‘Spray-on’ technique promises defect-free graphene

Despite its many desirable qualities, graphene still isn't as widely used as it could be because of the difficulty in applying it to different surfaces.

Now, however, a team from the University of Illinois at Chicago has devised a simple, low cost method of simply spraying the material on, which they say actually improves it in the process.

"Normally, graphene is produced in small flakes, and even these small flakes have defects," said Alexander Yarin, who co-led the research. "Worse, when you try to deposit them onto a large scale area, defects increase, and graphene's useful properties – its 'magic' – are lost."

The team's supersonic spray system produces very small droplets of graphene suspension, which disperse evenly, evaporate rapidly and reduce the tendency of the graphene flakes to aggregate.

To the researchers' surprise, they found that defects inherent in the flakes themselves disappeared as a by-product of the spray method. The result was a higher quality graphene layer.

The researchers demonstrated that the energy of the impact stretches the graphene and restructures the arrangement of its carbon atoms into the perfect hexagons of flawless graphene.

"Imagine something like Silly Putty hitting a wall – it stretches out and spreads smoothly," noted Yarin. "That's what we believe happens with these graphene flakes. They hit with enormous kinetic energy, and stretch in all directions. We're tapping into graphene's plasticity – it's actually restructuring."

While there have been other attempts to produce graphene without defects or to remove flaws after manufacture, these have proved difficult and prohibitively expensive.

This new method of deposition, which allows graphene to 'heal' its defects during application, is simple, inexpensive, and can be performed on any substrate with no need for post-treatment, Yarin said.

Laura Hopperton

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