Solution-based Process Could Produce Tuned Graphene in Bulk

Pulsed voltages add new wrinkle to electrochemical exfoliation of graphene

2 min read
Solution-based Process Could Produce Tuned Graphene in Bulk
Photo: National Cheng Kung University

Researchers in Taiwan have developed a solution-based process for producing graphene that is tuned to exhibit specific electrical and mechanical properties. While solution-based exfoliation of graphene has been possible for some time, this new approach uses pulses of an electrical voltage rather than a constant voltage to produce the desired effects.

The researchers believe that their work, which was reported in the journal Nanotechnology, could pave the way for new applications for graphene in drug delivery or electronics.

Graphene production methods have been seen as an obstacle to the use of the material in a range of applications for which it has been targeted.  The mechanical exfoliation of graphene sheets from graphite, while producing the best quality graphene for electronic applications, is decidedly un-scalable. And production methods that are more scalable lack the quality necessary for these same electronic applications. A solution-based process that can be ramped up to yield high volumes of graphene that possesses the electrical and mechanical properties one desires would cause a dramatic upshift in graphene’s commercial development.

“Whilst electrochemistry has been around for a long time it is a powerful tool for nanotechnology because it’s so finely tunable,” said Mario Hofmann, a researcher at National Cheng Kung University in Taiwan, in a press release. “In graphene production we can really take advantage of this control to produce defects.”

The trick to getting exactly the right defects in the graphene depended not only on using a pulsed voltage, but also being able to carefully monitor how the graphene was changing in the solvent process. To monitor this change, the researchers found that they could simply observe the transparency of the solution.

As part of their work, the researchers tested the quality of the graphene produced via their method as a transparent conductor (the application for which graphene is being considered as a potential replacement for indium tin oxide). The resistance of their graphene films (at 50 percent transparency) was 30 times that of other graphene-based transparent conductors.

In future research, the Taiwan-based team will look at how altering the duration of the pulses impacts the exfoliation process both in terms of producing greater quantities of final product as well as gaining greater control on the defects engineered into the 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.

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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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