Li-decorated graphyne as high-capacity hydrogen storage media: First-principles plane wave calculations

Taking into account the van der Waals correction, the characteristics of the Li-decorated graphyne as the hydrogen storage medium have been explored using first-principles plane wave calculations. We find that Li atom can be adsorbed not only over the center of large hexagon (H_L site) but also over the center of small hexagon (H_S site). For double-side Li decorations, there are 14H₂ molecules can be adsorbed on Li-decorated graphyne primitive cell with the adsorption energy of 0.19 eV/H₂. As a result, the hydrogen storage capacity of 13.0 wt% can be obtained. This suggests that the Li-decorated graphyne system can serve as a high-capacity hydrogen storage medium.     

对物理化学考研中van der Waals方程及其应用考点的分析

对物理化学考研中van der Waals方程及其应用的考点进行深入分析,使考物理化学科目的考生能很好的理解和掌握此考点。     

范德华力对硅基微悬臂梁抗粘附稳定性的影响

通过在硅微悬臂梁与基底表面上涂覆低表面能的憎水性OTS(CH3(CH2)17SiCl3)膜,以除去接触面间的表面张力;把梁与基底均接地,以除去接触面间的静电力,研究仅有范德华力作用时,硅微悬臂梁结构的抗粘附稳定性.根据两接触面均为粗糙表面的微观实际接触模型,在接触表面产生塑性变形的情况下,计算范德华粘附能大小,并分析表面形貌对其影响,得到粗糙表面接触的微梁抗粘附临界长度.     

Towards van der Waals Epitaxial Growth of GaAs on Si using a Graphene Buffer Layer

Van der Waals growth of GaAs on silicon using a two‐dimensional layered material, graphene, as a lattice mismatch/thermal expansion coefficient mismatch relieving buffer layer is presented. Two‐dimensional growth of GaAs thin films on graphene is a potential route towards heteroepitaxial integration of GaAs on silicon in the developing field of silicon photonics. Hetero‐layered GaAs is deposited by molecular beam epitaxy on graphene/silicon at growth temperatures ranging from 350 °C to 600 °C under a constant arsenic flux. Samples are characterized by plan‐view scanning electron microscopy, atomic force microscopy, Raman microscopy, and X‐ray diffraction. The low energy of the graphene surface and the GaAs/graphene interface is overcome through an optimized growth technique to obtain an atomically smooth low­ temperature GaAs nucleation layer. However, the low adsorption and migration energies of gallium and arsenic atoms on graphene result in cluster‐growth mode during crystallization of GaAs films at an elevated temperature. In this paper, we present the first example of an ultrasmooth morphology for GaAs films with a strong (111) oriented fiber‐texture on graphene/silicon using quasi van der Waals epitaxy, making it a remarkable step towards an eventual demonstration of the epitaxial growth of GaAs by this approach for heterogeneous integration.     

Epitaxy of Layered Orthorhombic SnS–SnSxSe(1−x) Core–Shell Heterostructures with Anisotropic Photoresponse

Vertical and in‐plane heterostructures based on van der Waals (vdW) crystals have drawn rapidly increasing attention owning to the extraordinary properties and significant application potential. However, current heterostructures are mainly limited to vdW crystals with a symmetrical hexagonal lattice, and the heterostructures made by asymmetric vdW crystals are rarely investigated at the moment. In this contribution, it is reported for the first time the synthesis of layered orthorhombic SnS–SnS_xSe_(1?x) core–shell heterostructures with well‐defined geometry via a two‐step thermal evaporation method. Structural characterization reveals that the heterostructures of SnS–SnS_xSe_(1?x) are in‐plane interconnected and vertically stacked, constructed by SnS_xSe_(1?x) shell heteroepitaxially growing on/around the pre‐synthesized SnS flake with an epitaxial relationship of (303)_SnS//(033)_SnSxSe(1?x), [010]_SnS//[100]_SnSxSe(1?x). On the basis of detailed morphology, structure and composition characterizations, a growth mechanism involving heteroepitaxial growth, atomic diffusion, as well as thermal thinning is proposed to illustrate the formation process of the heterostructures. In addition, a strong polarization‐dependent photoresponse is found on the device fabricated using the as‐prepared SnS?SnS_xSe_(1?x) core–shell heterostructure, enabling the potential use of the heterostructures as functional components for optoelectronic devices featured with anisotropy.     

Electronic properties of Bilayer Fullerene onions

HOMO–LUMO gaps of the bilayer fullerene onions were investigated. For this purpose, HOMO and LUMO energies for the isolated fullerenes were calculated using the parameterization of the tight binding method with the Harrison–Goodwin modification. Then, by the consideration of the van der Waals interaction, the thermodynamical stability of possible combinations of the fullerene molecules was verified and the unstable forms were excluded. Next, the difference of the Fermi levels of the outer and inner shells was calculated by the consideration of the hybridization of the orbitals by using the geometric parameters. The results were obtained by the combination of these calculations.     

A Model for Liquid-Striped Liquid Phase Separation in Liquids of Anisotropic Polarons

The phase separation between a striped polaron liquid at the particular density and a high density polaron liquid is described by a modified Van der Waals scheme. The striped polaron liquid represents the pseudo gap matter or Wigner-like polaron phase at 1/8 doping in cuprate superconductors. The model includes the tendency of pseudo-Jahn-Teller polarons to form anisotropic directional bonds at a preferential volume with the formation of different “liquid phases”. The model gives the coexistence of a first low density polaron striped liquid and a second high density liquid that appears in cuprate superconductors for doping larger than 1/8. We discuss how the strength of anisotropic bonds controls the variation the phase separation scenarios for complex systems in the presence of a quantum critical point where the phase separation vanishes.     

Behavior of a nonconformal mixture via computer simulation

A binary 50% mixture of soft spheres is studied via nonequilibrium molecular dynamics, and the equilibrium and nonequilibrium radial distribution functions for a nonconformal mixture with a mass ratio of 10 and a size ratio of about 2 are examined. This model system is related to the real methane/decane mixture, and it is shown that apparently anomalous properties of this mixture, especially the viscosity, could perhaps be understood in terms of the local or ambient mole fraction. In addition, the postulates of the Van der Waals one fluid conformal solution theory are discussed, and a mixing rule for the mass is derived.     

Numerical simulation of the head-on collision of two equal-sized drops with van der Waals forces

The head-on collision of two equal-sized drops in a hyperbolic flow is investigated numerically. An axisymmetric volume-of-fluid (VOF) method is used to simulate the motion of each drop toward a symmetry plane where it interacts and possibly coalesces with its mirror image. The volume-fraction boundary condition on the symmetry plane is manipulated to numerically control coalescence. Two new numerical methods have been developed to incorporate the van der Waals forces in the Navier–Stokes equations. One method employs a body force computed as the negative gradient of the van der Waals potential. The second method employs the van der Waals forces in terms of a disjoining pressure in the film depending on the film thickness. Results are compared to theory of thin-film rupture. Comparisons of the results obtained by the two methods at various values of the Hamaker constant show that the van der Waals forces calculated from the two methods have qualitatively similar effects on coalescence. A study of the influence of the van der Waals forces on the evolution and rupture of the film separating the drops reveals that the film thins faster under stronger van der Waals forces. Strong van der Waals forces lead to nose rupture, and small van der Waals forces lead to rim rupture. Increasing the Reynolds number causes a greater drop deformation and faster film drainage. Increasing the viscosity ratio slows film drainage, although the effect is small for small viscosity ratio.