Stabilizing a graphene platform toward discrete components

© 2016 Author(s).We report on statistical analysis and consistency of electrical performances of devices based on a large scale passivated graphene platform. More than 500 graphene field effect transistors (GFETs) based on graphene grown by chemical vapor deposition and transferred on 4 in. SiO2/Si substrates were fabricated and tested. We characterized the potential of a two-step encapsulation process including an Al2O3 protection layer to avoid graphene contamination during the lithographic process followed by a final Al2O3 passivation layer subsequent to the GFET fabrication. Devices were investigated for occurrence and reproducibility of conductance minimum related to the Dirac point. While no conductance minimum was observed in unpassivated devices, 75% of the passivated transistors exhibited a clear conductance minimum and low hysteresis. The maximum of the device number distribution corresponds to a residual doping below 5 × 1011 cm−2 (0.023 V/nm). This yield shows that GFETs integrating low-doped graphene and exhibiting small hysteresis in the transfer characteristics can be envisaged for discrete components, with even further potential for low power driven electronics.This study was partly funded by the European Union through the projects Grafol (No. 285275) and Graphene Flagship (No. 604391 and Core1 No. 696656)

Thirty Gigahertz Optoelectronic Mixing in Chemical Vapor Deposited Graphene

© 2016 American Chemical Society. The remarkable properties of graphene, such as broadband optical absorption, high carrier mobility, and short photogenerated carrier lifetime, are particularly attractive for high-frequency optoelectronic devices operating at 1.55 μm telecom wavelength. Moreover, the possibility to transfer graphene on a silicon substrate using a complementary metal-oxide-semiconductor-compatible process opens the ability to integrate electronics and optics on a single cost-effective chip. Here, we report an optoelectronic mixer based on chemical vapor-deposited graphene transferred on an oxidized silicon substrate. Our device consists in a coplanar waveguide that integrates a graphene channel, passivated with an atomic layer-deposited Al2O3 film. With this new structure, 30 GHz optoelectronic mixing in commercially available graphene is demonstrated for the first time. In particular, using a 30 GHz intensity-modulated optical signal and a 29.9 GHz electrical signal, we show frequency downconversion to 100 MHz. These results open promising perspectives in the domain of optoelectronics for radar and radio-communication systems

Partitioning of the pesticide trifluralin between dissolved organic matter and water using automated SPME-GC/MS

Solid-phase microextraction (SPME) was used to determine the equilibrium association constant for a pesticide, trifluralin (TFR), with dissolved organic matter (DOM). After optimization of the SPME method for the analysis of TFR, partition coefficients (KDOM) with three different sources of DOM were determined in buffered solutions at pH 7. Commercial humic acids and DOM fractions isolated from two surface waters were used. The values of log KDOM varied from 4.3 to 5.8, depending on the nature of the organic material. A good correlation was established between log KDOM and DOM properties (as measured with the H/O atomic ratio and UV absorbance), in agreement with literature data. This is consistent with the effect of polarity and aromaticity for governing DOM-pollutant associations, regardless of the origin of DOM. This association phenomenon is relevant to better understand the behavior of pesticides in the environment since it controls part of pesticide leaching and fate in aquatic systems

Nanocrystalline diamond coatings: Effects of time modulation bias enhanced HFCVD parameters

Nanocrystalline diamond NCD coatings could improve the performances of cutting tools if the adhesion on cobalt-cemented tungsten carbide WC–Co substrates was optimized and maintained during diamond deposit. In this study, a time modulated polarized growth process during diamond hot filament chemical vapor deposition (HFCVD) method was used. NCD coatings were deposited on cobalt-cemented tungsten carbide (WC–10% Co) substrates previously coated with tantalum or zirconium nitride–molybdenum bilayer as interlayer systems to control carbon and cobalt diffusion. Continuous films consisted of diamond clusters. Their size decreased when the applied bias voltage increased and substrate temperature decreased. Raman analyses confirmed the reduction of crystallite size and formation of nanocrystalline diamond films by time modulated biased substrate HFCVD process. Scratch tests showed that the NCD/interlayer systems/WC–10% Co displayed very good film adhesion interesting for cutting tools applications compared to NCD/WC–10% Co. In addition using an interlayer system could offer additional protection when diamond coating was deteriorated. This technique seems to be promising for industrial applications in the field of machining tools when increasing the thickness of the diamond layer by only extending the time modulated deposition process