Researchers at MIT have developed a controlled chemical way to flake graphene from bulk graphite - which is effectively a stack of flat graphene layers.
The flakes are good - transistors have been made on them - but not perfect.
According to MIT's Professor Michael Strano who lead the work, the technique makes it possible to produce A-B stacked layers, with the atoms in one layer centred over the spaces between atoms in the next, that yields desirable electronic properties.
"If you want a whole lot of bilayers that are A-B stacked, this is the only way to do it," he said.
To allow traditional planar processing, like that used to make silicon ICs, it is desirable to form perfect graphene directly on the surface of a substrate.
Currently, there is no way to do this, although techniques are improving.
In the mean time, to experiment with graphene for electronics, it is flaked from blocks of graphite using sticky tape and manoeuvred onto a substrate.
These flakes are a mixture of sizes, thicknesses and quality, and so deposition is followed by a game of hunt-the-suitable-flake for any particular research project.
Strano's process is aimed at increasing the consistency of such flakes and involves adding iodine chloride (ICl) or iodine bromide (IBr) to graphite.
The compounds worm their way into the bulk material, forming layers of ICl or IBr between graphene layers within the graphite.
This makes the graphite fragile and mild ultrasonic sonic agitation causes it to fall into flakes.
With ICl, 35-40% of the flakes have two layers, and with IBr the same proportion have three layers.
And the flakes produced can be as big as 50µm2 in area.
"Graphene is a very fragile material, so it requires gentle processing," said Strano. "Because this dispersion process can be very gentle, we end up with much larger flakes" than anyone has made using other methods.
The lab also has a way to sort-out larger flakes by controlled evaporation.
Hole mobilities in the final material mounted on a substrate are up to 400cm2/Vs said MIT - compared to mobility in the range 50-400cm2/Vs for holes in doped silicon, and 1,500-3000cm2/Vs for similar thickness sticky-tape graphene on a SiO2 surface.
Record-breaking mobilities in graphene are only seen, said MIT, in mono-layer material at low temperatures away from a substrate.
If the method can be improved to deliver 90% concentration of the desired flake thickness, commercial applications could be possible.
"A similar solvent-based method for making single-layer graphene is already being used to manufacture some flat-screen television sets," said MIT.
"This is definitely a big step" toward making bilayer or trilayer devices, added Strano.