Nano knowledge - Applying nanotechnology for better metrology

20 June 2013

At the heart of all scientific endeavour is metrology, the science of measurement. So, as guardian of the SI system – Système International d’Unités – in the UK, the National Physical Laboratory (NPL) is vital to all scientific research, now and in the future. An EPSRC Knowledge Transfer Secondment has strengthened ties between NPL and the London Centre for Nanotechnology (LCN), a joint UCL and Imperial College venture, bringing us a step closer to more accurate measurement of current.

Big issues, tiny solutions

LCN is developing superconducting nanowires for applications in quantum metrology. This involves taking conventional superconducting material and making a structure 20 to 30 nanometres in cross section – a thousand times thinner than a human hair.

Professor Paul Warburton, head of the UCL Quantum Nanoelectronics Group, explained the significance of the work, “The interest in nanowire superconductors is both in terms of the fundamental physics, as well as the potential to fabricate a useful current-measuring device using them.

“One of the jobs of the National Physical Laboratory is to maintain precise standards for different units, such as the volt, the kilogram, the amp and so on. At the moment it can’t be done as accurately for the amp as it can for other units, so the NPL are looking at new ways of defining the amp. With this secondment, we were able to help.”

Dr Jon Fenton, the secondee, split his time during the six months between facilities at LCN and NPL. He explained,

“As nanotechnology in general becomes more important, the currents that are being used to move signals around circuits tend to get smaller and smaller. So your ability to define them accurately becomes more important. Industry goes to NPL, ultimately, to calibrate their amp. Nanowire superconductors can be used to derive a quantum standard for the SI unit the amp, because you can use them to give you a very precise definition of current. This is predicted to be more accurate than the way NPL currently calculates it.”

A good balance

Dr Fenton explained the benefits of the partnership for UCL, “The secondment made good sense for us because it brought in expertise from NPL, as well as the opportunity to make use of specialist equipment that we needed for this project. Of course, they also provided the funding necessary to advance the research for a few months.”

It was a fair exchange. JT Janssen a researcher at NPL who worked on the project with Dr Fenton said, “UCL have a long experience in superconductive quantum effects and can fabricate these structures, whilst NPL possesses the know-how and infrastructure to make precision measurements under the right conditions. In that sense it was an ideal collaboration, in which both partners could achieve results not possible on their own. Although a quantum-phaseslip based current standard is not yet a reality, a number of interesting scientific results have been published and work continues.”

Reaching the nano-community

Dr Fenton is pleased that he is able to share his research with the scientific community, having submitted a paper based partly on the work undertaken during the secondment, “Getting this paper published is an achievement for me. Having extra funding just to be able to do the work was really useful, and at this stage of the research, when a final product is some way off, publication of exciting advancements in the field is the mark of success.”

More information

NbSi nanowire quantum-phase-slip circuits: DC supercurrent blockade, microwave measurements and thermal analysis, C. H. Webster, J. C. Fenton, T. T. Hongisto, S.P. Giblin, A.B. Zorin and P.A. Warburton, Physical Review B, 87, 144510 (2013).