Move over sticky tape: a splattering of zinc atoms and a dash of acid is the best way to peel off single layers of graphene, the atom-thin form of carbon that electrons can zip through with incredible efficiency and speed.
This technique is so precise that it might be possible to create electrical circuits using only graphene components, which could allow this exotic material to realise its potential as the basis for ultra-efficient, super-fast computer chips.
Graphene was first discovered in 2004 when Andre Geim and Konstantin Novoselov, both at the University of Manchester, UK, used sticky tape to pull single layers of the stuff off a piece of graphite.
But although its discoverers picked up the physics Nobel prize, until now it has proved difficult to remove single layers of graphene from specific locations, which is essential if you want to use it to build circuits on computer chips.
Now, James Tour from Rice University in Houston, Texas, and colleagues have come up with a simple but effective way of doing this. they used a common laboratory technique known as sputtering to coat the top layer of a stack of graphene sheets with zinc metal: the zinc atoms collide with the stack but only have enough energy to damage the first layer.
Hydrochloric acid is then used to dissolve the zinc, removing this weakened first layer but leaving the other layers intact.
This gives researchers the ability to etch graphene with unprecedented precision – and create samples of a very exact thickness. “We are able to remove one layer at a time. before this, lithography could never give you single atom precision. If you wanted to remove a layer, you would have to remove lots and lots of layers,” says Tour.
He envisages using the technique to scrape off just the right number of layers from multi-layer graphene stacks, leaving behind pre-determined spots that are exactly one, two or three layers thick.
This level of control is important because the number of layers in a graphene stack determines its properties. For example, a single layer of graphene behaves like a metal whereas a double layer is like a semiconductor and can be built into a transistor. “The ability to have a single layer right next to a double layer next to triple layer is very attractive,” says Tour. “You could build a series of devices very close to each other in any pattern you want, just by removing portions of each layer.”
“This could result in a set of different electronic components all made of, and interconnected by, graphene,” says Vitor Pereira from the National University of Singapore, who is not part of the research team. Such all-graphene devices would “explore the advantages of graphene to the fullest”, he says and “help realise one of the ultimate goals in graphene-based electronics: all-graphene electronic circuits”.
Zakaria Moktadir of the Nano Research Group at the University of Southampton, UK agrees, adding that all-graphene circuits could bring us a step closer to building ultra-fast computer chips, as well as more sophisticated sensors and touchscreens.
Tour is confident that his “new tool” will open the door for even more complex and exotic devices to be built with graphene. “We have provided a wrench for people who have never had one before. It is up to them to see what they can do with it,” he says.
Now this degree of precision has been reached in the vertical direction, the next coup would be to get that same level of control laterally. Horizontal precision would allow trillions of one-atom-thick transistors to fit onto a chip, says Mokatadir.
Journal reference: Science, DOI: 10.1126/science.1199183
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