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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]

The lunar soils evolution over time is mainly caused by space weathering that includes the impacts of varying-sized meteoroids and charged particles implantation of solar/cosmic winds as well. It has long been established that space weathering leads to the formation of outmost amorphous layers (50–200 nm in thickness) embedded nanophase iron (npFe0) around the mineral fragments, albeit the origin of the npFe0 remains controversial. The Chang'e-5 (CE-5) mission returned samples feature the youngest mare basalt and the highest latitude sampling site , providing an opportunity to seek the critical clues for understanding the evolution of soils under space weathering. Here, we report the surface microstructures of the major minerals including olivine, pyroxene, anorthite, and glassy beads in the lunar soil of CE-5. Unlike the previous observations, only olivine in all crystals is surrounded by a thinner outmost amorphous SiO 2 layer (∼10 nm thick) and embedded wüstite nanoparticles FeO (np-FeO, 3–12 nm in size) instead of npFe0. No foreign volatile elements deposition layer and solar flare tracks can be found on the surface or inside the olivine and other minerals. This unique rim structure has not been reported for any other lunar, terrestrial, Martian, or meteorite samples so far. The observation of wüstite FeO and the microstructures support the existence of an intermediate stage in space weathering for lunar minerals by thermal decomposition. [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]

[Display omitted] • Theoretical models are established to analyze the interface mechanical behaviors when a droplet infiltrates the microstructures. • The physical mechanism of compressive stability and excellent wettability on the Salvinia surface is theoretically revealed. • The effects of surface geometry and microstructure characteristics parameters on the compressive stability and wettability of the biomimetic surface are discussed. • The geometric structure relationships for designing highly stable superhydrophobic surfaces are proposed. The surface of Salvinia had superhydrophobicity and kept good compressive stability, which was mainly attributed to the dense microscopic eggbeater structure villi on the surface. By means of force equilibrium, a theoretical model was established to analyze the interface mechanical behaviors when a droplet infiltrates the microstructures. Based on the minimum energy principle, a theoretical model was presented to analyze the process of a droplet spreading on the surface of Salvinia reaching a steady state. Combined with numerical simulations, it was found that the superhydrophobicity and compressive stability of the Salvinia were dependent on the morphological and geometric parameters of the microstructure (edge angle φ , number of branching n , width W and spacing D , etc.). By adjusting these geometrical parameters, the surface of the biomimetic structure can maintain a stable Cassie state at 0.63 kPa pressure, and the apparent contact angle is controllable in the range of 121°−169.8°. The research results provide a theoretical foundation for the structural design of superhydrophobic surfaces with high stability and tunable wettability. [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]

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]

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]

Abstract: The static and dynamic instabilities of a torsional MEMS/NEMS actuator caused by capillary effects are studied, respectively. An instability number, η, is defined, and the critical gap distance, , between the mainplate and the substrate is derived. According to the values of η and g, the instability criteria of the actuator are presented. The dimensionless motion equation of the MEMS/NEMS torsional actuator is derived when it makes nonlinear oscillation under capillary force. The qualitative analysis of the nonlinear equation is made, and the phase portraits are presented on the phase plane. In addition, the bifurcation phenomena in the system are also analyzed. [Copyright &y& Elsevier]

The effective elastic modulus and fracture toughness of the nanofilm were derived with the surface relaxation and the surface energy taken into consideration by means of the interatomic potential of an ideal crystal. The size effects of the effective elastic modulus and fracture toughness were discussed when the thickness of the nanofilm was reduced. And the dependence of the size effects on the surface relaxation and surface energy was also analyzed. [ABSTRACT FROM AUTHOR]

A theoretical model is presented to investigate the size-dependent elastic moduli of nanostructures with the effects of the surface relaxation surface energy taken into consideration. At nanoscale, due to the large ratios of the surface-to-volume, the surface effects, which include surface relaxation surface energy, etc., can play important roles. Thus, the elastic moduli of nanostructures become surface- and size-dependent. In the research, the three-dimensional continuum model of the nanofilm with the surface effects is investigated. The analytical expressions of five nonzero elastic moduli of the nanofilm are derived, and then the dependence of the elastic moduli is discussed on the surface effects and the characteristic dimensions of nanofilms. [ABSTRACT FROM AUTHOR]

Abstract: The influence of van der Waals (vdW) force on the stability of electrostatic torsional nano-electro-mechanical systems (NEMS) actuators is analyzed in the paper. The dependence of the critical tilting angle and voltage is investigated on the sizes of structure with the consideration of vdW effects. The pull-in phenomenon without the electrostatic torque is studied, and a critical pull-in gap is derived. A dimensionless equation of motion is presented, and the qualitative analysis of it shows that the equilibrium points of the corresponding autonomous system include center points, stable focus points, and unstable saddle points. The Hopf bifurcation points and fork bifurcation points also exist in the system. The phase portraits connecting these equilibrium points exhibit periodic orbits, heteroclinic orbits, as well as homoclinic orbits. [Copyright &y& Elsevier]

The influence of van der Waals (vdW) and Casimir forces on the stability of the electrostatic torsional nanoelectrome-chanical systems (NEMS) actuators is analyzed in the paper. With the consideration of vdW and Casimir effects, the dependence of the critical tilting angle and pull-in voltage on the sizes of structure is investigated. And the influence of vdW torque is compared with that of Casimir torque. The modified coefficients of vdW and Casimir torques on the pull-in voltage are, respectively, calculated. When the gap is sufficiently small, pull-in can still take place with arbitrary small angle perturbation because of the action of vdW and Casimir torques even if there is not electrostatic torque. And the critical pull-in gaps for two cases are, respectively, derived. [ABSTRACT FROM AUTHOR]

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]

A correction to the article "The size-dependent elastic properties of nanofilm with surface effects," presented in the December 15, 2006 issue is presented.

The development of suitable red phosphors to obtain improved white color stands a good chance to serve in the new generation of white light-emitting diodes. Owing to multi-elements via doping and oxidation of reduced valence state of lanthanide or transition metal ions, most of the reported phosphors usually suffer from complex synthetic processes and unstable color of the lighting industry cycle. In this work, we present a new red emitting and stable Sr3Eu2B4O12 phosphor with regard to its special structure. It crystallizes as an orthorhombic cell, with Sr and Eu atoms co-occupying three different lattice sites in the space group of Pnma (no. 62). It is proposed that the long bond distance between activators minimizes the content quenching, while the high disorder of location restricts the thermal quenching. This phosphor emits bright red light with good color purity under UV excitation, with the luminescence intensity and quantum yield tunable via the fabrication temperature. Through a preliminary optimization of the synthesis process, the Sr3Eu2B4O12 phosphor prepared at 1250 °C has high quantum yields of about 94.7% and excellent thermal stability of 85.6% intensity retention at 150 °C relative to the initial value at room temperature. The calculated Judd–Ofelt intensity parameters (Ω2, Ω4) further clarified that the Eu3+ site in Sr3Eu2B4O12 had lower symmetry without an inversion center, and more distorted local environment and structural rigidity of the host, predicting excellent thermal stability. Finally, a warm pc-WLED device has been produced by mixing as-prepared Sr3Eu2B4O12 powders and commercial BaMgAl10O17:Eu2+ and (Sr, Ba)2SiO4:Eu2+ phosphors, which exhibits a high color rendering index (Ra = 83.4) along with a color temperature at around 4102 K. The present work indicates that the Sr3Eu2B4O12 phosphor is an efficient red component with excellent thermal stability for white-light production of near-UV-excited w-LEDs. [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]

Searching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs‐based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6Sn2As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record‐high Tc among all synthesized SnAs‐based compounds. Meanwhile, the conductive channel transfers from the out‐of‐plane pz orbital to the in‐plane px+py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p‐orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems. [ABSTRACT FROM AUTHOR]

Searching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs‐based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6Sn2As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record‐high Tc among all synthesized SnAs‐based compounds. Meanwhile, the conductive channel transfers from the out‐of‐plane pz orbital to the in‐plane px+py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p‐orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems. [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]

Here we report the structure, electrical and magnetic properties of polycrystalline Ba(Mn 1 − x Cr x) 2 As 2 (x =0.0-0.1) and Ba 0.8 K 0.2 (Mn 1 − x Cr x) 2 As 2 (x =0.0-0.4). Upon the substitution of Cr for Mn in BaMn 2 As 2 semiconductor, it is found that the resistivity can be substantially decreased by five orders in magnitude without changing the structural symmetry. The XPS and Hall measurements demonstrate that the valence of doped Cr is +3 instead of expected Cr2＋, which can effectively introduce electron carriers. Meanwhile, a magnetic transition shows up at ∼ 40 K with small saturated moment of M sat =0.02 μ B /Mn(Cr) and a low coercive field of H c =135 Oe. The transition may originate from the change in spin re-orientation from ideal AFM to canted AFM state. For p -type AFM metal Ba 0.8 K 0.2 Mn 2 As 2 , doping Cr3＋ equivalently provides electrons to compensate the holes, leading to a metal–semiconductor transition and a similar canted AFM state. Our results demonstrate that majority carriers, resistivity and magnetism in BaMn 2 As 2 can be controlled through relatively low levels of Cr3＋ doping. • Cr of +3 valance serves as a strong electron donor. • Light doping of Cr3＋ changes the resistivity by five orders in magnitude. • Cr3＋ substitution induces a canted transition in magnetism at low temperature. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gas (2DEG) with high electron mobility is highly desired to study the emergent properties and to enhance future device performance. Here we report the formation of 2DEG with high mobility at the interface between rock-salt BaO and perovskite SrTiO3. The interface consists of the ionically compensated BaO1 â€" δ layer and the electronically compensated TiO2 layer, which is demonstrated as a perfect interface without lattice mismatch. The so-formed interface features metallic conductivity with ultralow square resistance of 7.3 Ă— 10âˆ'4 Ω/â—» at 2 K and high residual resistance ratios R 300 K/ R 2 K up to 4200. The electron mobility reaches 69000 cm2â‹...Vâˆ'1â‹...sâˆ'1 at 2 K, leading to Shubnikovâ€"de Haas oscillations of resistance. Density functional theory calculations reveal that the effective charge transfers from BaO to the Ti 3 dxy orbital occur at the interface, leading to the conducting TiO2 layer. Our work unravels that BaO can adapt itself by removing oxygen to minimize the lattice mismatch and to provide substantial carriers to SrTiO3, which is the key to forming 2DEGs with high mobility at the interfaces. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals material is a focus of research for its widespread application in optoelectronics, memories, and spintronics. The ternary compound Nb2SiTe4 is a van der Waals semiconductor with excellent air stability and small cleavage energy, which is suitable for preparing a few layers counterpart to explore novel properties. Here, properties of bulk Nb2SiTe4 with large in-plane electrical anisotropy are demonstrated. It is found that hole carriers dominate at a temperature above 45 K with a carrier active energy of 31.3 meV. The carrier mobility measured at 100 K is about 213 cm2⋅V−1⋅s−1 in bulk Nb2SiTe4, higher than the reported results. In a thin flake Nb2SiTe4, the resistivity ratio between the crystalline axes of a and b is reaching about 47.3 at 2.5 K, indicating that there exists a large anisotropic transport behavior in their basal plane. These novel transport properties provide accurate information for modulating or utilizing Nb2SiTe4 for electronic device applications. [ABSTRACT FROM AUTHOR]

We investigate the structural variation and physical properties of layered La2M5As3O2 (M = Cu, Ni) compound upon Co doping. It is found that the substitution of Co ion just induces the monotonous change of lattice constants without observing the anomalous kink in superconducting La2(Cu1–xNix)5As3O2 solid-solutions. Meanwhile, this doping barely changes As–As bond length in [M5As3]2– subunit (±2%), being significantly smaller than 7% shrinkage of that in La2(Cu1–xNix)5As3O2. Therefore, the doping dependence of crystal structure exhibits similar trend with Ba1–xKxFe2As2 without the interference of As1–As2 bonding, implying that the Co substitution for Cu/Ni is hole-doped. In terms of physical property, La2(Cu1–xCox)5As3O2 turns into itinerant ferromagnetic metal, while La2(Ni1–xCox)5As3O2 shows paramagnetism and suppressed structural phase transition upon Co-doping. The distinct structural variation and absence of superconductivity provide important clues to understand the effect of As–As bond in [M5As3]2– subunit. [ABSTRACT FROM AUTHOR]

We present the superconducting (SC) property and high-robustness of structural stability of kagome CsV3Sb5 under in situ high pressures. For the initial SC-I phase, its Tc is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at P ∼ 10 GPa. With further increasing pressure, an SC-II phase emerges at P ∼ 15 GPa and persists up to 100 GPa. The Tc rapidly increases to the maximal value of 5.2 K at P = 53.6 GPa and slowly decreases to 4.7 K at P = 100 GPa. A two-dome-like variation of Tc in CsV3Sb5 is concluded here. The Raman measurements demonstrate that weakening of E2g mode and strengthening of E1g mode occur without phase transition in the SC-II phase, which is supported by the results of phonon spectra calculations. Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near EF, i.e., disappearance of Z2 invariant. Meanwhile, the Fermi surface enlarges significantly, consistent with the increased carrier density. The findings here suggest that the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC. [ABSTRACT FROM AUTHOR]

Abstract: Background: Surveillance data for rabies in Guangxi Province in China showed that human rabies cases have gradually increased since 1996. Objective: To evaluate the epidemiology of rabies at the molecular level and provide suggestions for effective prevention of rabies in Guangxi. Study design: Since 2000, 1569 brains from suspected rabid animals were collected from different areas of Guangxi. Rabies virus was isolated from 42 samples. RT-PCR was used to amplify a 455 nucleotide segment of the 3′-terminal of the N gene. The sequencing data from that segment was used for phylogenetic analysis. Results: Nucleotide homology comparisons and phylogenetic tree analysis based on this sequence indicated that all the rabies virus isolates from Guangxi belonged to genotype 1 and could be divided into four groups. Groups I, II and IV included 23, 10 and 8 isolates, respectively. These had nucleotide homologies of 97.1–100%, 98.2–100% and 99.1–99.6%, respectively. Only the GXN119 strain belonged to group III. Group I had two group-specific mutations: T90N and E110D. Group II had one group-specific mutation of T42S. Conclusions: This study showed that rabies virus isolates from Guangxi have a close genetic relationship and topographical distribution. [Copyright &y& Elsevier]

Three layered compounds CsLiCoS 2 , CsAgCoS 2 and CsLiFeS 2 have been synthesized by conventional solid-state reaction method. All of three compounds exhibit semiconducting behavior in electrical transport with small thermal activation energy gap. The crystal structure of CsLiCoS 2 is isostructural to ThCr 2 Si 2 -type CsCo 2 S 2 with random mixture of Li+ and Co2+. The latter two compounds exhibit √2 ​× ​√2 ​× ​1 superstructure of ThCr 2 Si 2 -type because the monovalent Ag+/Li+ and divalent Co2+/Fe2+ independently occupy inequivalent sites in [AMS 2 ]- layer. Through comprehensive investigation of the crystallographic lattice in CsAMS 2 , a phase boundary between disorder and ordered phases may be identified, which highlights the importance of the atomic size and lattice mismatch in determining the crystal structure. Image 1 • Three layered sulfides CsAMS 2 (A ​= ​Li, Ag; M ​= ​Co, Fe) are synthesized by solid state reaction method. • Introducing monovalent Li+/Ag+ could significantly change the structure and property of Co-based sulfides. • A phase boundary between random and ordered occupation in the [AMS 2 ]- layers is determined by the atomic size difference. [ABSTRACT FROM AUTHOR]

Background: Guangxi is the province most seriously affected by rabies virus (RABV) in China. Those most affected by RABV each year are people in rural areas, where dogs are the main cause of human infection with the virus.Methods: In this study, we established a rabies vaccination demonstration program that included eradication, core, and peripheral areas. This program was implemented for 9 years and comprised three stages: 12 counties in the first stage (2008-2010), 21 counties in the second stage (2011-2013), and then extending to all counties of Guangxi Province in the third stage (2014-2016). The program included a dog vaccination campaign, surveillance of clinically healthy dogs who may be potential RABV carriers, monitoring anti-RABV antibody titers in vaccinated dogs, and compiling and reporting statistics of human rabies cases.Results: The target effectiveness was achieved in the eradication, core, and peripheral areas in all three stages. The vaccination demonstration program successfully promoted RABV vaccination of domestic dogs throughout Guangxi Province by drawing upon the experience gained at key points. Compared with a vaccination coverage rate of 39.42-46.85% in Guangxi Province overall during 2003-2007, this rate gradually increased to 48.98-52.67% in 2008-2010, 60.24-69.67% in 2011-2013, and 70.09-71.53% in 2014-2016, thereby meeting World Health Organization requirements. The total cases of human rabies in the province decreased from 602 in 2004 to 41 cases in 2017.Conclusions: The present pilot vaccination program obviously increased the rabies vaccination and seroconversion rates, and effectively reduced the spread of rabies from dogs to humans as well as the number of human rabies cases, thus successfully controlling rabies in Guangxi. [ABSTRACT FROM AUTHOR]