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Novel Graphene-Making Process Is More Efficient

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Researchers at the California Institute of Technology say they've come up with a new method for producing graphene at room temperature, which could lead to commercial uses for the one-atom-thick material in devices like solar cells, flexible electronics and large-panel flat displays.

The innovative manufacturing technique and the unique properties of the resultant graphene have been described in the journal Nature Communications.

Graphene, 200 times stronger than steel, could transform a number of scientific and engineering fields, most especially electronics, through what is known as its electrical mobility - a measure of the ease with which electrons can move across its surface - which is orders of magnitude better than the silicon presently used in most electronic devices, the researchers say.

However, producing graphene on an industrial scale is a challenge, and most existing manufacturing techniques require extremely high temperatures on the order of 1,800 degrees F, the Caltech researchers note.

"Previously, people were only able to grow a few square millimeters of high-mobility graphene at a time, and it required very high temperatures, long periods of time, and many steps," says physics professor Nai-Chang Yeh, corresponding author for the new study.

In addition, the graphene created at high temperatures tends to be prone to developing deformations that compromise its electronic properties, the researchers say.

The Caltech manufacturing process involves heated copper, used to catalyze the growth of graphene. For the technique to work, the researchers discovered, it requires an extremely clean surface on the copper, without any copper oxide present.

Caltech scientist David Boyd developed a method for cleaning the surface of the copper in the vacuum conditions needed for the creation of graphene.

Hydrogen plasma - hydrogen gas electrically charged to separate its electrons from the protons - was found capable of removing the copper oxide, and at a much lower temperature.

Initial experiments showed that not only did the technique remove copper oxide, it simultaneously produced a layer of graphene as well.

At first, Boyd says, this puzzled him until he realized that a couple of faulty valves were allowing methane gas to leak into his experimental chamber.

"The valves were letting in just the right amount of methane for graphene to grow," he says, noting that the methane was providing the carbon atoms needed for graphene creation.

The ability to create graphene without extreme heating can not only reduce manufacturing costs, the researchers say, but the resulting material has fewer defects than thermal expansion and contraction from extreme heating and cooling can introduce.

That means fewer postproduction steps are needed, Yeh points out.

"Typically, it takes about ten hours and nine to ten different steps to make a batch of high-mobility graphene using high-temperature growth methods," he says. "Our process involves one step, and it takes five minutes."

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