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In this paper, regression tree ensembles (bagged and boosted) have been utilized in predicting atomic coordinate of Carbone nanotubes (CNTs). The aim of this study is to use ensembles classifiers to compute the atomic coordinates of Carbone nanotubes rather than other simulation tools. The dataset we used in this paper are provided by the UCI Repository of Machine Learning and it has a total of (10721) instances with (8) attributes (five as inputs and three as outputs) and it has no missing data. Various performance measures are also calculated to evaluate the classifiers we employed. The results show that there is a slight difference in performance between bagged and boosted trees, however, they are preferable classifiers for carbon atom coordinates prediction due to their high accuracy and short computation time. Using these predicted atomic coordinates as early coordinates for the simulation tool, the actual atomic coordinates can be retrieved in minutes or seconds instead of days by minimizing the iterations in the computation process. [ABSTRACT FROM AUTHOR]

A thermionic energy converter with a nickel collector and cesium vapor as a working gas was studied, and an abnormally low value of the surface work function of ≈1 eV was obtained if the collector was covered by a thin carbon layer. Scanning electron microscopy x-ray microanalysis data of the elemental composition of the collector's surface after its long exposure to plasma indicate that the carbon structure was intercalated with cesium atoms, and this change to surface structure can be a reason for the anomalously low work function ∼1 eV. The thermionic energy converter with such a collector demonstrated high heat-to-electric power conversion efficiency up to ∼20%. [ABSTRACT FROM AUTHOR]

We present here the study of the individual hypervelocity massive projectiles (440-540 keV, 33-36 km/s Au4004+ cluster) impact on 1-layer free-standing graphene. The secondary ions were detected and recorded separately from each individual impact in the transmission direction using a time-of-flight mass spectrometer. We observed C1-10± ions emitted from graphene, the projectiles which penetrated the graphene, and the Au1-3± fragment ions in mass spectra. During the projectile-graphene interaction, the projectile loses ~15% of its initial kinetic energy (~0.18 keV/atom, 72 keV/projectile). The Au projectiles are neutralized when approaching the graphene and then partially ionized again via electron tunneling from the hot rims of the holes on graphene, obtaining positive and negative charges. The projectile reaches an internal energy of ~450-500 eV (~4400-4900 K) after the impact and then undergoes a ~90-100 step fragmentation with the ejection of Au1 atoms in the experimental time range of ~0.1 µs. [ABSTRACT FROM AUTHOR]

Nanowires-dispersed polycrystalline graphene has been recently explored as a transparent conducting material for applications such as solar cells, displays, and touch-screens. Metal nanowires and polycrystalline graphene play synergetic roles during the charge transport in the material by compensating for each other's limitations. In the present work, we develop and employ an extensive computational framework to study the essential characteristics of the charge transport not only on an aggregate basis but also on individual constituents' levels in these types of composite thin-films. The method allows the detailed visualization of the percolative current pathways in the material and provides the direct evidence of current crowding in the 1-D nanowires and 2-D polygraphene sheet. The framework is used to study the effects of several important governing parameters such as length, density and orientation of the nanowires, grain density in polygraphene, grain boundary resistance, and the contact resistance between nanowires and graphene. We also present and validate an effective medium theory based generalized analytical model for the composite. The analytical model is in agreement with the simulations, and it successfully predicts the overall conductance as a function of several parameters including the nanowire network density and orientation and graphene grain boundaries. Our findings suggest that the longer nanowires (compared to grain size) with low angle orientation (<40°) with respect to the main carrier transport direction provide significant advantages in enhancing the conductance of the polygraphene sheet. We also find that above a certain value of grain boundary resistance (>60 × intra-grain resistance), the overall conductance becomes nearly independent of grain boundary resistance due to nanowires. The developed model can be applied to study other emerging transparent conducting materials such as nanowires, nanotubes, polygraphene, graphene oxide, and their hybrid nanostructures. [ABSTRACT FROM AUTHOR]

Graphene confinement provides a new physical and mechanical environment with ultrahigh van der Waals pressure, resulting in new quasi-two-dimensional phases of few-layer ice. Polymorphic transition can occur in bilayer constrained water/ice system. Here, we perform a comprehensive study of the phase transition of AA-stacked bilayer water constrained within a graphene nanocapillary. The compression-limit and superheating-limit (phase) diagrams are obtained, based on the extensive molecular-dynamics simulations at numerous thermodynamic states. Liquid-to-solid, solid-to-solid, and solid-to-liquid-to-solid phase transitions are observed in the compression and superheating of bilayer water. Interestingly, there is a temperature threshold (∼275 K) in the compression-limit diagram, which indicates that the first-order and continuous-like phase transitions of bilayer water depend on the temperature. Two obviously different physical processes, compression and superheating, display similar structural evolution; that is, square ice-nanotube arrays (BL-VHDI) will bend first and then transform into bilayer triangular AA stacking ice (BL-AAI). The superheating limit of BL-VHDI exhibits local maxima, while that of BL-AAI increases monotonically. More importantly, from a mechanics point of view, we propose a novel mechanism of the transformation from BL-VHDI to BL-AAI, both for the compression and superheating limits. This structural transformation can be regarded as the "buckling failure" of the square-ice-nanotube columns, which is dominated by the lateral pressure. [ABSTRACT FROM AUTHOR]

This work analyzes carrier transport, the relaxation of non-equilibrium charge, and the electronic structure of fluorinated graphene (FG) films with graphene quantum dots (GQDs). The FG films with GQDs were fabricated by means of chemical functionalization in an aqueous solution of hydrofluoric acid. High fluctuations of potential relief inside the FG barriers have been detected in the range of up to 200 mV. A phenomenological expression that describes the dependence of the time of non-equilibrium charge emission from GQDs on quantum confinement levels and film thickness (potential barrier parameters between GQDs) is suggested. An increase in the degree of functionalization leads to a decrease in GQD size, the removal of the GQD effect on carrier transport, and the relaxation of non-equilibrium charge. The study of the electronic properties of FG films with GQDs has revealed a unipolar resistive switching effect in the films with a relatively high degree of fluorination and a high current modulation (up to ON/OFF~104-105) in transistor-like structures with a lower degree of fluorination. 2D films with GQDs are believed to have considerable potential for various electronic applications (nonvolatile memory, 2D connections with optical control and logic elements). [ABSTRACT FROM AUTHOR]

Based on first-principles calculations we show that the two-dimensional pentagonal (pt) structures, the compositions of pt-BN2, pt-C, and pt-Fe2S, are stable. As a common feature, they are composed of 3 components: 2 stretched honeycomb sublattices and 1 square sublattice, conferring flexibility of tailoring the properties peculiar to the graphene. Although the Dirac dispersion relation is removed in metallic pt-BN2 and insulating pt-C due to the hybridization of two honeycomb sublattices, it survives in pt-Fe2S because of the suppression of such hybridization between different spins. As a result, in the dispersion relation of pt-Fe2S spin-polarized and anisotropic Dirac cones occur. We suggest that such type of dispersion relation can be used to produce spin-filter effect by applying electric bias in a specific direction. [ABSTRACT FROM AUTHOR]

The van der Waals interaction between a lipid membrane and a substrate covered by a graphene sheet is investigated using the Lifshitz theory. The reflection coefficients are obtained for a layered planar system submerged in water. The dielectric response properties of the involved materials are also specified and discussed. Our calculations show that a graphene covered substrate can repel the biological membrane in water. This is attributed to the significant changes in the response properties of the system due to the monolayer graphene. It is also found that the van der Waals interaction is mostly dominated by the presence of graphene, while the role of the particular substrate is secondary. [ABSTRACT FROM AUTHOR]

A theoretical study is conducted to search for Dirac cones in two-dimensional carbon allotropes with square symmetry. By enumerating the carbon atoms in a unit cell up to 12, an allotrope with octatomic rings is recognized to possess Dirac cones under a simple tight-binding approach. The obtained Dirac cones are accompanied by flat bands at the Fermi level, and the resulting massless Dirac-Weyl fermions are chiral particles with a pseudospin of S = 1, rather than the conventional S = 1/2 of graphene. The spin-1 Dirac cones are also predicted to exist in hexagonal graphene antidot lattices. [ABSTRACT FROM AUTHOR]

We investigated the magnetic field dependence of the Hall and the bend resistances in the ballistic regime for a single layer graphene Hall bar structure containing a pn-junction. When both regions are n-type the Hall resistance dominates and Hall type of plateaus are formed. These plateaus occur as a consequence of the restriction on the angle imposed by Snell's law allowing only electrons with a certain initial angles to transmit though the potential step. The size of the plateau and its position is determined by the position of the potential interface as well as the value of the applied potential. When the second region is p-type, the bend resistance dominates, which is asymmetric in field due to the presence of snake states. Changing the position of the pn-interface in the Hall bar strongly affects these states and therefore the bend resistance is also changed. Changing the applied potential, we observe that the bend resistance exhibits a peak around the charge-neutrality point (CNP), which is independent of the position of the pn-interface, while the Hall resistance shows a sign reversal when the CNP is crossed, which is in very good agreement with a recent experiment [J. R. Williams and C. M. Marcus, Phys. Rev. Lett. 107, 046602 (2011)]. [ABSTRACT FROM AUTHOR]

Graphene deposited on planar surfaces often exhibits sharp and localized folds delimiting seemingly planar regions, as a result of compressive stresses transmitted by the substrate. Such folds alter the electronic and chemical properties of graphene, and therefore, it is important to understand their emergence, to either suppress them or control their morphology. Here, we study the emergence of out-of-plane deformations in supported and laterally strained graphene with high-fidelity simulations and a simpler theoretical model. We characterize the onset of buckling and the nonlinear behavior after the instability in terms of the adhesion and frictional material parameters of the graphene-substrate interface. We find that localized folds evolve from a distributed wrinkling linear instability due to the nonlinearity in the van der Waals graphene-substrate interactions. We identify friction as a selection mechanism for the separation between folds, as the formation of far apart folds is penalized by the work of friction. Our systematic analysis is a first step towards strain engineering of supported graphene, and is applicable to other compressed thin elastic films weakly coupled to a substrate. [ABSTRACT FROM AUTHOR]

Ab initio calculations, based on the planewave pseudopotential method and the density functional theory, have been reported on the changes in the electronic and structural properties of short carbon atomic chains held rigidly between hydrogenated thin armchair graphene nanoribbons (Na-AGNR) of dimer line numbers Na = 4 and 5. We have considered chains of several lengths (n = 4-9 atoms) and with different forms of attachment with the AGNRs. It is found that odd-numbered chains are metallic in nature, with chemical bonding more like ... C==C==C==C... (as in cumulene). Even numbered chains show semiconductor structure when held between 4-AGNR and semi-metallic nature when held between 5-AGNR, in both cases characterized by chemical bonding more like ... C[Single_Bond]C=C[Single_Bond]C=C... (as in polyyne). [ABSTRACT FROM AUTHOR]

A combination of wide‐angle X‐ray scattering (WAXS) and pair distribution function analysis was used to investigate the structural changes occurring in beech wood and apricot tree pruning samples during slow and fast pyrolysis up to 1400°C (1673 K). WAXS curve modeling with the program CarbX provides unique information about the arrangement of graphene layers described by intralayer, interlayer, disorder and dispersion structural parameters. Pair distribution function modeling in PDFgui revealed imperfections in single graphene sheets, such as bond shortening and curvature, when refinement is performed in different r ranges. The concentration of inorganic species, along with heating rate, influences the final structure of pyrolysis products. The heating rate was more important than sample composition for an increase in extent of the single graphene layer and average chord length, while the average graphene coherent stack height depended on both composition and heating rate. Higher fractions of inorganic material increased the average interlayer spacing and the number of graphene layers per stack. Atomic level structural changes of pyrolized beech and apricot plant material were modeled using two different approaches: total wide‐angle X‐ray scattering curve fitting and pair distribution function analysis. It is shown that the information obtained from the combination of these two analytical techniques is complementary, while using only one can provide a partial and incomplete view of structural changes. [ABSTRACT FROM AUTHOR]

Single crystal graphene has been getting lots of attention due to the lack of grain boundaries which ensures its distinguished intrinsic properties and good performance in graphene-based devices. Hence, the realization of single crystal graphene growth with tunable size and high crystallinity will be of great importance in commercial production and widespread applications. Recently, numerous studies have focussed on the controlled single crystal graphene growth, and great advancements have been made in the synthesis of large-sized single-crystal graphene (LSSG) by chemical vapor deposition (CVD). In this review, current developments of CVD-grown LSSG and its future prospects are presented and discussed. We emphasize on growth methods and growth mechanisms over transition-metal Cu and Cu alloys for deeper insights in control of size and crystallinity. [ABSTRACT FROM AUTHOR]

Novel processable conductive bionanocomposites containing different loadings of graphite nanoplatelets (GNPs) were developed and examined in the experiments. At the same GNPs loadings, the bionanocomposites with interfacial compatibilizer, maleated PLA (ma‐PLA), exhibited higher mechanical and thermo‐mechanical properties compared to neat PLA and those without ma‐PLA. The strong interaction from incorporated interfacial compatibilizer with GNPs was evidenced on the fractured surface. With the micromechanical models, the mechanical properties of the bionanocomposites were evaluated. Also, their thermal and rheological properties were tested and analyzed. An approximately twofold decrease in complex viscosity was achieved for the bionanocomposites with interfacial compatibilizer. For electrical conductivity, at 5–7 wt% GNPs loadings the electrical conduction path was constructed inside the PLA matrix through the formation of the effective three‐dimensional conductive networks. It was interestingly noted that above the percolation threshold the increasing GNPs loading did not contribute to the higher but lower AC conductivity. The corresponding mechanisms in AC conductivity were elucidated and discussed. POLYM. COMPOS., 40:389–400, 2019. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Polypropylene (PP) was filled with synthetic graphite (SG) and graphene nanoplatelets (G) at different weight fractions. Composites were prepared by the melt mixing process by using a co‐rotating twin screw extruder. Mechanical tests were carried out to determine tensile and flexural properties of composites. Dynamic Mechanical Analysis of composites was performed to determine their thermo‐mechanical properties, such as storage modulus and loss modulus. Scanning Electron Microscopy was used to observe the fracture surfaces of the composites after tensile tests. The effect of SG and G on thermal properties such as melting and crystallization temperature, thermal conductivity, thermal stability, and coefficient of thermal expansion of PP was investigated. Tensile strength and flexural strength of PP increased with the addition of 10 wt% SG. The highest thermal conductivity achieved in this study at 50 wt% SG and 3 wt% G loading was 4.6 W/mK. POLYM. COMPOS., 40:277–287, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract Two vastly different types of load-displacement responses observed in graphitic nanostructures under nano-compression are compared in terms of serration behaviors. Different from commonly encountered linear/nonlinear elastic deformation, a periodic serration behavior related to plastic flow is observed in amorphous carbon nanospheres. The true stress-strain relation exhibits a sole feature of type C serration, and comprehensive statistical, dynamical and fractal analyses further demonstrate a chaotic characteristic of dynamics for those serration events. When entering a quasi-steady flow stage, the elastic stress in each serration event could maintain a relatively stable level near ∼135 MPa, very close to the interlayer shear stress (ISS) of single crystalline graphite (∼140 MPa). This finding indicates the dependence of shear deformation on weak van der Waals interaction (elastic constant C 44), instead of other structural factors associated with high elastic constants of graphite cells. Based on the experimental results, a microscale ISS-driven shearing mechanism is proposed. The local flexibility induced by small graphene lamellas may facilitate interfacial slip between neighboring domains with commensurate contact. Such slip mode may be responsible for the mechanical serration phenomenon in graphitic materials. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Unlike single layer graphene, in the case of AB -stacked bilayer graphene (BLG) one can induce a non-zero energy gap by breaking the inversion symmetry between the two layers using a perpendicular electric field. This is an essential requirement in field-effect applications, particularly since the induced gap in BLG systems can be further tuned by the magnitude of the external electric field. Doping is another way to modify the electronic properties of graphene based systems. We investigate here BLG systems doped with boron and nitrogen in the presence of external electric field, in the framework of density functional theory (DFT) calculations. Highly doped BLG systems are known to behave as degenerate semiconductors, where the Fermi energy depends on the doping concentration but, in addition, we show that the electronic properties drastically depend also on the applied electric field. By changing the magnitude and the orientation of the electric field, the gap size and position relative to the Fermi level may be tuned, essentially controlling the effect of the extrinsic doping. In this context, we discuss in how far the external electric field may suitably adjust the effective doping and, implicitly, the conduction properties of doped BLG systems. [ABSTRACT FROM AUTHOR]

We formulate the blended force-based quasicontinuum method for multilattices and develop rigorous error estimates in terms of the approximation parameters: choice of atomistic region, blending region, and continuum finite element mesh. Balancing the approximation parameters yields a convergent atomistic/continuum multiscale method for multilattices with point defects, including a rigorous convergence rate in terms of the computational cost. The analysis is illustrated with numerical results for a Stone-Wales defect in graphene. [ABSTRACT FROM AUTHOR]

Graphene gels have attracted intense research due to their excellent gravimetric performances in supercapacitors. However, their low volumetric capacitance and cycling stability limit their practical application. In this work, three-dimensional (3D) reduced graphene aerogel (RGAs) with hierarchical porous and high electrical conductivity were synthesized via simple low temperature chemical reduction method using graphene oxide as precursor and L-cysteine as reducing and functional agent. The sample RGAs-8 that prepared after reduction for 8 h displayed the highest mass density, higher electrical conductivity and cross-linked porous structure. Electrochemical measurements showed that the gravimetric capacitance and the volumetric capacitance of RGAs-8 reached as high as 203.9 F g −1 and 293.6 F cm −3 at 0.5 A g −1 in 6 M KOH aqueous electrolyte, respectively. In particular, the capacitance of RGAs-8 showed no capacitance loss even after 300,000 charge/discharge cycles, clearly demonstrating a robust long-term stability. [ABSTRACT FROM AUTHOR]

Relatively-low long-term stabilities of perovskite solar cells (PSCs) despite the excellent photovoltaic properties are a critical obstacle to their practical applications. A stack of poly(3,4-ethyle nedioxy thiophene):poly(styrenesulfonate) (PEDOT:PSS)/indium tin oxide (ITO) is widely used as a key element in p-i-n perovskite PSC structures, but is also one of the major sources for degrading the performance of the PSCs, mostly resulting from the high acidity of PEDOT:PSS. Here, we first employ gold(III) chloride (AuCl 3 )-doped graphene (GR) as a protecting layer between PEDOT:PSS and ITO for improving the efficiency and durability of the PSCs. The AuCl 3 -GR PSC shows maximum power conversion efficiencies (PCEs) of 15.77/15.90% for forward/reverse condition at a AuCl 3 concentration of 10 mM, much larger than those (14.16/14.21%) of the PSC without GR. After 30 days under ambient condition, the former PSC retains 67% of its original PCE with the operation of the latter PSC being stopped. The enhancement of the PCE and the stability result from the improvement in the protection of ITO as well as in the collection of holes by the inclusion of the AuCl 3 -GR. [ABSTRACT FROM AUTHOR]

Mercury (Hg) pollution caused by coal-fired power plants has raised global concerns, and it is imperative for developing a new low cost technology to control Hg emissions. Single atom iron catalyst with graphene-based substrates (Fe/GS) which has high catalytic activity and high selectivity is a promising material for removal of mercury pollution. The adsorption characteristics of mercury species on single atom iron catalysts with different graphene-based substrates were investigated systematically using first-principles calculation. It is found that the support effects of graphene-based substrates have a significant influence on adsorption characteristic of mercury species, and the support effects can be well understood through electronic structure analysis. Fermi softness is a good descriptor for adsorption activity of Fe/GS which can be an indicator for design and optimization of new materials. Fe/GS may be a new material for removal of Hg 0 pollutant, and the temperature has an inhibitory effect on mercury species adsorption. Furthermore, the findings can provide a novel perspective for adsorption and oxidation of Hg and lay a foundation for the further study of graphene-based support effects in single atom catalysts. [ABSTRACT FROM AUTHOR]

Abstract Two-dimensional materials, and especially carbon-based 2D materials, have gained a special reputation and status in many engineering fields and applications recently; because they can be engineered by various methods to precisely yield the properties desired by the designers. One of the most important techniques used for engineering these structures is to create nanopores in them. The varied effects of nanopores in graphene sheets and some other 2D materials have already been studied. In this work, for the first time, the effects of nanopores on the mechanical properties of C 3 N sheets have been evaluated. Using the molecular dynamics method, various types of achievable vacancy and divacancy pores in C 3 N sheets have been specified, and the formation energy for each type has been calculated. The formation energy for a vacancy formed by removing a carbon atom or a nitrogen atom is 2.63 eV or 1.31 eV, respectively. In comparing the formation energies for different types of vacancies and divacancies, it was observed that the removal of carbon atom in the structure of C 3 N requires much more energy, and that the highest amount of energy is needed for removing two carbon atoms in two types of divacancies. Since graphene sheets with a large number of vacancies do not fail easily and remain intact, these sheets can be considered as suitable candidates for 'straintronic' applications. By studying the effect of pore density on the mechanical properties of C 3 N sheets it was observed that at pore densities lower than 5%, C 3 N sheets exhibit better mechanical properties than graphene, and thus, they can be a better option for straintronic applications. Graphical abstract Unlabelled Image Highlights • The effects of nanopores on the mechanical properties of C 3 N sheets have been evaluated. • Various types of achievable vacancy and divacancy pores were derived. • The formation energy for each type has been calculated. • The removal of carbon in the structure of C 3 N requires much more energy. • C 3 N sheets with pore densities lower than 5% are better option for straintronics. [ABSTRACT FROM AUTHOR]

Abstract Current graphene/metal composites are mostly limited to the cases of using graphene oxide (GO) which contains a high level of defects. In this work, the high-quality graphene nanoplatelets (GNPs) were used as starting graphene material to prepare the GNP/Cu composite. Oxygen plasma treatment was employed to conduct the surface functionalization of GNPs by grafting the considerable oxygen-functional groups but without noticeably damaging the graphene structure. It was found that the plasma-treated GNPs (P-GNPs) exhibited not only a good dispersability in ethanol/water, but also an enhanced electrostatic affinity with Cu powder, resulting in the P-GNP/Cu composite with a uniform GNP distribution and a good interfacial bonding. At 1 vol% GNP loading, the P-GNP/Cu composite presented a largely enhanced yield strength of 188 MPa with a relatively high failure elongation of 21%, significantly outperforming the composite with untreated GNPs (158 MPa, 12%). The enhanced strength could be explained by the load transfer mechanism and agreed approximately with the prediction of a modified shear-lag model. The good ductility was attributed to the prominent dislocation storage capability of P-GNP/Cu composite. Therefore, the oxygen plasma treatment provides a general and effective strategy to improve graphene distribution and mechanical properties of graphene/metal composites. [ABSTRACT FROM AUTHOR]

Graphene microcrystal (GMC) is a type of glassy carbon fabricated from lignin, in which the microcrystals of graphene are chemically bonded by sp3 carbon atoms, forming a glass-like microcrystal structure. The lignin is refined from sugarcane bagasse using an ethanol-based organosolv technique which is used for the fabrication of GMC by two technical schemes: The pyrolysis reaction of lignin in a tubular furnace at atmospheric pressure; and the hydrothermal carbonization (HTC) of lignin at lower temperature, followed by pyrolysis at higher temperature. The existence of graphene nanofragments in GMC is proven by Raman spectra and XRD patterns; the ratio of sp2 carbon atoms to sp3 carbon atoms is demonstrated by XPS spectra; and the microcrystal structure is observed in the high-resolution transmission electron microscope (HRTEM) images. Temperature and pressure have an important impact on the quality of GMC samples. With the elevation of temperature, the fraction of carbon increases, while the fraction of oxygen decreases, and the ratio of sp2 to sp3 carbon atoms increases. In contrast to the pyrolysis techniques, the HTC technique needs lower temperatures because of the high vapor pressure of water. In general, with the help of biorefinery, the biomass material, lignin, is found to be qualified and sustainable material for the manufacture of GMC. Lignin acts as a renewable substitute for the traditional raw materials of glassy carbon, copolymer resins of phenol formaldehyde, and furfuryl alcohol-phenol. [ABSTRACT FROM AUTHOR]

Metal-graphene nanolayered composites (MGNLCs), composed of alternating layers of metal (copper here) and graphene layers, are new emerging engineering materials with outstandingly enhanced mechanical properties thanks to the high intrinsic in-plane strength and modulus of one-atom-thick layers of graphene. In this paper, mechanical behavior and elastic-plastic deformation mechanisms of MGNLCs subjected to uniaxial tensile loading were investigated based on molecular dynamics (MD) simulations. Stress-strain curves of the composite samples and their elastic properties were obtained and compared with their pure metal counterparts. In addition, influence of thickness of the metal layers on the composite performance was determined which seems tough or even impossible to be dealt with by the experimental techniques. Graphene inclusion outstandingly increased strength and failure strain of the composites and remarkably improved their stiffness and toughness. Graphene layers could provide effective barriers against shearing flows and dislocation propagation of the metal layers and made the applied strain energy spread out more evenly inside the material. [ABSTRACT FROM AUTHOR]

Abstract: The role of interlayer rotation on the electrical transport of few layer graphene (FLG) is rarely considered. In this paper, the impact of twisting angle on physical and electrical properties of synthetic single crystal bilayer and few layer graphene deposited on thermal SiO2 substrate is systematically studied. Bernal AB‐stacked graphene layers show low carrier mobility due to strong interlayer coupling and substrate scattering. A dramatic increase in carrier mobility and conductivity is observed when the graphene layers are twisted. A field effect mobility up to 15000 cm2 V−1 s−1 and 460 nm mean free path is measured on a twisted three‐layer graphene at room temperature is among the highest for graphene transferred to SiO2. In average, twisted graphene shows a fivefold improvement compared to AB stacked graphene in terms of mobility and conductivity, regardless of twist angles. [ABSTRACT FROM AUTHOR]

Graphene, a single two-dimensional sheet of carbon atoms with an arrangement mimicking the honeycomb hexagonal architecture, has captured immense interest of the scientific community since its isolation in 2004. Besides its extraordinarily high electrical conductivity and surface area, graphene shows a long spin lifetime and limited hyperfine interactions, which favors its potential exploitation in spintronic and biomedical applications, provided it can be made magnetic. However, pristine graphene is diamagnetic in nature due to solely sp2 hybridization. Thus, various attempts have been proposed to imprint magnetic features into graphene. The present review focuses on a systematic classification and physicochemical description of approaches leading to equip graphene with magnetic properties. These include introduction of point and line defects into graphene lattices, spatial confinement and edge engineering, doping of graphene lattice with foreign atoms, and sp3 functionalization. Each magnetism-imprinting strategy is discussed in detail including identification of roles of various internal and external parameters in the induced magnetic regimes, with assessment of their robustness. Moreover, emergence of magnetism in graphene analogues and related 2D materials such as transition metal dichalcogenides, metal halides, metal dinitrides, MXenes, hexagonal boron nitride, and other organic compounds is also reviewed. Since the magnetic features of graphene can be readily masked by the presence of magnetic residues from synthesis itself or sample handling, the issue of magnetic impurities and correct data interpretations is also addressed. Finally, current problems and challenges in magnetism of graphene and related 2D materials and future potential applications are also highlighted. [ABSTRACT FROM AUTHOR]

We perform molecular dynamic simulations to investigate the effects of orientation and grain boundary (GB) on shock response of graphene, including shock-induced slip and spall. For compression under different loading orientations, the critical resolved shear stress for slip is constant along a given growth direction (armchair or zigzag) in single-crystal graphene, and spall initiates in elastically deformed graphene via tension-induced debonding. For bicrystal graphene, the locations of compression-induced slip and initial spall are influenced by preexisting stress field at GB and the interactions between GB and shock waves, respectively. Both of these two factors are related to GB structure, including the density of pentagon-heptagon pairs at GB. However, bicrystals show negligible anisotropy in shock-compression response. For polycrystalline graphene at high shock strength, slips initiate at GBs and triple junctions under shock compression, develop along GBs or toward grain interior, and serve as nucleation sites for spall damage. [ABSTRACT FROM AUTHOR]

Hollow structured graphene-polyaniline spheres (GSA/PANI HS) were prepared via a facile and efficient Pickering emulsion polymerization using sulfonated graphene (GSA) as Pickering stabilizer. In our procedure, amphiphilic sulfonated graphene (GSA) was first synthesized and used to stabilize an oil phase containing aniline. Upon aniline polymerization at the oil/water interface, graphene-polyaniline hollow sphere (GSA/PANI HS) with a rough outer surface and a smooth inner surface, was generated. The size as well as the electrochemical properties of GSA/PANI HS could be easily adjusted by varying the amphipathicity and concentration of GSA, and the oil-water volume ratios of the Pickering emulsions. The synthesized GSA/PANI HS exhibited superior performance in supercapacitors compared to the common stacked two-dimensional GSA/PANI composite owing to its unique hollow structure, which provides a larger accessible surface area and reduces the transport length for both charge and ion The specific capacitance of GSA/PANI HS can reach 546 F g −1 , more than two folds higher than stacked two-dimensional GSA/PANI composite. In addition, GSA/PANI HS reveals enhanced capacitance retention at higher scan rates (76% from 5 to 500 mV s −1 ) and current densities (83.5% from 0.5 to 10 A g −1 ), demonstrating superior electrochemical accessibility of the 3D hollow nanostructure. Furthermore, good cycling stability is also demonstrated, which render them interesting candidates for future electrochemical energy storage systems. This approach represents a simple, convenient and controllable route for the preparation of hollow graphene-polyaniline nanostructures for high performance supercapacitor applications. [ABSTRACT FROM AUTHOR]

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10-21 m2/s, which corresponds to an activation-barrier height of ~1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene. [ABSTRACT FROM AUTHOR]

In the present paper, molecular dynamic simulations have been conducted to investigate the nanopores creation on 10% of boron and nitrogen doped polycrystalline graphene by silicon and diamond nanoclusters. Two types of nanoclusters based on silicon and diamond are used to investigate their effect for the fabrication of nanopores. Therefore, three different diameter sizes of the clusters with five kinetic energies of 10, 50, 100, 300 and 500 eV/atom at four different locations in boron or nitrogen doped polycrystalline graphene nanosheets have been perused. We also study the effect of 3% and 6% of boron doped polycrystalline graphene with the best outcome from 10% of doping. Our results reveal that the diamond cluster with diameter of 2 and 2.5 nm fabricates the largest nanopore areas on boron and nitrogen doped polycrystalline graphene, respectively. Furthermore, the kinetic energies of 10 and 50 eV/atom can not fabricate nanopores in some cases for silicon and diamond clusters on boron doped polycrystalline graphene nanosheets. On the other hand, silicon and diamond clusters fabricate nanopores for all locations and all tested energies on nitrogen doped polycrystalline graphene. The area sizes of nanopores fabricated by silicon and diamond clusters with diameter of 2 and 2.5 nm are close to the actual area size of the related clusters for the kinetic energy of 300 eV/atom in all locations on boron doped polycrystalline graphene. The maximum area and the average maximum area of nanopores are fabricated by the kinetic energy of 500 eV/atom inside the grain boundary at the center of the nanosheet and in the corner of nanosheet with diameters of 2 and 3 nm for silicon and diamond clusters on boron and nitrogen doped polycrystalline graphene. [ABSTRACT FROM AUTHOR]

For the first time, a simple and rapid sonochemical technique for preparing of pure Cd 2 SiO 4 nanostructures has been developed in presence of various surfactants of SDS, CTAB and PVP. Uniform and fine Cd 2 SiO 4 nanoparticle was synthesized using of polymeric PVP surfactant and ultrasonic irradiation. The optimized cadmium silicate nanostructures added to graphene sheets and Cd 2 SiO 4 /Graphene nanocomposite synthesized through pre-graphenization. Hydrogen storage capacity performances of Cd 2 SiO 4 nanoparticle and Cd 2 SiO 4 /Graphene nanocomposite were compared. Obtained results represent that Cd 2 SiO 4 /Graphene nanocomposites have higher hydrogen storage capacity than Cd 2 SiO 4 nanoparticles. Cd 2 SiO 4 /Graphene nanocomposites and Cd 2 SiO 4 nanoparticles show hydrogen storage capacity of 3300 and 1300 mAh/g, respectively. [ABSTRACT FROM AUTHOR]

The wettability of graphene-coated SiC single crystal (CGn/SiCsc) by liquid Cu (99.99%) was investigated by a sessile drop method in vacuum conditions at temperature of 1100 °C. The graphene layer was produced via a chemical vapor deposition routine using 4H-SiC single crystal cut out from 6″ wafer. A dispensed drop technique combined with a non-contact heating of a couple of materials was applied. The Cu drop was squeezed from a graphite capillary and deposited on the substrate directly in a vacuum chamber. The first Cu drop did not wet the CGn/SiCsc substrate and showed a lack of adhesion to the substrate: the falling Cu drop only touched the substrate forming a contact angle of θ0 = 121° and then immediately rolled like a ball along the substrate surface. After settling near the edge of the substrate in about 0.15 s, the Cu drop formed an asymmetric shape with the right and left contact angles of different values (θR = 86° and θL = 70°, respectively), while in the next 30 min, θR and θL achieved the same final value of ~ 52°. The second Cu drop was put down on the displacement path of the first drop, and immediately after the deposition, it also did not wet the substrate (θ = 123°). This drop kept symmetry and the primary position, but its wetting behavior was unusual: both θR and θL decreased in 17 min to the value of 23° and next, they increased to a final value of 65°. Visual observations revealed a presence of ~ 2.5-mm-thick interfacial phase layer reactively formed under the second drop. Scanning electron microscopy (SEM) investigations revealed the presence of carbon-enriched precipitates on the top surface of the first Cu drop. These precipitates were identified by the Raman spectroscopy as double-layer graphene. The Raman spectrum taken from the substrate far from the drop revealed the presence of graphene, while that obtained from the first drop displacement path exhibited a decreased intensity of 2D peak. The results of SEM investigations and Raman spectroscopy studies suggest that the presence of graphene layer on the SiC substrate suppresses but does not completely prevent chemical interaction between liquid Cu drop and SiC. Both chemical degradation (etching) and mechanical degradation of the graphene layer during drop rolling due to high adhesion of the Cu drop to the SiC substrate are responsible for mass transfer through the 2nd drop/substrate interface that in turn results in significant changes of structure and chemistry of the drop and the interface. [ABSTRACT FROM AUTHOR]

A Li + -OH − exfoliation system was designed to prepare graphene in water without surfactants or sonication. Due to the positive charge transferred from intercalating Li + ions to adjacent C atoms, OH − could add on the graphene sheets and further promote their affinity to water, resulting in efficient exfoliation of graphene in water. The as-prepared graphene concentration was up to 0.09 mg·mL −1 , and sheet sizes range from 1 to 2 μm. Detailed characterizations revealed the formation of high-quality and few-layer graphene sheets and confirmed the addition of hydroxyl groups on graphene sheets during exfoliation. This strategy has potential in scalable production of graphene in aqueous phase. [ABSTRACT FROM AUTHOR]

Amorphous carbon film is vastly applied for low-friction protective coatings at contact sliding surfaces. However before reaching steady low friction status, the film always endures a high friction period known as the “run-in” period, sometimes taking thousands of sliding cycles, causing remarkable energy dissipation. Here, we report that the run-in period of amorphous carbon film could be drastically shortened to 22 ± 5 cycles by fabricating a 5-nm graphene nanocrystallite cap layer. The cap layer gave rise to rapid formation of graphene nanocrystallized transfer film, which responds to the short run-in period. We found two key factors for the rapid formation of transfer film. Firstly, the cap layer had lower wear resistance than the amorphous carbon, severing as a quick-wearing sacrificial layer. Secondly, the nanocrystallization of transfer film was mainly due to friction-induced restructuring of graphene nanocrystallite but not friction-induced heat. In addition, the friction test of amorphous carbon film covered with multilayer graphene micro-flakes also verified that friction-induced rapid restructuring of graphene sheets at sliding surfaces resulted in short run-in period. [ABSTRACT FROM AUTHOR]

This work reports the catalytic performance of vertically-oriented graphenes (VGs) supported manganese oxide catalysts toward toluene decomposition in post plasma-catalysis (PPC) system. Dense networks of VGs were synthesized on carbon paper (CP) via a microwave plasma-enhanced chemical vapor deposition (PECVD) method. A constant current approach was applied in a conventional three-electrode electrochemical system for the electrodeposition of Mn 3 O 4 catalysts on VGs. The as-obtained catalysts were characterized and investigated for ozone conversion and toluene decomposition in a PPC system. Experimental results show that the Mn 3 O 4 catalyst loading mass on VG-coated CP was significantly higher than that on pristine CP (almost 1.8 times for an electrodeposition current of 10 mA). Moreover, the decoration of VGs led to both enhanced catalytic activity for ozone conversion and increased toluene decomposition, exhibiting a great promise in PPC system for the effective decomposition of volatile organic compounds. [ABSTRACT FROM AUTHOR]

Abstract: The response of E‐glass/epoxy composites filled with two‐dimensional (2D) graphene nanoplatelets (GnPs) and exfoliated graphene nanoplatelets (xGnPs), and one‐dimensional (1D) multiwalled carbon nanotubes (MWCNTs) to microwave is compared in the 8–12 GHz frequency range. The nanocomposites are prepared with 1.0, 1.4, 1.8, 2.2, and 2.6 wt.% of each type of nanofiller. The results of the complex permittivity shows that the E‐glass/epoxy composites filled with GnPs and xGnPs have superior dielectric properties as compared to that of MWCNTs‐filled composites. However, calculations and simulations of reflection loss (RL) have predicted poor microwave absorbing strength of GnPs and xGnPs composites as compared to that of MWCNTs. The calculations of AC conductivity and skin depth show that GnPs‐ and xGnPs‐filled hybrid composites have very large AC conductivity and short skin depth, which can suppress the ability of the composites to absorb electromagnetic waves. The decrease in wt.% of GnPs below 1.0 has improved the microwave absorption in hybrid composites. [ABSTRACT FROM AUTHOR]

Nowadays, rubber nanocomposites filled with graphene are endowed with promising future, because graphene has unique and outstanding mechanical, electrical, and thermal properties. This article summarizes the preparation and functionalization of graphene, and introduces the preparation, properties, and the latest achievement of graphene/rubber nanocomposites. Meanwhile it draws conclusions about factors that influence the properties of graphene‐based rubber composites. Finally, it gives the outlook and prospect about the development of graphene‐based rubber nanocomposites in future. POLYM. COMPOS., 39:1006–1022, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

A multi-band absorber constructed from prism-incorporated one-dimensional photonic crystal (1D-PhC) containing graphene defects is achieved theoretically in the visible and near-infrared (vis-NIR) spectral range. By means of the transfer matrix method (TMM), the effect of structural parameters on the optical response of the structure has been investigated. It is possible to achieve multi-peak and complete optical absorption. The simulations reveal that the light intensity is enhanced at the graphene plane, and the resonant wavelength and the absorption intensity can also be tuned by tilting the incidence angle of the impinging light. In particular, multiple graphene sheets are embedded in the arrays, without any demand of manufacture process to cut them into periodic patterns. The proposed concept can be extended to other two-dimensional (2D) materials and engineered for promising applications, including selective or multiplex filters, multiple channel sensors, and photodetectors. [ABSTRACT FROM AUTHOR]

By using the scattering matrix formalism, it is studied the optical properties of one dimensional photonic crystals made of multiple layers of dielectric and uniaxial anisotropic single negative electric metamaterial with Drude type responses, with inclusions of graphene in between the dielectric-dielectric interfaces (DGMPC). The transmission spectra for transverse electric (TE) and magnetic (TM) polarization are presented as a function of the incidence angle, the graphene chemical potential, and the metamaterial plasma frequencies. It is found for the TM polarization the tunability of the DGMPC optical response with the graphene chemical potential, which can be observed by means of transmission or reflexion bands around the metamaterial plasmon-polariton frequency, with bandwidths depending on both the incidence angle and the metamaterial plasma frequency. Also, the transmission band is observed when losses in the metamaterial slabs are considered for finite systems. The conditions for the appearance of these bands are shown analytically. We consider this work contributes to open new possibilities to the design of photonic devices with DGMPCs. [ABSTRACT FROM AUTHOR]

ABSTRACT One of disadvantages of polymer composites is poor electrical and thermal conductivity. As a first step in this direction, graphene-modified polypropylene polymer is being developed to improve its electrical and thermal conductivity. Two techniques were investigated: surface coating and extrusion. In the case of coating technique, the percolation threshold was found to be 0.5 wt % of graphene and electrical conductivity of polypropylene increased around 13 log cycles. Coating technique breaks the agglomerations due to magnetic stirring followed by sonication and gives homogeneous graphene-coated polypropylene pellets. When polymer melts under compression molding, the graphene platelets network formed on the surface of polypropylene pellets as well as through-the-thickness of the molded disk, which provide continuous network of graphene. However, in extrusion technique, graphene segregated and did not disperse properly in polypropylene. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45833. [ABSTRACT FROM AUTHOR]

We investigate the effects of Dirac points on the magneto‐optical absorption of graphene superlattices (SLs) in a weak perpendicular magnetic field. It is shown that the absorption spectrum exhibits a resonant peak structure whose characteristics depend on the properties and number of these points. For SLs with only one Dirac point, the spectrum consists of resonant peaks satisfying the same selection rule as that for monolayer graphene, except for one of these peaks. For SLs with extra Dirac points, the resonant peaks arise from transition between singlet subbands or between doublet subbands and satisfy a circular polarization and peak intensity dependent selection rule. [ABSTRACT FROM AUTHOR]

Several transition metals other than the largely used Cu and Ni can be, in principle, employed to catalyze carbon precursors for the chemical vapor deposition of graphene, because the thermodynamics of their alloying with carbon is well known. For example, the wealth of information in the Co-C phase diagram can be used to predict the properties of graphene grown in this way. It is, in fact, expected that growth occurs at a temperature higher than in Ni, with beneficial consequences to the mechanical and electronic properties of the final product. In this work, the growth of graphene onto Co film is presented together with an extensive Raman characterization of the structural properties of the material so far obtained. Previous results reporting the full coverage with negligible defective areas, in spite of discontinuities in the underlying metal, are confirmed, together with the occurrence of strain in the graphene sheet. Strain is deeply investigated in this work, in view of possible employment in engineering the material properties. The observed strain is ascribed to the high thermal mismatch with the substrate, even if an effect of the crystallographic transition of Co cannot be excluded. [ABSTRACT FROM AUTHOR]

The Fe-FeO-graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded to analyze the process of the pulsed wire discharge. The as-prepared samples--under different charging voltages--were recovered and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM). Curved and loose graphene films that were anchored with spherical Fe and FeO nanoparticles were obtained at the charging voltage of 8-10 kV. The present study discusses the mechanism by which the Fe-FeO-graphene nanocomposite material was formed during the pulsed wire discharge process. [ABSTRACT FROM AUTHOR]

In the present work, microstructure and mechanical behavior of the graphene nanoplates (GNPs) reinforced pure Al (GNPs/Al) composites prepared by the pressure infiltration method was investigated. No Al 4 C 3 phase was detected in the composites, while GNPs have been well bonded with the Al matrix. It is suggested that the reaction between pure Al matrix and graphene could also be inhibited by using graphene with fewer defects. It has been found that the mechanical properties of the composites could be significantly improved by the addition of graphene. After addition of 0.54 wt% GNPs, the improvement of the yield and tensile strength before the extrusion was 116% and 45%, respectively. However, after the extrusion treatment, the corresponding increment of the yield and tensile strength was increased to 228% and 93%, respectively. Moreover, the fracture surface of the GNPs/Al composites before and after the extrusion treatment was mainly characterized by the lamellar structure with bridging of GNPs and the fine equiaxed structure with the pulling-out of the GNPs, respectively. Based on the modified shear-lag model, the strengthening mechanism of the GNPs/Al composites has been discussed, and the effect of GNPs and the extrusion treatment on the yield strength of the composites have been analyzed. [ABSTRACT FROM AUTHOR]

Interlayer distance induced Rashba spin splitting is predicted in graphene and monolayer iodinated arsenene (As-I) van der Waals heterostructures based on first-principle calculations. The equilibrium structure of graphene/As-I exhibits a linear Dirac-like dispersion relation at K point in Brillouin zone. With the change of interlayer distance, large and tunable Rashba spin splitting can be realized from zero to more than 100 meV. Projected band structure analysis is performed, which indicates a strong relation between the extent of band splitting and the hybridization of C and As orbitals near the Fermi level. Meanwhile, charge density difference calculations reveal a pronounce charge transfer between graphene and As-I with varying interlayer distances, leading to the change of built-in electric filed along z direction that modifies the electronic structures significantly. Our work may make a special contribution to the realization and application of spintronic devices based on van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

Graphene nanosheets (GNSs) and multiwalled carbon nanotubes (MWCNTs) were treated with a nonionic surfactant polyvinylpyrrolidone (PVP), and its effects on dispersion state, surface chemistry, structure, and morphology of MWCNTs and GNSs, as well as on the microwave absorbing properties, mechanical properties of GNSs/MWCNTs/cyanate ester nanocomposites were analyzed respectively. Results show that surfactant plays an important role in dispersing the GNSs and MWCNTs in a solvent and polymer. The mechanical properties, such as impact fracture toughness and flexural strength all showed significant improvements after the treatment. The above observations are attributed to the unique amphiphile structures of PVP, which improved the interface characteristic between matrix and the fillers. Besides, PVP can effectively enhance interfacial interactions which gave rise to improved dispersion and wetting of GNSs and MWCNTs in polymer matrix. Unlike chemical functionalization techniques, however, the surfactant treatment exhibited little adverse effect on microwave absorption properties of the nanocomposite. POLYM. COMPOS., 39:110–118, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Graphene nanosheets (GNS) have attracted lots of attention as an ideal reinforcement in Al matrix composites. However, there are still challenges limiting the performance of the composites, such as the homogenous distribution of GNS in Al matrices, the structural integrity of GNS after ball-milling, and the interfacial bonding between GNS and Al matrices. This work presents a new approach to grow GNS on Al powders at 600 °C by in-situ chemical vapor deposition (CVD) process, using methane as the carbon source, and Cu as the catalyst. The GNS coated Cu reinforced Al matrix bulk composites (Cu@GNS/Al) from the composite powders was fabricated by powder metallurgy (PM) technique. It was found that Cu 2+ from CuCl 2 can easily anchor onto the surfaces of Al particles uniformly though a nanoscale-disperse-method in alcohol, enabling the homogenously dispersion of Cu particles in Al matrices after being reduced from Cu 2+ in hydrogen. With the assistance of Cu particles, network-liked GNS was successfully synthesized in-situ and strongly bonded with Al, resulting in a good mechanical performance of the composites. It is indicated that the tensile strength of the composites was improved by ~ 200% compared to the unreinforced pure Al. The strengthening mechanism was mainly ascribed to the load transfer of GNS, precipitation strengthening of Al 2 Cu compounds after 400 °C annealing and dislocation strengthening. [ABSTRACT FROM AUTHOR]