By: Peter Byrley, University of California, Riverside

Image: CC0 Public Domain

A smartphone touchscreen is an impressive piece of technology. It displays information and responds to a user’s touch. But as many people know, it’s easy to break key elements of the transparent, electrically conductive layers that make up even the sturdiest rigid touchscreen. If flexible smartphones, e-paper and a new generation of smart watches are to succeed, they can’t use existing touchscreen technology.

We’ll need to invent something new – something flexible and durable, in addition to being clear, lightweight, electrically responsive and inexpensive. Many researchers are pursuing potential options. As a graduate researcher at the University of California, Riverside, I’m part of a research group working to solve this challenge by weaving mesh layers out of microscopic strands of metal – building what we call metal nanowire networks.

These could form key components of new display systems; they could also make existing smartphones’ touchscreens even faster and easier to use.

The problem with indium tin oxide

A standard smartphone touchscreen has glass on the outside, on top of two layers of conductive material called indium tin oxide. These layers are very thin, transparent to light and conduct small amounts of electrical current. The display lies underneath.

When a person touches the screen, the pressure of their finger bends the glass very slightly, pushing the two layers of indium tin oxide closer together. In resistive touchscreens, that changes the electrical resistance of the layers; in capacitive touchscreens, the pressure creates an electrical circuit.

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Flexible electrocaloric fabric of nanowire array can cool.
Image: Qing Wang/Penn State

The utilization of nanowires has opened a new branch of science for many researchers. While some have focused on applying this technology to energy systems, researchers from Penn State are using the nanowires to develop solid state personal cooling systems.

A new study from the university shows that nanowires could help develop a material for lightweight cooling systems, which could be incorporated into firefighting gear, athletic uniforms, and other wearables.

“Most electrocaloric ceramic materials contain lead,” says Qing Wang, professor of materials science and engineering at Penn State. “We try not to use lead. Conventional cooling systems use coolants that can be environmentally problematic as well. Our nanowire array can cool without these problems.”

This from Penn State:

Electrocaloric materials are nanostructured materials that show a reversible temperature change under an applied electric field. Previously available electrocaloric materials were single crystals, bulk ceramics, or ceramic thin films that could cool, but are limited because they are rigid, fragile, and have poor processability. Ferroelectric polymers also can cool, but the electric field needed to induce cooling is above the safety limit for humans.

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Reginald Penner (pictured) and doctoral candidate developed a nanowire-based batter that can be charged hundreds of thousands of times.
Image: Daniel A. Anderson/UC Irvine

Researchers at the University of California, Irvine may have just developed the ever-lasting battery.

A recent study, published in ACS Energy Letters, details a nanowire-based battery material that can be recharged hundreds of thousands of times – making more realistic the idea of a battery that would never need to be replaced.

Potential applications for the battery range from computers and smartphones to cars and spacecrafts.

Highly-conductive nanowires have always been thought appropriate for battery design, but were held back by the fact that their fragility causes them to breakdown after multiple charging cycles. By coating a gold nanowire in a manganese dioxide shell and encasing the assembly in an electrolyte, the researchers have turn the frail structure into something that has almost infinite recharging capabilities.

Mya Le Thai, a doctoral candidate, led the charge on the research – cycling the tested electrode up to 200,000 times over a three month period without loss of capacity or damage to the nanowire.

“Mya was playing around, and she coated this whole thing with a very thin gel layer and started to cycle it. She discovered that just by using this gel, she could cycle it hundreds of thousands of times without losing any capacity,” said Reginald M. Penner, chair of UC Irvine’s chemistry department and ECS member. “That was crazy, because these things typically die in dramatic fashion after 5,000 or 6,000 or 7,000 cycles at most.”

Thai believes that this study shows that nanowire-based batteries could be commercially viable, and potentially the next big break in battery technology.

The nanowires were created through a process called meniscus-mask lithography.
Image: Tour Group/Rice University

Scientists and researchers around the world are always looking for ways to improve technology. While we’ve been making smaller circuits to improve semiconductors for some time now, we’ve just about reached the physical limits of shrinking nanowires. However, this newly developed technique allows for the formation of the tiniest wires yet.

A new technique has been developed that uses water to create patterns of wires less than 10 nanometers wide.

“This could have huge ramifications for chip production since the wires are easily made to sub-10-nanometer sizes,” said lead author James M. Tour. “There’s no other way in the world to do this en masse on a surface.”

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