Number Of Graphene Layers Research Articles

Sensitivity Comparison between Monolayer Graphene and Multilayer Graphene

Graphene is an excellent piezoresistive material. The gauge factor of graphene mirrors the sensitivity of electromechanical devices. This paper mainly studies the gauge factors of different layers of graphene under different deformation conditions. Specifically, a theoretical model was combined with linearized Boltzmann transport equation, and the density function theory (DFT) to explore how the layer number of graphene affects sensitivity. The results show that monolayer graphene is slightly more sensitive than two-layer graphene, and significantly more sensitive than three-layer graphene and four- layer graphene. In particular, monolayer graphene remains highly sensitive under large deformation conditions, which gives monolayer graphene a significant advantage over other layers of graphene. Furthermore, a microelectromechanical system (MEMS) pressure sensor was proposed with monolayer graphene, and compared with previous similar sensors with multilayer graphene in terms of sensitivity.

Nonlocal Timoshenko shear beam model for multilayer curved graphene nano-switches

Graphene sheets are the basis of nano-electromechanical switches, which offer a unique insight into the world of quantum mechanics. In this paper, we proposed a new size-dependent multi-beam shear model for investigating the pull-in instability of multilayer graphene/substrate nano-switches within the context of the Timoshenko beam theory. As the graphene/substrate bemas bent toward the graphene layer due to the thermomechanical mismatch, the impact of curvature is considered in the proposed model. Also, the impact of the Casimir attraction is incorporated in the developed model by taking into account the limited conductivity of interacting surfaces. The scale dependency of the materials is considered in the framework of the nonlocal elasticity. To simulate the nano-switch and explore the pull-in instability, a finite element procedure is developed. The proposed approach is verified by comparing the pull-in voltage to published data. Finally, the role of influential parameters, including size dependency, length, initial gap, curvature, and the number of graphene layers on instability voltage of nano-switch, are investigated.

WAYS OF CHANGING THE STRUCTURAL-MORPHOLOGICAL, PHYSICO-CHEMICAL AND ELECT­RICAL PROPERTIES OF GRAPHENES

A literature analysis of sources on synthesis methods and their influence on the structural-morphological, physico-chemical, and electrochemical properties of graphene and graphene-like structures was carried out. It was established that these properties have a clear dependence on the synthesis method, starting materials, and the composition of the synthesis medium.
 The main ways of changing graphene's structural-morphological, physico-chemical and electrical properties are changes in the synthesis method and conditions that affect the formation of σ-bonds and π-bonds. The presence of these bonds regulates the number of graphene layers and the formation of van der Waals interactions between them, as well as the formation of edge structural defects responsible for electrokinetic and catalytic properties. Changing the gas medium to a liquid one greatly simplifies the synthesis of graphene. Still, in the case of a liquid nitrogen medium, simultaneously with a 2-dimensional structure, it is possible to form 3-dimensional particles up to tens of nanometers in size. Aqueous medium and plasma-arc synthesis methods are the most attractive for obtaining materials with electron-donor conductivity, which have attractive electrochemical and catalytic properties for use in chemical current sources and fuel cells. Using an aqueous environment requires mandatory further heat treatment at temperatures above 250 0C to se­parate chemisorbed water from the structure, which complicates the synthesis procedure. The advantage of the plasma-arc method for the synthesis of graphene and other carbon nanostructures is its ability to shorten the stages of the synthesis of graphene, the possibility of modifying them directly during the synthesis process by changing the environment, easy management, and obtaining a clean final pro­duct. In the modern practice, this method is limited to obtaining coatings on a solid carrier.

Dual-function photonic spin Hall effect sensor for high-precision refractive index sensing and graphene layer detection.

In this paper, a photonic spin Hall effect (PSHE) sensor for high-precision refractive index (RI) detection and graphene layer number detection is proposed. Numerical analysis is performed by the transfer matrix method. The graphene material is introduced into the layered topology to stimulate the generation of PSHE phenomenon, and both H polarization and V polarization displacements occur simultaneously. The effects of parameters such as chemical potential, relaxation time, and external temperature on the PSHE shift are also discussed. The displacement of H polarization can be used for RI detection, and the measurement range (MR), sensitivity (S), figure of merit (FOM), and detection limit (DL) are 1.1-1.5, 127.85 degrees/RIU, 2412, and 2.08×10-5, respectively. The superior sensing performance provides a theoretical possibility for the detection of solids, liquids, and gases. The shift characteristic of V polarization is appropriate for detecting the number of layers in graphene, with a MR and S of 1-9 layers and 4.54 degrees/layer. The impacts of dielectric loss on sensor performance are also considered. We hope that the proposed PSHE multifunctional sensor can improve a theoretical idea for novel sensor design.

Graphene electrochemistry: ‘Adiabaticity’ of electron transfer

Graphene materials currently open new perspectives to electrochemical systems, providing high electron transfer rates, electrochemical stability in a wide potential range, and ability to control these properties, for instance, by introducing impurity atoms. One of the most important electrochemical characteristics of the graphene is the heterogeneous electron transfer rate (or electrochemical activity). However, contradictory results have been presented on the electrochemical activity of graphene, and how structural defects, the number of graphene layers, and the graphene substrate alter its activity. We found here that the question of an electron transfer regime on graphene, which is disputable and rarely considered, is critically important in understanding its electrochemical activity. We provide an evidence of different electron transfer regimes for O2/O2− and ferrocenium/ferrocene redox on the graphene electrode, that result in different structure-activity relationships. Our results contribute to further understanding of the graphene electrochemistry.

Role of Temperature and Time Exposure for Controlled and Accelerated Synthesis of Graphene Oxide Using Tour Method

Synthesis of graphene oxide (GO) with the Tour method has been studied. In this procedure, phosphoric acid was mixed with sulfuric acid in the ratio of 1:9, and then potassium permanganate and graphite with the ratio of 6:1 was added in an ice bath at the variation of oxidation times of 1, 7 and 24 h and temperatures of 40, 50 and 60 °C. The GOs were characterized by UV–Visible spectroscopy, Fourier Transform InfraRed (FT-IR) spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), and Transmission Electron Microscopy (TEM). The results show that the GO oxidized at 40 °C for 7 h (GO-7-40) has been successfully formed indicating that GO-7-40 is the most efficient GO. The GO-7-40 is characterized by a peak at 2θ = 10.89° in the XRD diffractogram, resulting calculation of the average distance between graphene layer (d) of 0.81 nm. The average number of graphene layers (n) is 4, the oxidation level (C/O) is 1.50 according to EDX data, λmax at 226 nm attributes to π→π* transitions of C=C bond in UV-Vis spectrum, and the functional groups such as O-H, C=C, C-OH, and C-OC are observed in FT-IR spectrum.

Molecular dynamics simulation of frictional strengthening behavior of graphene on stainless steel substrate

During the last few years, friction studies of graphene applied to stainless-steel materials have mainly focused on the macroscopic scale, but the friction behavior and friction mechanism of graphene on stainless-steel surfaces at the nanoscale are still unclear. Here, the frictional behavior of graphene on stainless-steel was analyzed by molecular dynamics simulations. The results show that the average adsorption energy between stainless-steel and graphene is large, but the graphene/stainless-steel system exhibits frictional strengthening behavior. The frictional strengthening behavior decreases with the increase of the number of graphene layers. In addition, the frictional strengthening behavior appears only in localized regions of graphene on the stainless-steel surface. We demonstrate that the polycrystalline character of stainless-steel is a key factor in the appearance of frictional strengthening behavior. The presence of stainless-steel grain boundaries causes the change of graphene adsorption state, which leads to the appearance of graphene friction forcing behavior. Moreover, the multi-element characteristics of stainless-steel exacerbate the influence of grain boundaries on the graphene adsorption state. The correlation between stainless-steel grain boundaries and graphene frictional behavior provides insight into the application of graphene on stainless-steel surfaces.

Adsorption of hydrogen isotopes on graphene

We investigated the possibility of using graphene for control of hydrogen isotopes by exploring adsorption, reflection, and penetration of hydrogen isotopes on graphene using molecular dynamics. Reflection is the dominant interaction when hydrogen isotopes have low incident energy. Adsorption rates increase with increasing incident energy until 5 eV is reached. After 5 eV, adsorption rates decrease as incident energy increases. At incident energies greater than 5 eV, adsorption rates increase with the number of graphene layers. At low incident energies (<1 eV), no isotopic effects on interactions are observed since the predominant interaction is derived from the force of π electrons. Between 1 eV and 50 eV, heavier isotopes exhibit higher adsorption rates and lower reflection rates than lighter isotopes, due to the greater momentum of heavier isotopes. Adsorption rates are consistently higher when the incident angle of the impacting atoms is smaller between 0.5 eV and 5 eV. At higher energies (>5 eV), larger incident angles lead to higher reflection and lower penetration rates. At high incident energies (>5 eV), crumpled graphene has higher adsorption and lower penetration rates than wrinkled or unwrinkled graphene. The results obtained in this research study will be used to develop novel nanomaterials that can be employed for tritium control.

Thermal properties of quantum rings in monolayer and bilayer graphene

In this work, we use two different statistical mechanics formalisms like, Shannon and Tsallis formalisms (extensive and non-extensive), to study the thermodynamic properties of quantum rings (QRs) in monolayer and bilayer graphene under a uniform external magnetic field. To this goal, we first employ a simplified model to obtain energy eigenvalues of monolayer and bilayer graphene quantum rings. Then, by applying the Shannon and Tsallis formalisms, we have calculated the entropy, specific heat, magnetization, and magnetic susceptibility of monolayer and bilayer graphene. Our results show that thermodynamic quantities in the Shannon formalism have oscillation behaviors with increasing external magnetic fields. Unlike the Shannon formalism, the obtained properties by the Tsallis formalism show a peak structure. Also, the peak location depends on the number of graphene layers.

Verification of experimental results with simulation on production of few-layer graphene by liquid-phase exfoliation utilizing sonication

Graphene, an extraordinary tow-dimensional carbon nanostructure, has attracted global attention due to its electronic, mechanical, and chemical properties; therefore, there is a need to find out an economical mass production method to produce graphene. In the present research, the aim is to find out optimal conditions for exfoliation of few-layers graphene (FLG) in a water–ethanol green solution. We varied different parameters of the ultrasonic probe like power quantity and time duration of sonication to investigate the effects on the number of graphene layers and density of graphene in the solution. Also, an attempt has been made to predict the acoustic pressure distribution by solving the wave equation in various output powers of the ultrasonic probe (sonotrode) using numerical simulations. The simulations and experimentations verify each other. Concluding that modifying the output power at the same condition will significantly alter the acoustic pressure inside the sonoreactor. The difference in acoustic pressure at 90% output power of our experimentations is much higher than in other conditions. Experimentation results utilizing UV–visible spectra, SEM (Scanning electron microscope), TEM (Transmission electron microscope) images and Raman spectrum indicate that the minimum thickness and maximum exfoliation for these samples are acquired for sonication at 90% of the maximum effective output power of the sonicator being 264 W for 55 min.

Tunable optical bistability in graphene Tamm plasmon/Bragg reflector hybrid structure at terahertz frequencies

Tunable optical bistability (OB) plays an active role in the manipulation of optical switches. Here, by combining graphene with one-dimensional photonic crystal (1D PC) with a defect layer, we theoretically design a simple multilayer structure to manipulate OB. Through the coupling of Tamm plasmon (TP) and defect mode (DM), an induced narrow peak can be generated in the original wide reflection angle, so it presents a richer situation of OB. The theoretical results show that the OB can be adjusted by optimizing the Fermi energy, the number of graphene layers. In addition, the effects of incident angle, the thickness of defect layer, and other structural parameters on OB are also clarified. We believe the above results can provide a new paradigm for the construction of controllable bistable devices.

Accelerated Ultrafast Magnetization Dynamics at Graphene/CoGd Interfaces.

Atomically thin graphene layers can act as a spin-sink material when adjacent to a nanoscale magnetic surface. The enhancement in the extrinsic spin-orbit coupling (SOC) strength of graphene plays an important role in absorbing the spin angular momentum injected from the magnetic surface after perturbation with an external stimulus. As a result, the dynamics of the excited spin system is modified within the magnetic layer. In this paper, we demonstrate the modulation of ultrafast magnetization dynamics at graphene/ferrimagnet interfaces using the time-resolved magneto-optical Kerr effect (TRMOKE) technique. Magnetically modified interfaces with a systematic increase in the number of graphene layers coupled with the 10 nm-thick Co74Gd26 layer are studied. We find that the variation in the dynamical parameters, i.e., ultrafast demagnetization time, remagnetization times, decay time, effective damping, precessional frequency, etc., observed at different time scales is interconnected. The demagnetization time and decay time for the ferrimagnet become approximately two times faster than the corresponding intrinsic values. We found a possible correlation between the demagnetization time and damping. The effect is more pronounced for the interfaces with monolayer graphene and graphite. The spin-mixing conductance is found to be approximately 0.8 × 1015 cm-2. The effect of SOC, pure spin current, the appearance of structural defects, and thermal properties at the graphene/ferrimagnet interface are responsible for the modifications of several dynamical parameters. This work demonstrates some important properties of the graphene/ferrimagnet interface which may unravel the possibilities of designing spintronic devices with elevated performance in the future.

Multilayer graphene-based radiation modulator for adaptive infrared camouflage with thermal management

Graphene film is a promising thermal camouflage and thermal management material because of its thin, light, flexible structural characteristics and controllable broad-spectrum electromagnetic radiation modulation properties. In this study, a thermal radiation modulator (TRM) based on multilayer graphene (MLG) was studied by simulation and an equivalent transmission line model. The physical mechanism underlying the spectral characteristics and the sensitivity of infrared (IR) radiation modulation to the number of graphene layers is revealed. Furthermore, to solve the problem of thermal instability in the MLG-based TRM, a design scheme integrating a TRM and a meta-absorber is proposed. By electrical control of the MLG, the improved modulator can achieve dynamic emissivity modulation in the wavelength ranges of 3–5 µm and 8–14 µm for adaptive thermal camouflage while maintaining a high emissivity at 5–8 µm for radiative cooling. The compatibility of tunable IR emission and radiative heat dissipation enables graphene to be used for thermal camouflage in complex environments and at high temperatures. The results not only promote the exploration of advanced thermal camouflage materials or devices but also provide inspiration for the application of graphene in thermal management, thermophotovoltaics, IR displays and communications.

Characteristics of secondary electron emission from few layer graphene on silicon (111) surface

As a typical two-dimensional (2D) coating material, graphene has been utilized to effectively reduce secondary electron emission from the surface. Nevertheless, the microscopic mechanism and the dominant factor of secondary electron emission suppression remain controversial. Since traditional models rely on the data of experimental bulk properties which are scarcely appropriate to the 2D coating situation, this paper presents the first-principles-based numerical calculations of the electron interaction and emission process for monolayer and multilayer graphene on silicon (111) substrate. By using the anisotropic energy loss for the coating graphene, the electron transport process can be described more realistically. The real physical electron interactions, including the elastic scattering of electron–nucleus, inelastic scattering of the electron–extranuclear electron, and electron–phonon effect, are considered and calculated by using the Monte Carlo method. The energy level transition theory-based first-principles method and the full Penn algorithm are used to calculate the energy loss function during the inelastic scattering. Variations of the energy loss function and interface electron density differences for 1 to 4 layer graphene coating GoSi are calculated, and their inner electron distributions and secondary electron emissions are analyzed. Simulation results demonstrate that the dominant factor of the inhibiting of secondary electron yield (SEY) of GoSi is to induce the deeper electrons in the internal scattering process. In contrast, a low surface potential barrier due to the positive deviation of electron density difference at monolayer GoSi interface in turn weakens the suppression of secondary electron emission of the graphene layer. Only when the graphene layer number is 3, does the contribution of surface work function to the secondary electron emission suppression appear to be slightly positive.

Exploring Interfaces Through Synchrotron Radiation Characterization Techniques: A Graphene Case

AbstractRecently, many breakthroughs have been made in graphene research, allowing scientists to explore and understand the material world from a two‐dimensional (2D) perspective. The interface issue of graphene is the most important, because all of its atoms are exposed to the interface for this atomically thin material. The 2D nature necessitates a sensitive and non‐destructive interface probe to detect the structure and properties. Synchrotron radiation (SR) characterization techniques, with the ultra‐high resolution and extremely wide energy range, have been utilized with increasing frequency to explore the challenging interface sciences. In this review, these interface characterization techniques based on SR and how they monitor the structure evolution of graphene in different interfaces such as graphene–substrate and graphene–graphene interface are first introduced. Graphene's layer number, interlayer spacing, and stacking order are governed by these interfaces, determining the final properties. Then, the property detection and modulation in different interfaces of graphene are also discussed. Finally, the current challenges and outlook on the future development for SR techniques to characterize graphene interface are presented.

3D Graphene Foam by Chemical Vapor Deposition: Synthesis, Properties, and Energy-Related Applications.

In this review, we highlight recent advancements in 3D graphene foam synthesis by template-assisted chemical vapor deposition, as well as their potential energy storage and conversion applications. This method offers good control of the number of graphene layers and porosity, as well as continuous connection of the graphene sheets. The review covers all the substrate types, catalysts, and precursors used to synthesize 3D graphene by the CVD method, as well as their most viable energy-related applications.

Evaluating and manipulating bonding strength at multilayer graphene-copper interface via plasma functionalization

Interface bonding is crucial in fabricating graphene/copper composite because of immiscibility and poor wettability of C–Cu and weak force between graphene layers. Meanwhile, it is challenging to quantitatively evaluate the bonding strength of graphene-included interface. Here, bonding at multilayer graphene-copper interface is effectively manipulated by graphene functionalization via plasma treatments on graphene/copper foils before they are stacked and consolidated to composite, and a quantitative method is proposed for evaluating the bonding strength by tensile testing on bulk specimens with single interfaces across the whole section. The experimental results indicate that oxygen plasma functionalization is more effective in improving the interface bonding, by which a strength of at least 154 MPa comparable to the tensile strength of pure copper is achieved with the layer number of graphene even up to ∼30. The enhancement mechanisms for the interface bonding strength are also discussed based on the microstructure analysis and molecular dynamics simulations.

Effect of Graphene Nanofibers on the Morphological, Structural, Thermal, Phase Transitions and Mechanical Characteristics in Metallocene iPP Based Nanocomposites

Several nanocomposites were prepared by extrusion from a commercial metallocene-type isotactic polypropylene (iPP) and different amounts of two types of graphene (G) nanofibers: ones with a high specific surface, named GHS, and the others with a low specific surface, labeled as GLS. The number of graphene layers was found to be around eight for GLS and about five in the GHS. Scanning electron microscopy (SEM) images of the resultant iPP nanocomposites showed a better homogeneity in the dispersion of the GLS nanofibers within the polymeric matrix compared with the distribution observed for the GHS ones. Crystallinity in the nanocomposites turned out to be dependent upon graphene content and upon thermal treatment applied during film preparation, the effect of the nature of the nanofiber being negligible. Graphene exerted a noticeable nucleating effect in the iPP crystallization. Furthermore, thermal stability was enlarged, shifting to higher temperatures, with increasing nanofiber amount. The mechanical response changed significantly with nanofiber type, along with its content, together with the thermal treatment applied to the nanocomposites. Features of nanofiber surface played a key role in the ultimate properties related to superficial and bulk stiffness.

Surface stability and electronic structure of CuNi alloy (111) as a potential catalyst for graphene growth-a density-functional theory study

Controlling the number of graphene layers during its growth is essential in realizing its practical application as a transparent conductive electrode. Growth with CuNi alloy catalysts can effectively control the number of graphene layers. However, research at the experimental level has not been supported by research at the theoretical level. Therefore, we will study the growth of graphene on a CuNi catalyst using the density functional theory (DFT). However, in this paper, we only focus on studying the stability of the surface of CuNi as a preliminary study. Based on geometry optimization, CuNi (111) has a wrinkled surface in the slab model due to the anisotropy shift of the atoms. Furthermore, CuNi (111) has a surface energy of 1.511 J/m2, which is between the surface energies of its components. This condition indicates that CuNi (111) has excellent stability. When forming CuNi alloy, electrons in the Cu 4s and Ni 3d orbitals have an enormous contribution in forming the metallic bonds indicated by a significant shift of the band center energy and change of the number of states at the Fermi level. Our results show that the CuNi system can become a potential catalyst for graphene growth.

In‐Situ Growth of High‐Quality Customized Monolayer Graphene Structures for Optoelectronics

AbstractHigh‐quality customized monolayer graphene structures are a prerequisite for various applications such as electronics, optoelectronics, and energy devices. Top‐down photolithography is the main method for graphene patterning, but it is greatly affected by complex manufacturing processes and residual photoresist. Recently, bottom‐up methods based on catalyst or precursor patterning have been developed. Although these methods can achieve high‐resolution graphene patterns, it is difficult to control the number of graphene layers and has a high defect density. Here, the authors propose a selective area reconstruction method for in‐situ growth of high‐quality monolayer graphene structures on copper substrates. The method utilizes selective oxidation and high‐temperature reduction technologies, which can effectively regulate the surface characteristics of the copper substrate, thereby precisely controlling the nucleation and growth behavior of the customized graphene structure. The feature size of the fabricated graphene structure is less than 1 µm and it has high monolayer coverage and extremely low defect density. The performance of the photoluminescence device and photodetector based on the customized monolayer graphene structure is characterized. The method provides a new approach for the direct growth of high‐quality, scalable, and high‐precision functional graphene structures, which is expected to have great potential in the optoelectronic applications.