Submerged in liquid, graphene gets faster
Researchers have found that submersion in liquid can overcome graphene’s Achilles’ heel—sensitivity to its electrical environment.
This single-atom-thick honeycomb of carbon atoms is lighter than aluminum, stronger than steel, and conducts heat and electricity better than copper. As a result, scientists around the world are trying to turn it into better computer displays, solar panels, touch screens, integrated circuits, and biomedical sensors, among other possible applications.
However, it has proven extremely difficult to reliably create graphene-based devices that live up to its electrical potential when operating at room temperature and pressure.
According to the experts, graphene may have the highest electron mobility of any known material. In practice, however, the measured levels of mobility, while significantly higher than in other materials like silicon, have been considerably below its potential.
“The problem is that, when you make graphene, you don’t get just graphene. You also get a lot of other stuff,” says 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.”
A number of researchers had proposed that the charged impurities that are omnipresent on the surface of graphene were the main culprits, but it wasn’t completely certain. Also, several other theories had been advanced to explain the phenomenon.
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.
“These liquids suppress the electrical fields from the impurities, allowing the electrons to flow with fewer obstructions,” Bolotin says.
Now that the source of the degradation in electrical performance of graphene has been clearly identified, it should be possible to come up with reliable device designs, Bolotin says.