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We report on investigations about limitations of the Hall resistance quantization accuracy (4×10−7) measured in Hall bars based on monolayer and bilayer exfoliated graphene deposited on Si/SiO 2 substrates (best results in such devices). Transport measurements at low magnetic field (including quantum corrections) reveal that charge carrier scattering is mainly caused by charged impurities. In the QHE regime, dissipation occurs through quasi-elastic inter-Landau level (LL) scattering assisted by large local electric fields. We propose that charged impurities are responsible for an enhancement of such inter-LL transitions and cause the low breakdown currents (≈1µA) observed in the narrow (

We report on quantization tests of the quantum Hall effect in monolayer and bilayer graphene based devices which are fabricated from natural graphite by micromechanical exfoliation. Measurements of the Hall resistance R H with relative uncertainties in the range of 10−7 performed using a cryogenic current comparator based resistance bridge have been combined with high-precision longitudinal resistance R xx measurements to demonstrate that the quantization of R H in such graphene based devices agrees with the theoretical prediction with a relative accuracy of about 2 parts in 107. For a BL sample, the characterizations which have been carried out reveal the existence of a ν=−4 Hall resistance plateau flat within 2 parts in 106 over a finite range of electron density. At the center of the plateau, the Hall resistance agrees with R K /4 within 1.5 part in 107. Besides, a sample fabricated from a ML was also characterized: an agreement between the Hall resistance and R K /2 on the ν=2 plateau within 3 parts in 107 has been demonstrated.

We report on the fabrication of graphene based devices using the micromechanical exfoliation of natural graphite and their electrical characterization including metallic contact resistance measurements, mobility and density charge carriers measurements. The first and major application aimed is the quantrum Hall effect (QHE) metrology. The samples fabricated, from both monolayer and bilayer graphene flakes, with rather low contact resistance (typically a few tens or hundreds of Ω) enable the performance of QHE quantization tests exact within uncertainties of some part in 107. The limitations of this record accuracy are suggested by the results of the extensive characterizations performed (small size samples (

Graphene Hall bars prepared from exfoliated natural graphite of large size and high quality have been measured in the quantum Hall effect regime. The monolayer Graphene sheet shows Hall quantization robust upon applying very large current. Low longitudinal resistance is found up to 10 muA with finite width h/2e2 Hall plateau at 4.2 K and 16 T. The TiAu/Graphene contact resistance is found low, typically 20 Omega to 50 Omega. The results strongly indicate that Graphene is a promising new material for quantum metrology.