Graphene on silicon carbide (SiC) has been shown to give an accurate resistance standard and to outperform the presently used gallium arsenide (GaAs) devices in many aspects. Now, researchers at the Centre for Metrology and Accreditation of MIKES (Mittatekniikan keskus) in Espoo, Finland have shown that the measurements can be performed at lower magnetic fields and on industrially produced material ('Precision quantum Hall resistance measurement on epitaxial graphene device in low magnetic field' by Satrapinski et al, Applied Physics Letters vol 103 issue 17; DOI: 10.1063/1.4826641).
The quantum resistance standard is an ultimate test of materials. This resistance, based on the quantum Hall effect in two-dimensional (2D) structures, allows very accurate realization of resistance in terms of two fundamental constants of nature: elementary charge (e) and Planck constant (h). It is hence independent of other factors and may therefore be used as a universal standard for resistance.
Quantum resistance measurements require a high applied magnetic field and a low cryogenic temperature. Earlier precision measurements on graphene have been performed in a magnetic field of about 10 Tesla or more, and at temperatures of about 0.3K or below. But now the researchers at MIKES have demonstrated that highly accurate measurements can be obtained at lower magnetic fields (ranging from 8 Tesla down to 3 Tesla) even when the measurement temperature was not less than 1.5K.
Using MIKES's self-developed precision resistance bridge based on a cryogenic current comparator (CCC), the correctness of the quantum Hall resistance of the graphene device could be verified with accuracy much better than 1 part per million.
Picture: Graphene-based quantum Hall standard of resistance developed in collaboration between MIKES and Aalto University on graphene supplied by Graphensic.
The measurements were performed on industrially produced material supplied by Graphensic AB of Link?ping, Sweden (Europe's first commercial supplier of graphene on silicon carbide), which applies a high-growth-temperature method to produce the graphene. Photolithographic patterning and electrical contacts were made by Aalto University in Espoo.
"It is very interesting to see how the material and its growth can be pushed to maintain the exceptional properties of graphene," comments Alexandre Satrapinski, who is in charge of graphene research at MIKES.
