Graphene is a sheet of carbon just one atom thick and is a promising material for making molecular devices of the future thanks to its unique electronic and mechanical properties that include extremely high electrical conductivity and exceptional strength. The material is normally transferred onto a target substrate using polymers, like PMMA, or other intermediate interfaces, like thermal release tape. These interfaces leave behind residues that can adversely affect graphene’s pristine properties.

The new technique, developed by Paulo Araujo’s and Jing Kong’s groups at MIT does not require such intermediate membranes or glues. "The simplest way of understanding our process is to think of laminating graphene onto a surface," explains Araujo.

Temperature-controlled laminating machine

The researchers began by synthesising graphene flakes on both sides of a copper foil sheet – a standard way to grow high-quality graphene – and then literally sandwiched the flakes between the flexible surface in question and a layer of protective paper. Next, they placed the sandwich between two plastic sheets, such as those made of PET. The resulting heterostructure then went into a laminating machine in which the temperature could be controlled, and the components bonded together. The plastic film and protective paper were then removed and the remaining material (copper foil, graphene sheet and target substrate) immersed in a copper etchant that completely dissolved away the metal.

"Scientists are coming up with ever better ways to grow high-quality graphene sheets using techniques like chemical vapour deposition, and what we are offering is a simple recipe to transfer the material while avoiding the contaminants that are the bain of conventional glue-based procedures,” Araujo told nanotechweb.org. "Our technique could help make high-quality flexible touchscreens, flexible light-emitting diodes and sensors, gas filters and solar cells from graphene, to name but a few applications."

Other 2D materials

And that is not all: other newly discovered and technologically important materials, such as boron nitride, transition metal dichalcogenides and oxides might also be transferred onto flexible substrates using the new MIT method.

The team says that it now studying how temperature affects the lamination transfer process and looking more closely at the structure of the transferred material. "Even though we have shown that residue-free transfer is possible, the films we transferred could be more continuous," says team member Luiz Pimenta. "The lack of continuity might well be welcome for applications like filters but not so much so for high-quality touchscreen devices."

Applying the transfer technique to rigid substrates may also be more difficult than for transfer onto flexible ones. "It is worth reminding ourselves that although flexible devices are technologically appealing for a host of futuristic applications, many traditional devices, such as logic circuits, for example, are still strongly connected to rigid boards," said team member Yi Song.

More details about the research can be found in PNAS doi: 10.1073/pnas.1306508110.

Further reading

Flexible graphene transistor breaks new records (Dec 2012)
Graphene makes field emission devices flexible and more efficient (Sep 2011)
Flexible organic solar cells equipped with graphene electrodes (Sep 2012)
Grain boundary defects affect graphene's strength (Aug 2012)
Chlorine has got graphene covered (Aug 2013)
Shedding more light on CNTs (Feb 2013)