But graphene's electrons expand, in a sense, to cover large swaths, effectively riding over impurities like the tires of a monster truck over potholes. As a result, they go 100 times farther than silicon's—nearly a micrometer.
"It's so highly conductive," Geim says, "immediately the first thought, and the current thought, are for application to electronics."
The material that can replace silicon for the least cost will ultimately rule the day, but at scales of tens of atoms, graphene might perform as well as silicon or better, Kim says.
Of course, there are a few potential snags in the vision of nanometer-size circuits stamped onto Frisbee-size graphene wafers. Graphene is already "ridiculously" hyped, says Collins of U.C. Irvine. When a material is only three years old, he says, "it's kind of hard to start comparing that to something like silicon."
One problem is that Frisbee. Georgia Tech's de Heer reported some success with his method of cooking silicon carbide so that carbon atoms bubble to the top in one or a few atomic layers. But so far he has not observed the quantum Hall effect, suggesting that something crucial separates his graphene from the kind made with adhesive tape.
Then there is the challenge of how to toggle currents on and off in graphene. Silicon and other semiconductors transmit electrons of certain energies but block those of other energies. Nanotubes share this property, referred to as a band gap, but graphene does not.
The Light on the Graphene Horizon
Researchers have some ideas how to get over that hurdle. Geim's group reported in March that it had dialed a current up and down by shaping single-layer graphene into a very narrow hourglass. The presence of an electron in the waist of the hourglass blocked other electrons from passing—at room temperature, no less.
In another approach, Kim's group, working with IBM researchers, sliced graphene into 10-nanometer-wide ribbons, team member Jarillo-Herrero reported at the March meeting of the American Physical Society. Electrons carry energy only in specific amounts, or levels, and according to the team, electrons confined in graphene strips required larger doses of energy to reach the next level, creating a kind of band gap.
Etching these small shapes raises yet other problems. The carving process does not always work, although Geim expects that graphene can piggyback on improvements in silicon etching. It also leaves graphene with ragged edges, because the electrons that made chemical bonds with the excised carbon atoms remain like loose threads, interfering with passing electrons and dragging down the ribbon's current. Kim says graphene enthusiasts will have to find some way to mend the frayed ends.
"The nanotube solves that problem rather nicely by rolling up on itself," Collins says. "The ideal thing would be if … we could come up with some structure that combines the two." Or if researchers learn to more precisely manipulate nanotubes, they would regain much of their attractiveness, says Jarillo-Herrero.
At least a decade probably remains before graphene will have to walk the walk. Silicon will have no real competitors, Geim says, until it reaches 10 nanometers. "The death of silicon was announced many, many times before," he says. "It's not easy to stop a train, if you try. And silicon is much bigger than that." For now, graphene is the little engine that might.
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2 Comments
Add CommentWhy not use one half of a graphene hourglass as an electrical lead to a nanotube? Hence no bulky wire to attach to the elegant nanotube?
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Sounds like an ideal material to capture and conduct solar energy. GO BLUE!
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