Structural and electronic properties of epitaxial graphene grown on SiC (0001) at low argon pressure

Consider advances are being made to develop new technologies capable of fast in-situ tracing of agricultural toxins. In this work, we reported a simple carbaryl sensor with very high sensitivity using graphene interdigitated ion selective field effect transistor (ISFET). The graphene films were first prepared on polycrystalline copper foil by a low-pressure chemical vapor deposition method, and then transferred onto the interdigitated electrodes of ISFETs by a chemical etching technique. The biorecognition is based on the enzymatic inhibition of carbaryl towards urease. As expected, the weaker enzymatic activity of urease in addition of carbaryl would result in the weaker current response. It was demonstrated that the interdigitated ISFET sensor could achieve high sensitivity to detect carbaryl as low as 10−8 μg mL−1 and the current response of the device showed a good linearity against the logarithm of carbaryl concentration Ccarbaryl with a regression equation ΔIds = −0.4 − 0.6 logCcarbaryl (mA) (R2 = 0.99) in the concentration range from 2.58 × 10−7 to 2.58 × 10−2 μg mL−1. In conlusion, such convenient graphene-based ISFET configuration could be advantageously extended for on-line screening of other pesticide and herbicide agents

By combining rheology, light scattering, small angle X-ray scattering and simulations we explore the glassy dynamics of soft colloids using microgels and charged particles interacting by steric and screened Coulomb interactions, respectively. In the supercooled regime, the structural relaxation time (SRT) of both systems grows steeply with volume fraction, reminiscent of the behavior of colloidal hard sphere systems [1]. This suggests that softness has no impact on the growth of the SRT on approaching the glass transition, as confirmed by computer simulations. We show that the onset of a finite yield-stress, occurring within the supercooled regime, systematically corresponds to a minimum of the stretching exponent characterizing the decay of the two-time intensity autocorrelation function.Softness becomes relevant only at very large packing fractions, when the system falls out of equilibrium. In this non-equilibrium regime, the SRT depends surprisingly weakly on packing fraction and time correlation functions exhibit compressed exponential decays consistent with internal stress-driven relaxation. The transition to this novel regime coincides with the onset of an anomalous decrease of local order with increasing density, reminiscent of the reentrant glass transition predicted theoretically in ultrasoft systems [2,3], and corresponds to a weakening of the volume fraction dependence of the plateau modulus of the suspensions. We propose that these peculiar dynamics result from a competition between the non-equilibrium aging dynamics of the glassy state and the tendency of soft systems to refluidize at high packing fractions.

Insertion of two-dimensional (2D) materials in optical systems modifies their electrodynamical response. In particular, the Brewster angle undergoes an up-shift if a substrate is covered with a conducting 2D material. This work theoretically and experimentally investigates this effect related to the 2D induced current at the interface. The shift is predicted for all conducting 2D materials and tunability with respect to the Fermi level of graphene is evidenced. Analytical approximations for high and low 2D conductivities are proposed and avoid cumbersome numerical analysis of experimental data. Experimental demonstration using spectroscopic ellipsometry has been performed in the UV to NIR range on mono-, bi- and trilayer graphene samples. The non-contact measurement of this modified Brewster angle allows to deduce the optical conductivity of 2D materials. Applications to telecommunication technologies can be considered thanks to the tunability of the shift at 1.55 μm.

Aqueous dispersions of graphene-derived monolayers form liquid crystal at rather low concentrations due to the high aspect ratio of these flakes [1,2]. If graphene oxide dispersions are easily obtained in water, reduced graphene oxide necessitates the use of surfactants [3]. Preparing organized materials and thin films from these dispersions then requires a good control of the liquid crystal ordering during the deposition and the drying of the films.The flakes easily align at high shear [4,5], which has allowed us to complete previous optical characterizations of the various graphene layers (birefringence and linear dichroism). However at low shear or under small dispalcements, thin films often show peculiar patterns (such as the periodic textures shown in Fig.1). We have shown how to create and stabilize large-sized periodic textures. The patterns have been characterized under optical and electronic microscopies. Their stability can be explained by the competition between the anchoring field of the substrate and the presence of a yield stress resulting from the peculiar elastic and rheological properties of the graphene oxide liquid crystals. Our results also clarify why long-standing hypotheses on the presence of exotic phases [1] at large concentrations are present in the literature.References[1] Z. Xu, C. Gao Nat Commun., 2, 571 (2011).[2] C. Zakri et al., Phil. Trans. A, 371, 20120499 (2013).[3] C. Zamora et al, J. Phys. Chem. Lett. 3, 2425 (2012).[4] P. Poulin et al, Proc Natl Acad Sci USA, 113, 11088 (2016).[5] S-H Honga, T.Z. Shena and J. K. Songa, Liquid Crystals, 42, 261 (2015)

Thin and ultrathin metal coatings are increasingly required by the electronics and optics industries onall types of substrates. However, the adhesion of noble metals is very poor on non-metallic substrates like glass,other oxide materials and polymers. By contrast, CVD graphene has a strong adhesion energy (~0.31-0.45 J.m-2depending on the number of layers) on glass [1]. On the other hand, graphene oxide (GO) was recently shown topromote adhesion of ZnO nanoparticles and subsequent ZnO films on glass or silicon substrates [2].In this work we use GO/Au nanoparticles (NP) composite thin films as bifunctional materials to bothpromote adhesion on glass and assist the deposition of copper in electroless wet industrial coating processes. Wediscuss the influence of the NP density, surface treatment and deposition parameters on the homogeneity andadhesion of the GO/Au NP and copper layers.[1] S. P. Koenig, N. G. Boddeti, M. L. Dunn, and J. S. Bunch, 2011, Nat. Nano. 6, 543‑546[2] Q. Ma, X. Zhu, D. Zhang, and S. Liu, 2014, J. Mater. Chem. C 22, 8956‑8961

In this work, we explore the preparation and deposition of graphene oxide (GO)-metal (gold and palladium) nanoparticles (NPs) composites as thin films via wet routes. The properties of such films are examined, in view of Surface Enhanced Raman Spectroscopy (SERS) applications and as adhesion promoter thin films. It has been indeed shown that the encapsulation of metal NP within a few layers of graphene greatly improves the stability, reproducibility and sensitivity of SERS effect [1]. On the other hand, graphene oxide films decorated with metal nanoparticles are good non-etching adhesion promotors candidates for electroless deposition of metal thin films on non-metal substrates like glass or polymers [2, 3]. We discuss the preparation of the suspensions and the parameters (GO dispersion concentration, withdrawal speed and immersion time, functionalization of the substrates) which permit a good control of the deposition by dip-coating. The structure of the resulting thin films is characterized by Atomic Force Microscopy (AFM), Phase Shifting Interferometry (PSI) and Raman spectroscopy to determine the topography, thickness and homogeneity of the deposited layers. Their SERS and adhesion properties are then discussed.References[1] Y. Liu, Y. Hu, and J. Zhang, J. Phys. Chem. C, 2014, 1187, p. 8993‑ 8998.[2] S. P. Koenig, N. G. Boddeti, M. L. Dunn, and J. S. Bunch,2011, Nat. Nanotechnol.,6, p. 543‑ 546.[3] Q. Ma, X. Zhu, D. Zhang, and S. Liu, 2014, J. Mater. Chem. C,22, p. 8956‑ 8961.