MIT researchers give graphene band gap and open the door for post-silicon electronic devices
By Darren Quick
June 28, 2011
Earlier this year we ran a story on molybdenite, a mineral that held an advantage over graphene for use in electronic devices due to the existence of "band gaps" in the material that are needed for devices such as transistors, computer chips and solar cells. Now MIT researchers have overcome that deficiency by finding a way to produce graphene in significant quantities in a two- or three-layer form with the layers arranged just right to give the material the much-desired band gap.
The standard method for making graphene involves using adhesive tape to pick up tiny flakes of the material from a block of highly purified graphite. This technique doesn't exactly lend itself to commercial-scale production and makes producing quantities large enough for anything other than small-scale laboratory research a challenge.
Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering at MIT, says the new method developed at MIT can be carried out at a scale that opens up the possibility of real, practical applications and makes it possible to produce the precise arrangement of layers - called A-B stacked, where the atoms in one layer are centered over spaces between atoms in the next - that yields desirable electronic properties.
When compounds of bromine or chlorine are introduced into a block of graphite they insert themselves regularly between every other layer, or in some cases every third layer, pushing the layers slightly farther apart. Strano and his team found that when graphite is dissolved, it naturally comes apart where the added atoms lie, forming graphene flakes two or three layers thick.
"Because this dispersion process can be very gentle, we end up with much larger flakes" than anyone has made using other methods, Strano says. "Graphene is a very fragile material, so it requires gentle processing."
The flakes produced by this method are as large as 50 square micrometers in area, which they say is large enough to be useful for electronic applications and one of the most promising candidates for post-silicon electronics. To prove the point, they were able to manufacture some simple transistors on the material.
Strano says the new approach is industrially relevant and graphene can now be used to explore the development of new kinds of electronic and optoelectronic devices. While he won't predict exactly how long it will take to develop the new method to the point of commercial applications, Strano says the research is coming about at a breakneck pace and that this is definitely a big step toward making bilayer and trilayer devices.