Researchers Unzip Carbon Nanotubes to Make Ribbons of Graphene

A new route to the narrow graphene ribbons needed in electronics

3 min read

16 April 2009—Graphene, a one-atom-thick sheet of carbon with remarkable electrical properties, shows promise for future generations of high-speed transistors. It may have uses as diverse as the production of sensors or as scaffolding for tissue regeneration. But research is still in the early stages, in part because it’s so difficult to produce large quantities of graphene.

Now two research groups are reporting ways to make graphene ribbons, ranging in width from a few nanometers to a few hundred nanometers. The width matters because it, along with the shape of the edges of the ribbons, affects the conductivity of the graphene; ribbons narrower than about 10 nm confine the movement of electrons and act as semiconductors, while wider ribbons act as metallic conductors. Both methods start with carbon nanotubes and ”unzip” them to form flat ribbons of graphene.

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How the First Transistor Worked

Even its inventors didn’t fully understand the point-contact transistor

12 min read
A phot of an outstretched hand with several transistors in the palm of it.

A 1955 AT&T publicity photo shows [in palm, from left] a phototransistor, a junction transistor, and a point-contact transistor.

AT&T ARCHIVES AND HISTORY CENTER
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The vacuum-tube triode wasn’t quite 20 years old when physicists began trying to create its successor, and the stakes were huge. Not only had the triode made long-distance telephony and movie sound possible, it was driving the entire enterprise of commercial radio, an industry worth more than a billion dollars in 1929. But vacuum tubes were power-hungry and fragile. If a more rugged, reliable, and efficient alternative to the triode could be found, the rewards would be immense.

The goal was a three-terminal device made out of semiconductors that would accept a low-current signal into an input terminal and use it to control the flow of a larger current flowing between two other terminals, thereby amplifying the original signal. The underlying principle of such a device would be something called the field effect—the ability of electric fields to modulate the electrical conductivity of semiconductor materials. The field effect was already well known in those days, thanks to diodes and related research on semiconductors.

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