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Published: 8 August 2012  
Related category(ies):
Innovation  |  Industrial research


Countries involved in the project described in the article:
United Kingdom
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Nano tool may transform how we define electrical current

Researchers in the United Kingdom have developed a novel nanodevice that could revolutionise the way electrical current is defined today. Presented in the journal Nature Communications, the study demonstrates how using specially designed gale drive waveforms can increase the accuracy of a semiconductor quantum-dot pump.

Scanning electron microscope image of the electron pump. The arrow shows the direction of electron pumping. The hole in the middle of the electrical control gates where the electrons are trapped measures ~0.0001 mm across. © NPL
Scanning electron microscope image of the electron pump. The arrow shows the direction of electron pumping. The hole in the middle of the electrical control gates where the electrons are trapped measures ~0.0001 mm across.
©  NPL

National Physical Laboratory (NPL) and University of Cambridge scientists developed accurate electrical currents by using nanodevices. This electron pump has the capacity to pick up electrons one at a time and then move them across a barrier. The end result is a well-defined electrical current.

According to the researchers, this innovative device handles single electrons to stimulate electrical current. This development could potentially replace today's ampere, which depends on measurements of mechanical forces on current-carrying wires.

The team tested the exact shape of the voltage pulses that manipulate the trapping and ejection of electrons. They succeeded in accelerating the overall rate of pumping without losing accuracy, because they changed the voltage slowly while trapping electrons, and then changed the voltage quickly when ejecting them.

The outcome? They pumped nearly a billion electrons per second, accounting for a 300-fold increase over the previous record for an accurate electron pump, established by the United States–based National Institute of Standards and Technology (NIST) 16 years ago.

They calculated the current with an accuracy of one part per million, despite the fact that the resulting current was small, totalling 150 picoamperes (e.g. 10 billion times smaller than the current used when boiling a kettle). This unprecedented result is a boon for researchers investigating the precise and fast control of single electrons, and it could lead to the redefinition of the ampere unit.

'Our device is like a water pump in that it produces a flow by a cyclical action,' said co-author Masaya Kataoka of the Quantum Detection Group at NPL. 'The tricky part is making sure that exactly the same number of electronic charge is transported in each cycle. The way that the electrons in our device behave is quite similar to water; if you try and scoop up a fixed volume of water, say in a cup or spoon, you have to move slowly otherwise you'll spill some. This is exactly what used to happen to our electrons if we went too fast.'

Commenting on the research, lead author Stephen Giblin, of the Quantum Detection Group at NPL, said: 'For the last few years, we have worked on optimising the design of our device, but we made a huge leap forward when we fine-tuned the timing sequence. We've basically smashed the record for the largest accurate single-electron current by a factor of 300.

'Although moving electrons one at a time is not new, we can do it much faster, and with very high reliability — a billion electrons per second, with an accuracy of less than one error in a million operations. Using mechanical forces to define the ampere has made a lot of sense for the last 60 or so years, but now that we have the nanotechnology to control single electrons we can move on.'

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National Physical Laboratory (NPL)
University of Cambridge
Nature Communications

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