Researchers at MIT and the University of Michigan have developed a scalable method of producing graphene by applying graphene directly on materials such as large sheets of glass.
Currently, most methods of making graphene first grow the material on a film of metal, such as nickel or copper, said A. John Hart, the Mitsui Career Development Associate Professor of Mechanical Engineering at MIT.
‘To make it useful, you have to get it off the metal and onto a substrate, such as a silicon wafer or a polymer sheet, or something larger like a sheet of glass,’ Hart said in a statement. ‘But the process of transferring it has become much more frustrating than the process of growing the graphene itself, and can damage and contaminate the graphene.’
The new work, Hart said, still uses a metal film as the template – but instead of making graphene only on top of the metal film, it makes graphene on the film’s top and bottom. The substrate in this case is silicon dioxide, with a film of nickel on top of it.
Using chemical vapour deposition (CVD) to deposit a graphene layer on top of the nickel film, Hart said, yields not only graphene on top of the nickel layer, but also on the bottom. The nickel film can then be peeled away, leaving the graphene on top of the non-metallic substrate.
This way, there’s no need for a separate process to attach the graphene to the intended substrate – whether it’s a large plate of glass for a display screen, or a thin, flexible material that could be used as the basis for a lightweight, portable solar cell, for example.
‘You do the CVD on the substrate, and, using our method, the graphene stays behind on the substrate,’ Hart said.
The work was done also in collaboration with Michigan-based glass manufacturer, Guardian Industries.
‘To meet their manufacturing needs, it must be very scalable,’ Hart said. The company currently uses a float process, where glass moves along at a speed of several metres per minute in facilities that produce hundreds of tons of glass every day. ‘We were inspired by the need to develop a scalable manufacturing process that could produce graphene directly on a glass substrate,’ Hart said.
With the work still at an early stage Hart cautioned: ‘We still need to improve the uniformity and the quality of the graphene to make it useful.’
The potential of the process, however, could be significant.
‘The ability to produce graphene directly on non-metal substrates could be used for large-format displays and touch screens, and for ‘smart’ windows that have integrated devices like heaters and sensors,’ he said.
Hart said that the approach could also be used for small-scale applications, such as integrated circuits on silicon wafers, if graphene can be synthesised at lower temperatures than were used in the present study.
‘This new process is based on an understanding of graphene growth in concert with the mechanics of the nickel film,’ he said. ‘We’ve shown this mechanism can work. Now it’s a matter of improving the attributes needed to produce a high-performance graphene coating.’
The process, described in a paper published in Scientific Reports, was developed by a team of nine researchers led by Hart. Lead authors of the paper are Dan McNerny, a former MIT postdoc who is now at Michigan, and Viswanath Balakrishnan, a former MIT postdoc who is now at the Indian Institute of Technology.
UK firms are pioneering the production techniques that could bring graphene to the masses. Click here to read more.