Controlling Traffic on the Electron Highway: Researching Graphene

On an otherwise normal day in the lab, Eva Andrei didn’t expect to make a major discovery. Andrei, a physics professor at Rutgers University, was using graphite – the material in pencils – to calibrate a scanning tunneling microscope. As part of the process, she turned on a very powerful magnetic field. When she looked up to see the material’s electronic spectrum, she was astonished. “We saw huge, beautiful peaks up there, just incredible. And they didn’t make any sense,” she recalled.

Remembering a lecture she’d recently attended, she realized the graphite had separated out into sheets just one atom thick. This material, known as graphene, has bizarre electronic properties. But even for graphene, the spectrum she saw was strange. In fact, no one had ever seen anything like it before. As Andrei described it, her colleague “went berserk in the corridor and just yelled ‘Graphene!’” Andrei had made a serendipitous discovery – a new electric phenomenon.

This was neither the first nor last time that electrons’ movement in graphene would surprise and elate scientists. One of the most impressive things about graphene is how fast electrons move through it. They travel through it more than 100 times faster than they do through the silicon used to make computer chips. In theory, this suggests that manufacturers could use graphene to make superfast transistors for faster, thinner, more powerful touch-screens, electronics, and solar cells.

But what makes graphene so amazing also hinders its use: Electrons flow through its honeycomb structure too easily. Unlike silicon, graphene lacks a bandgap. Bandgaps are the amount of energy an electron must gain to free itself from an atom and move to other atoms to conduct a current. Like a toll on a highway, electrons need to “pay” with energy to proceed. Electronic devices use bandgaps as gates to control where and when electrons flow. Lacking bandgaps, graphene’s structure acts like an electron superhighway with no stop signs.

Graphene’s electrons are so wild and can’t be tamed; it’s hard to create a gap,” said Andrei.

That lack of a bandgap makes graphene currently very difficult to use in modern electronics. Researchers supported by the Department of Energy’s (DOE’s) Office of Science are investigating ways to overcome this challenge and others to direct graphene’s electron traffic.”

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