In two new studies, physicists demonstrate that graphene can greatly improve electrical circuits required for wearable and flexible electronics such as smart health patches, bendable smartphones, helmets, large folding display screens, and more.

The ultrathin carbon material is an incredibly strong electrical and thermal conductor, making it a perfect ingredient to enhance semiconductor chips found in many electrical devices.

But while graphene-based research has been fast-tracked, the nanomaterial has hit roadblocks: in particular, manufacturers have not been able to create large, industrially relevant amounts of the material. New research from the laboratory of Nai-Chang Yeh , the Thomas W. Hogan Professor of Physics, is reinvigorating the graphene craze.

In two new studies, the researchers demonstrate that graphene can greatly improve electrical circuits required for wearable and flexible electronics such as smart health patches, bendable smartphones, helmets, large folding display screens, and more.

In one study , published in ACS Applied Materials & Interfaces, the researchers grew graphene directly onto thin two-dimensional copper lines commonly used in electronics. The results showed that the graphene not only improved the lines' conducting properties but also protected the copper-based structures from usual wear and tear. For instance, they showed that graphene-coated copper structures could be folded 200,000 times without damage, as compared to the original copper structures, which started cracking after 20,000 folds. The results demonstrate that graphene can help create flexible electronics with longer lifetimes.

The second study, published in ACS Applied Nano Materials, demonstrated that gold coated in graphene could better withstand the sweat of a person's body, and thus would make better implantable biosensors. Gold is a common ingredient used in the development of implantable biosensors, or smart patches—nanoscale devices for monitoring various health conditions. Graphene slows down the rate at which the gold is corroded.

The two studies, in addition to a third study in ACS Applied Materials & Interfaces showing that graphene can protect electrical circuits produced via inkjet printers, used the Yeh group's unique method for growing graphene. In 2015, Yeh and her colleagues, including senior research scientist David Boyd, announced that they had figured out a better, more cost-effective, and environmentally friendly way to grow graphene on materials. Called plasma-enhanced chemical vapor deposition, the method can be used to grow high-quality graphene sheets, only one atom thick, at room temperature in about 15 minutes. This is in contrast to other methods that require much higher temperatures, harsh chemicals, and take several hours to complete.

"Flexible and wearable electronics can be made of soft materials like polymers that can't sustain high temperatures," says Chen-Hsuan (Steve) Lu (MS '20), a Caltech graduate student and lead author of the three studies. "Our method allows us to grow graphene directly on the substrates at a low temperature, preventing any damage to sensitive materials."

Yeh adds that their graphene-growth method, which can be scaled up for industrial needs, is compatible with a host of other applications in addition to flexible and wearable electronics.

"Our method is highly compatible with all kinds of substrates, ranging from tiny, nanostructure metals, to semiconducting materials, to even plastics. Because we don't require high temperatures, this method can be used on different substrates for many applications," she says.

Pink Plasma

The group's method for growing sheets of graphene is performed in their basement laboratory. A ray of plasma, which glows pink, is used to activate a gas of hydrogen and methane molecules and break them down into smaller fragments. The sample, such as a two-dimensional copper line, is then immersed in the plasma, and the carbon from the gas gets deposited onto the surface in thin sheets that are one atom thick. The final surface with the graphene will appear shinier.

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Graphene Boosts Flexible and Wearable Electronics

In two new studies, physicists demonstrate that graphene can greatly improve electrical circuits required for wearable and flexible electronics such as smart health patches, bendable smartphones, helmets, large folding display screens, and more.