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Many researches have shown that nanotwinned structure and graphene reinforcing phase can improve the mechanical properties of aluminum (Al) metal, but the synergistic effect of the two on nanoindentation mechanical response of Al matrix composites is rarely reported. In this research, based on molecular dynamics simulations, the nanoindentation mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned Al matrix composites are studied. The effect of the inclination angle and spacing of the twin boundaries (TBs), the insertion position of the graphene sheet, the graphene coating and the layer number of the graphene sheet on the nanoindentation mechanical properties of the Al matrix composites is analyzed. The nanoindentation mechanical properties of nanotwinned Al strongly depend on the inclination angle of TBs, and the dislocation slip modes mainly includes three types: hard mode I (dislocation pile-up penetration mode), soft mode I (partial dislocation parallel twin boundary slip mode) and hard mode II (dislocation limited slip mode). Moreover, as the twin boundary spacing increases, the dislocation slip mode starts to weaken until the nanoindentation mechanical properties are insensitive to the twin inclination orientation. The insertion of the graphene sheet weakens the indentation mechanical properties of the nanotwinned Al matrix composite, which is attributed to the interaction of the graphene with the dislocations and the subsequent absorption of part of them. The weakening effect depends on the distance between the graphene/Al interface and the plastic zone. What's more, graphene coating can improve the indentation mechanical properties of composites. In addition to the load bearing effect of graphene in the elastic stage, this strengthening effect is also attributed to the combined action of graphene and TBs in the plastic stage, which makes the dense dislocation network widely distributed around the indentation of graphene coating and induces the interfacial strain hardening. [ABSTRACT FROM AUTHOR]

Based on the Lennard-Jones potential function, a theoretical model of atoms/ions interaction with finite-size (doped) graphene is presented to investigate the mechanical behaviors of atoms/ions adsorption and migration on the surface of finite-size boron, nitrogen and boron nitride doped graphene. The results show that boron, nitrogen and boron nitride doping can change the interaction between atoms/ions and graphene, and the type, position and domain size of doping elements have significant effects on the adsorption sites and adsorption energy of atoms/ions. The stable adsorption sites, adsorption heights and adsorption energy of atoms/ions on the surface of doped graphene can be controlled by regulating the doping elements. Meanwhile, boron, nitrogen and boron nitride doping can affect the energy period and energy barrier of atoms/ions migration on graphene surface. The proper design of boron, nitrogen and boron nitride doping position, size and distribution can effectively control the atom/ion migration behavior on graphene surface. This research work can provide a theoretical reference for atoms/ions carriers, molecular sieves and ion battery electrodes based on doped graphene and graphene heterostructures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adhesive forces of a single anisole on G-OH/Gr surface are got via AFM experiments. • Anisole exhibits two types of adhesive forces on G-OH surface. • Hydroxyl group has significant effect on the adhesive force of G-OH to anisole. • Conformational changes of anisole cause two peaks of its force-height curve to G-OH. Measuring and understanding interaction forces between hydroxylated graphene (G-OH) and aromatic compounds is significant for the applications of composites based on G-OH, such as 3D graphene derivatives preparation and wastewater treatment. In this research, the adsorption/separation mechanical behavior of anisole on graphene and G-OH surfaces was investigated by atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. The adsorption and separation curves of anisole on graphene and G-OH surfaces were obtained by experiments, and the adhesive forces of a single anisole were achieved by the Poisson statistics method. It is found that there are two types of adhesive forces between anisole and G-OH. For graphene and anisole, two extreme values are got by the adsorption and separation processes, and the adhesive force obtained by the separation process is approximately equal to one type of adhesive force between anisole and G-OH. Furthermore, MD simulation results reveal that the maximum adhesive force of anisole on the G-OH surface depends on its position relative to the hydroxyl group, and anisole has a greater affinity near the hydroxyl group. The position and planar angle of the anisole conformations cause the difference in adhesive forces. [ABSTRACT FROM AUTHOR]

In drug delivery systems, graphene materials are promising drug carriers. Drug molecules are loaded on graphene through π-π interaction between graphene and benzene ring structure, which is widely found in organic drug molecules. Then the drug molecules are released under different conditions, such as different environmental pH, at lesion site. In the application, the adsorption and desorption between benzene ring structure in drug molecules and graphene play a key role. Herein, an experimental method for measuring the adhesion force between a single phenyl and graphene is proposed, and the adsorption and desorption mechanical properties of a benzene ring structure on graphene surface at different environmental pH are firstly measured. The experimental results show that the adhesion force decreases with the increase of environmental pH. Moreover, molecular dynamics simulations show that the influence of pH on adhesion force is mainly realized by changing the electrostatic potential distribution on graphene surface, and the interaction force between a single benzene and graphene changes from attractive to repulsive with the increase of environmental alkalinity. In addition, a molecular dynamics model for the dynamic adsorption and desorption capacities of benzene molecules on graphene surface at different quantity of ions is established. Benzene molecules can achieve full adsorption on the surface of graphene when there are 10 and 20 hydrogen ions. And benzene molecules can achieve full desorption on the surface of graphene when there are 10 and 20 hydroxide ions. [Display omitted] [ABSTRACT FROM AUTHOR]

Based on the van der Waals (vdW) interaction potential and the bending rigidity of graphene, the self-scrolling mechanical behaviors of monolayer graphene flake induced by carbon nanotube (CNT)/black phosphorus nanotube (BPNT) are studied, and the analytical expressions of critical radius of CNT/BPNT are derived when the graphene flakes spontaneously scroll round them. The factors affecting the critical radius of nanotubes are systematically analyzed, which include the axial length ratio between nanotube and graphene, wrapping angle of graphene, temperature, type and layer number of nanotube. It is found that the axial length ratio between nanotube and graphene has a significant effect on the critical radius. The critical radius of nanotubes increases with the decrease of the axial length ratio, and the critical radius of double-walled carbon nanotube (DWCNT) increases faster than that of single-walled carbon nanotube (SWCNT) and BPNT. When the SWCNT and graphene have the same axial length, the critical radius of SWCNT induced completely wrapping of monolayer graphene is about 0.4757 nm, which is in good agreement with the simulation results in the literature. The wrapping angle of graphene can also affect the critical radius of nanotubes, which increases with the increase of wrapping angle. Furthermore, the influence of environmental temperature, the type and layer number of nanotubes on the critical radius of nanotubes is discussed, respectively. [ABSTRACT FROM AUTHOR]

The superb mechanical properties make graphene an ideal candidate material for impact protection. Combining molecular dynamics simulations and theoretical analyses, the deformation and failure modes, energy absorption of single-layer graphene under ballistic impact are investigated. According to numerical and theoretical results, the expression for residual velocity of projectile after impact is given. The dependence of deformation and failure modes, energy absorption mechanisms, specific penetration energy (SPE) on impact velocity is analyzed. The results show that during low-velocity impact, there are conical deformation region (CDR), star-like crack and monoatomic carbon chain in graphene. Energy absorption mechanisms of graphene are mainly local deformation and fracture. With increasing impact velocity, the size of CDR decreases. The star-like crack gradually transforms into circular hole. When impact velocity is high enough, carbon atoms within projectile projection area in graphene will be ejected in the form of debris. The kinetic energy (KE) loss of projectile is converted into KE of debris carbon atoms and fracture energy of carbon bonds. Besides, it is also found that SPE (dominant factors are deformation of conical region and KE increments) exhibits a decreasing–increasing trend with increasing impact velocity. When impact velocity is the same, SPE decreases with increasing projectile diameter. [Display omitted] • Energy absorption of graphene under ballistic impact is studied by MD simulations. • The expression for residual velocity of rigid projectile after impact is given. • The dependence of deformation and failure modes on impact velocity is discussed. • Energy absorption mechanism of graphene during impact process is analyzed. • The effect of impact velocity on specific penetration energy is studied. [ABSTRACT FROM AUTHOR]

Young's modulus, failure strength, and failure strain of precracked graphene are investigated via finite element method based on molecular structure mechanics in this research. The influence of distribution, length, and orientation of precrack and graphene sizes on these mechanical properties is analyzed. The ratio of precrack length and graphene width is defined as P value, and its particular value Pc can be found, at which the variation trends of Young's modulus, failure strength, and strain have changes with increasing P value. In addition, the fracture toughness of precracked graphene is investigated, and the stress intensity factor (SIF) is calculated according to the Griffith criterion in classical fracture mechanics. The numerical values of the SIF are about 3.20-3.37 MPa√m, which are compared with the experimental results, and the simulations verify the applicability of the classical fracture mechanics to graphene. [ABSTRACT FROM AUTHOR]

In field of drug delivery, graphene is a potential material as drug carrier due to its large specific surface area and excellent chemical stability. Many kinds of drug molecules can be adsorbed on graphene surface through single or multiple benzene ring structures in drug molecules. Graphene loaded with drug molecules needs to be transported to the lesion site through blood. The content of water molecules in blood accounts for 92%. Therefore, the influence of water molecule on adsorption performance cannot be ignored. Here, the influence and mechanism of water molecule on the adsorption properties between benzene molecule and graphene is studied. The adsorption models of benzene molecule on graphene surface in vacuum and water environments are established, respectively. The adhesion energy, adhesion force and stable adsorption position of benzene molecule in two environments are analyzed by molecular dynamics simulation and potential function theory. Moreover, a model of preadsorption of a single water molecule on graphene surface is further presented, which explains the reason of the difference in adsorption performance in vacuum and water environment from the perspective of energy. The preadsorption of water molecule on graphene surface promotes the adsorption of benzene molecule. [Display omitted] [ABSTRACT FROM AUTHOR]

• Compressive properties of 3D graphene are studied by theory and MD simulations. • The unified constitutive relations of three kinds of 3D graphene are derived. • Compressive deformation mechanisms of three kinds of 3D graphene are discussed. • The configuration-property relationships of 3D graphene are elucidated. • Energy absorption capacities of three kinds of 3D graphene are analyzed. Combining molecular dynamics (MD) simulations and continuum modeling, the uniaxial in-plane compressive properties of honeycomb three-dimensional (h3D), triangle-like 3D (t3D) and non-equilateral hexagon 3D (nh3D) graphene are investigated to elucidate configuration-property relationships, and the constitutive relations of three kinds of 3D graphene are derived to evaluate the compressive mechanical properties. Based on theoretical and MD simulation results, it is found that the compressive stress-strain responses of 3D graphene can be divided into five stages. The compressive mechanical properties and deformation mechanisms of each stage are different. When 3D graphene is compressed, graphene sidewalls undergo rotations, bending and buckling deformations, collapses. Because graphene sidewalls of h3D graphene are prone to undergo buckling deformations, there is large locking strain in h3D graphene. For t3D and nh3D graphene, their high plateau stress is attributed to unique configurations. Moreover, we also find that with increasing graphene sidewall width, Young's modulus and plateau stress of 3D graphene gradually decrease. In addition to the above investigations, the energy absorption mechanisms and compression-unloading stress-strain curves of 3D graphene are also studied. It is found that there are extraordinary compression-recovery properties and energy absorption capacities in 3D graphene. Finally, the selection criteria of 3D graphene are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Many studies have shown that both the nanotwinned structure and the graphene reinforcing phase can improve the mechanical properties of aluminum, but the synergistic effect of the two on the strengthening and toughening mechanisms of aluminum matrix composites has rarely been reported. In this work, the mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned aluminum matrix composites under uniaxial tensile load are studied by molecular dynamics simulations. The effects of the distribution patterns of graphene and twin boundaries (TBs), their angles and the number of graphene layers on the mechanical behaviors of graphene/nanotwinned aluminum matrix composites are analyzed. It is found that the synergistic effect of TBs and graphene results in secondary reinforcement of aluminum matrix composites in the plastic stage, resulting in enhanced strength and toughness. Moreover, the elastic modulus, strength and toughness of graphene/nanotwinned aluminum matrix composites increase linearly with the number of graphene layers. By analyzing the microscopic deformation and dislocation evolution of aluminum matrix composites, the mechanisms of dislocation derivation and propagation induced by graphene and TBs are explored. In addition, it is found that there is a competition between graphene and TBs for the dislocation evolution, and the graphene can weaken the dislocation blocking effect of TBs. Finally, it is proved that the angle between graphene and TBs will weaken the mechanical properties of the composites. The effect of the TB angle on the mechanical properties of graphene/nanotwinned aluminum matrix composites is discussed in three cases, depending on the stress-strain curve and the microstructure deformation mechanism. • The effect of graphene and TBs on mechanical properties of Al-matrix is studied. • The influence of distribution patterns and layer number of graphene is analyzed. • The effect of the inclination angle of TBs and graphene is considered. • The mechanisms of dislocation derivation and propagation is explored. [ABSTRACT FROM AUTHOR]

The mechanical properties of bicrystalline graphene nanoribbons with various tilt grain boundaries (GBs) which typically consist of repeating pentagon–heptagon ring defects are investigated based on the method of molecular structural mechanics. The GB models are constructed via the theory of disclinations in crystals, and the elastic properties and ultimate strength of bicrystalline graphene nanoribbons are calculated under uniaxial tensile loads in perpendicular and parallel directions to grain boundaries. The dependence of mechanical properties is analyzed on the chirality and misorientation angles of graphene nanoribbons, and the experimental phenomena that Young's modulus and ultimate strength of bicrystalline graphene nanoribbons can either increase or decrease with the grain boundary angles are further verified and discussed. In addition, the influence of GB on the size effects of graphene Young's modulus is also analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pH effect of adhesion force of benzene on graphene is quantitatively studied. • The edge effect of adhesion force is confirmed by experiment. • The potential function method is used to reveal the mechanism of pH effect. • The edge effect is explained by the vdW and electrostatic interaction. Graphene materials, as drug carriers, play an important role in the specific drug delivery system. The drug molecules with aromatic structures can be adsorbed on the surface of graphene in vitro through π-π stacking interaction and released directionally at the lesion under special temperature and pH-value environment. This paper proposes a new experimental method and theoretical model for the purpose to study the effect and mechanism of environmental pH and edge of graphene on the adsorption mechanical properties between graphene and benzene. The experimental results based on atomic force microscope show that the acidic environment is more conducive to the adsorption of benzene on the surface of graphene than the alkaline environment. The adsorption performance of benzene at the center of graphene is better than that at the edge. Moreover, based on experimental results, mechanisms of pH effect and edge effect are revealed by potential function theory. The pH effect is influenced by the change of electrostatic interaction in different pH environments. In addition, edge effect is mainly dominated by van der Waals interaction. This study solves the problem of specific influence mechanism of pH on π-π stacking interaction using mechanical means for the first time, and shows that graphene as a drug carrier has strong pH response characteristics and great application potential. [ABSTRACT FROM AUTHOR]

Advanced hierarchical hybrid nanostructures of polar, conductive and catalytic chemical traps/carbon with rationally tailored components, structures, and chemistries are important in determining the performance of lithium-sulfur (Li–S) batteries. Herein we propose a facile strategy to prepare 3D-structured CNF@graphene-CoSe (CNF@G L -CoSe) cable/sheath heterostructure with the in-situ formed CoSe as a catalyst for graphene-like carbon growth and Se as a catalyst promoter. The architecture integrates high electrical conductivity, effective ion transport, notable polysulfide entrapment, and polysulfide redox kinetics, availing lithium/sulfur conversion when applied as an interlayer in a Li–S battery. As expected, the battery delivered a low decay of 0.053% per cycle over 700 cycles at 1 C. The capacity even remained 649.4 and 524.5 mA h g−1 at 4 and 6 C, respectively. Furthermore, an areal capacity of about 3 mA h cm−2 at 0.1 C after long-term tests can still maintain with sulfur loading of 4.5 mg cm−2. A facile effective strategy to prepare 3D-structured CNF@graphene-CoSe cable/sheath heterostructure with the in situ formed CoSe as a catalyst for graphene-like carbon growth and Se as a catalyst promoter, achieving significant enhancement in electrochemical performance of Li–S batteries. [Display omitted] • In situ constructing CNF@graphene-CoSe cable/sheath heterostructure. • CoSe catalyzes the growth of graphene sheath and Se as a catalyst promoter. • Synergism of conductivity, absorption and catalysis. • Enabling excellent performance as an interlayer. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) graphene possesses a variety of excellent properties. It is worth using 2D graphene as building block to construct novel three-dimensional (3D) graphene which "inherits" superb performance of 2D graphene. Combining theoretical calculations and finite element method (FEM) based on molecular structural mechanics, the effects of graphene sidewall width, junction structure, in-plane domain size and in-plane overall shape on the elastic properties of zigzag honeycomb 3D graphene and three types of triangle-like 3D graphene are investigated, and the analytical expressions for Young's modulus of triangle-like 3D graphene are derived. The results of FEM are consistent with those of theoretical method. It is found that as graphene sidewall width increases, in-plane/out-of-plane Young's moduli of the above-mentioned 3D graphene first decrease and then tend to stabilize. For the armchair and zigzag triangle-like 3D graphene (sidewall width remains unchanged) with rectangular in-plane overall shape, the Young's modulus will vary with in-plane domain size. These results show that the elastic properties of 3D graphene are strongly dependent on structural size. In addition, junction structure has little influence on the elastic properties of 3D graphene. • A novel triangle-like 3D graphene containing sp3-sp3 carbon bond is constructed. • The size-dependent Young's modulus of triangle-like 3D graphene is investigated. • Analytical expressions of Young's modulus of triangle-like 3D graphene are derived. • The influencing factors for elastic properties of 3D graphene are studied by FEM. [ABSTRACT FROM AUTHOR]

The facile method to functionalize graphene oxide through surface modification with acetone was studied and improved. The resulting nanomaterials showed variable characteristics as the surface energy could be tailored according to the combination (proportion of H2O to acetone) of mixed solvent under sonication. Stability test and contact angle measurement showed that the treated graphene oxide exhibited different dispersibility and wettability. SEM images of graphene oxide films corroborated the changes in chemical composition of the sheets. FT-IR, XPS, and TGA observation provided direct evidence for chemical composition changes occurred on the surface. The presence of alkyl chain could decrease the surface energy and obviously control the hydrophilicity of the graphene oxide sheets. These results will provide significant guidance for the study of graphene-based bio-materials and nano-composites. [ABSTRACT FROM AUTHOR]

Abstract: Molecular structural mechanics based finite element method is applied to study the influence of the two types of Stone–Wales defects on the elastic properties of monolayer and multilayer graphene nanofilms. Models with spatial frame structures are developed to simulate the graphene crystal with Stone–Wales defects based on the linkage between the inter-atomic potential energy in molecular mechanics and the strain energy in classical structural mechanics. Several possible influencing factors, including the number and types of Stone–Wales defects, the distance between two defects and the position of defects in the graphene, are taken into account to evaluate Young''s moduli and Poisson''s ratios of armchair and zigzag monolayer graphene nanofilms. It is shown that the Stone–Wales defects have remarkable influence on the elastic properties of monolayer graphene. In addition, the size-dependent Young''s moduli and Poisson''s ratios of multilayer graphene nanofilms are also investigated when the Stone–Wales defects in surface layers are taken into consideration. [Copyright &y& Elsevier]

The static and dynamic mechanical behaviors of atoms/ions migrating on graphene surface are investigated via theoretical and numerical calculations, and a design idea of nano-scale device that can be used for atoms/ions screening is proposed on this basis. By using the Fourier expansion of the interaction potential between atoms, the analytical expression of the interaction force between an atom/ion and infinitely large graphene is derived. The dependence of the interaction force on the vertical distance from the atom/ion to graphene surface and the atomic/ionic types are analyzed. Based on the interaction force, a dynamics governing equation for the migration of atoms/ions on graphene surface is established, and the dynamics behaviors of atoms/ions when they migrate on the graphene surface at different initial velocities are studied. Taking lithium-ion as an example, it is found that there are three migration states along the armchair direction of graphene. No matter which migration state, the lithium-ion will eventually be stably adsorbed above the center of a hexagonal carbon ring (the hollow site). By adjusting the initial velocity, the lithium-ion can be steadily adsorbed at the specified sites, so as to control the migration distance of lithium-ion. What's more, the functional relationship between the critical initial velocity of the lithium-ion and the stable adsorption sites on graphene surface is given, and the influence of the vertical distance from the lithium-ion to graphene surface on the migration process is analyzed. In addition, the dynamics behaviors of the migration of different atoms/ions on graphene surface are studied, and it is found that the migration of alkali metal particles is more free with the increase of atomic number, and the stable site is further away from the initial position, which is in good agreement with the results of molecular dynamics simulation in the literature. Besides, the effects of initial position, damping and migration path on the dynamics behaviors of atoms/ions migrating on graphene surface are also studied. Finally, on the basis of theoretical results, a design idea of graphene-based nano-scale device is proposed, which can be used to screen specified atoms/ions and control their in and out positions. Image 1 • The mechanical behaviors of atoms/ions migrating on graphene are investigated. • The dependence of dynamics behavior of atoms/ions on initial velocity is studied. • The influence of atomic/ionic types on the dynamics behavior is described. • The effects of initial position, damping and migration path are considered. • A design idea of graphene-based nanodevice for atoms/ions screening is proposed. [ABSTRACT FROM AUTHOR]

The adsorption and migration behaviors of atoms/ions on the surface of infinite single-layer graphene are studied with the influence of surface corrugation taken into consideration. Based on Lennard-Jones (L-J) potential and Fourier expansion, the analytical expressions of the interaction potential and force between a single atom/ion and sinusoidal corrugated graphene are derived. The effects of lattice period, chirality, wavelength and amplitude of surface sinusoidal ripples on the mechanical behaviors of atom/ion adsorption and migration on graphene surface are analyzed. The interaction potential and force between the adsorbed atom/ion and graphene are found to be periodic when the lattice period of graphene and the wavelength of surface sinusoidal ripples meet a certain coupling relationship. Moreover, the periods of interaction potential and force, equilibrium position and diffusion barrier of the adsorbed atom/ion on the graphene surface can be regulated by changing the wavelength and amplitude of the sinusoidal ripples. Taking lithium-ion (Li1+) as an example, by changing the wavelength of the sinusoidal ripples, the equilibrium sites of a lithium-ion on the surface of graphene can be readjusted, and the magnitude and amount of the energy barriers that it gets over can be regulated when the lithium-ion moves along the surface of graphene. What is more, the amplitude of the sinusoidal ripples can significantly influence the tangential force exerted by the graphene on the moving lithium-ion. Finally, it is found that the migration of an adsorbed atom/ion on the surface of sinusoidal corrugated graphene is also dependent on the chirality of graphene. The magnitude and period of the energy barrier and tangential force are both different when a lithium-ion migrates on the graphene surface in its different chiral directions. This research may be helpful to lithium-ion batteries, monoatomic device design, and atoms/ions screening. Image 1 • The migration behaviors of atoms/ions on sinusoidal graphene surface are studied. • The interaction potential and force are periodic under a specified condition. • The periods can be regulated by changing the wavelength of sinusoidal ripples. • The amplitude of sinusoidal ripples can influence the migration tangential force. • The migration behavior of atoms/ions on graphene surface depends on its chirality. [ABSTRACT FROM AUTHOR]

The layered metal phosphorus trichalcogenides (MPTs) are a newly emerging van der Waals material family with bandgaps ranging from 1.3 to 3.5 eV, which are promising candidates for optoelectronic devices. By using the excited multiple energy levels of FePSe3, a high‐performance FePSe3 photodetector, which shows tunable response speed in the range of ultraviolet (UV) to near‐infrared (NIR), is designed. The FePSe3 photodetector exhibits a high photoresponsivity of 236.18 A·W−1 under 532 nm laser illumination (laser power density P = 1 mW cm−2). The properties of FePSe3 can be modulated by oxygen plasma treatment, which transfer to oxygen‐doped FePSe3 (FePSe3‐O). Moreover, the speed of the FePSe3‐O photodetector can be improved more than 240 times compared to the intrinsic FePSe3 photodetector under NIR illumination (λ = 808 nm). In addition, the FePSe3‐graphene heterojunction can significantly improve the photoresponsivity and simultaneously prolong the response time of the device due to the FePSe3/graphene interfacial barrier. These results suggest that intrinsic, doped FePSe3 and its heterojunction can be used as multifunctional photodetectors with tunable response speeds. [ABSTRACT FROM AUTHOR]

Abstract The micro-mechanical responses of an electrode dominate its electrochemical performance and lifetime. Herein, an experimental method is proposed to investigate the micro-strain/stress of graphene electrodes during galvanostatic charge/discharge cycling. The characteristic Raman peak of the graphene electrode is acquired in situ in a modified coin cell as a function of time. And two mechanical models are established, including microscale plane strain and plane stress with Li-induced-stiffening. Combining the mechanical models and the measured 2D peak, the micro-strain and micro-stress of the graphene electrode are quantitatively characterized. Furthermore, the deformation mechanism and rate-dependent characteristics are discussed. Excepting slight compressive loads by the solid–electrolyte interface film, the graphene experiences an increasing tensile strain/stress with increasing capacity. The stresses significantly depend on the charge/discharge rate, where higher stresses are induced at higher currents with a multiplicative relationship between the stress and current increments. The origins of the stress differences between macroscale and microscale involve the elongation of the intralayer C−C bonds caused by intercalated Li between the graphene layers and a microscopic concentration gradient. This work enhances the understanding of the microscopic mechano-electro-chemical mechanism of graphene electrodes and facilitates theoretical modeling of the stress with Li concentration and current. Graphical abstract Image 106365 [ABSTRACT FROM AUTHOR]

The negative Poisson's ratio (NPR) of graphene is studied via molecular dynamics (MD) simulations when epoxy groups are orderly arranged on its surface. When two epoxy groups are located on the same side of the zigzag bridge in a representative cell of graphene, a ripple area appears on the graphene surface. A truss structure model of the ripple is presented to reveal the nature of the NPR phenomenon due to the de-wrinkling effect during stretching. Based on this, the wrinkle region is defined as a periodic distribution unit, and it is evenly distributed along the X- and Y-direction in the 5 nm × 5 nm graphene, then it is found that graphene exhibits a remarkable negative Poisson's ratio phenomenon. In addition, the results show that the oxygen atoms proportion of graphene significantly influence its NPR, and the NPR is the most remarkable when the proportion of oxygen atoms is 4.2 %. [Display omitted] • NPR of graphene caused by epoxy group was studied by theoretical and MD method. • A truss structure model was presented to reveal the nature of NPR phenomenon. • The designed graphene containing epoxy groups exhibits remarkable NPR phenomenon. • NPR of graphene containing epoxy groups depends on the proportion of oxygen atoms. • GO with 4.2 % oxygen atoms has the most remarkable NPR. [ABSTRACT FROM AUTHOR]

The Poisson's ratio of the in-plane pristine armchair and zigzag graphene under uniaxial tensile loading is studied by molecular dynamics simulations, which indicates that Poisson's ratio strongly depends on the tensile strain. At the critical strain, the Poisson's ratio will transform from positive to negative, and the critical strain of the zigzag is far less than that of armchair. The study on the representative cell of graphene shows that the intrinsic nature of strain-induced negative Poisson's ratio (NPR) is the competition between the variation rates of bond length and bond angle. Meanwhile, the critical strain that induces NPR has significant size effects, which depends on the proportion of representative cells at the width boundary in the whole graphene. What's more, 5-8-5 defect has a significant effect on the NPR phenomenon of graphene. By introducing 5-8-5 defects into in-plane graphene, the critical strain value that induces NPR can be effectively regulated by adjusting the distribution modes and percentage of defects. The distributions of 5-8-5 defects adjacent to each other in the X-direction and Y-direction can significantly reduce the critical strain value. Furthermore, by increasing the percentage of 5-8-5 defects in graphene, the critical strain value can be reduced to about 50%, and the 5-ring defect plays a vital role in reducing the critical strain value. Based on this, a penta-graphene consisting entirely of 5-rings is constructed, and its Poisson's ratio is studied. The results confirm that the critical strain that induces NPR is 0. In a word, the NPR of in-plane pristine graphene can be induced by tensile strain, 5-8-5 defects can regulate the critical strain value of NPR, and penta-graphene is a perfect NPR material. [Display omitted] • Poisson's ratio will transform positive to negative at critical strain. • NPR originates from competition between the variation rates of bond length and bond angle. • The critical strain that induces NPR of graphene has significant size effects. • The distributions and percentage of 5-8-5 defects significantly reduce the critical strain. • The critical strain that induces NPR for a penta-graphene consisting entirely of 5-rings is 0. [ABSTRACT FROM AUTHOR]

In this work, we report a facile approach to synthesis of highly fluffy and wrinkled reduced graphene oxide by simple freeze-drying and microwave-expanding method in vacuum. Compared with thermal reduced graphene oxide (RGO), the as-synthesized freeze drying and microwave reduced graphene oxide (FMGO) electrodes exhibit an improved electrochemical performance with high specific capacitance of 246 F g −1 at scan rate 5 mV s −1 and good cycle stability for application in supercapacitors. The outstanding performance of FMGO as a supercapacitor is attributed to the highly fluffy and wrinkled graphene which permits the creation of three-dimensional networks to induce fast electron and ion transport, thus eventually leading the significantly improved electrochemical capacitive behaviors. [ABSTRACT FROM AUTHOR]

We report the dc and rf performance of graphene rf field-effect transistors, where the graphene films are grown on copper by using the chemical vapour deposition (CVD) method and transferred to SiO2/Si substrates. Composite materials, benzocyclobutene and atomic layer deposition Al2O3 are used as the gate dielectrics. The observation of n- and p-type transitions verifies the ambipolar characteristics in the graphene layers. While the intrinsic carrier mobility of CVD graphene is extracted to be 1200 cm2/V·s, the parasitic series resistances are demonstrated to have a serious impact on device performance. With a gate length of 1 µm and an extrinsic transconductance of 72 mS/mm, a cutoff frequency of 6.6 GHz and a maximum oscillation frequency of 8.8 GHz are measured for the transistors, illustrating the potential of the CVD graphene for rf applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] A surface-to-surface contact between graphene and SnO2 nanoplates is synthesized for the first time. [•] The synthesized method is easier to implement without template. [•] The as-synthesized materials exhibit high-performance supercapacitor than pure SnO2 and other SnO2/graphene nanocomposites. [ABSTRACT FROM AUTHOR]

Wafer-scale graphene field-effect transistors are fabricated using benzocyclobutene and atomic layer deposition Al2O3 as the top-gate dielectric. The epitaxial-graphene layer is formed by graphitization of a 2-inch-diameter Si-face semi-insulating 6H-SiC substrate. The graphene on the silicon carbide substrate is heavily n-doped and current saturation is not found. For the intrinsic characteristic of this particular channel material, the devices cannot be switched off. The cut-off frequencies of these graphene field-effect transistors, which have a gate length of 1 μm, are larger than 800 MHz. The largest one can reach 1.24 GHz. There are greater than 95% active devices that can be successfully applied. We thus succeed in fabricating wafer-scale gigahertz graphene field-effect transistors, which paves the way for high-performance graphene devices and circuits. [ABSTRACT FROM AUTHOR]

Graphene is a new promising candidate for application in radio-frequency (RF) electronics due to its excellent electronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors (RF-FETs). Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum oscillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits. [ABSTRACT FROM AUTHOR]