires transparent electrodes - the devices' glass surface is coated with a barely visible pattern made of conductive material. The new electrodes developed by scientists at ETH Zurich in Switzerland have a higher conductivity and are more transparent than those made of indium tin oxide, the standard material used in smartphones and tablets today.

This is a clear advantage - the more transparent the electrodes, the better the screen quality. The more conductive they are, the more quickly and precisely the touchscreen will work. "Indium tin oxide is used because the material has a relatively high degree of transparency and the production of thin layers has been well researched, but it is only moderately conductive," said Patrik Rohner, a PhD student at ETH. To produce more conductive electrodes, researchers opted for gold and silver, which conduct electricity much better.

However, because these metals are not transparent, the scientists had to make use of the third dimension. "If you want to achieve both high conductivity and transparency in wires made from these metals, you have a conflict of objectives," said Dimos Poulikakos, professor at ETH. "As the cross-sectional area of gold and silver wires grows, the conductivity increases, but the grid’s transparency decreases," said Poulikakos.

Researchers used metal walls only 80 to 500 nanometres thick, which are almost invisible when viewed from above. Since they are two to four times taller than they are wide, the cross-sectional area, and thus the conductivity, is sufficiently high. These tiny metal walls were produced using a printing process known as Nanodrip.

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 3D structure to be built up drop by drop. The researchers managed to create this special form of droplet by perfectly balancing the composition of metallic ink and the electromagnetic field used.

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.