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A series of novel cyano-substituted bipyridine derivatives were obtained in good yields (45–72%) via the reaction of malononitrile dimer with isomeric azachalcones. For all synthesized compounds, spectral-fluorescent properties were carefully investigated, and correlation thereof with chemical structure was found. The developed approach represents a novel convenient method for the preparation of functionalized bipyridines containing unique combination of structural fragments.

Localized electrons subject to applied magnetic fields can restart to propagate freely through the lattice in delocalized magnetic Bloch states (MBSs) when the lattice periodicity is commensurate with the magnetic length. Twisted graphene superlattices with moir\'e wavelength tunability enable experimental access to the unique delocalization in a controllable fashion. Here we report the observation and characterization of high-temperature Brown-Zak (BZ) oscillations which come in two types, 1/B and B periodicity, originating from the generation of integer and fractional MBSs, in the twisted bilayer and trilayer graphene superlattices, respectively. Coexisting periodic-in-1/B oscillations assigned to different moir\'e wavelengths, are dramatically observed in small-angle twisted bilayer graphene, which may arise from angle-disorder-induced in-plane heteromoir\'e superlattices. Moreover, the vertical stacking of heteromoir\'e supercells in double-twisted trilayer graphene results in a mega-sized superlattice. The exotic superlattice contributes to the periodic-in-B oscillation and dominates the magnetic Bloch transport.

Platelets, which are anucleate blood cells, should have the capacity to respond to an external stimulus within 1 second. This capacity is maintained by calcium signaling, the process of intracellular signal transmission mediated by an increase of the calcium ion concentration in the cytosol due to calcium release from the endoplasmic reticulum through the inositol trisphosphate receptor channel (IP3R). The increase of the calcium concentration in the platelet cytosol is not monotonous, but rather has an oscillatory character, similar to the processes in many other cell types. The regularities that underlie the development of these oscillations were subjected to theoretical and experimental analysis in the present study. Total internal reflection microscopy of platelets immobilized on fibrinogen and loaded with the Fura-2 calcium-sensitive fluorescent label was used to monitor the dynamics of calcium concentration. The mathematical model of the IP3R–ATPase pair from [15] modified to take the platelet parameters into account was used to describe the process of oscillation development. The results of the study demonstrated a characteristic peak shape for calcium oscillations in the platelet: theoretical description of the peak shape essentially required the introduction of corrections that had the physical meaning of cooperative IP3R activation.

With reference to the activity of the Kama Innovation Cluster "Innokam", the paper considers some issues of the integration of project management mechanisms into the investment strategy of the cluster structures. Such a strategy implemented by Innocam's structures in the context of open innovation encompasses a set of innovative projects, including the creation of engineering centers for the development of flexible production systems, the design of high technologies, new generation robotic complexes, etc. The study describes some features of an innovative cluster functioning in the environment of open innovations, which is characterized by a high level of uncertainty. The article introduces the business model of the strategic partnership of "Innokam" structures, which is focused on the environment of open innovations. Tools for strategic analysishave been developed, the results of which are used by Innokam structures when creatingan array of input data necessary for the design of a project ma nagement strategy. The research explores the mechanism and principles of the development of the project management strategy in relation to the investment activities of the Innocam structures. Taking into account the specifics of the functioning of these structures, the scenario planning methodology has been modernized and a tool for selecting the best variant of the project management strategy has been proposed. The paper includes proposals on the construction of a multi-level management system, taking into account the specific features of Innokam’s investment activities. With respectto each level of management, criteria are given for assessing the effectiveness of the system. The research has justified the use of controlling that fulfills the role of feedback in the management system, which allows one to evaluate the effectiveness of the project strategy implemented by Innocam's structures

Bulk amorphous materials have been studied extensively and are widely used, yet their atomic arrangement remains an open issue. Although they are generally believed to be Zachariasen continuous random networks

Indium selenide, a post-transition metal chalcogenide, is a novel two-dimensional (2D) semiconductor with interesting electronic properties. Its tunable band gap and high electron mobility have already attracted considerable research interest. Here we demonstrate strong quantum confinement and manipulation of single electrons in devices made from few-layer crystals of InSe using electrostatic gating. We report on gate-controlled quantum dots in the Coulomb blockade regime as well as one-dimensional quantization in point contacts, revealing multiple plateaus. The work represents an important milestone in the development of quality devices based on 2D materials and makes InSe a prime candidate for relevant electronic and optoelectronic applications., 13 pages, 3 figures

We report on the use of graphene for room temperature on-chip detection and generation of pulsed terahertz (THz) frequency radiation, exploiting the fast carrier dynamics of light-generated hot carriers, and compare our results with conventional low-temperature-grown gallium arsenide (LT-GaAs) photoconductive (PC) switches. Coupling of picosecond-duration pulses from a biased graphene PC switch into Goubau line waveguides is also demonstrated. A Drude transport model based on the transient photoconductance of graphene is used to describe the mechanism for both detection and generation of THz radiation.

Graphene placed on hexagonal-boron nitride (h-BN) experiences a superlattice (Moiré) potential, which leads to a strong reconstruction of graphene's electronic spectrum with new Dirac points emerging at sub-eV energies. Here we study the effect of such superlattices on graphene's Raman spectrum. In particular, the 2D Raman peak is found to be exquisitely sensitive to the misalignment between graphene and h-BN lattices, probably due to the presence of a strain distribution with the same periodicity of the Moiré potential. This feature can be used to identify graphene superlattices with a misalignment angle smaller than 2°.

An overview of results obtained in the field of planetary atmosphere studies in Russia in 2007–2010 prepared by the Commission on Planetary Atmospheres of the National Geophysical Committee for the National Report on Meteorology and Atmospheric Sciences to the XXV General Assembly of the International Union of Geodesy and Geophysics (Melbourne, 28 June–7 July 2011) [1, 2] is presented.

We report a stoichiometric derivative of graphene with a fluorine atom attached to each carbon. 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 Ohm per square) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting Young's modulus of 100 N/m and sustaining strains of 15%. Fluorographene is inert and stable up to 400C even in air, similar to Teflon., to appear in Small 2010

Parameterization of the spectral dependence of the optical characteristics of Martian aerosols has been proposed for processing the results of measurements of outgoing radiation. A method for retrieving the altitude profiles of the microphysical characteristics of Martian aerosols from the limb spectrometry of the OMEGA instrument of the Mars Express mission have been developed. For one of the observational sessions, the altitude profiles of the concentration and the modal radius of the size distribution function of aerosol particles retrieved with the proposed parameterization are presented. For the purpose of the interpretation of the data acquired from the optical remote sensing of planetary atmospheres, we consider how the spectral dependence of aerosol optical characteristics, in particular the volume coefficients of aerosol scattering and absorption and the phase function, can be parameterized in a specified, probably wide, spectral range. The method of such a parameterization has been proposed for the cases of a fixed chemical composition of the aerosol materials dominating in the atmosphere. It has been shown that these cases allow the required spectral dependences to be presented as a function of a small number of parameters, for which the parameters of the size distribution function of aerosol particles can be successfully used. However, since such direct calculations of the aerosol characteristics require an inadmissibly long period of time for the tasks of interpretation of the remote sensing data, an algorithm for organizing the parameterization function as a special, preliminary generated computer database has been suggested. This database provides the continuity in the dependence on the parameters, the specified computation accuracy, and the required output speed of the results. As a specific application, the parameterization of the spectral dependence of the optical characteristics of the Martian aerosols has been proposed for the tasks of processing the results of measurements of outgoing radiation. As a result, the method for retrieving the altitude profiles of the microphysical characteristics of Martian aerosols from the limb spectrometric measurements of the OMEGA instrument of the Mars Express mission has been developed. For one of the observational sessions, the altitude profiles of the concentration and the modal radius of the size distribution function of aerosol particles retrieved with the proposed parameterization are presented.

We have performed the first experimental investigation of quantum interference corrections to the conductivity of a bilayer graphene structure. A negative magnetoresistance - a signature of weak localisation - is observed at different carrier densities, including the electro-neutrality region. It is very different, however, from the weak localisation in conventional two-dimensional systems. We show that it is controlled not only by the dephasing time, but also by different elastic processes that break the effective time-reversal symmetry and provide invervalley scattering., 4 pages, 4 figures (to be published in PRL)

Resonant tunnelling through two impurities has been observed in a vertical double-barrier GaAs/AlGaAs tunnelling diode. It manifests itself as a peak in the I-V characteristic near the conductance threshold. Analysis of the position of the current peak, its shape and the shift in magnetic field parallel to the current provides information about the characteristics of the two impurities. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Advances in theory are needed to match recent progress in measurements of coupled semiconductor resonators supporting terahertz plasmons. Here, we present a field-based model of plasmonic resonators that comprise gated and ungated two-dimensional electron systems. The model is compared to experimental measurements of a representative system, in which the interaction between the gated and ungated modes leads to a rich spectrum of hybridized resonances. A theoretical framework is thus established for the analysis and design of gated low-dimensional systems used as plasmonic resonators, underlining their potential application in the manipulation of terahertz frequency range signals.

We present an on-chip time domain terahertz (TD-THz) system in which picosecond pulses are generated in low-temperature-grown gallium arsenide (LT-GaAs) and detected in graphene. The detected pulses were found to vary in amplitude, full width at half maximum (FWHM), and DC offset when sampled optically at different locations along a 50-μm-long graphene photoconductive (PC) detector. The results demonstrate the importance of detection location and switch design in graphene-based on-chip PC detectors.

We demonstrate the excitation and electrostatic modulation of a planar, resonant plasmonic circuit, comprised of a two-dimensional electron system (2DES) integrated into three different on-chip, terahertz-frequency coplanar waveguides. We utilise a Schottky gate formed across the 2DES in one device to create a resonant cavity in which the carrier concentration, and therefore the cavity resonant frequency, can be tuned by application of a negative DC gate bias, or using an external magnetic field. Using this technique, we demonstrate tuneable plasmon and magnetoplasmon generation and detection at frequencies up to ∼ 400 GHz, by injection of terahertz pulses into the 2DES from the waveguide region.

Contrary to some recent observations of a gradual increase of 1/f -noise with decreasing carrier density in a 2DEG in Si and a 2DHG in GaAs, we have observed a non-monotonic variation of noise power in a 2DEG in Si. We discuss the role of the following effects in the noise near the carrier density where ∂R /∂T changes its sign: i) formation of an electron glass; ii) percolation transition; iii) existence of a narrow impurity band at the Si-SiO2 interface. We also analyse the effect of temperature fluctuations in the observed non-monotonic behaviour of the noise power. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A comparative study of Coulomb blockade oscillations in a small quantum ring with effective radius 100 nm in ordinary tunnelling and anomalous open regimes is performed. We demonstrate that even though there is no tunnelling barrier between the ring and 2D electron sea in this ring, gigantic Coulomb blockade-like oscillations can be observed. Gate voltage, DC bias and temperature dependences of the ring conductance were experimentally studied at temperatures 0.24-1.4K and magnetic fields up to 1.5T. These studies show the principal differences between Coulomb blockade oscillations in the tunnelling regime and in the open state. The fundamental single-electron period of the oscillations is found to be the same in both regimes. The role of backscattering processes is concluded to be the reason for the existence of strong Coulomb blockade effects in the open state of the ring.

We demonstrate the feasibility of using graphene as a conductive electrode for the generation and detection of surface acoustic waves at 100 s of MHz on a lithium niobate substrate. The graphene interdigitated transducers (IDTs) show sensitivity to doping and temperature, and the characteristics of the IDTs are discussed in the context of a lossy transmission line model.

Letter.-- et al., Superlattices have attracted great interest because their use may make it possible to modify the spectra of two-dimensional electron systems and, ultimately, create materials with tailored electronic properties. In previous studies (see, for example, refs 1, 2, 3, 4, 5, 6, 7, 8), it proved difficult to realize superlattices with short periodicities and weak disorder, and most of their observed features could be explained in terms of cyclotron orbits commensurate with the superlattice. Evidence for the formation of superlattice minibands (forming a fractal spectrum known as Hofstadter's butterfly) has been limited to the observation of new low-field oscillations and an internal structure within Landau levels. Here we report transport properties of graphene placed on a boron nitride substrate and accurately aligned along its crystallographic directions. The substrate's moiré potential acts as a superlattice and leads to profound changes in the graphene's electronic spectrum. Second-generation Dirac points appear as pronounced peaks in resistivity, accompanied by reversal of the Hall effect. The latter indicates that the effective sign of the charge carriers changes within graphene's conduction and valence bands. Strong magnetic fields lead to Zak-type cloning of the third generation of Dirac points, which are observed as numerous neutrality points in fields where a unit fraction of the flux quantum pierces the superlattice unit cell. Graphene superlattices such as this one provide a way of studying the rich physics expected in incommensurable quantum systems and illustrate the possibility of controllably modifying the electronic spectra of two-dimensional atomic crystals by varying their crystallographic alignment within van der Waals heterostuctures. © 2013 Macmillan Publishers Limited. All rights reserved., This work was supported by the European Research Council, the Körber Foundation, the Office of Naval Research, the Air Force Office of Scientific Research and the Royal Society.

Capacitance measurements provide a powerful means of probing the density of states. The technique has proved particularly successful in studying 2D electron systems, revealing a number of interesting many-body effects. Here, we use large-area high-quality graphene capacitors to study behavior of the density of states in this material in zero and high magnetic fields. Clear renormalization of the linear spectrum due to electron-electron interactions is observed in zero field. Quantizing fields lead to splitting of the spin- and valley-degenerate Landau levels into quartets separated by interaction-enhanced energy gaps. These many-body states exhibit negative compressibility but the compressibility returns to positive in ultrahigh B. The reentrant behavior is attributed to a competition between field-enhanced interactions and nascent fractional states. 102JW Times Cited:0 Cited References Count:34

The above question is frequently asked by theorists who are interested in graphene as a model system, especially in context of relativistic quantum physics. We offer an experimental answer by describing electron transport in suspended devices with carrier mobilities of several 10(6) cm(2) V(-1) s(-1) and with the onset of Landau quantization occurring in fields below 5 mT. The observed charge inhomogeneity is as low as ≈10(8) cm(-2), allowing a neutral state with a few charge carriers per entire micrometer-scale device. Above liquid helium temperatures, the electronic properties of such devices are intrinsic, being governed by thermal excitations only. This yields that the Dirac point can be approached within 1 meV, a limit currently set by the remaining charge inhomogeneity. No sign of an insulating state is observed down to 1 K, which establishes the upper limit on a possible bandgap.

We experimentally study the effect of different scattering potentials on the $1/f$ noise generated in graphene devices on silica substrates. The noise in nominally identical devices is seen to behave in two distinct ways as a function of carrier concentration, changing either monotonically or nonmonotonically. We attribute this to the interplay between long- and short-range scattering mechanisms. Water is found to significantly enhance the noise magnitude and change the type of noise behavior. By using a simple model, we show that water is a source of long-range scattering.

In this paper, we present scanning gate microscopy (SGM) measurements on a graphene quantum point contact, carried out under ambient conditions. Images obtained in SGM display two-dimensional maps of sample resistance, as a function of the position of a biased AFM tip and the voltage applied to the tip. In our studies, a graphene quantum point contact was fabricated using local anodic oxidation. Performing SGM imaging on the resulting device structure shows that the resistance through the graphene QPC is strongly affected by the electric field of the AFM tip at the position of the QPC.

We investigate the electronic properties of heterostructures based on ultrathin hexagonal boron nitride (h-BN) crystalline layers sandwiched between two layers of graphene as well as other conducting materials (graphite, gold). The tunnel conductance depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Exponential behaviour of I-V characteristics for graphene/BN/graphene and graphite/BN/graphite devices is determined mainly by the changes in the density of states with bias voltage in the electrodes. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field; it offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.

International audience; An AOST Fourier spectrometer of the Phobos-Soil project is intended for studying Mars and Phobos by means of measurements of IR radiation spectra of the Martian surface and atmosphere, the Phobos surface, and the spectrum of solar radiation passing through the Martian atmosphere on its limb. The main scientific problems to be solved with the spectrometer on Mars are measurements of methane content, search for minor constituents, and study of diurnal variations in the temperature and atmospheric aerosol. The spectrometer will also study the Martian and Phobos surface both remotely and after landing. The spectral range of the instrument is 2.5-25 μm, the best spectral resolution (without apodization) is 0.6 cm−1, and the instantaneous field of view is 2.5°. The recording time of one spectrum is equal to 5 s in solar observations and 50 s in observations of Mars and Phobos. The instrument has self-thermal stabilization and two-axis pointing systems, as well as a built-in radiation source for flight calibration. The spectrometer mass is 4 kg, and power consumption is up to 13 W. Scientific problems, measurement modes, and, briefly, engineering implementation of the experiment are discussed in this work.

Devices made from graphene encapsulated in hexagonal boron-nitride exhibit pronounced negative bend resistance and an anomalous Hall effect, which are a direct consequence of room-temperature ballistic transport on a micrometer scale for a wide range of carrier concentrations. The encapsulation makes graphene practically insusceptible to the ambient atmosphere and, simultaneously, allows the use of boron nitride as an ultrathin top gate dielectric.

Letter.-- et al., In graphene, electron–electron interactions are expected to play a significant role, as the screening length diverges at the charge neutrality point and the conventional Landau theory that enables us to map a strongly interacting electronic liquid into a gas of non-interacting fermions is no longer applicable1, 2. This should result in considerable changes in graphene’s linear spectrum, and even more dramatic scenarios, including the opening of an energy gap, have also been proposed3, 4, 5. Experimental evidence for such spectral changes is scarce, such that the strongest is probably a 20% difference between the Fermi velocities vF found in graphene and carbon nanotubes6. Here we report measurements of the cyclotron mass in suspended graphene for carrier concentrations n varying over three orders of magnitude. In contrast to the single-particle picture, the real spectrum of graphene is profoundly nonlinear near the neutrality point, and vF describing its slope increases by a factor of more than two and can reach ≈3×106 m s−1 at n, This work was supported by the Engineering and Physical Sciences Research Council (UK), the Royal Society, the Air Force Office of Scientific Research, the Office of Naval Research and the Körber Foundation.

Transport measurements have been a powerful tool for discovering electronic phenomena in graphene. We report nonlocal measurements performed in the Hall bar geometry with voltage probes far away from the classical path of charge flow. We observed a large nonlocal response near the Dirac point in fields as low as 0.1 tesla, which persisted up to room temperature. The nonlocality is consistent with the long-range flavor currents induced by the lifting of spin/valley degeneracy. The effect is expected to contribute strongly to all magnetotransport phenomena near the neutrality point., United States. Office of Naval Research, United States. Air Force. Office of Scientific Research

We report capacitors in which a finite electronic compressibility of graphene dominates the electrostatics, resulting in pronounced changes in capacitance as a function of magnetic field and carrier concentration. The capacitance measurements have allowed us to accurately map the density of states D, and compare it against theoretical predictions. Landau oscillations in D are robust and zero Landau level (LL) can easily be seen at room temperature in moderate fields. The broadening of LLs is strongly affected by charge inhomogeneity that leads to zero LL being broader than other levels. Times Cited: 17

International audience; The AOST Fourier spectrometer being developed for the Phobos-Soil project is intended for remote probing in the 2.5-25-μm region. This spectral region includes not only reflected and transmitted solar radiation, but also the intrinsic thermal radiation of the celestial body being studied. The maximum spectral resolution, taking into account apodization, is 0.9cm-1, and the field-of-view angle is 2.5°. The device has its own thermal-stabilization and two-axis guidance systems, as well as an absolute-blackbody simulator for calibration. The time to record one interferogram ranges from 5to50sec. The mass of the device is 4kg, and its power requirement is as much as 10W

We have fabricated graphene devices with a top gate separated from the graphene layer by an air gap--a design which does not decrease the mobility of charge carriers under the gate. This gate is used to realise p-n-p structures where the conducting properties of chiral carriers are studied. The band profile of the structures is calculated taking into account the specifics of the graphene density of states and is used to find the resistance of the p-n junctions expected for chiral carriers. We show that ballistic p-n junctions have larger resistance than diffusive ones. This is caused by suppressed transmission of chiral carriers at angles away from the normal to the junction., Comment: to be published in Nano Letters

We have investigated terahertz (THz) frequency magnetoplasmon resonances in a two-dimensional electron system through the direct injection of picosecond duration current pulses. The evolution of the time-domain signals was measured as a function of magnetic field, and the results were found to be in agreement with calculations using a mode-matching approach for four modes observed in the frequency range above 0.1 THz. This introduces a generic technique suitable for sampling ultrafast carrier dynamics in low-dimensional semiconductor nanostructures at THz frequencies.

We have performed the first experimental investigation of quantum interference corrections to the conductivity of a bilayer graphene structure. A negative magnetoresistance--a signature of weak localization--is observed at different carrier densities, including the electroneutrality region. It is very different, however, from the weak localization in conventional two-dimensional systems. We show that it is controlled not only by the dephasing time, but also by different elastic processes that break the effective time-reversal symmetry and provide intervalley scattering.

We study 1/f‐noise in the 2DEG of a Si‐MOSFET which shows the apparent MIT: the change of the sign of dR/dT with decreasing carrier density. In addition to an increase of noise with decreasing electron density we have observed a dip in the noise power near the MIT. We discuss the role of the following contributions to the observed behaviour: a) the effect of temperature fluctuations near the MIT; b) existence of an impurity band in SiO2; c) formation of an electron glass. Our analysis shows that neither a) nor c) manifest themselves in the observed noise. The gradual increase of the noise power with decreasing electron density is in agreement with the existence of a percolation transition.

Nature Physics 7, 701–704 (2011); published online 24 July 2011; corrected after print 21 December 2011. In the version of this Letter originally published, the prefactor in equation (2) should have been -8/π2Nf. This error has been corrected in the HTML and PDF versions of the Letter.

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 >1012Ω) 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.