30 May 2014

Researchers create high-quality graphene with shockingly simple supersonic spray system

Graphene as metal hexagon things

By using a supersonic nozzle more commonly found at the business end of rocket and jet engines, researchers at the University of Illinois at Chicago have devised a very simple and inexpensive way of producing high-quality, defect-free sheets of graphene on a range of substrates (materials). Other methods at producing large quantities of defect-free graphene have so far been very elusive – and, for the purposes that we’re interested in (replacing silicon in microelectronics), anything less than defect-free just won’t do.

The method, developed by the University of Illinois in association with some researchers in South Korea, is painfully simple which is usually a very good sign, when it comes to scaling a process up to industrial levels. Basically, the researchers take a commercially available graphene suspension (a fluid with low-quality graphene flakes dispersed in it), and then use a supersonic spray gun to deposit the graphene on a substrate. No further treatment is required, apparently.

Supersonic graphene deposition
Supersonic graphene deposition

Usually, this process would just lead to the substrate being covered unevenly in the suspension, with random aggregations of graphene flakes that lack the awesome properties that we’ve come to know and love. But, of course, this being graphene, something magical seems to happen when it’s sprayed at supersonic speeds: When the graphene hits the substrate, there’s enough kinetic energy that it spreads out perfectly into a thin, single-atom-thick layer of pristine graphene. “Imagine something like Silly Putty hitting a wall it stretches out and spreads smoothly,” says Alexander Yarin, co-leader of the research. “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.”

The secret sauce, if there is any (it really is a depressingly simple approach) is the use of a de Laval nozzle. The de Laval nozzle is a stretched hourglass shape, with a pinch in the middle that forces fluids to accelerate to supersonic speeds, and then to shape the exhaust. The nozzle is usually used in rocket and jet engines, to accelerate the pressurized gases and to generate more thrust. In this case, it’s just about accelerating the graphene suspension so that it leaves with enough kinetic energy to trigger the Silly Putty Effect. [DOI: 10.1002/adfm.201400732 - "Self-Healing Reduced Graphene Oxide Films by Supersonic Kinetic Spraying"]

This is what perfect graphene looks like: A monolayer of carbon atoms

Because this really is just supersonic spraying, and because no post-processing is required, the researchers say the method can be used to coat many different materials and shapes with high-quality graphene. I’m not aware of spraying being used in current chip fabrication processes, but I don’t think it would be hard to include it (it’s a lot simpler than current chemical vapor deposition techniques). [Read: Graphene aerogel is seven times lighter than air, can balance on a blade of grass.]

Moving forward, the Chicagoans and Koreans want to scale this method up, with the hope of fostering the development of industrial scale applications of graphene. Over the last few months, we’ve seen a few methods of high-quality graphene production that work on the small scale, and could potentially work on the industrial scale but now it’s time for a research lab to put its money where its mouth is and actually try some industrial-scale production. With the amount of research that’s going into graphene, I wouldn’t be surprised if that occurs this year.

Courtesy Extremetech


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