Graphene joins the race to redefine the ampere

May 12, 2013
Credit: University of Manchester

A new joint innovation by the National Physical Laboratory (NPL) and the University of Cambridge could pave the way for redefining the ampere in terms of fundamental constants of physics. The world's first graphene single-electron pump (SEP), described in a paper today in Nature Nanotechnology, provides the speed of electron flow needed to create a new standard for electrical current based on electron charge.

The (SI) comprises seven base units (the metre, kilogram, second, , ampere, mole and candela). Ideally these should be stable over time and universally reproducible. This requires definitions based on fundamental constants of nature which are the same wherever you measure them.

The present definition of the Ampere, however, is vulnerable to drift and instability. This is not sufficient to meet the accuracy needs of present and certainly future electrical measurement. The highest global measurement authority, the Conférence Générale des Poids et Mesures, has proposed that the ampere be re-defined in terms of the electron charge.

The frontrunner in this race to redefine the ampere is the single-electron pump (SEP). SEPs create a flow of individual electrons by shuttling them in to a quantum dot – a particle holding pen – and emitting them one at a time and at a well-defined rate. The paper published today describes how a graphene SEP has been successfully produced and characterised for the first time, and confirms its properties are extremely well suited to this application.

A good SEP pumps precisely one electron at a time to ensure accuracy, and pumps them quickly to generate a sufficiently large current. Up to now the development of a practical electron pump has been a two-horse race. Tuneable barrier pumps use traditional semiconductors and have the advantage of speed, while the hybrid turnstile utilises and has the advantage that many can be put in parallel. Traditional metallic pumps, thought to be not worth pursuing, have been given a new lease of life by fabricating them out of the world's most famous super-material - graphene.

Previous metallic SEPs made of aluminium are very accurate, but pump electrons too slowly for making a practical current standard. Graphene's unique semimetallic two-dimensional structure has just the right properties to let electrons on and off the quantum dot very quickly, creating a fast enough - at near gigahertz frequency - to create a current standard. The Achillies heel of metallic pumps, slow pumping speed, has thus been overcome by exploiting the unique properties of graphene.

The scientist at NPL and Cambridge still need to optimise the material and make more accurate measurements, but today's paper marks a major step forward in the road towards using graphene to redefine the ampere.

The realisation of the ampere is currently derived indirectly from resistance or voltage, which can be realised separately using the quantum Hall effect and the Josephson Effect. A fundamental definition of the ampere would allow a direct realisation that National Measurement Institutes around the world could adopt. This would shorten the chain for calibrating current-measuring equipment, saving time and money for industries billing for electricity and using ionising radiation for cancer treatment.

Current, voltage and resistance are directly correlated. Because we measure resistance and voltage based on – electron charge and Planck's constant - being able to measure current would also allow us to confirm the universality of these constants on which many precise measurements rely.

Graphene is not the last word in creating an ampere standard. NPL and others are investigating various methods of defining current based on . But today's paper suggests graphene SEPs could hold the answer. Also, any redefinition will have to wait until the Kilogram has been redefined. This definition, due to be decided soon, will fix the value of electronic charge, on which any electron-based definition of the ampere will depend.

Today's paper will also have important implications beyond measurement. Accurate SEPs operating at high frequency and accuracy can be used to make collide and form entangled electron pairs. Entanglement is believed to be a fundamental resource for quantum computing, and for answering fundamental questions in quantum mechanics.

Malcolm Connolly, a research associate based in the Semiconductor Physics group at Cambridge, says: "This paper describes how we have successfully produced the first graphene single-electron pump. We have work to do before we can use this research to redefine the ampere, but this is a major step towards that goal. We have shown that graphene outperforms other materials used to make this style of SEP. It is robust, easier to produce, and operates at higher frequency. Graphene is constantly revealing exciting new applications and as our understanding of the material advances rapidly, we seem able to do more and more with it."

Explore further: Demystifying nanocrystal solar cells

More information: Gigahertz quantized charge pumping in grapheme quantum dots, Nature Nanotechnology, DOI: 10.1038/nnano.2013.73

Related Stories

Redefining the kilogram and the ampere

Sep 29, 2011

New research using graphene presents the most precise measurements of the quantum Hall effect ever made, one of the key steps in the process to redefine two SI units.

New nanodevice builds electricity from tiny pieces

Jul 06, 2012

(Phys.org) -- A team of scientists at the National Physical Laboratory (NPL) and University of Cambridge has made a significant advance in using nano-devices to create accurate electrical currents. Electrical ...

Switchyard for single electrons

Feb 25, 2008

German scientists achieved to transfer very small charge "packets", comprising a well-defined number of few electrons, between metallic electrons precisely by using a single-electron pump. A single-electron transistor, being ...

Graphene's high-speed seesaw

Apr 30, 2013

A new transistor capable of revolutionizing technologies for medical imaging and security screening has been developed by graphene researchers from the Universities of Manchester and Nottingham.

Recommended for you

Demystifying nanocrystal solar cells

Jan 28, 2015

ETH researchers have developed a comprehensive model to explain how electrons flow inside new types of solar cells made of tiny crystals. The model allows for a better understanding of such cells and may ...

Researchers use oxides to flip graphene conductivity

Jan 26, 2015

Graphene, a one-atom thick lattice of carbon atoms, is often touted as a revolutionary material that will take the place of silicon at the heart of electronics. The unmatched speed at which it can move electrons, ...

Researchers make magnetic graphene

Jan 26, 2015

Graphene, a one-atom thick sheet of carbon atoms arranged in a hexagonal lattice, has many desirable properties. Magnetism alas is not one of them. Magnetism can be induced in graphene by doping it with magnetic ...

The latest fashion: Graphene edges can be tailor-made

Jan 23, 2015

Theoretical physicists at Rice University are living on the edge as they study the astounding properties of graphene. In a new study, they figure out how researchers can fracture graphene nanoribbons to get ...

Nanotechnology changes behavior of materials

Jan 23, 2015

One of the reasons solar cells are not used more widely is cost—the materials used to make them most efficient are expensive. Engineers are exploring ways to print solar cells from inks, but the devices ...

User comments : 7

Adjust slider to filter visible comments by rank

Display comments: newest first

viajerodelespacio
1 / 5 (2) May 12, 2013
Could this have an impact on Ohm's Law?
AntonKole
1 / 5 (6) May 12, 2013
Great to here.
vacuum-mechanics
1 / 5 (8) May 12, 2013
Graphene is not the last word in creating an ampere standard. NPL and others are investigating various methods of defining current based on electron charge. But today's paper suggests graphene SEPs could hold the answer. Also, any redefinition will have to wait until the Kilogram has been redefined. This definition, due to be decided soon, will fix the value of electronic charge, on which any electron-based definition of the ampere will depend.

By the way, it is interesting to note that nowadays we still do not understand what the 'electron charge' is, how the same charge repel while different one attract? Maybe understanding the charge mechanism (as below) could help a better redefinition the ampere standard.
http://www.vacuum...21〈=en
210
1 / 5 (4) May 12, 2013
Graphene is not the last word in creating an ampere standard. NPL and others are investigating various methods of defining current based on electron charge. But today's paper suggests graphene SEPs could hold the answer. Also, any redefinition will have to wait until the Kilogram has been redefined. This definition, due to be decided soon, will fix the value of electronic charge, on which any electron-based definition of the ampere will depend.

By the way, it is interesting to note that nowadays we still do not understand what the 'electron charge' is, how the same charge repel while different one attract? Maybe understanding the charge mechanism (as below) could help a better redefinition the ampere standard.
http://www.vacuum...21〈=en


Ummm? I need a little more data on the dynamics of the concept of " vacuum media" etc, etc,
210
1 / 5 (3) May 12, 2013
Great to here.


Oh...and great to Hear, too...!

word-
rsklyar
1 / 5 (4) May 14, 2013
How British swindlers from the University of Sussex and the University of Cambridge are stealing in their cheating journals Nature Materials and "Measurement Science and Technology" at https://connect.i...sr/blogs (Impertinent cheating ... & A robbery …)
rsklyar
1 / 5 (4) May 28, 2013
P. S. Some other British swindlers have already hide these links. That is why the correct ones are at http://www.scribd.com/r_sklyar

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.