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❱ ❱ Flexible conductive material using silver and

graphene (opposite) could spell the end of shattered telephone screens (below)

Graphene potato stamp sorts out brittle smart phone screens


he problem has been that indium tin oxide, which is currently used to make smart phone screens, is brittle and expensive. The primary constituent, indium, is also a rare metal and is ecologically damaging to extract. Silver, which has been

shown to be the best alternative to indium tin oxide, is also expensive. The breakthrough from physicists at the University of Sussex has been to combine silver nanowires with graphene – the two dimensional carbon material. The new hybrid material matches the performance of the existing technology at a fraction of the cost. In particular, the way in which these materials are assembled is new. Graphene is a single layer of atoms, and can float on water. “While silver nanowires have been used in touch screens before, no one has tried to combine them with graphene,” Dalton explains. “What’s exciting about what we are doing is the way we put down the graphene layer. We float the graphene particles on the surface of water, then pick them up with a rubber stamp, a bit like a potato stamp, and lay it on top of the silver nanowire film in whatever pattern we like.” The stamp itself is made from poly(dimethyl siloxane) - the same silicone rubber used in kitchen utensils and medical implants. This breakthrough technique is inherently scalable. It would be relatively simple to combine silver nanowires and

12 /// Electronics Testing 2018

Scientists at the University of Sussex may have found a solution to the long- standing problem of brittle smart phone screens. Professor Alan Dalton and his team have developed a new way to make smart phone touch screens that are cheaper, less brittle, and more environmentally friendly. On top of that, the new approach also promises devices that use less energy, are more responsive and do not tarnish in the air.

graphene in this way on a large scale using spraying machines and

patterned rollers. This means that brittle mobile phone screens might soon be a thing of the past. “The addition of graphene to the silver nanowire network also increases its ability to conduct electricity by around a factor of 10,000,” Dalton adds. “This means we can use a fraction of the amount of silver to get the same,

or better, performance. As a result, screens will be more responsive and use less power.”

Although silver is also a rare

metal, like indium, the amount needed to coat a given area is very small when combined with graphene. Since graphene is produced from natural graphite – which is relatively abundant - the cost for making a touch sensor drops dramatically. One of the issues with using silver is that it tarnishes in air. But the graphene

layer prevents this from happening by stopping

contaminants in the air from attacking the silver. “What we’ve also seen is that when we bend the hybrid films

repeatedly the electrical properties don’t change, whereas you see a drift in the films without graphene that people have developed previously. This paves the way towards one day developing completely flexible devices,” Dalton concludes. EE

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