March 14, 2012

Breaking The Speed Barrier For Graphene Devices



Now, writing in the Mar. 13 issue of the journal Nature Communications, a team of Vanderbilt physicists reports that they have nailed down the source of the interference inhibiting the rapid flow of electrons through graphene-based devices and found a way to suppress it. This discovery allowed them to achieve record-levels of room-temperature electron mobility — the measure of the speed that electrons travel through a material — three times greater than those reported in previous graphene-based devices.


“The problem is that, when you make graphene, you don´t get just graphene. You also get a lot of other stuff,” said Kirill Bolotin, assistant professor of physics, who conducted the study with research associate A.K.M. Newaz. “Graphene is extraordinarily susceptible to external influences so the electrical fields created by charged impurities on its surface scatter the electrons traveling through the graphene sheets, making graphene-based transistors operate slower and heat up more.”



At the same time, the experiment didn´t find evidence supporting one of the alternative theories, that ripples in the graphene sheets were a significant source of electron scattering

In order to get a handle on the mobility problem, Bolotin´s team suspended sheets of graphene in a series of different liquids and measured the material´s electric transport properties. They found that graphene´s electron mobility is dramatically increased when graphene is submerged in electrically neutral liquids that can absorb large amounts of electrical energy (have large dielectric constants). They achieved the record-level mobility of 60,000 using anisole, a colorless liquid with a pleasant, aromatic odor used chiefly in perfumery.



According to the physicist, there is also a potential advantage to graphene´s extraordinary sensitivity to its environment that can be exploited. It should make extremely sensitive sensors of various types and, because it is made entirely of carbon, it is biocompatible and so should be ideal for biological sensors.



Image Caption: An image of a suspended graphene device made by a scanning probe microscope. The graphene sheet is the orange-colored layer suspended between six rectangular columns made of silicon dioxide and capped by gold. (Credit: A.K.M. Newaz / Bolotin Lab)


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