Etching Graphene

06 March 2011
Posted by Chris Smith.

With a breakthrough that could hasten the arrival of a new generation of even more powerful microprocessors, scientists have discovered how to etch single sheets of graphene.

Seen down a microscope this material resembles a flat sheet of six-membered rings of carbon atoms which, stacked up into many millions of layers, makes graphite.  But, peeled apart into individual atom-thick sheets, graphene has a range of interesting properties including being highly deformable as well as electrically conductive and yet sufficiently thin to also be transparent.

Zinc metal, applied in patterns to multilayer graphene, can selectively remove only one layer of the graphene.Consequently, technologists think it could hold the key to the next generation of computer displays and might even be fashioned into extremely small transistors for microchips.

But the problem has been how to "etch" or cut stacks of graphene in order to create the required architecture.  Now, writing in Science, Rice University researcher Jim Tour and his team think they have stumbled on the solution.

Setting out originally to make graphane - in which hydrogen atoms are attached to the edges of a piece of graphene, rendering it non-conductive - the team "sputtered" metallic zinc onto a sheet and then dissolved this off with acid, reasoning that the resulting hydrogen gas would add itself to the graphene where the zinc was, making graphane.

Instead they were shocked to see that the zinc dissolved away leaving perfect holes in just single sheets of the graphene. And by applying a mask to some graphene so that only some areas became zinc coated, the team found that they could precisely etch away individual parts of the graphene sheets producing any pattern they desired, including even making the nano-equivalent of a linocut owl!

The technique works because the zinc atoms have sufficient energy to knock out and replace some of the carbon atoms they hit, also causing oxygen to be added to the edge of the sheet where the zinc lands.  When the zinc is then dissolved with an acid solution the hydrogen that results from the reaction prises free the individual oxygen-flanked sheet, floating it away.

"This offers precision engineering at the resolution of the individual atom," says Tour. "Even in a thousand years' time you won't see people getting better than that!"

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