Researchers at Northwestern University in Chicago have made a giant step in overcoming one of the hurdles blocking the development of graphene for use in everyday devices – that it’s difficult to electrically ‘turn off’ the flow of current through it.
Now scientists have found a way of chemically altering the material to ‘tune’ its electronic properties and make it more functional.
The ultra-thin material called graphene could help develop super fast electronics
Until now the most prevalent strategy is the ‘Hummers method’, a process developed in the 1940s that oxidises graphene, but that method relies upon harsh acids that irreversibly damage the fabric of the graphene lattice.
Researchers at Northwestern's McCormick School of Engineering and Applied Science have recently developed a new method to oxidise graphene without the collateral damage encountered in the Hummers method.
Their oxidation process is also reversible, which enables further tunability over the resulting properties of their chemically modified graphene.
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THE WONDER OF GRAPHENE
Graphene is a single atomic layer of carbon atoms bound in a hexagonal network.
Similar to another important nanomaterial - carbon nanotubes - graphene is incredibly strong - around 200 times stronger than structural steel.
A sheet as thin as cling film can support an elephant.
It also conducts electricity and heat better than any other known material.
It not only promises to revolutionise semiconductor, sensor, and display technology, but could also lead to breakthroughs in fundamental quantum physics research.
Scientists believe it could one day be used to make transparent conducting materials, biomedical sensors and even extremely light, yet strong, aircraft of the future.
‘Performing chemical reactions on graphene is very difficult,’ said Mark C. Hersam, professor of materials science and engineering at the McCormick School. ‘Typically, researchers employ aggressive acidic conditions, such as those utilized in the Hummers method, that damage the lattice and result in a material that is difficult to control.
‘In our method, however, the resulting graphene oxide is chemically homogeneous and reversible - leading to well-controlled properties that can likely be exploited in high-performance applications.’
To create the graphene oxide, researchers leaked oxygen gas (O2) into an ultra-high vacuum chamber. Inside, a hot tungsten filament was heated to 1500C, causing the oxygen molecules to dissociate into atomic oxygen. The highly reactive oxygen atoms then uniformly inserted into the graphene lattice.
The resulting material possesses a high degree of chemical homogeneity. Spectroscopic measurements show that the electronic properties of the graphene vary as a function of oxygen coverage, suggesting that this approach can tune the properties of graphene-based devices.
‘It's unclear if this work will impact real-world applications overnight,’ Hersam said. ‘But it appears to be a step in the right direction.’
Next, researchers will explore other means of chemically modifying graphene to develop a wider variety of materials, much like scientists did for plastics in the last century.
‘Maybe oxygen isn't enough,’ Hersam said. ‘Through chemical modification, the scientific community has developed a wide range of polymers, from hard plastics to nylon. We hope to realize the same degree of tunability for graphene.’
In 2010, University of Manchester professors Andre Geim and Konstantin Novoselov won the physics Nobel prize for their work on graphene.