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The recently observed helicity-sensitive response, occurring in graphene based field-effect transistors (FETs) is interpreted as a result of the intrinsic phase asymmetry of these devices and interference of plasmons in the FET channel. The graphene-based plasmonic interferometers presented in this work enable the room temperature detection of THz radiation as well as allows us to distinguish between the rotation direction of circular polarized waves. To illustrate the broadband nurture of the observed effects, similar measurements were carried out at both THz and mid-infrared frequencies. The precise control of the carriers type and their concentration throughout the channel length allows us to demonstrate the helicity-sensitive response over a wide range of the gate potentials (from negative to positive values). We experimentally show that the formation of p–n junction inside the graphene channel leads to additional scattering of excited plasma waves, resulting in the suppression of their interference and consequent reduction of the helicity-sensitive contribution.

We present a study of the structural features of polycrystalline a diamond film (PCDF) synthesized by the microwave plasma-enhanced chemical vapor deposition method from a hydrogen/pentane mixture and consider its photoelectric response to synchrotron radiation. Raman spectroscopy analysis of the PCDF cross-section revealed the presence of sp2-hybridized inclusions. As the distance from the PCDF growth surface increases, the amount of the non-diamond phase also increases, while its morphology changes from amorphous to crystalline graphite-like carbon. The investigation of the photoelectric response of PCDF was carried out at the "Cosmos" station using synchrotron radiation from the VEPP-4M storage ring. The PCDF detector exhibited maximum sensitivity at low bias voltage. This effect was attributed to the increased efficiency of collecting photo-induced charge carriers from the diamond to the sp2-hybridized inclusions followed by their subsequent transport through conductive paths along the boundaries between diamond crystallites. [ABSTRACT FROM AUTHOR]

Abstract The shape of coherent anti-Stokes Raman scattering (CARS) spectral line depends on the ratio of the vibrational and electronic contributions to the third-order susceptibility of the material. The G-mode (1590 cm−1) of graphene and carbon nanotubes (CNTs) exhibits opposite features in the CARS spectrum, showing “dip” and “peak,” respectively. Here, we consider the CARS spectra of graphene and carbon nanotubes in terms of Fano formalism describing the line shapes of CARS resonances. We show that imaging at only 1590 cm−1 is not sufficient to separate the constituents of a composite material consisting of both graphene and CNTs. We propose an algorithm to map the graphene and CNTs in a composite material.

Water pollution is nowadays a global problem and the effective detection of pollutants is of fundamental importance. Herein, a facile, efficient, robust, and rapid (response time < 2 min) method for the determination of important quinone-based industrial pollutants such as hydroquinone and benzoquinone is reported. The recognition method is based on the use of screen-printed electrodes as sensing platforms, enhanced with carbon-based nanomaterials. The enhancement is achieved by modifying the working electrode of such platforms through highly sensitive membranes made of Single- or Multi-Walled Carbon Nanotubes (SWNTs and MWNTs) or by graphene nanoplatelets. The modified sensing platforms are first carefully morphologically and electrochemically characterized, whereupon they are tested in the detection of different pollutants (i.e., hydroquinone and benzoquinone) in water solution, by using both cyclic and square-wave voltammetry. In particular, the sensors based on film-deposited nanomaterials show good sensitivity with a limit of detection in the nanomolar range (0.04 and 0.07 μM for SWNT- and MWNT-modified SPEs, respectively) and a linear working range of 10 to 1000 ppb under optimal conditions. The results highlight the improved performance of these novel sensing platforms and the large-scale applicability of this method for other analytes (i.e., toxins, pollutants).

It was demonstrated that optical modulation together with simultaneous terahertz (THz) imaging application enables an increase in contrast by an order of magnitude, thereby illustrating the technique as a convenient contactless tool for characterization of graphene deposited on high-resistivity silicon substrates. It was shown that the single- and double-layer graphene can be discriminated and characterized via variation of THz image contrast using a discrete frequency in a continuous wave mode. Modulation depth of 45% has been reached, and the contrast variation from 0.16 up to 0.23 is exposed under laser illumination for the single- and double-layer graphene, respectively. The technique was applied in the development and investigation of graphene-based optical diffractive elements for THz imaging systems. [ABSTRACT FROM AUTHOR]

We propose an original technique for the fabrication of terahertz (THz) metasurfaces comprising a 3D printed regular array of polymer hemispheres covered with a thin conductive layer. We demonstrate that the deposition of a thin metal layer onto polymer hemispheres suppresses the THz reflectivity to almost zero, while the frequency range of such a suppression can be considerably broadened by enhancing the structure with graphene. Scaling up of the proposed technique makes it possible to tailor the electromagnetic responses of metasurfaces and allows for the fabrication of various components of THz photonics.

We experimentally and theoretically investigated the effects of ionizing radiation on a stack of graphene sheets separated by polymethyl methacrylate (PMMA) slabs. The exceptional absorption ability of such a heterostructure in the THz range makes it promising for use in a graphene-based THz bolometer to be deployed in space. A hydrogen/carbon ion beam was used to simulate the action of protons and secondary ions on the device. We showed that the graphene sheets remain intact after irradiation with an intense 290 keV ion beam at the density of 1.5 × 1012 cm−2. However, the THz absorption ability of the graphene/PMMA multilayer can be substantially suppressed due to heating damage of the topmost PMMA slabs produced by carbon ions. By contrast, protons do not have this negative effect due to their much longer mean free pass in PMMA. Since the particles’ flux at the geostationary orbit is significantly lower than that used in our experiments, we conclude that it cannot cause tangible damage of the graphene/PMMA based THz absorber. Our numerical simulations reveal that, at the geostationary orbit, the damaging of the graphene/PMMA multilayer due to the ions bombardment is sufficiently lower to affect the performance of the graphene/PMMA multilayer, the main working element of the THz bolometer, which remains unchanged for more than ten years.

We studied electromagnetic properties of pyrolytic carbon (PyC) films with thicknesses from 9 nm to 110 nm. The PyC films consisted of randomly oriented and intertwined graphene flakes with a typical size of a few nanometers were synthesized by chemical vapor deposition (CVD) at 1100 °C on a quartz substrate. The reflectance and transmittance of these films in Ka-band, 26–37 GHz, were studied both experimentally and theoretically. The discovered remarkably high absorption loss of up to 50% of incident power, along with chemical stability, makes PyC films attractive for electromagnetic (EM) interference shielding in space and airspace communication systems, as well as in portable electronic devices occupying this frequency slot. Since, in practical applications, the PyC film should be employed for coating of dielectric surfaces, two important issues to be addressed are: (i) which side (front or back) of the substrate should be covered to ensure maximum absorption losses; and (ii) the frequency dependence of absorbance/transmittance/reflectance of binary PyC/quartz structures in the Ka-band.

Electrical transport properties and magnetoresistance of single-wall carbon nanotubes (SWCNT) films were investigated within temperature range (2 – 300) K and in magnetic fields up to 8 T. A crossover between metallic (dR/dT > 0) and non-metallic (dR/dT < 0) temperature dependence of the resistance as well as low-temperature saturation of the resistance in high bias regime indicated on the diminishing of role of the contact barriers between individual nanotubes essential for the charge transport in SWCNT arrays. The magnetoresistance (MR) data demonstrated influence of weak localization and electron-electron interactions on charge transport properties in SWCNT films. The low-field negative MR with positive upturn was observed at low temperatures. At T > 10 K only negative MR was observed in the whole range of available magnetic fields. The negative MR can be approximated using 1D weak localization (WL) model. The low temperature positive MR is induced by contribution from electron-electron interactions. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6311

A set of epoxy resin-based composites filled with 0.25 – 2.0 wt.% of commercially available exfoliated graphite (EG) and thick graphene (TG), prepared by suspending EG particles in cyclohexane, and submitting the suspension to a series of grinding and ultrasonic dispersion steps, was produced. The microstructure of such epoxy-graphite composites has been studied by the impulse acoustic microscopy technique. According to acoustic microscopy data, exfoliated graphite microparticles have been well dispersed in the epoxy matrix. TG nanoflakes demonstrated persistent tendency to clustering and formation of agglomerates. The addition of graphite particles in small amount (0.25 – 2.0 wt.%) did not influence the bulk elastic properties of epoxy-graphite composite materials. Being extremely lightweight, 0.003 g cm−3, EG had a lower percolation threshold than TG, at the level of 1-1.5 wt.% against 2.1-3.2 wt.%, respectively. As a result, epoxy composites filled with 1.0-2.0 wt.% EG provided high electromagnetic (EM) interference shielding both at microwave and THz frequencies. In contrast, no significant influence of TG loading was observed at low weight fraction (up to 2 wt.%) on the EM performance of epoxy composites.