An international comparison of phase angle standards between the novel impedance bridges of CMI, INRIM and METAS

We report here the results of a comparison of electrical impedance standards aimed at evaluating four novel digital impedance bridges developed by the national metrology institutes CMI, INRIM and METAS. This comparison, which is the first of its kind, involved phase angle impedance standards developed by TÜBITAK UME with phase angles of  ± 30° and  ± 60°, and magnitudes ranging from about 100 Ω to 1 MΩ. The comparison demonstrated agreement among the measurement results obtained with the different bridges, and allowed us to gather information on the stability of the phase standards and on more critical aspects related to the characterization of the bridges

Inductive voltage divider calibration with sampling method

This paper presents an automatic system developed at METAS for the calibration of inductive voltage dividers (IVD). The used method is primary for the n/10 ratio. With the described improvements, the calibration of IVDs has been made easier, faster and more reproducible than with the manual system used before. The uncertainties which can be reached with this new system are 28·10-9 for the in phase and quadrature parts at a frequency of 1 kHz

Impedance simulator for automatic calibration of LCR meters: proof-of-principle experiment

Peer Reviewe

Observation of High Accuracy Resistance Quantization in CVD Graphene

A prime technique to produce graphene is Chemical Vapor Deposition (CVD). In this paper, the first observation of high accuracy resistance quantization in CVD graphene samples grown on polycrystalline copper foils is shown. High precision measurements performed using a cryogenic current comparator reveal a resistance quantization accuracy of 100 parts in 109

Comparative study of single and multi domain CVD graphene using large-area Raman mapping and electrical transport characterization

We systematically investigate the impact of granularity in CVD graphene films by performing Raman mapping and electrical characterization of single (SD) and multi domain (MD) graphene. In order to elucidate the quality of the graphene film, we study its regional variations using large-area Raman mapping and compare the G and 2D peak positions of as-transferred chemical vapor deposited (CVD) graphene on SiO 2 substrate. We find a similar upshift in wavenumber in both SD and MD graphene in comparison to freshly exfoliated graphene. In our case, doping could play the dominant role behind the observation of such upshifts rather than the influence due to strain. Interestingly, the impact of the polymer-assisted wet transfer process is the same in both the CVD graphene types. The electrical characterization shows that SD graphene exhibits a substantially higher (a factor 5) field-effect mobility when compared to MD graphene. We attribute the low sheet resistance and mobility enhancement to a decrease in charge carrier scattering thanks to a reduction of the number of grain boundaries and defects in SD graphen

Restoring the Electrical Properties of CVD Graphene via Physisorption of Molecular Adsorbates

Chemical vapor deposition (CVD) is a powerful technique to produce graphene for large-scale applications. Polymer-assisted wet transfer is commonly used to move the graphene onto silicon substrates, but the resulting devices tend to exhibit p-doping, which decreases the device quality and reproducibility. In an effort to better understand the origin of this effect, we coated graphene with n-methyl-2-pyrrolidone (NMP) and hexamethyldisilazane (HMDS) molecules that exhibit negligible charge transfer to graphene but bind more strongly to graphene than ambient adsorbents. Using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), electrical transport measurements, and quantum mechanical computer simulations, we show that the molecules help in the removal of p-doping, and our data indicate that the molecules do this by replacing ambient adsorbents (typically O2 and water) on the graphene surface. This very simple method of improving the electronic properties of CVD graphene by passivating its surface with common solvent molecules will accelerate the development of CVD graphene-based devices