Graphene-based materials can have well-defined nanometer pores and can exhibit low frictional water flow inside them, making their properties of interest for filtration and separation. We investigate permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions. The laminates are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves, blocking all solutes with hydrated radii larger than 4.5 angstroms. Smaller ions permeate through the membranes at rates thousands of times faster than what is expected for simple diffusion. We believe that this behavior is caused by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The anomalously fast permeation is attributed to a capillary-like high pressure acting on ions inside graphene capillaries.

A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported. Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives. Fluorographene is a high-quality insulator (resistivity >10(12) Ω) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting a Young's modulus of 100 N m(-1) and sustaining strains of 15%. Fluorographene is inert and stable up to 400 °C even in air, similar to Teflon.

When metal nanoparticles are arranged in an ordered array, they may scatter light to produce diffracted waves. If one of the diffracted waves then propagates in the plane of the array, it may couple the localized plasmon resonances associated with individual nanoparticles together, leading to an exciting phenomenon, the drastic narrowing of plasmon resonances, down to 1–2 nm in spectral width. This presents a dramatic improvement compared to a typical single particle resonance line width of >80 nm. The very high quality factors of these diffractively coupled plasmon resonances, often referred to as plasmonic surface lattice resonances, and related effects have made this topic a very active and exciting field for fundamental research, and increasingly, these resonances have been investigated for their potential in the development of practical devices for communications, optoelectronics, photovoltaics, data storage, biosensing, and other applications. In the present review article, we describe the basic physical principles and properties of plasmonic surface lattice resonances: the width and quality of the resonances, singularities of the light phase, electric field enhancement, etc. We pay special attention to the conditions of their excitation in different experimental architectures by considering the following: in-plane and out-of-plane polarizations of the incident light, symmetric and asymmetric optical (refractive index) environments, the presence of substrate conductivity, and the presence of an active or magnetic medium. Finally, we review recent progress in applications of plasmonic surface lattice resonances in various fields.

. We demonstrate below that singular-phase behaviour can be achieved by using plasmonic nanostructures (see Fig. 1 ) we solve the problem of inherent losses and create the complete darkness yielding to phase singularities. By using graphene hydrogenation, we estimate the detection limit of our nanomaterials at a level of 0.1fg/mm 2 , which is 4 orders of magnitude better than reported in literature for SPR. We also show that suggested nanomaterials can be applied for biosensing and provide an unprecedented sensitivity in the absence of labels. Topologically protected darkness and phase sensitivity of coupled LPR. Consider a light reflection from a thin film placed on a dielectric substrate. In the visible range, there exists a set of n, k (here n n ik   is the refractive index of the film) for which the reflection is exactly zero.This set is shown by the solid brown curve in Fig. 1(c), where for concreteness the film thickness d is chosen to be 170nm, angle of incidence =60 and the substrate is made of glass. In principle, it is possible to achieve these values of n, k by using a dielectric film near the Brewster angle. Although the enhanced phase sensitivity near the Brewster angle is used in Brewster angle microscopy 20 (and ellipsometry, in general), it is not widely used in biophysics since local electric fields for dielectric substrates are small. On the other hand, metal films can generate much stronger local fields due to plasmons and, therefore, provide a better phase sensitivity.Unfortunately, it is quite difficult to achieve phase singularity using a continuous metal film. For example, dispersion relations n(), k() for gold yield the curve shown at the top of the image and result in non-zero reflection for gold films across the entire visible spectrum (measured ellipsometric reflection from a 170nm gold film is shown in the top panel of Fig. 1(c)). 5The situation is different for a nanomaterial with DCLP. Using such plasmonic nanomaterials, one can manipulate effective n eff (), k eff () and make them to intersect the zero reflection line in Fig. 1(c). The middle panel in this figure shows the effective dispersion curve and the measured reflection from the gold nanostripe structure schematically shown in Fig. 1(a) 27. One can see a narrow plasmon resonance with the half-width of 12nm and quality of about Q~200. The detailed analysis shows that the light intensity reaches zero at certain wavelength and angle of incidence, which results in a singular behaviour of phase in the Fourier space.Indeed, the zero reflection line (the brown curve) separates two different regions in the (n, k) plane due to a nature of Fresnel reflection coefficients. Because the dispersion curve for the nanostructured gold starts in one of these regions and finishes in the other, it implies that it will always intersect the line of zero reflection curve due to the Jordan theorem 28 (which states that the line connecting two different regions separated by a boundary always intersects the boundary), see Fig 1(c). Relativ...

We demonstrate that optical transparency of any two-dimensional system with a symmetric electronic spectrum is governed by the fine structure constant and suggest a simple formula that relates a quasi-particle spectrum to an optical absorption of such a system. These results are applied to graphene deposited on a surface of

Graphene oxide (GO) membranes continue to attract intense interest due to their unique molecular sieving properties combined with fast permeation rates 1-9 . However, the membranes' use has been limited mostly to aqueous solutions because GO membranes appear to be impermeable to organic solvents 1 , a phenomenon not fully understood yet. Here, we report efficient and fast filtration of organic solutions through GO laminates containing smooth two-dimensional (

Surface-enhanced Raman scattering (SERS) exploits surface plasmons induced by the incident field in metallic nanostructures to significantly increase the Raman intensity. Graphene provides the ideal prototype two-dimensional (2d) test material to investigate SERS. Its Raman spectrum is well-known, graphene samples are entirely reproducible, height controllable down to the atomic scale, and can be made virtually defect-free. We report SERS from graphene, by depositing arrays of Au particles of well-defined dimensions on a graphene/SiO(2) (300 nm)/Si system. We detect significant enhancements at 633 nm. To elucidate the physics of SERS, we develop a quantitative analytical and numerical theory. The 2d nature of graphene allows for a closed-form description of the Raman enhancement, in agreement with experiments. We show that this scales with the nanoparticle cross section, the fourth power of the Mie enhancement, and is inversely proportional to the tenth power of the separation between graphene and the center of the nanoparticle. One important consequence is that metallic nanodisks are an ideal embodiment for SERS in 2d.

Flexible barrier films preventing permeation of gases and moistures are important for many industries ranging from food to medical and from chemical to electronic. From this perspective, graphene has recently attracted particular interest because its defect-free monolayers are impermeable to all atoms and molecules. However, it has been proved to be challenging to develop large-area defectless graphene films suitable for industrial use. Here we report barrier properties of multilayer graphitic films made by gentle chemical reduction of graphene oxide laminates with hydroiodic and ascorbic acids. They are found to be highly impermeable to all gases, liquids and aggressive chemicals including, for example, hydrofluoric acid. The exceptional barrier properties are attributed to a high degree of graphitization of the laminates and little structural damage during reduction. This work indicates a close prospect of graphene-based flexible and inert barriers and protective coatings, which can be of interest for numerous applications.