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Super low-cost manufacturing method could provide inexpensive flexible electronics and more.

Like the ubiquitous carbon nanotube, graphene is another wonder substance composed entirely of carbon molecules. In fact, you can think of carbon nanotubes as sheets of graphene rolled into a tube. Graphite is also made from sheets of graphene stacked atop one another.

There are a few things about graphene that make it a fairly desirable material. First is its ability to conduct electricity and it does so quite well. Research into this property of graphene has made the future of flexible electronics quite tantalizing.

Second is its strength as compared to other substances on a molecular level. Graphene is 200 times stronger than steel, and the strongest of any material tested at present. This property also makes it ideal for flexible applications as the circuits constructed of graphene are much less likely to break under distortion.

The only trouble with graphene is until now it's been expensive or wasteful to produce. Typically, graphite oxide would be rendered into graphene using either high temperatures or toxic chemicals. While the heat treatment is less problematic than the chemical variety, it still has some drawbacks. If the chemists wanted to mix the graphene with another substance, such as a polymer, the intense heat may destroy the other substance. In the chemical treatment, the mixture substance could prevent a reaction with the graphite oxide, making the technique useless.

Jiaxing Huang, an assistant professor with Northwestern's McCormick School of Engineering and Applied Science, along with Rodolfo Cruz-Silva, a postdoctoral fellow, and Laura J. Cote, a graduate student under Huang, may have, in a flash of inspiration, made the former techniques obsolete. In fact, about the only piece of modern technology necessary for Huang's process is an ordinary camera flash.

Huang says of the process, “The light pulse offers very efficient heating through the photothermal process, which is rapid, energy efficient and chemical-free.” By simply positioning the camera flash over graphite oxide and firing the bulb, the substance is instantly reduced to graphene.

The process is both incredibly simple and remarkably versatile. Not only does the flash instantly transform the graphite oxide, it will also bond it to an insulating polymer, creating a conducting composite.

Another approach is to etch a circuit design onto a sheet of overhead transparency and use it as a mask. Similar to photo-lithography, where the flash's intense light falls, the graphite oxide will be converted to graphene while the dark areas will remain unchanged. The beauty of this simple process is that while graphene is a great electrical conductor, graphite oxide is the exact opposite – a great electrical insulator. This produces, instantly, a precursory flexible circuit.

Huang's group still has more planned to improve the process. At present they have used only thick films in their research, but intend to refine the technique in order to create circuits on a single-atom sheet. A quick and easy micropatterning system is not out of the realm of possibility.

Should a single layer circuit printing process come about, manufacturers would simply have to alternate layers of the circuit with layers of normal graphite oxide or another single-atom, flexible insulator, and inexpensive, flexible and durable electronic parts are right around the corner. Some such electronic systems already exist, but they lack the efficiency at manufacturing level that Huang's technique could provide. It could be a boon for both military and consumer system alike.

An excerpt of the Northwestern trio's work can be found here.





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