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The article discusses how cunning refinements can improve electron transport in polycrystalline graphene by pushing the boundaries and the sizes of the grains. Researchers are facing challenges in the nucleation stage and growth of the material on metal surfaces like copper. Several approaches that affect the creation of large single crystals are also discuss such as using polycrystalline copper, surface energy minimization, and the electronic properties of graphene.

Liquid phase exfoliation of two-dimensional (2D) materials from their bulk counterparts has attracted a lot of attention due to its applications in the large-scale synthesis of these materials. Herein, detailed molecular dynamics simulations to understand the exfoliation process of graphene followed by an in-situ exfoliation experiment of graphite suspended in polyacrylonitrile (PAN) using a well-known electro-spinning technique were performed. Submicron-scale fibers reinforced with graphene exhibited multi-fold improvements in terms of mechanical (stiffness, elastic modulus), thermal (degradation temperature) and electrochemical (ionic conductivity) properties. This method is a unique way of synthesizing in-situ composites with large lengths and submicron-diameter fibers. The present technique and the key ideas can be readily extended to other 2D materials as well. Image 1 [ABSTRACT FROM AUTHOR]

Abstract The capability of graphene to adopt a property from an adjacent material is investigated by measuring the electrochemical performance of a monolayer graphene placed on top of thin cobalt oxide (Co 3 O 4) nanosheets. In this assembly, monolayer graphene works as an interfacial layer which inhibits the direct contact of the actual electroactive material and electrolyte during electrochemical reaction. The results show that while graphene is electrochemically inert, it behaves as an active material to catalyze oxygen evolution reaction (OER) once placed on top of Co 3 O 4 nanosheets. The graphene-covered Co 3 O 4 model system shows electrochemical performance similar to Co 3 O 4 indicating complete transference of the electrochemical property of the metal oxide to the graphene. Based on density functional theory (DFT) calculations, charge transfer from graphene to Co 3 O 4 is the key factor for turning the electrochemically inactive graphene to an apparent active material. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Composite materials with carbon nanotube and graphene additives have long been considered as exciting prospects among nanotechnology applications. However, after nearly two decades of work in the area, questions remain about the practical impact of nanotube and graphene composites. This uncertainty stems from factors that include poor load transfer, interfacial engineering, dispersion, and viscosity-related issues that lead to processing challenges in such nanocomposites. Moreover, there has been little effort to identify selection rules for the use of nanotubes or graphene in composite matrices for specific applications. This review is a critical look at the status of composites for developing high-strength, low-density, high-conductivity materials with nanotubes or graphene. An outlook of the different approaches that can lead to practically useful nanotube and graphene composites is presented, pointing out the challenges and opportunities that exist in the field. [ABSTRACT FROM AUTHOR]

Graphitic solids are typically produced via high temperature and energy consuming processing (e.g. sintering) of carbon particles. Here, we demonstrate the mechano-chemical assembly of functionalized graphene layers into 3D graphitic solids via room temperature and low energy consuming processing. The chemical functional groups on graphene layers are interconnected at room temperature under pressure leading to porous three-dimensional structures with tunable mechanical and electrical properties. The formation of mechano-chemistry induced atomic scale junctions and their impact on mechanical properties of graphene assembled carbon materials are demonstrated through nano-indentation experiments and confirmed using DFT and molecular dynamics simulations. The results show room temperature consolidation routes of graphene layers into bulk carbon solids. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical reduction of CO2 provides an opportunity to reach a carbon‐neutral energy recycling regime, in which CO2 emissions from fuel use are collected and converted back to fuels. The reduction of CO2 to CO is the first step toward the synthesis of more complex carbon‐based fuels and chemicals. Therefore, understanding this step is crucial for the development of high‐performance electrocatalyst for CO2 conversion to higher order products such as hydrocarbons. Here, atomic iron dispersed on nitrogen‐doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO2 reduction to CO. Fe/NG has a low reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen‐confined atomic Fe moieties on the nitrogen‐doped graphene layer is confirmed by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. The CO2 reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N4) embedded in nitrogen‐doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene. [ABSTRACT FROM AUTHOR]

Vertical integration of van der Waals (vdW) materials with atomic precision is an intriguing possibility brought forward by these two-dimensional (2D) materials. Essential to the design and analysis of these structures is a fundamental understanding of the vertical transport of charge carriers into and across vdW materials, yet little has been done in this area. In this report, we explore the important roles of single layer graphene in the vertical tunneling process as a tunneling barrier. Although a semimetal in the lateral lattice plane, graphene together with the vdW gap act as a tunneling barrier that is nearly transparent to the vertically tunneling electrons due to its atomic thickness and the transverse momenta mismatch between the injected electrons and the graphene band structure. This is accentuated using electron tunneling spectroscopy (ETS) showing a lack of features corresponding to the Dirac cone band structure. Meanwhile, the graphene acts as a lateral conductor through which the potential and charge distribution across the tunneling barrier can be tuned. These unique properties make graphene an excellent 2D atomic grid, transparent to charge carriers, and yet can control the carrier flux via the electrical potential. A new model on the quantum capacitance's effect on vertical tunneling is developed to further elucidate the role of graphene in modulating the tunneling process. This work may serve as a general guideline for the design and analysis of vdW vertical tunneling devices and heterostructures, as well as the study of electron/spin injection through and into vdW materials. [ABSTRACT FROM AUTHOR]

Abstract: The advancement in high power lasers has urged the requisite of efficient optical limiting materials for both eye and sensor protection. The discovery of atomically thin 2D transition metal dichacogenides with distinctive properties has paved the way for a variety of applications including optical limiting. Until recently, the optical limiting effect exhibited by 2D materials is inferior to the benchmark materials fullerene (C60) and graphene. This article reports the optical limiting activity of the 2D transition metal dichalcogenide, titanium disulfide (TiS2) nanosheets, using optical and photoacoustic z‐scan techniques. The 77% nonlinear optical limiting exhibited by the TiS2 sheets with 73% linear‐transmittance is superior to that of any other existing 2D dichalcogenide sheets, graphene, and the benchmark optical limiting material, C60. The enhanced nonlinear response is attributed to the concerted effect of 2‐photon and the induced excited state absorptions. By using photoacoustic z‐scan, a unique tool developed to determine the nonlinear optical limiting mechanism in materials, it is found that the optical limiting exhibited by TiS2 2D sheets and graphene are mainly due to nonlinear absorption rather than scattering effects. These results have opened the door for 2D‐dichalcogenide‐materials‐based highly efficient optical limiters, especially at low fluences. [ABSTRACT FROM AUTHOR]

2D atomic crystals such as single layer graphene (SLG) and hexagonal boron nitride (hBN) have been shown to be 'unexpectedly permeable' to hydrogen ions under ambient conditions with the proton conductivity rising exponentially with temperature. Here, the first successful addition of SLG made by a chemical vapor deposition (CVD) method is shown to an operational direct methanol fuel cell significantly enhancing the performance of the cell once the temperature is raised above 60 °C, the temperature at which the proton conductivity of SLG is higher than the Nafion membrane on which it is mounted. Above this temperature, the resistance to proton transport of the system is not affected by the graphene but the barrier properties of graphene inhibit methanol crossover. The performance of the fuel cell is shown to increase linearly with coverage of SLG above this temperature. Results show that the maximum power density is increased at 70 °C by 45% in comparison to the standard membrane electrode assembly without graphene. In addition, a membrane with CVD hBN shows enhanced performance across the entire temperature range due to better proton conductivity at lower temperatures. [ABSTRACT FROM AUTHOR]

Graphenide solutions in NMP have been prepared by dispersing potassium intercalated graphite with the assistance of 18-crown-6. The highest graphenide solubility achieved is 1.5 mg mL−1. Graphenide solutions have been applied to spin graphene/SWCNT hybrid fibers. [ABSTRACT FROM AUTHOR]

Nonfunctionalized and functionalized fluorographene systems are studied of which acid functionalized system shows greater magnetic moment. This is experimentally verified and the hysteresis and low temperature studies reveal paramagnetic behaviour. The inherent paramagnetism along with the fluorine content is utilized in its development as a dual modal agent for proton and 19F MRI. [ABSTRACT FROM AUTHOR]

Ultrathin inorganic nanosheets that enable fast electrochemical reaction kinetics are highly required in many energy-related applications. Herein, we report a simple strategy for in situ assembly of ultrathin NiCo2O4 nanosheets with enriched surface active sites on graphene surface in a vertical orientation way by employing polyaniline (PANI) as the structure coupling bridge between the two components (denoted by NiCo2O4-P-G). The as-made ultrathin NiCo2O4 nanosheets are rich in metal ions in high valence state and oxygen defective sites, and feature 3D open frameworks with hierarchical pore structure. It has been found that the nitrogen species derived from PANI building blocks as bridging sites tend to bond with metal ions, which effectively tune the electronic structural states and result in strong coupling effects with the NiCo2O4 nanosheets. Benefiting from these structural characteristics, the as-made NiCo2O4-P-G hybrids, when used as pseudocapacitive electrode materials, can deliver a high specific capacitance of 966 F g-1 (based on the mass of the active NiCo2O4 component) and an excellent rate capability of ca. 84% even the current density increased by 100 times and long-term stability. As the precious metal-free electrocatalyst for the oxygen evolution (OER) reaction, the NiCo2O4-P-G hybrids are also able to deliver a low overpotential of 0.32 V at a current density of 10 mA cm-2 in 0.1 M KOH aqueous electrolyte (only 70% iR compensation), holding promise for high performance yet cheap electrocatalysts for the OER reaction. [ABSTRACT FROM AUTHOR]

Here, pyridinic nitrogen dominated graphene aerogels with/without iron incorporation (Fe-NG and NG) are prepared via a facile and effective process including freeze-drying of chemically reduced graphene oxide with/without iron precursor and thermal treatment in NH3. A high doping level of nitrogen has been achieved (up to 12.2 at% for NG and 11.3 at% for Fe-NG) with striking enrichment of pyridinic nitrogen (up to 90.4% of the total nitrogen content for NG, and 82.4% for Fe-NG). It is found that the Fe-NG catalysts display a more positive onset potential, higher current density, and better four-electron selectivity for ORR than their counterpart without iron incorporation. The most active Fe-NG exhibits outstanding ORR catalytic activity, high durability, and methanol tolerance ability that are comparable to or even superior to those of the commercial Pt/C catalyst at the same catalyst loading in alkaline environment. The excellent ORR performance can be ascribed to the synergistic effect of pyridinic N and Fe-N x sites (where iron probably coordinates with pyridinic N) that serve as active centers for ORR. Our Fe-NG can be developed into cost-effective and durable catalysts as viable replacements of the expensive Pt-based catalysts in practical fuel cell applications. [ABSTRACT FROM AUTHOR]

3D CoNi2S4-graphene-2D-MoSe2 (CoNi2S4-G-MoSe2) nanocomposite is designed and prepared using a facile ultrasonication and hydrothermal method for supercapacitor (SC) applications. Because of the novel nanocomposite structures and resultant maximized synergistic effect among ultrathin MoSe2 nanosheets, highly conductive graphene and CoNi2S4 nanoparticles, the electrode exhibits rapid electron and ion transport rate and large electroactive surface area, resulting in its amazing electrochemical properties. The CoNi2S4-G-MoSe2 electrode demonstrates a maximum specific capacitance of 1141 F g-1, with capacitance retention of ≈108% after 2000 cycles at a high charge-discharge current density of 20 A g-1. As to its symmetric device, 109 F g-1 at a scan rate of 5 mV s-1 is exhibited. This pioneering work should be helpful in enhancing the capacitive performance of SC materials by designing nanostructures with efficient synergetic effects. [ABSTRACT FROM AUTHOR]

Novel composites made of two dimensional (2D) MoS 2 nanosheets and graphene (G) have been fabricated by a combined approach of chemical vapor deposition and hydrothermal technique. The G film helps to mediate the growth and dispersion of MoS 2 nanosheets, of which the unique role of G in the MoS 2 growth is revealed by density functional theory study. The results show that the hexagonal lattice carbon of the G film can easily interact with sulfur species derived from reaction precursors, which favors the uniform growth of 2D MoS 2 . The unique function of the G film demonstrated here can be extended to other carbon substrates for growing 2D MoS 2 nanosheets. The G-MoS 2 composites consisting of two types of 2D materials are tested as the binder-free counter electrodes (CEs) for dye-sensitized solar cells, showing a high power conversion efficiency of 7.1% that is comparable to the expensive Pt CEs. The 2D G film in the hybrids has two functions: the active sites for dispersing the electrochemically active MoS 2 crystals and the high electrical conducting matrix for fast charge transfer. This synergistic effect may help to shed a light on the functionalization of other inorganic materials to G for advanced energy applications. [ABSTRACT FROM AUTHOR]

Lithium-oxygen batteries (LOBs) and direct methanol fuel cells (DMFCs) are both attractive technologies for the development of future energy storage and conversion devices, while the lack of highly active electrocatalysts has largely hampered their large-scale commercial applications. In the present work, we have demonstrated the controllable synthesis of nitrogen and sulfur codoped graphene (NS-G) nanosheets via a simple and cost-effective approach. Owing to their distinctive structural advantages, such as large surface areas, good flexibility, coexistence of N and S atoms with tunable doping contents and positions, and high electrical conductivity, the obtained NS-G sheets exhibit low discharge-recharge voltage gaps and high round-trip efficiencies as well as exceptional rate capability when used as cathode materials for LOBs. Furthermore, the NS-G layers are also identified to be an ideal substrate for the decoration of ultrafine Pt nanoparticles. Benefiting from the synergetic effects, exceptional electrocatalytic properties including high activity, strong poison tolerance, and outstanding long-term stability are observed for the resulting Pt/NS-G hybrid toward methanol oxidation reaction, which are significantly superior to those for Pt/undoped graphene and commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

Chronic diseases are becoming more prevalent, and the complexities of managing patients continue to escalate, since their care must be balanced between the home and clinical settings. Diabetes is the most advanced example, where self-monitoring has been shown to be necessary. Glucometers are point-of-care (POC) devices that have become standard platforms at home and clinical settings. Similarly, many other POC biosensors have also been developed. Enzymes are often used in these sensors because of their specificity and the reaction products can be electrochemically transduced for the measurement. When enzymes are immobilized to an electronically active substrate, enzymatic reactions can be transduced by direct electron transport. This paper describes an approach for the development of graphene-based POC devices. This includes modifying enzymes for improved performance, developing methods to bind them to the graphene surface, incorporation of the functionalized graphene on a field-effect transistor (FET), and integration into a microfluidic device suitable for home use. This paper describes an approach for the development of a graphene-based POC biosensor platform using glucose as an example of target molecule. [ABSTRACT FROM AUTHOR]

Batteries have become fundamental building blocks for the mobility of modern society. Continuous development of novel battery chemistries and electrode materials has nourished progress in building better batteries. Simultaneously, novel device form factors and designs with multi-functional components have been proposed, requiring batteries to not only integrate seamlessly to these devices, but to also be a multi-functional component for a multitude of applications. Thus, in the past decade, along with developments in the component materials, the focus has been shifting more and more towards novel fabrication processes, unconventional configurations, and additional functionalities. This work attempts to critically review the developments with respect to emerging electrochemical energy storage configurations, including, amongst others, paintable, transparent, flexible, wire or cable shaped, ultra-thin and ultra-thick configurations, as well as hybrid energy storage-conversion, or graphene-incorporated batteries and supercapacitors. The performance requirements are elaborated together with the advantages, but also the limitations, with respect to established electrochemical energy storage technologies. Finally, challenges in developing novel materials with tailored properties that would allow such configurations, and in designing easier manufacturing techniques that can be widely adopted are considered. [ABSTRACT FROM AUTHOR]

A self-assembled MoSe 2 nanolayers/reduced graphene oxide (MoSe 2 /rGO) foam was prepared using a hydrothermal method. The samples were systematically investigated by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. Electrochemical performances were evaluated in two-electrode cells versus metallic lithium. It is demonstrated that the obtained MoSe 2 /rGO nanocomposites show three-dimensional architecture and excellent electrochemical performance as anode materials for Li-ion batteries. The specific capacity of MoSe 2 /rGO anode can reach up to 650 mAh g −1 at a current rate of 0.1C in the voltage range 0.01–3.0 V (vs. Li/Li + ), which is higher than the theoretical capacity of MoSe 2 (422 mAh g −1 ). Additionally, the fabricated half cells have shown good rate capability and long cycling stability with 10.9% capacity loss after 600 cycles under a current density of 0.5C. The excellent performance of the synthesized MoSe 2 /rGO is attributed to its unique nanostructure, including nanolayered MoSe 2 , highly conductive rGO networks and mechanically stable 3D architecture. [ABSTRACT FROM AUTHOR]

Thegate-controllability of the Fermi-edge onset of interband absorptionin graphene can be utilized to modulate near-infrared radiation inthe telecommunication band. However, a high modulation efficiencyhas not been demonstrated to date, because of the small amount oflight absorption in graphene. Here, we demonstrate a ∼40% amplitudemodulation of 1.55 μm radiation with gated single-layer graphenethat is coupled with a silicon microring resonator. Both the qualityfactor and resonance wavelength of the silicon microring resonatorwere strongly modulated through gate tuning of the Fermi level ingraphene. These results promise an efficient electro-optic modulator,ideal for applications in large-scale on-chip optical interconnectsthat are compatible with complementary metal-oxide-semiconductor technology. [ABSTRACT FROM AUTHOR]

Conventionalwisdom suggests that decreasing dimensions of dielectricmaterials (e.g., thickness of a film) should yield increasing capacitance.However, the quantum capacitance and the so-called “dead-layer”effect often conspire to decrease the capacitance of extremely smallnanostructures, which is in sharp contrast to what is expected fromclassical electrostatics. Very recently, first-principles studieshave predicted that a nanocapacitor made of graphene and hexagonalboron nitride (h-BN) films can achieve superior capacitor properties.In this work, we fabricate the thinnest possible nanocapacitor system,essentially consisting of only monolayer materials: h-BN with grapheneelectrodes. We experimentally demonstrate an increase of the h-BNfilms’ permittivity in different stack structures combinedwith graphene. We find a significant increase in capacitance belowa thickness of ∼5 nm, more than 100% of what is predicted byclassical electrostatics. Detailed quantum mechanical calculationssuggest that this anomalous increase in capacitance is due to thenegative quantum capacitance that this particular materials systemexhibits. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) contains several chemical functional groups that are attached to the graphite basal plane and can be manipulated to tailor GO for specific applications. It is now revealed that the reaction of GO with ozone results in a high level of oxidation, which leads to significantly improved ionic (protonic) conductivity of the GO. Freestanding ozonated GO films were synthesized and used as efficient polymer electrolyte fuel cell membranes. The increase in protonic conductivity of the ozonated GO originates from enhanced proton hopping, which is due to the higher content of oxygenated functional groups in the basal planes and edges of ozonated GO as well as the morphology changes in GO that are caused by ozonation. The results of this study demonstrate that the modification of dispersed GO presents a powerful opportunity for optimizing a nanoscale material for proton-exchange membranes. [ABSTRACT FROM AUTHOR]

Gate-controllable transmission ofterahertz (THz) radiation makesgraphene a promising material for making high-speed THz wave modulators.However, to date, graphene-based THz modulators have exhibited onlysmall on/off ratios due to small THz absorption in single-layer graphene.Here we demonstrate a ∼50% amplitude modulation of THz waveswith gated single-layer graphene by the use of extraordinary transmissionthrough metallic ring apertures placed right above the graphene layer.The extraordinary transmission induced ∼7 times near-filedenhancement of THz absorption in graphene. These results promise complementarymetal–oxide–semiconductor compatible THz modulatorswith tailored operation frequencies, large on/off ratios, and highspeeds, ideal for applications in THz communications, imaging, andsensing. [ABSTRACT FROM AUTHOR]

If not for its inherently weak opticalabsorption at visible andinfrared wavelengths, graphene would show exceptional promise foroptoelectronic applications. Here we show that by nanopatterning agraphene layer into an array of closely packed graphene nanodisks,its absorption efficiency can be increased from less than 3% to 30%in the infrared region of the spectrum. We examine the dependenceof the enhanced absorption on nanodisk size and interparticle spacing.By incorporating graphene nanodisk arrays into an active device, wedemonstrate that this enhanced absorption efficiency is voltage-tunable,indicating strong potential for nanopatterned graphene as an activemedium for infrared electro-optic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) atomic layers such as graphene, and metal chalcogenides have recently attracted tremendous attention due to their unique properties and potential applications. Unfortunately, in most cases, the free-standing nanosheets easily re-stack due to their van der Waals forces, and lose the advantages of their separated atomic layer state. Here, a bottom-up approach is developed to build three-dimensional (3D) architectures by 2D nanosheets such as MoS2 and graphene oxide nanosheets as building blocks, the thin nature of which can be well retained. After simply chemical reduction, the resulting 3D MoS2-graphene architectures possess high surface area, porous structure, thin walls and high electrical conductivity. Such unique features are favorable for the rapid diffusions of both lithium ions and electrons during lithium storage. As a consequence, MoS2-graphene electrodes exhibit high reversible capacity of ≈1200 mAh g−1, with very good cycling performance. Moreover, such a simple and low-cost assembly protocol can provide a new pathway for the large-scale production of various functional 3D architectures for energy storage and conversions. [ABSTRACT FROM AUTHOR]

Single-layered molybdenum disulphide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for the next generation of nanoelectronics. Here, we report the controlled vapour phase synthesis of molybdenum disulphide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. Furthermore, a nucleation-controlled strategy is established to systematically promote the formation of large-area, single- and few-layered films. Using high-resolution electron microscopy imaging, the atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain boundary formation are evaluated. Grain boundaries consisting of 5- and 7- member rings are directly observed with atomic resolution, and their energy landscape is investigated via first-principles calculations. The uniformity in thickness, large grain sizes, and excellent electrical performance signify the high quality and scalable synthesis of the molybdenum disulphide atomic layers. [ABSTRACT FROM AUTHOR]

Monolayermolybdenum disulfide (MoS2) with a directband gap of 1.8 eV is a promising two-dimensional material with apotential to surpass graphene in next generation nanoelectronic applications.In this Letter, we synthesize monolayer MoS2on Si/SiO2substrate via chemical vapor deposition (CVD) method andcomprehensively study the device performance based on dual-gated MoS2field-effect transistors. Over 100 devices are studied toobtain a statistical description of device performance in CVD MoS2. We examine and scale down the channel length of the transistorsto 100 nm and achieve record high drain current of 62.5 mA/mm in CVDmonolayer MoS2film ever reported. We further extract theintrinsic contact resistance of low work function metal Ti on monolayerCVD MoS2with an expectation value of 175 Ω·mm,which can be significantly decreased to 10 Ω·mm by appropriategating. Finally, field-effect mobilities (μFE) ofthe carriers at various channel lengths are obtained. By taking theimpact of contact resistance into account, an average and maximumintrinsic μFEis estimated to be 13.0 and 21.6 cm2/(V s) in monolayer CVD MoS2films, respectively. [ABSTRACT FROM AUTHOR]

Although lithium ion batteries havegained commercial success owingto their high energy density, they lack suitable electrodes capableof rapid charging and discharging to enable a high power density criticalfor broad applications. Here, we demonstrate a simple bottom-up approachtoward single crystalline vanadium oxide (VO2) ribbonswith graphene layers. The unique structure of VO2-grapheneribbons thus provides the right combination of electrode propertiesand could enable the design of high-power lithium ion batteries. Asa consequence, a high reversible capacity and ultrafast charging anddischarging capability is achieved with these ribbons as cathodesfor lithium storage. A full charge or discharge is capable in 20 s.More remarkably, the resulting electrodes retain more than 90% ofthe initial capacity after cycling more than 1000 times at an ultrahighrate of 190C, providing the best reported rate performance for cathodesin lithium ion batteries to date. [ABSTRACT FROM AUTHOR]

Abstract: We present the study on the structure and adsorption properties of reduced graphene oxide subjected to thermal treatment in temperature range of 1100–2000°C under flowing argon. The morphology and composition analyses reveal that the defective carbon materials remaining after volatilization of oxygen and hydrogen rearrange into highly ordered hexagonal carbon layers during thermal treatment at 2000°C. The surface area of the resulting carbon layers increases to a value more than fourfold over that of the starting precursor materials. These results offer useful insights to understand the thermal behavior of the carbonaceous decomposition materials. [Copyright &y& Elsevier]

Graphene and hexagonal boron nitride (h-BN) have similar crystal structures with a lattice constant difference of only 2%. However, graphene is a zero-bandgap semiconductor with remarkably high carrier mobility at room temperature, whereas an atomically thin layer of h-BN is a dielectric with a wide bandgap of ?5.9 eV. Accordingly, if precise two-dimensional domains of graphene and h-BN can be seamlessly stitched together, hybrid atomic layers with interesting electronic applications could be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically patterned h-BN atomic layers. Our approach can create periodic arrangements of domains with size ranging from tens of nanometres to millimetres. The resulting graphene/h-BN atomic layers can be peeled off the growth substrate and transferred to various platforms including flexible substrates. We also show that the technique can be used to fabricate two-dimensional devices, such as a split closed-loop resonator that works as a bandpass filter. [ABSTRACT FROM AUTHOR]

Abstract: Large area nitrogen (N)-doped graphene films were grown on copper foil by chemical vapor deposition. The as-grown films consisted of a single atomic layer that was continuous across the copper surface steps and grain boundaries, and could be easily transferred to a variety of substrates. N-doping was confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy, and elemental mapping. N atoms were suggested to mainly form a “pyrrolic” nitrogen structure, and the doping level of N reached up to 3.4at.%. The N-doped graphene exhibited an n-type behavior, and nitrogen doping would open a band gap in the graphene. This study presents use of a new liquid precursor to obtain large area, continuous and mostly single atom layer N-doped graphene films. [Copyright &y& Elsevier]

Abstract: Graphene coating on copper (Cu) is shown to increase the resistance of the metal to electrochemical degradation by one and half orders of magnitude. Detailed electrochemical characterization in aggressive chloride environment shows the impedance of Cu increasing dramatically and the anodic and cathodic current densities of the coated Cu becoming nearly 1–2 orders of magnitude smaller when coated with graphene. The observations are counterintuitive as graphite in contact with metals increases metallic corrosion. The results can bring paradigm changes in the development of anti-corrosion coatings using conformal, ultrathin graphene films. [Copyright &y& Elsevier]

Strong in-plane bonding and weak van der Waals interplanarinteractionscharacterize a large number of layered materials, as epitomized bygraphite. The advent of graphene (G), individual layers from graphite,and atomic layers isolated from a few other van der Waals bonded layeredcompounds has enabled the ability to pick, place, and stack atomiclayers of arbitrary compositions and build unique layered materials,which would be otherwise impossible to synthesize via other knowntechniques. Here we demonstrate this concept for solids consistingof randomly stacked layers of graphene and hexagonal boron nitride(h-BN). Dispersions of exfoliated h-BN layers and graphene have beenprepared by liquid phase exfoliation methods and mixed, in variousconcentrations, to create artificially stacked h-BN/G solids. Thesevan der Waals stacked hybrid solid materials show interesting electrical,mechanical, and optical properties distinctly different from theirstarting parent layers. From extensive first principle calculationswe identify (i) a novel approach to control the dipole at the h-BN/Ginterface by properly sandwiching or sliding layers of h-BN and graphene,and (ii) a way to inject carriers in graphene upon UV excitationsof the Frenkell-like excitons of the h-BN layer(s). Our combined approachcould be used to create artificial materials, made predominantly frominter planar van der Waals stacking of robust bond saturated atomiclayers of different solids with vastly different properties. [ABSTRACT FROM AUTHOR]

Nanoscale antennas sandwiched between two graphene monolayersyielda photodetector that efficiently converts visible and near-infraredphotons into electrons with an 800% enhancement of the photocurrentrelative to the antennaless graphene device. The antenna contributesto the photocurrent in two ways: by the transfer of hot electronsgenerated in the antenna structure upon plasmon decay, as well asby direct plasmon-enhanced excitation of intrinsic graphene electronsdue to the antenna near field. This results in a graphene-based photodetectorachieving up to 20% internal quantum efficiency in the visible andnear-infrared regions of the spectrum. This device can serve as amodel for merging the light-harvesting characteristics of opticalfrequency antennas with the highly attractive transport propertiesof graphene in new optoelectronic devices. [ABSTRACT FROM AUTHOR]

We show that graphene films synthesized by chemical-vapor-deposition enables detection of trace amounts of nitrogen dioxide (NO2) and ammonia (NH3) in air at room temperature and atmospheric pressure. The gas species are detected by monitoring changes in electrical resistance of the graphene film due to gas adsorption. The sensor response time was inversely proportional to the gas concentration. Heating the film expelled chemisorbed molecules from the graphene surface enabling reversible operation. The detection limits of ∼100 parts-per-billion (ppb) for NO2 and ∼500 ppb for NH3 obtained using our device are markedly superior to commercially available NO2 and NH3 detectors. [ABSTRACT FROM AUTHOR]

A method for the preparation of highly oxidized nitrogen-doped carbon nanotubes (N-CNTs) from KMnO4 C H2SO4 solution is described. The atomic ratio of C=O in oxidized N-CNTs is as low as 1.2. The x-ray photoelectron spectroscopy results show that about 75% of the carbon atoms are oxidized and bound to oxygen-containing functional groups. The oxidation reaction mainly occurs at the outer sidewalls, which destroys the graphene stack to an sp3-rich structure and helps to preserve the tubular structure of the inner N-CNTs. The oxidized N-CNTs show an energy gap of 2.1 eV. [ABSTRACT FROM AUTHOR]

Highly conductive reduced graphene oxide (GO) polymer nanocomposites are synthesized by a well-organized in situ thermochemical synthesis technique. The surface functionalization of GO was carried out with aryl diazonium salt including 4-iodoaniline to form phenyl functionalized GO (I-Ph-GO). The thermochemically developed reduced GO (R-I-Ph-GO) has five times higher electrical conductivity (42 000 S/m) than typical reduced GO (R-GO). We also demonstrate a R-I-Ph-GO/polyimide (PI) composites having more than 104 times higher conductivity (∼1 S/m) compared to a R-GO/PI composites. The electrical resistances of PI composites with R-I-Ph-GO were dramatically dropped under ∼3% tensile strain. The R-I-Ph-GO/PI composites with electrically sensitive response caused by mechanical strain are expected to have broad implications for nanoelectromechanical systems. [ABSTRACT FROM AUTHOR]

We report that graphene coatings do not significantly disrupt the intrinsic wetting behaviour of surfaces for which surface-water interactions are dominated by van der Waals forces. Our contact angle measurements indicate that a graphene monolayer is wetting-transparent to copper, gold or silicon, but not glass, for which the wettability is dominated by short-range chemical bonding. With increasing number of graphene layers, the contact angle of water on copper gradually transitions towards the bulk graphite value, which is reached for ~6 graphene layers. Molecular dynamics simulations and theoretical predictions confirm our measurements and indicate that graphene's wetting transparency is related to its extreme thinness. We also show a 30-40% increase in condensation heat transfer on copper, as a result of the ability of the graphene coating to suppress copper oxidation without disrupting the intrinsic wettability of the surface. Such an ability to independently tune the properties of surfaces without disrupting their wetting response could have important implications in the design of conducting, conformal and impermeable surface coatings. [ABSTRACT FROM AUTHOR]

Abstract: Capacitive photocurrent spectroscopy is used to probe the electronic states of graphene-oxide, and reduced graphene-oxide. Three peaks are observed whose intensities scale with the oxygen coverage. The energy of these peaks correlate with the luminescence spectra reported for graphene-oxide. Using a fitting procedure, the density of states for graphene oxide is extracted from the data. It consists of the π/π∗ states along with a distribution of mid-gap states centered at three different energies near the Dirac point. X-ray photoelectron spectroscopy measurements are used to identify the oxygen functional groups corresponding to the observed state distribution. [Copyright &y& Elsevier]

We report electronic transport measurements in nanoscale graphene transistors with gold and platinum electrodes whose channel lengths are shorter than 100 nm and compare them with transistors with channel lengths from 1 μm to 50 μm. We find a large positive gate voltage shift in charge neutrality point (NP) for transistors made with platinum electrodes but negligible shift for devices made with gold electrodes. This is consistent with the transfer of electrons from graphene into the platinum electrodes. As the channel length increases, the disparity between the measured NP using gold and platinum electrodes disappears. [ABSTRACT FROM AUTHOR]

Abstract: Graphene-supported Pt and Pt3M (M=Co and Cr) alloy nanoparticles are prepared by ethylene glycol reduction method and characterized with X-ray diffraction and transmission electron microscopy. X-ray diffraction depicted the face-centered cubic structure of Pt in the prepared materials. Electron microscopic images show the high dispersion of metallic nanoparticles on graphene sheets. Electrocatalytic activity and stability of the materials is investigated by rotating-disk electrode voltammetry. Oxygen reduction activity of the Pt3M/graphene is found to be 3–4 times higher than that of Pt/graphene. In addition, Pt3M/graphene electrodes exhibited overpotential 45–70mV lower than that of Pt/graphene. The high catalytic performance of Pt3M alloys is ascribed to the inhibition of formation of (hydr) oxy species on Pt surface by the alloying elements. The fuel cell performance of the catalysts is tested at 353K and 1atm. Maximum power densities of 790, 875, and 985mW/cm2 are observed with graphene-supported Pt, Pt3Co, and Pt3Cr cathodes, respectively. The enhanced electrocatalytic performance of the Pt3M/graphene (M=Co and Cr) compared to that of Pt/graphene makes them a viable alternative to the extant cathodes for energy conversion device applications. [Copyright &y& Elsevier]

Two-dimensional materials, such as graphene and monolayer hexagonal BN (h-BN), are attractive for demonstrating fundamental physics in materials and potential applications in next-generation electronics. Atomic sheets containing hybridized bonds involving elements B, N and C over wide compositional ranges could result in new materials with properties complementary to those of graphene and h-BN, enabling a rich variety of electronic structures, properties and applications. Here we report the synthesis and characterization of large-area atomic layers of h-BNC material, consisting of hybridized, randomly distributed domains of h-BN and C phases with compositions ranging from pure BN to pure graphene. Our studies reveal that their structural features and bandgap are distinct from those of graphene, doped graphene and h-BN. This new form of hybrid h-BNC material enables the development of bandgap-engineered applications in electronics and optics and properties that are distinct from those of graphene and h-BN. [ABSTRACT FROM AUTHOR]

Graphite oxide is one of the main precursors of graphene-based materials, which are highly promising for various technological applications because of their unusual electronic properties. Although epoxy and hydroxyl groups are widely accepted as its main functionalities, the complete structure of graphite oxide has remained elusive. By interpreting spectroscopic data in the context of the major functional groups believed to be present in graphite oxide, we now show evidence for the presence of five- and six-membered-ring lactols. On the basis of this chemical composition, we devised a complete reduction process through chemical conversion by sodium borohydride and sulfuric acid treatment, followed by thermal annealing. Only small amounts of impurities are present in the final product (less than 0.5 wt% of sulfur and nitrogen, compared with about 3 wt% with other chemical reductions). This method is particularly effective in the restoration of the ?-conjugated structure, and leads to highly soluble and conductive graphene materials. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) materials such as graphene and hexagonal boron nitride (h‐BN) have attracted interest as a conductor/insulator pair in next‐generation devices because of their unique physical properties; however, the thermal transport at the interfaces must be understood to accurately predict the performance of heterostructures composed of these materials. Time‐domain thermoreflectance (TDTR) is used to estimate the thermal boundary conductance (TBC) at the interface of h‐BN and graphene to be 34.5 (+11.6/−7.4) MW m−2 K−1. The advantage of TDTR is that it does not need to create a large temperature gradient at the interface of heterostructures, but it has not yet been used for h‐BN/graphene interface. Phonon transmission and TBC at the h‐BN/graphene interface are predicted by two different formulations of the diffuse mismatch model (DMM) for anisotropic materials. The analysis of phonon transmission and temperature dependence of TBC establishes the flexural branch in the ab‐plane, and the c‐plane longitudinal acoustic branch of graphene and h‐BN are the dominant contributors when implementing both the DMM models. The methodology developed herein can be used to analyze heterostructures of other 2D materials. [ABSTRACT FROM AUTHOR]

State-of-the-art ultra-sensitive blood glucose-monitoring biosensors, based on glucose oxidase (GOx) covalently linked to a single layer graphene (SLG), will be a valuable next generation diagnostic tool for personal glycemic level management. We report here our observations of sensor matrix structure obtained using a multi-physics approach towards analysis of small-angle neutron scattering (SANS) on graphene-based biosensor functionalized with GOx under different pH conditions for various hierarchical GOx assemblies within SLG. We developed a methodology to separately extract the average shape of GOx molecules within the hierarchical assemblies. The modeling is able to resolve differences in the average GOx dimer structure and shows that treatment under different pH conditions lead to differences within the GOx at the dimer contact region with SLG. The coupling of different analysis methods and modeling approaches we developed in this study provides a universal approach to obtain detailed structural quantifications, for establishing robust structure-property relationships. This is an essential step to obtain an insight into the structure and function of the GOx-SLG interface for optimizing sensor performance. [ABSTRACT FROM AUTHOR]

Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts. [ABSTRACT FROM AUTHOR]

Large-area chemical vapor deposited graphene/boron-nitride (G/BN) thin films are co-transferred layer-by-layer to silicon-di-Oxide (SiO2) substrates, and transistors are constructed and examined. Raman spectra and high resolution transmission electron microscopy imaging show films of high quality. The graphene/boron-nitride/SiO2 devices have a significantly increased peak electron/hole mobility of 3400/2200 cm2/Vs with a reduced effective doping density over reference graphene/SiO2 devices. The mobility dependence as a function of carrier density is compared with a physically based empirical model and is in agreement with the improvements due to a consistent reduction in the substrate induced phonon and impurity scattering and an improvement in the overall surface quality owed to the boron-nitride interlayer that separates the graphene from the SiO2. Large-area G/BN thin films are promising for future high performance thin film electronic devices. [ABSTRACT FROM AUTHOR]

The study of two-dimensional (2D) electronic systems is of great fundamental significance in physics. Atomic layers containing hybridized domains of graphene and hexagonal boron nitride (h-BNC) constitute a new kind of disordered 2D electronic system. Magnetoelectric transport measurements performed at low temperature in vapor phase synthesized h-BNC atomic layers show a clear and anomalous transition from an insulating to a metallic behavior upon cooling. The observed insulator to metal transition can be modulated by electron and hole doping and by the application of an external magnetic field. These results supported by ab initio calculations suggest that this transition in h-BNC has distinctly different characteristics when compared to other 2D electron systems and is the result of the coexistence between two distinct mechanisms, namely, percolation through metallic graphene networks and hopping conduction between edge states on randomly distributed insulating h-BN domains. [ABSTRACT FROM AUTHOR]