Layer Graphene Sheets Research Articles

Impact dynamics of metallic nano particles in collision with graphene nano sheets

In this paper impact of metallic nanoparticles on graphene sheets was investigated via non equilibrium molecular dynamics (NEMD) approach. Upon unique feature of graphene to absorb motion energy of the materials impacted on it, systems based on graphene can be an appropriate solution for the purpose of damping. The proposed model was validated by available experimental data and simulation. It was demonstrated that mechanics of impact is not a multidimensional problem, therefore it can be studied by molecular dynamics. Effect of velocity of the particles, impact angle and number of the graphene sheets on the coefficient of restitution of the metallic nanoparticles was researched. Contrarily to macro systems, it was observed by increasing the velocity of impact, coefficient of restitution decreased. Also by increasing impact angle, coefficient of restitution changed with the formula: e(theta)=0.418(theta)^2-0.045(theta)-0.396. By increasing the graphene sheets, the coefficient reduced significantly. Negative coefficient of restitution was observed for some cases, which was reported also on other works about nanostructures. It was shown a single graphene layer can withstand 3.64 times more than a 20 layer graphene sheet toward impacting.

Iron functionalization on graphene nanoflakes using thermal plasma for catalyst applications

Graphene nanoflakes (GNFs), a stack of 5–20 layers of graphene sheets, are generated here using methane decomposition in a thermal plasma followed by homogeneous nucleation of the 2-dimensional structures in the gas stream. The GNFs are functionalized with nitrogen and iron to improve their electrocatalytic activity. The iron functionalization step is carried out as a post-processing step within the same thermal plasma reactor used to grow the nanoparticles. Two different iron precursors are tested in the reactor, iron powder and iron (II) acetate solution. The iron source carried by a nitrogen flow is injected in the argon plasma, and parameters such as the plasma power, pressure, and the exposure time during functionalization are optimized for enhanced catalyst activity. Structure and composition of the resulting catalysts are characterized, and their electrocatalytic performances in terms of onset potential, half wave potential and current density show an increase compared to the non-functionalized GNFs. This study proves the ability to entirely produce a pure and highly crystalline graphene-based non-noble metal catalyst using a thermal plasma single batch process with simple precursors such as methane and nitrogen gas, and an iron powder or iron acetate solution.

Orthotropic patterns of visco-Pasternak foundation in nonlocal vibration of orthotropic graphene sheet under thermo-magnetic fields based on new first-order shear deformation theory

In the present research, vibration and instability of orthotropic graphene sheet subjected to thermo-magnetic fields are investigated. Orthotropic visco-Pasternak foundation is considered to analyze the influences of orthotropy angle, damping coefficient, normal and shear modulus. New first-order shear deformation theory is utilized due to accuracy of its polynomial functions compared to other theories of plate. Motion equations are obtained by means of Hamilton’s principle and then solved analytically. Influences of various parameters such as small scale, magnetic field, orthotropic viscoelastic surrounding medium, thickness and aspect ratio of single layer graphene sheet on the vibration characteristics of nanoplate are discussed in detail. The results indicate that the stability of single layer graphene sheet is strongly dependent on applied magnetic field. Therefore, the mechanical behavior of single layer graphene sheet can be improved by applying magnetic field. The results of this investigation can be used in design and manufacturing of micro/nano mechanical systems.

Using Reduced Graphene Oxide As Conducting Layer of Plating through Holes of a Printed Circuit Board

Graphene is a popular material because of its unique two-dimensional (2D) structure and intrigued physical and chemical properties. Graphene materials, including single layer and multi-layer graphene sheets, have recently drawn extensive attention due to their outstanding electrical and thermal properties. In the traditional metallization process of through holes of printed circuit boards (PCBs), copper electroless deposition process has been commonly used. It has environmentally unfriendly characteristics because it contains precious metal (i.e., Pd), formaldehyde and chelating agents. In contrast, reduced graphene oxide (rGO) has no these issues and can replace the copper electroless deposition of PCBs because the rGO process for copper metallization is simpler than that of copper electroless deposition. Herein, we used rGO process to replace the copper electroless deposition process in order to achieve a green fabrication process. In this study, the effect of different conditioners for uniform adsorption of graphene oxide (GO) on the sidewalls of through holes of a PCB was investigated. We used different conditioners to chemically modify the substrate surfacefor uniform adsorption of GO. Following the GO adsorption, the adsorbed GO was reduced to rGO on the substrate surface. Then, the rGO-coated sidewall becomes conductive to replace the copper seed layer by electroless deposition. Finally, the rGO-coated through holes were successfully plated in an acidic copper bath with a high throwing power and these through holes could pass thermal shock reliability test.

Layer Number Dependence of Li+ Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution

Bulk and surface electrochemical reactivity converge on ultrathin electrochemical interfaces such as few-layer graphene (FLG). In spite of the many recent works regarding the use of exfoliated graphene materials for charge storage, we still lack a detailed mechanistic understanding of how Li+ intercalates in FLG. Li+ intercalation in graphitic carbon is known to proceed through a staging mechanism, where intercalation occurs at selected interlayers at a time, rather than randomly on any available empty interlayer galleries, until reaching the nominal composition LiC6. Thus, on graphite this process is strongly dependent on the number of neighboring empty galleries at any given time. FLG naturally displays a limited number of galleries, therefore, we hypothesize that this process will also necessarily be distributed unevenly. In this study, we applied FLG (1-10 layers) to explore the alkaline ion uptake mechanisms. Chemical vapor deposition methods with varies recipes were applied to grow double and multilayer graphene. By multicycle wet transfer of bilayer graphene, 2-8 layer graphene with well-defined area and low defect density. Direct growth of multilayer graphene (>10 layers) serves as control group. Photolithography method was used to generate micro patterns on graphene as “point of entry” for Li+intercalation. Lithium ion intercalation on FLG, as measured via cyclic voltammetry, shows a staging-type process, which has strong dependence on the number of layers of graphene sheets that compose the electrode. On a graphene electrode with less than five layers, the numbers of intercalation/de-intercalation peaks were limited due to the lack of graphene interlayer galleries to stabilize Li ions. Those peaks broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate spatial resolved changes in the surface conductivity of FLG during SEI evolution. The fabrication of “ionic channels” on the FLG electrode provided preferential positions for Li ion insertion. The role of these channels can be evidenced using a Li-ion sensitive SECM imaging technique through localized flux measurements. This work highlights the impact of nano-structure and micro-structure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using atomically thin graphene interface. Figure 1

In-situ functionalization of aniline oligomer onto layered graphene sheet and study of its application on electrochemical detection of ascorbic acidin food samples

In-situ functionalization of aniline oligomer onto layered graphene sheet and study of its application on electrochemical detection of ascorbic acidin food samples

Modelling of particle-laden flow inside nanomaterials.

In this paper, we demonstrate the usage of the Nernst-Planck equation in conjunction with mean-field theory to investigate particle-laden flow inside nanomaterials. Most theoretical studies in molecular encapsulation at the nanoscale do not take into account any macroscopic flow fields that are crucial in squeezing molecules into nanostructures. Here, a multi-scale idea is used to address this issue. The macroscopic transport of gas is described by the Nernst-Planck equation, whereas molecular interactions between gases and between the gas and the host material are described using a combination of molecular dynamics simulation and mean-field theory. In particular, we investigate flow-driven hydrogen storage inside doubly layered graphene sheets and graphene-oxide frameworks (GOFs). At room temperature and with slow velocity fields, we find that a single molecular layer is formed almost instantaneously on the inner surface of the graphene sheets, while molecular ligands between GOFs induce multi-layers. For higher velocities, multi-layers are also formed between graphene. For even larger velocities, the cavity of graphene is filled entirely with hydrogen, whereas for GOFs there exist two voids inside each periodic unit. The flow-driven hydrogen storage inside GOFs with various ligand densities is also investigated.

Multipole Trefftz method implementation in free vibration of a graphene sheet with multiple vacancy defects

The single and multiple vacancy defects in a single layer graphene sheet can affect its mechanical properties. Also, these defects can be inverted to greater holes as amorphous construction when the graphene sheet is working in room temperature. In some cases, these defects can be modelled as circular holes. In this article, multipole Trefftz method as well as translational addition theorem are employed to consider effects of circular defects on behavior of freely vibrating circular graphene sheet. Nonlocal thin plate theory is used to solve the problem. According to the direct-searching approach, the natural frequencies are determined as the minimum singular value of the truncated finite system using the singular value decomposition (SVD) technique. The computational efficiency and convergence of the present analytical method are examined. Accuracy and stability of results are validated by literature. Effects of boundary conditions, geometrical properties and nonlocal parameter on vibrational modes are investigated. Results reveal that the eccentricity, nonlocality and number of holes have significant effects on the natural frequencies.

Pullout strength of graphene and carbon nanotube/epoxy composites

An atomistic multiscale modelling approach is used to simulate the nonlinear pullout behaviour of interlinked single walled carbon nano tubes (SWCNT) and single layer graphene sheets (SLGS) embedded in an epoxy polymer. The pullout forces have been computed for various configurations of nanocomposites (SWCNT-SWCNT, SLGS-SLGS and hybrid SLGS-SWCNT), also by evaluating the effect provided by three different interlink compounds. The interfacial strength due to fibre pullout predicted by the hybrid atomistic-FE model is compared against experimental and molecular dynamics results available in open literature. The results show the specific deformation characteristics (localised auxetics) that provide an increase of pullout forces and interfacial strength with the use of the links.

Nonlinear thermo-elastic bending behavior of graphene sheets embedded in an elastic medium based on nonlocal elasticity theory

This paper investigates the large deflection behavior of orthotropic single layered graphene sheet (SLGS) embedded in a Winkler–Pasternak elastic medium under a uniform transverse load in thermal environments. Using the nonlocal differential constitutive relations of Eringen, the SLGS is modeled as a nonlocal orthotropic plate. Using the principle of virtual work, the coupled nonlinear equilibrium equations are obtained based on first-order shear deformation theory (FSDT) and the von Kármán geometrical model. The differential quadrature (DQ) discretized form of the governing equations with clamped and simply supported boundary conditions is derived. The Newton–Raphson iterative scheme is used to solve the resulting system of nonlinear algebraic equations. Effects of small scale parameter, thermal environment, width-to-length elasticity ratio, aspect ratio, thickness, elastic foundation, load value and boundary conditions are considered in detail. The results show that, unlike the simply supported boundary conditions, increase of small scale parameter plays a decreasing role in effect of thermal environment on the deflections of nanoplates with clamped edges. It is also observed that increasing the plate thickness, thermal load effects decline noticeably and depending on the small scale value the thermal loads do not have any significant effect on the results beyond a specified thickness.

Fabrication and Characterization of Few Layered Graphene Sheet Decked with CeO2 Nano Particles for Dye Sensitized solar cell Application

Fabrication and Characterization of Few Layered Graphene Sheet Decked with CeO2 Nano Particles for Dye Sensitized solar cell Application

Dislocation Nucleation in Nickel-Graphene Nanocomposites Under Mode I Loading

Graphene has superior mechanical properties, and previous studies have shown that it can be used as a fiber laminate in metal-graphene nanocomposites. Our research outlines the advantages and disadvantages of different Ni-graphene nanocomposite laminates. Using molecular dynamics, Ni-graphene nanocomposites are studied under mode I loading normal to the graphene laminate plane. The stress intensity factor (\(K_{\text{I}}\)) is predicted for the nanocomposite at varying distances between a simulated crack and the graphene sheet(s) in the Ni-matrix. We find that \(K_{\text{I}}\) of the Ni-matrix is reduced with the addition of graphene sheet. However, for a single graphene sheet in the Ni-matrix, \(K_{\text{I}}\) increases with increased spacing between the crack and the graphene sheet. This is due to the change in the crack-generated stress field in the region between the Ni-matrix containing the crack and the graphene sheet, which leads to the lower stress values at which dislocation nucleation occurs compared to single-crystal Ni. For multiple layers of graphene sheets in the Ni-matrix, we find that failure occurs exclusively by delamination at a lower stress than the one-layer case. This research concludes that fabricated Ni-graphene nanocomposites can be tuned for optimal fracture strength by the structural arrangement of graphene sheets within the Ni-matrix.

Low Energy Intraband Plasmons and Electron Energy Loss Spectra of Single and Multilayered Graphene

We present a theory for the calculation of the low energy intraband plasmon frequencies and the electron energy loss (EEL) spectra of single layer and multilayer graphene sheets. Our calculation shows that the number of plasmons that can be excited is equal to the number of graphene layers in the sample. One of these is the dominant in-phase plasmon having a square root dependence on the wave number at low wave vectors, whereas the others are out-of-phase plasmons having near linear dependences on the wave number. The EEL spectra of a single layer graphene shows a single peak at the plasmon frequency, which has been observed experimentally. The EEL spectra of all multilayer graphenes have two peaks, one corresponding to the dominant in-phase plasmon and the other due to the out of phase plasmons. We predict that careful measurement of the EEL of multilayer graphene will show both peaks due to the low energy intraband plasmons.

Optimizing Water Transport through Graphene-Based Membranes: Insights from Nonequilibrium Molecular Dynamics.

Recent experimental results suggest that stacked layers of graphene oxide exhibit strong selective permeability to water. To construe this observation, the transport mechanism of water permeating through a membrane consisting of layered graphene sheets is investigated via nonequilibrium and equilibrium molecular dynamics simulations. The effect of sheet geometry is studied by changing the offset between the entrance and exit slits of the membrane. The simulation results reveal that the permeability is not solely dominated by entrance effects; the path traversed by water molecules has a considerable impact on the permeability. We show that contrary to speculation in the literature, water molecules do not pass through the membrane as a hydrogen-bonded chain; instead, they form well-mixed fluid regions confined between the graphene sheets. The results of the present work are used to provide guidelines for the development of graphene and graphene oxide membranes for desalination and solvent separation.

Equivalent mechanical boundary conditions for single layer graphene sheets

To describe and analyse mechanical structures due to external loads, equation of motion must be supplemented with appropriate boundary conditions. When nanomechanical structures (especially layered systems) are considered, satisfying the boundaries is more challenging. It may be essential to develop a specific methodology for any system in such scale and configuration. This work introduces a general approach for boundary conditions of monolayer graphene sheets as the most important part of future sensors and resonators in nanoelectromechanical systems. Comparing with the experiments, it has been demonstrated that the graphene sheets on the adhesive surfaces should be assumed as a hinged edge condition and not as a clamped one. As a result, inaccuracy of the commonly used rigid base as a clamped condition is proven due to comparison with a reported experiment. It is suggested that a flexible substrate can be replaced to have better accordance. A flexible silicon base with equilibrium distance equal to s = 2.5 Å and depth of potential well equal to ε = 0.02 eV is obtained as the best substrate for a square graphene sheet under doubly clamped edge conditions.

Environmental Synthesis of Few Layers Graphene Sheets Using Ultrasonic Exfoliation with Enhanced Electrical and Thermal Properties.

In this paper, we report how few layers graphene that can be produced in large quantity with low defect ratio from exfoliation of graphite by using a high intensity probe sonication in water containing liquid hand soap and PVP. It was founded that the graphene powder obtained by this simple exfoliation method after the heat treatment had an excellent exfoliation into a single or layered graphene sheets. The UV-visible spectroscopy, FESEM, TEM, X-ray powder diffraction and Raman spectroscopy was used to analyse the graphene product. The thermal diffusivity of the samples was analysed using a highly accurate thermal-wave cavity photothermal technique. The data obtained showed excellent enhancement in the thermal diffusivity of the graphene dispersion. This well-dispersed graphene was then used to fabricate an electrically conductive polymer-graphene film composite. The results demonstrated that this low cost and environmental friendly technique allowed to the production of high quality layered graphene sheets, improved the thermal and electrical properties. This may find use in the wide range of applications based on graphene.

Multifunctionality in graphene decorated with cobalt nanorods

Creating multifunctionality is always fascinating and required for various advance applications. We have prepared cobalt-graphene nanocomposite by co-reduction of graphite oxide and a divalent cobalt salt in water, at room temperature, by sodium borohydride. Microstructural study by high resolution transmission electron microscope (HRTEM) delineates that the nanocomposites consists of few layer of graphene sheets decorated by cobalt nanorods. The composite shows unusual photoluminescence in visible range due to defect decoration by cobalt nanorods, in spite of showing expected absorbance and magnetic properties. Functional nanomaterials with both magnetic and luminescence properties are important for application in biological systems.

Nonlinear dynamic response of single layer graphene sheets using multiscale modelling

Abstract In this paper, computationally efficient multiscale modelling considering material and geometric nonlinearities is employed for the first time to investigate the dynamic response of single layer graphene sheets under harmonic excitation. The constitutive relation at continuum level is derived from a strain energy density function as Tersoff–Brenner atomic interaction potential per unit area of a unit cell through Cauchy–Born rule. The governing equation of motion obtained using Hamilton's principle is solved using Newmark's direct time integration and shooting techniques to obtain steady state periodic response. The effects of material and geometric nonlinearities, size of the graphene sheet, boundary conditions, damping and loading parameters on the natural frequencies/response characteristics are investigated. The dynamic response depicts hardening nonlinearity with the dominant effect of geometric nonlinearity compared to material nonlinearity.

Nanomechanics analysis of perfect and defected graphene sheets via a novel atomic-scale finite element method

Due to their accuracy and reliability, atomistic-based methods such as molecular dynamics (MD) simulations have played an essential role in the field of predictive modeling of single layered graphene sheets (SLGSs) at the nanoscale. However, their applications are limited due to the computational costs. Additionally, consistent with the discrete nature of SLGSs, conventional continuum-based methods cannot be utilized to study the mechanical characteristics of these nanostructures. To overcome these issues, a new Atomic-scale Finite Element Method (AFEM) based on the Tersoff-Brenner potential has been developed in this study. Efficiency of the proposed method is demonstrated employing several numerical examples and its applicability is carefully testified in the case of perfect and defected SLGSs. To facilitate a better comparison, the mechanical behavior obtained by this method is compared with the one determined via MD simulation in various case studies. The results reveal that the proposed method has the accuracy of MD simulations and the speed of continuum-based approaches, simultaneously.

Mode-I stress intensity factor in single layer graphene sheets

We use the freely available software, LAMMPS, and the Tersoff potential to find the mode-I stress intensity factor during crack propagation in an edge-cracked single layer graphene sheet deformed at a constant axial strain rate. The axial stress and the stress intensity factor (SIF) at atoms’ locations are computed by using, respectively, the Virial theorem and either the stress at the atom located at the crack-tip or the average axial stress in the sheet. It is found that the two values of the SIF differ from each other by about 8%, and agree with those reported in the literature derived either analytically or from test data. The method proposed and used herein can be applied to find the SIF in any nanostructure.