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Molecular dynamics simulations is used to investigate the mechanical properties of three‐dimensional (3D) graphene under uniaxial tensile loading. The results show that the tensile deformation of 3D graphene exhibits size dependence along both armchair and zigzag directions. By analyzing the atomic von Mises stress and structural evolution, compared to the 3D graphene with smaller in‐plane cell size, the larger 3D graphene exhibits two typical deformation events, i.e., transverse structural shrinkage and axial elastic deformation. The fracture stress of 3D graphene is much smaller than that of 2D graphene because of its porous structure. However, the fracture strain of 3D graphene is larger than that of 2D graphene due to the larger transverse structural shrinkage along both armchair and zigzag directions. Effects of temperature, strain rate, and thickness of 3D graphene on the tensile behavior is investigated. The simulation results indicate that the fracture stress and the fracture strain decrease with increasing temperature and with decreasing strain rate. However, the fracture stress and the fracture strain is not dependent on the thickness of 3D graphene. The results in this paper suggest that 3D graphene with higher stretchability tunable by in‐plane cell size can be promising multifunctional materials for many engineering applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] The zigzag graphyne family structure displays semi-conductive characteristic. [•] The armchair graphyne family structure displays metallic characteristic. [•] With the length of C links increasing, the conductivity of graphyne family decreases. [•] The zigzag GNR-graphdiyne heterojunction shows superior rectification behavior. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations are used to investigate the mechanical properties of a silicon nanofilm covered with a defective graphene. Our results show that graphene not only enhances the mechanical properties of a silicon nanofilm but also unifies the mechanical properties of the ultrathin silicon nanofilms among different crystal orientations. The Young''s modulus and critical stress of the silicon nanofilm along four crystal orientations covered with graphene decrease as the thickness of the silicon nanofilm increases. In addition, we study the effects of monoatomic vacancies and Stone–Wales (SW) defects with various concentrations on the mechanical properties of a silicon nanofilm covered with defective graphene. The results show that Young''s modulus reduces linearly for monoatomic vacancies and a relatively smaller dependence is observed on SW defects, while the critical stress is more sensitive to the presence of both types of defects. The results in this paper demonstrate the significance of graphene in enhancing the mechanical properties of the silicon nanofilm. [Copyright &y& Elsevier]

Nonequilibrium molecular dynamics (NEMD) is used to investigate the thermal-transport properties of a silicon nanofilm covered with graphene (Gr/Si/Gr nanofilm). The investigation results demonstrate that graphene can enhance the thermal-transport properties and weaken the ballistic characteristics of silicon nanofilm. Under the action of a small strain, the thermal conductivity decreases with the growth of tensile and compressive strain, respectively. In addition, the higher-frequency phonons in graphene give more contributions to the variation of thermal conductivity of Gr/Si/Gr nanofilm under strain. The thermal conductivity of Gr/Si/Gr nanofilm increases linearly with the increase of temperature in the lower-temperature regime due to the quantum effect, and begins to clearly decrease when the temperature exceeds a definite value. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulations are used to investigate the mechanical properties of a silicon nanofilm covered with graphene. Our results show that graphene can enhance the mechanical properties of a silicon nanofilm. The Young’s modulus of the silicon structure covered with graphene decreases as the thickness of the silicon nanofilm increases. We also investigate the fracture process of the silicon structure covered with graphene. The results in this paper suggest that silicon structures covered with graphene open up opportunities for design of micro and nanoelectromechanical systems. [Copyright &y& Elsevier]

The success of fabricating single layer graphene and silicon nanofilm (could be as thin as single layer so far) has triggered enormous interest in exploring their unique physics and novel applications. An intuitive idea is to investigate what happens if we construct a heterostructure composed of these two sheets. In this paper, we perform nonequilibrium molecular dynamics simulations to systematically investigate the in-plane thermal transport in graphene/silicon/graphene (Gr/Si/Gr) heterostructures. The effects of Si film thickness, interfacial interaction strength, and length on the thermal conductivity of the Gr/Si/Gr heterostructures are explicitly considered. Our simulations identify a unified scaling law for thickness dependence of thermal conductivity of the Gr/Si/Gr heterostructures, despite different interfacial interaction forms are used (weak van der Waals interaction and strong covalent bonding). By quantifying relative contribution from phonon polarizations and defining heat flux onto single atom, we reveal and fully understand the different mechanisms governing the phonon transport in the Gr/Si/Gr heterostructures for the two different interfacial interaction forms. We also found that the thermal conductivity of Gr/Si/Gr heterostructure is nonmonotonically dependent on the van der Waals interaction strength between graphene and Si, but monotonically dependent on the graphene-silicon covalent bonding strength. Moreover, length dependence study shows that phonon transport in Gr/Si/Gr heterostructure becomes diffusive at much shorter length as compared with single layer graphene and bilayer graphene. Comparing to single and double graphene layers, the thermal conductivity of the Gr/Si/Gr heterostructure can be reduced with more than one order of magnitude for very long structures. These results suggest that Gr/Si/Gr heterostructures are promising for nanoscale devices due to their unique thermal transport properties. [ABSTRACT FROM AUTHOR]

Nanostructured thermoelectric materials are promising for modulating physical properties to achieve high thermoelectric performance. In this paper, thermal transport properties of armchair/zigzag graphene superlattice nanoribbons (A/Z graphene SLNRs) are investigated by performing nonequilibrium molecular dynamics simulations. The target of the research is to realize low thermal conductivity by introducing single-vacancy point defects. Our simulations demonstrate that the thermal conductivity of A/Z graphene SLNRs depends nonmonotonically on periodic length. In addition, introducing single-vacancy point defects into the superlattice nanoribbons could decrease the phonon tunneling in superlattice nanoribbons, so that the thermal conductivity could be reduced further. Furthermore, a monotonic dependence of the thermal conductivity of A/Z graphene SLNRs with length of zigzag part in periodic length is discovered. This phenomenon is explained by performing phonon property analysis. Our simulations deliver a detailed phonon transport in A/Z graphene SLNRs and provide useful guidance on how to engineer the thermal transport properties of A/Z graphene SLNRs for applications of nanoribbon-related devices in thermoelectrics. [ABSTRACT FROM AUTHOR]