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The SI unit of resistance is realized at NPL using a quantum Hall effect device. Recent research on graphene devices has enabled the quantum Hall effect to be realized at both lower magnetic fields and higher temperatures, whilst still retaining part per billion accuracies. The detailed findings are published in a recent edition of Metrologia.
NPL in collaboration with Oxford Instruments is developing a table-top primary standard of resistance incorporating both a graphene quantum Hall effect device and a cryogenic current comparator in the same cryostat, in order to provide a compact and easy-to-operate system for metrology laboratories.
Collaboration - NPL - Chalmers - University - Technology
The long-term collaboration between NPL, Chalmers University of Technology and Graphensic, has resulted in a big advance in graphene samples. Epitaxial graphene (epigraphene) has been grown on silicon carbide and has better performance at higher temperatures and lower magnetic field than was previously possible. In practical terms, it has also removed the difficult process of fine-tuning the carrier density and means the 'table-top' system can be warmed up and cooled back down and the plateau stays where it is set with no user intervention.
NPL, Chalmers University of Technology and the national metrology institute of Sweden (RISE) have demonstrated the metrological quality and stability of these types of devices for up to two years.
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