Scientists produce graphene in two- and three-layer form

Graphene, a form of pure carbon arranged in a lattice just one atom thick, has interested countless researchers with its unique strength and its electrical and thermal conductivity. But one key property it lacks - which would make it suitable for a plethora of new uses - is the ability to form a band gap, needed for devices such as transistors, computer chips and solar cells.

Now, a team of MIT scientists has found a way to produce graphene in significant quantities in a two- or three-layer form. When the layers are arranged just right, these structures give graphene the much-desired band gap - an energy range that falls between the bands, or energy levels, where electrons can exist in a given material.

''It's a breakthrough in graphene technology,'' says Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering at MIT. The new work is described in a paper published this week in the journal Nature Nanotechnology, co-authored by graduate student Chih-Jen Shih, Professor of Chemical Engineering Daniel Blankschtein, Strano and 10 other students and postdocs.

Graphene was first proven to exist in 2004 (a feat that led to the 2010 Nobel Prize in physics), but making it in quantities large enough for anything but small-scale laboratory research has been a challenge. The standard method remains using adhesive tape to pick up tiny flakes of graphene from a block of highly purified graphite (the material of pencil lead) - a technique that does not lend itself to commercial-scale production.

The new method, however, can be carried out at a scale that opens up the possibility of real, practical applications, Strano says, and makes it possible to produce the precise arrangement of the layers - called A-B stacked, with the atoms in one layer centered 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 says.