Making graphene in a flash
Aug 17, 2009
Researchers in the US have found that firing a camera flash at graphite oxide is enough to make graphene – atom-thick sheets of carbon first discovered in 2004 that possess unique mechanical and electrical properties. The new process could also be used to make complex patterns of graphene that could be integrated into fast and flexible carbon-based electronic circuits.
Chemists have previously sought to turn graphite oxide into graphene, but the reduction reactions involved in removing the oxygen typically take days and require strong reducing agents such as hydrazine. What is more, these chemical processes prevent other compounds from being added to the resulting graphene.
Now, via a surge of inspiration, Jiaxing Huang, a materials scientist at Northwestern University in Illinois, US, realized that a brief burst of light could perform the same reaction in a single millisecond. Key to the process is the photothermal effect: the camera flash delivers a pulse of energy that is converted to heat in the graphite oxide. "The pulse of energy from the camera flash induces a 'nano-explosion' in the graphite-oxide film," explains Huang. "Reduction takes place so rapidly that the film puffs out and expands by two orders of magnitude."
In a video released by the group, brown, transparent sheets of graphite oxide can be seen to blacken and expand, accompanied by a loud popping sound. Huang's team describes the resulting black material as "fluffy" – it is porous and only a fraction of the density of graphite. Further analysis showed that the material is made up of disordered graphene sheets and flakes that are well spaced from one another.
The team also showed that it could add plastic nanoparticles to the graphite oxide, so that when the mixture is exposed to the flash, its particles fuse together like liquid droplets, locking the graphene into a tough composite material.
Because the manufacturing process is clean, fast and simple, the team is confident that industrial-scale production of graphene through this process is possible. Peter Blake, who works with graphene suppliers Graphene Industries, based at Manchester University in the UK, agrees. "This is an intriguing proof-of-concept that will benefit greatly from other work that is going on in the same area," he told physicsworld.com.
Blake added that printable electronics would also benefit from this technology. One existing challenge is mounting graphene onto silicon or glass surfaces to design circuitry. It may be possible to use insulating graphite oxide to make the circuit then convert it to conducting graphene with a flash of light, he believes. Alternatively, light-resistant masks could be used to generate complex patterns of graphene.
To develop this research, Huang's team is now planning to use the process to make a nano-scale circuit, but the process is not quite as simple when it involves small amounts of material because heat generated by the light pulse may dissipate too quickly to trigger a reaction.
This research first appeared in the Journal of the American Chemical Society.
About the author
Lewis Brindley is a freelance science and technology writer based in Chelmsford, UK.