Lithium Diffusion in Silicon Encapsulated with Graphene

The model of a graphene (Gr) sheet putting on a silicon (Si) substrate is used to simulate the structures of Si microparticles wrapped up in a graphene cage, which may be the anode of lithium-ion batteries (LIBS) to improve the high-volume expansion of Si anode materials. The common low-energy defective graphene (d–Gr) structures of DV5–8–5, DV555–777 and SV are studied and compared with perfect graphene (p–Gr). First-principles calculations are performed to confirm the stable structures before and after Li penetrating through the Gr sheet or graphene/Si-substrate (Gr/Si) slab. The climbing image nudged elastic band (CI-NEB) method is performed to evaluate the diffusion barrier and seek the saddle point. The calculation results reveal that the d–Gr greatly reduces the energy barriers for Li diffusion in Gr or Gr/Si. The energy stability, structural configuration, bond length between the atoms and layer distances of these structures are also discussed in detail.

Atomic Level Insight into Wetting and Structure of Ag Droplet on Graphene Coated Copper Substrate—Molecular Dynamics versus Experiment

Understanding the atomic-level phenomena occurring upon the wetting of graphene-coated Cu with liquid Ag is pivotal for the description of the wetting phenomenon and the role of graphene as a diffusion barrier. We have performed molecular dynamics (MD) simulations and confronted with our present experimental results to characterize wetting behavior of graphene coated Cu surfaces. Perfect and defected graphene layers covering Cu surface were wetted with liquid Ag droplet at 1273 K. Structural and topological aspects are discussed to characterize structure of the liquid Ag droplet and a product of wetting reaction occurring on Cu/Gn and Cu/Gndef substrates, also including perfect graphene layer and a pure Cu surface. The obtained results reveal the importance of defects in graphene structure, which play a key role in wetting mechanism and the formation of AgCu alloy. As a consequence, we observe a change of the wetting behavior and topology of both bulk and adsorbed Ag atoms by using Voronoi analysis (VA). Despite the differences in time scale, atomistic simulations allowed us to catch the early stages of wetting, which are important for explaining the final stage of wetting delivered from experiment. Our findings reveal also graphene translucency to metal-metal interactions, observed in previous papers.

Quasi-Monocrystalline Graphene Crystallization on Liquid Copper Matrix

To access the properties of theoretical graphene, it is crucial to manufacture layers with a defect-free structure. The imperfections of the structure are the cause of deterioration in both electrical and mechanical properties. Among the most commonly occurring crystalline defects, there are grain boundaries and overlapping zones. Hence, perfect graphene shall be monocrystalline, which is difficult and expensive to obtain. An alternative to monocrystalline structure is a quasi-monocrystalline graphene with low angle-type boundaries without the local overlapping of neighboring flakes. The purpose of this work was to identify factors that directly affect the structure of graphene grown on a surface of a liquid metal. In the article the growth of graphene on a liquid copper is presented. Nucleating graphene flakes are able to move with three degrees of freedom creating low-angle type boundaries when they attach to one another. The structure of graphene grown with the use of this method is almost free of overlapping zones. In addition, the article presents the influence of impurities on the amount of crystallization nuclei formed, and thus the possibility to order the structure, creating a quasi-monocrystalline layer.

Effect of Stone-Wales Defect on Mechanical Properties of Gr/epoxy Nanocomposites

Due to its superior mechanical properties, graphene (Gr) has the potential to achieve high performance polymer-based nanocomposites. Previous studies have proved that defects in the Gr sheets could greatly reduce the mechanical properties of Gr, while the Stone-Wales (SW) defect was found to enhance the interfacial mechanical strength between Gr and epoxy. However, the combined effects of defects on the overall mechanical properties of Gr/epoxy nanocomposites have not been well understood. In this paper, the effect of the SW defect on the mechanical properties of Gr/epoxy nanocomposites was systematically investigated by using molecular dynamic simulations. The simulation results showed that the SW defect would degrade the mechanical properties of nanocomposites, including the Young’s modulus and in-plane shear modulus. Surprisingly, the transverse shear modulus could be remarkably enhanced with the existence of SW. The reinforcing mechanisms were mainly due to two aspects: (1) the SW defect could increase the surface roughness of the Gr, preventing the slippage between Gr and epoxy during the transverse shea; and (2) the nanocomposite with defective Gr enables a higher interaction energy than that with perfect graphene. Additionally, the effects of temperature, the dispersion and volume fraction of Gr were also investigated.

Исследование влияния водородного травления поверхности SiC на последующий процесс формирования пленок графена

The effect of temperature and duration of the 4H-SiC (0001) surface etching in hydrogen on the structural perfection of graphene films grown by the thermal destruction method was studied. Several technological regimes have been defined that allow etching of the substrate without changing the stoichiometric composition of the surface. It has been demonstrated that pre-growth etching in hydrogen at T = 1600 ° C for 1 min. allows one to obtain more uniform and structurally perfect graphene than etching at T = 1300 ° C for 30 minutes.

Al-doped graphene as an effective adsorber for some toxic derivatives of aromatic hydrocarbons

The density functional theory (DFT) was used to investigate some toxic derivatives of aromatic hydrocarbons adsorption on perfect graphene (pG) and graphene-doped with B/Al/Ga (BG/AlG/GaG). And the parallel and vertical adsorptions were considered for the position relation between the adsorbent and adsorbate. The adsorption energy, adsorption distance, charge transfer and density of states (DOS) were discussed in optimized structures. The greater adsorption energy, shorter adsorption distance and more charge transfer were found in AlG by studying the four kinds of molecules (phenol/m-cresol/PCP/p-NP) adsorption on pG/BG/AlG/GaG. Then, 10 derivatives adsorption on AlG were reported, and the adsorption energy increased in the order of pentachlorophenol [Formula: see text] 2,4,6-trichlorophenol [Formula: see text] 2,4-dichlorophenol [Formula: see text] p-cresol [Formula: see text] m-cresol [Formula: see text] phenol [Formula: see text] o-chlorophenol [Formula: see text] o-cresol [Formula: see text] 2,4,6-trintrotoluene [Formula: see text] para-nitrophenol. The interaction between these derivatives and the substrate was chemisorption for AlG and physisorption for pG. The oxygen atom in nitro group was more closer to the substrate than in hydroxyl group about optimized structures.