How to make graphene

Sellotape and sugar rub shoulders with high-temperature furnaces and low-pressure chambers in a rush to produce graphene, which aims to be the 21st century's successor to silicon

We have seen that graphene has massive potential, but how do we get hold of it?

Professors Andre Geim and Konstantin (Kostya) Novoselov famously used sellotape to separate a single layer of graphene from a graphite crystal, during an investigation of its usefulness in transistors.

The tabloid headline version of this part of Graphene's story is well known, thanks to a certain high-profile prize awarded last year.

Mechanical exfoliation, as it has become known, really does involve repeatedly flaking graphite with sticky tape, until you hit a single layer of carbon atoms.

But in fairness to the Nobel-winning team, we feel obliged to point out that then you have to get the monolayer off the sellotape.

Geim, Novoselov and their team had to dissolve the graphene-carrying tape in acetone, deposit the resulting flakes and other debris onto silicon and then go hunting with an optical microscope to find their prize. Not the work of five minutes.

And it would take a lot of sellotape to get a large quantity of graphene, and even then it would be a bit, well, bitty. Indeed, it is such a fabulously expensive way of making the material that an amount that might clothe the head of a pin would sell for upwards of an angelic $1,000.

Two approaches

So how does one go about making large, stable, and affordable monolayer sheets of this fabulous stuff? There are two main approaches: chemical vapour deposition (CVD) growth, and growth from a solid carbon source.

The former relies on manipulating temperatures and pressures to deposit carbon onto a copper or nickel substrate, typically from methane or C2H2 gas. Various combinations have been tried: for example, on a thin copper film, at low pressures, growth automatically stops after a single layer of graphene has formed. At atmospheric pressure, the graphene grows in multiple layers.

The second approach, meanwhile, involves depositing a source of carbon on a metal catalyst substrate and using an 800° furnace to grow the graphene across the catalyst. One group is using sugar as its seed material.

Fast-moving field

Rice University's professor Jim Tour, head of the department behind the sugar experiment, notes: "It is a lot of fun working in such a fast-moving field. Whatever you do is well received because of the excitement and interest in the area. So many people are working on things so rapidly, you can't sit and ponder for long."

He's not kidding: hundreds of research groups are working on the subject, and more than 3,000 papers on graphene are published every year.

"If you start working on something, someone else might just beat you out. You have to constantly generate ideas," Tour adds.

If you start working on something, someone else might just beat you out. You have to constantly generate ideas.

– Professor Jim Tour

As to which method will eventually win out, Tour is firmly behind the solid source, although he concedes that since he helped develop the technique, he has a vested interest in it.

"We would [favour growth from a solid carbon source], because it was developed here. But it is more general, and easier to make doped graphene [using this method], which will open up a band gap for you. CVD can sometimes be easier, though, so both will play a role."

In the manner of academics, Tour says that either technique is better than the sellotape-and-pencil approach which, he wryly observes, "doesn't scale well".

Meanwhile, Dr Leonid Ponomarenko, from the University of Manchester, argues the case for CVD. "It is suitable for large-scale production," he says. "The quality of graphene made this way is good enough for some immediate applications such as graphene-based touchscreens, LCD and solar cells," he says. A working prototype of a graphene-based touchscreen was demonstrated recently by Korean researchers, he adds.

The band gap that Tour mentions is a critical issue for graphene, to which we will return in the next article. We'll also take a look at some of its other weird and wonderful properties, including ballistic conduction and its astonishing strength.

In the next part of our series, we look at the 10 strangest facts about graphene. 

Read more of ZDNet UK's special coverage of Graphene: Future IT.


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