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How and Why: Graphene seems valuable for computers, batteries and other uses

Monday, October 25, 2010; 3:56 PM

Nanomaterials rarely burst into the public consciousness. They are, after all, visible only through an electron microscope, a $40,000 luxury most people will never attempt to use. But this year's Nobel Prize for Physics put the spotlight on graphene, a single-layer sheet of carbon molecules with borderline magical properties.

Scientists have been investigating small bits of carbon for a long time. Researchers stumbled upon tiny geodesic carbon spheres in 1985 and named them buckyballs, after gonzo architect and dome meister Buckminster Fuller. Six years later, scientists began experimenting with carbon nanotubes. But the thinnest possible carbon sheets, just a single atom thick, eluded physicists. They lacked the tools to shave a material that thin, and none of their chemical reactions could produce just one layer.

By now, from the Nobel Prize coverage, you may know that Scotch tape came to the rescue. In 2004, two Russian-born scientists at the University of Manchester stuck Scotch tape to a chunk of graphite, then repeatedly peeled it back until they had the tiniest layer possible.

Now that graphene is everyone's favorite nanomaterial, it raises some questions: What is graphene good for, and when is it going to change our lives? A bunch of research centers are working feverishly on the answers.

The first and best-known potential use for graphene is in computer chips. Today's chips rely on silicon, which is a great material because it's cheap and changes its behavior in response to tiny electrical voltages. But we're nearing the limit of its potential. If the speed and power requirements of computers keep increasing, they will push silicon to its melting point.

Graphene's electrons move 100 to 1,000 times faster than those of silicon, meaning less power will be required for the same computing capacity. Such blazing speed might also help produce ever-tinier computing devices with more power than your clunky laptop.

Nongjian Tao, an Arizona State University professor who studies the basic properties of graphene, also foresees graphene-based chemical sensors to detect explosives in luggage and volatile organic compounds in the air. "Graphene allows you to convert a chemical reaction into an electronic signal," he says.

Graphene also flaunts incredible strength and stiffness. In 2008, scientists at Columbia University proved it to be the world's strongest material, pound for pound. To put it into perspective, if you had a sheet of graphene as thick as a piece of cellophane, it would support the weight of a car. If paper were as stiff as graphene, you could hold a 100-yard-long sheet of it at one end without its breaking or bending.

This incredible strength raises all sorts of possibilities. If you took small flakes of graphene and mixed them into other materials, you could use those composites to build far stronger, lighter products - anything from airplanes to tennis racquets.

Graphene might also revolutionize electrical energy storage by vastly improving ultra-capacitors. These are the specialized batteries that can supply huge bursts of energy over a short period.

Ultra-capacitors have lots of uses. Their quick energy surge helps cranes hoist loads, for example. The problem is that existing models just can't store that much energy. Graphene, which could be stacked up to create vast expanses of surface area for electrochemical reactions, might change that.

Hybrid cars are a potential application. When you apply the brakes in your Prius, its special battery captures the energy normally lost as friction between brake pads and wheel. As you accelerate, that battery then releases its energy stores to get the car going again.

Today's hybrid car batteries are often made with nickel metal hydride. They are more powerful than the lead acid model that provides the power to turn on your conventional car, but not strong enough to provide rapid acceleration. (That's why your hybrid uses the gas engine when you put the pedal to the metal.) Even lithium, which is becoming more popular, is limited. Early prototypes suggest that graphene-based batteries might be more powerful and far longer-lived.

Graphene ultra-capacitors could also stabilize the energy grid.

The country's energy demands vary tremendously. During peak hours, most of our power plants are running full tilt. In the middle of the night, many of them just sit there doing nothing. If there were a cost-effective way to store energy made during the night, we could get by with fewer power plants. Most important, we could shutter the least efficient and least environmentally friendly plants.

Don't expect to buy graphene computers, batteries or tennis racquets anytime soon. The computer chips are probably the farthest along, but even the most optimistic materials scientists don't expect any microcomputing revolutions for at least a decade.

One of the biggest holdups is just finding a way to make graphene on an industrial scale.

The Scotch tape method was a major breakthrough: Laboratory scientists can pay undergraduates $10 per hour to create enough graphene flakes to fuel their research. But Motorola and Intel aren't going to feed their fabrication lines with legions of tape-wielding employees. The process, known in scientific circles as exfoliation, is slow, labor-intensive and inefficient. And it produces such small flakes of graphene that you could put about 2,000 of them on the head of a pin. We need a method to create sheets of the stuff.

There are some promising techniques out there. Rodney S. Ruoff, a University of Texas professor, is pioneering a chemical vapor method for creating larger pieces of graphene that has attracted interest from IBM and Texas Instruments, among others. He heats up methane (a molecule made of only carbon atoms) and hydrogen to 1,040 degrees Celsius and lets the chemicals react with a copper sheet, leaving behind a layer of graphene. It's currently the most promising method for making graphene on an industrial scale.

As chic as graphene is today, it's still really a material of the future. But there's so much money and excitement in graphene research, the future may be soon.

Palmer, a freelance writer based in New York, is a regular contributor to this column and to Slate.com's Explainer column.

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